Ring Gapping

What's the recommended procedure to install, fit and gap a new ring? I've got a ST .46, but I presume most ringed motors are similar.

If your talking about using a stock S.T. ring I wouldn't, they have
always been suspect in term of qc. I would contact Frank Bowman,
he makes excellent rings and you can send him your p&l, have it fitted
for a very reasonable price. His ph.# is 1-505-327-0696.

I'm glad to read this because I bought the rings from Frank at VSC.

I have bought 2 rings from Frank. His rings are made slightly oversize to compensate for wear. The first one was on a K&B 40S. All I had to do was hone the cyllinder. It was a first crank start, which is almost unheard of. The second was for a ST G21 .40. I honed the cyllinder, but also had to dress the ring ends to make it work. Looks good. I think I'll have him fit the next one.

If you have never done this before, send it out to somebody that has
experience, think about Don Blackburn and have him chrome the sleeve
and fit the ring. In my experience this is a job I don't do very well.

Typical ring gaps are 0.002 to 0.003 inches. Push the ring up the cylinder (use the piston as the "push tool" to where it would normally sit when the piston would be at TDC. Then measure the gap.

As to putting the ring on, I am not an expert, but I try to"roll" it onto the top of the piston, then slide it to the gap. Try not to distort it (which is really bad). I "think" it would be a good idea to rough up the cylinder walls (like a hone would do) which would help with seating the ring.

So my hope with this description is to excite someone who really knows what they are doing to give a better technique!

My thinking was what Alan said. However, I talked with Frank Bowman at the VSC, and he was pretty convincing that there should be no ring gap. I bought a couple of K&B 40 rings from him. He had a little cylinder which he fitted them to with no gap. I havn't tried them yet. I think the typical K&B factory ring will have a little gap.

Just an anecdote. I put several hundred flights on a K&B 4011 and got instant starts and good runs all along. I noticed that the prime needed for a one or two flip start steadily increased as the engine aged. Finally it shucked the seal off the front bering and started leaking fuel like crazy out the front end. I replaced the bearing, and while I had the engine apart replaced the ring with a factory ring. The old ring had an obvious gap. I did not do anything to the cylinder. The new ring ran in very quickly; the low prime instant starts were back and the engine was noticably stronger.

I just got off the phone with Mr. Bowman, I ordered a couple of rings
and asked what the gap should be, he said 1.5 thousands, I mentioned
that some people at VSC thought he advocated no gap. He stated that
they must have misunderstood him. The good news is if you send him your P&L he will fit the ring at no charge only return postage and the cost of the ring. If you have one of his rings then you only pay return postage or about 4.00. Is that a good deal or what?

After reading everyones suggestions I see this is typical of other engines I have worked on. Typical ring gap is .004" per inch of piston diameter for Chevy engines, go cart engines, briggs and straton engines, boat motors so the suggests of .003" sounds correct. The cylinder wall of a used engine gets glazed and a new ring will take for ever to seal so you must hone the cylinder. Run the hone in and out of the cylinder very fast for about 15 seconds using lots of oil to make 45 deg angle hash marks on the inside of the cylinder wall. You can probably do the same thing with 400 grit sand paper and your finger. Insert the new ring inside the cylinder and check the gap with a feeler gage. If the gap is too small file to fit using a hand file. I like to use a diamond dust coated finger nail file it works great.

>After reading everyones suggestions I see this is typical of
>other engines I have worked on. Typical ring gap is .004"
>per inch of piston diameter for Chevy engines, go cart
>engines, briggs and straton engines, boat motors so the
>suggests of .003" sounds correct. The cylinder wall of a
>used engine gets glazed and a new ring will take for ever to
>seal so you must hone the cylinder. Run the hone in and out
>of the cylinder very fast for about 15 seconds using lots of
>oil to make 45 deg angle hash marks on the inside of the
>cylinder wall. You can probably do the same thing with 400
>grit sand paper and your finger. Insert the new ring inside
>the cylinder and check the gap with a feeler gage. If the
>gap is too small file to fit using a hand file. I like to
>use a diamond dust coated finger nail file it works great.
>
>Gary Weaver [email protected]

Ron B.

Gary:

The .0015" gap recommended by Frank Bowman sounds much nearer correct to me.

The cylinder glaze thing is an old wives tale.In side by side comparison tests at our lab,GM,and others,there was no difference in ring seating IF the cylinder was straight and round within spec. Only if there's a ring hook at the top of the bore or other significant bore wear or distortion,is honing needed.If honing is indicated,it should be taken to the next standard oversize. Unnecessary honing is simply artificial wear. If the ring fits light tight,install it and run it.

Ron B.
F4Fguy

>What's the recommended procedure to install, fit and gap a
>new ring? I've got a ST .46, but I presume most ringed
>motors are similar.
>
>Mark Gerber

Ron B.
F4Fguy

The "rule of thumb" is ~.002"/1" of bore size,however,(as long as there's enough gap to keep the ring from butting at max temp)this is probably the least important fitting dimension re rings.We ran tests to determine the max/min gap an engine would tolerate and found,with the caveat above,that the engine didn't care,in terms of output,until blowby became intolerable.Admittedly,we only ran bore sizes from about 2.25" to 5.11",but there's no reason to expect smaller bores to act differently.The gaps I'm referring to here were as much as .035" in a 2.25" bore. As I said,blowby was terrible,and starting wasn't the best,and I certainly don't recommend such gaps,but power was still the same as at .005". On the other hand,side clearance,especially if due to wear,was critical.As soon as measureable side wear appeared in either ring or groove,especially the groove,performance began to drop. Apparently the mechanism is that side clearance increase allows more ring twist,which causes more side wear,causing more clearance,etc..... Circularity is also very important. For piston ported two strokes rings need to have negative circularity to avoid snagging in the ports.

Rings should NEVER be "walked" into the groove by placing one tip in the groove and helically working the ring into the groove.This will distort the ring and destroy the side seal which is what makes the thing work in the first place.If you don't have an installing cone or a ring expander,send it to someone who does.

I agree with much of what is said above but differ re. the minimum ring gap.
At less than 5 thou Tigres will heat up during consecutive loops and will take a lap or three to fully settle again. This leaning off in consecutive loops is the tell-tale sign that the gap is too small. 5 thou should be the starting point.
My source for this information is not just my own experience but Brian Eather’s also. If Bob Geiske is reading this he may care to add comment recalling his experiences of several years ago in collaboration with Brian.

1.GAPS:
At certain times in their production ST60s & 46s had virtually no ring gap from new and owners wondered why the engines heated up, leaned off and ran away. As long as the ring is made of good quality cast iron and is properly tensioned excellent power is still achieved with unusually large gaps eg. 10-12 thou. I'm not recommending 10-12 thou as a starting point but don't throw away a good ring too fast.

Re-tensioning a ring is quite easy. Clamp the ring using a nut and bolt through washers either side of the ring. (a sort of ring sandwich). Tighten this up having spread the ring by inserting a metal spacer in the gap so that the gap is say 160 thou.(The standard gap when not in the cylinder is usually around half that ie. 80thou.) Get this into a semi-darkened room and with a gas torch carefully and evenly heat the whole assembly to a cherry red color. You need the semi-darkened room to see this color clearly. Let is cool off on its own and when you unclamp it you will have a perfectly tensioned ring. You will feel the increased torque before you've flown a full lap.

2.HONING:
Use a three stone brake hone as this ensures you are keeping the cylinder as round as possible. Hold the handle in a vice. Using a light oil, push the cylinder onto the hone employing a twisting motion (I go clockwise). Pull it back using the same direction twisting motion (again for me that's clockwise). This technique ensures the correct cross hatching of the hone marks in the cylinder. Inspect the cylinder every several strokes and note where the shiny sections are as these are as yet un-honed. Quite often these shiny sections are where it matters ie. where the ring is located at the point of combustion. Keep honing until the shiny sections disappear and it's finished. Wash it thoroughly.

>I agree with much of what is said above but differ re. the
>minimum ring gap.
>At less than 5 thou Tigres will heat up during consecutive
>loops and will take a lap or three to fully settle again.
>This leaning off in consecutive loops is the tell-tale sign
>that the gap is too small. 5 thou should be the starting
>point.
>My source for this information is not just my own experience
>but Brian Eather’s also. If Bob Geiske is reading this he
>may care to add comment recalling his experiences of several
>years ago in collaboration with Brian.
>
>1.GAPS:
>At certain times in their production ST60s & 46s had
>virtually no ring gap from new and owners wondered why the
>engines heated up, leaned off and ran away. As long as the
>ring is made of good quality cast iron and is properly
>tensioned excellent power is still achieved with unusually
>large gaps eg. 10-12 thou. I'm not recommending 10-12 thou
>as a starting point but don't throw away a good ring too
>fast.
>
>Re-tensioning a ring is quite easy. Clamp the ring using a
>nut and bolt through washers either side of the ring. (a
>sort of ring sandwich). Tighten this up having spread the
>ring by inserting a metal spacer in the gap so that the gap
>is say 160 thou.(The standard gap when not in the cylinder
>is usually around half that ie. 80thou.) Get this into a
>semi-darkened room and with a gas torch carefully and evenly
>heat the whole assembly to a cherry red color. You need the
>semi-darkened room to see this color clearly. Let is cool
>off on its own and when you unclamp it you will have a
>perfectly tensioned ring. You will feel the increased torque
>before you've flown a full lap.
>
>
>2.HONING:
>Use a three stone brake hone as this ensures you are keeping
>the cylinder as round as possible. Hold the handle in a
>vice. Using a light oil, push the cylinder onto the hone
>employing a twisting motion (I go clockwise). Pull it back
>using the same direction twisting motion (again for me
>that's clockwise). This technique ensures the correct cross
>hatching of the hone marks in the cylinder. Inspect the
>cylinder every several strokes and note where the shiny
>sections are as these are as yet un-honed. Quite often these
>shiny sections are where it matters ie. where the ring is
>located at the point of combustion. Keep honing until the
>shiny sections disappear and it's finished. Wash it
>thoroughly.
>
>
>Cheers, Tim

Ron B.
F4Fguy

I repeat what I said in my post #10 above. There's no reason to hone unless the cylinder is badly worn or distorted. Rings will seat just fine on a "glazed" surface.We tested surfaces as smooth as 1mu RMSand had no difficulty getting a seal.

Trying to re-tension a ring is equally unecessary. If the ring is worn enough to show loss of tension,it's circularity will be off,as will the side faces. In fact it is side face wear of both ring and piston groove that cause loss of performance. Ring gaps,over wide ranges,make little or no difference in performance. It only takes a small change in flatness of ring side face or groove face,to show a drop in performance. Rings seal by gas pressure forcing them out against the wall from behind and above. Initial tension only has to be sufficient to establish contact completely around the cylinder. Additional tension only adds frictional drag. Going back to the gap,as i said above,too small a gap will cause ring butting,but in standard replacement rings this is very rare. If you suspect butting it's easily detected by examining the ring ends for shiny spots. Usually too small a gap will break the ring by compressive loading unless it's only marginally too small.

Having said all this,one final comment: If a ring is worn to the point of needing replacement,the new ring should never be placed on the old piston. Ring wear and piston groove wear go hand in hand. When rings are worn,the piston needs replacement or reconditioning before installing new rings.

Ron,
If this is true, I need to find a couple of ST60 pistons. Know anyone that has them? My ST60's have been rebuilt a number of times by myself and Tom Lay. I'd like to get a couple of them in really top notch shape for a new project. What about chroming the sleeves?
Alan Resinger

>Ron,
>If this is true, I need to find a couple of ST60 pistons.
>Know anyone that has them? My ST60's have been rebuilt a
>number of times by myself and Tom Lay. I'd like to get a
>couple of them in really top notch shape for a new project.
>What about chroming the sleeves?
>Alan Resinger

Ron B.
F4Fguy

The easy way ,of course,is to do as you said,replace the piston. But you can also re-machine the groove and install a spacer,or have an over size (in width only) ring made by one of the ring guys out there. Obviously you only remove as much as absolutely necessary,so we're talking a few thou here,but the groove must be absolutely flat and square to the axis of the cylinder. ST pistons generally have less groove wear than most as they're made of a high silicon(please! not silicone) alloy.

As to chroming,it's the only way to get back to original bore size. Since there's no oversize piston available,if you want the new ring to work,you have to plate and hone to get back to square one. If there's ANY measureable wear,taper(bigger at the top),or out of round,you have no choice except to plate. This is the one time to hone,because the new chrome has to mate to the ring,but, do not even attempt to do this with a "brake" hone. You'll end up with a bellmouthed or barrelled,out of round,tapered mess needing to be re-chromed.Take it to a shop which has a Sunnen or Micro-matic hone and ask them to hone it to size and to a "plateau" finish.This involves a 120-220 roughing at 45deg.,followed by 320-400 finish honing at 60deg,then a polish with 800-1200 at 45 deg. The different honing angles are to give an indication of when the previous hone marks are removed. The polishing is to develop flats between the hone marks to support the ring leaving the hone marks to retain oil. Beginning to see why the tuners get the big bucks?

Ron,

In a perfect world I agree with all your theory. You obviously know your stuff and don’t need the reassurance of my opinion.

Ron we don’t have an argument here. I’m simply saying what works in practice for ST46s and 60s in order to help those still using them.

So what are my points?
1. Honing the liner with even a few minor strokes is a way of observing its condition. If it’s got wobbly sides it won’t seal properly. My technique of cross hatching simply produces a nice even pattern and if the hone marks do hold some oil and assist with lubrication and cooling (which I suspect but can’t prove) so much the better.
2.Rings:
The world of ST46s and 60s is not perfect and compromises have to be made to make them go well. It’s interesting to note that Saito rings give only a fraction (if any) of the trouble you get from STs. This is because I suspect the Saito piston is made of better alloy(higher silicon) than the ST and is fitted with smaller clearances in the cylinder in the first place. The ST piston’s greater clearance asks far more of the ring than is ideal, particularly its ability to stay in touch with the cylinder wall in spite of the expanding forces from the charge which you so rightly describe. Tensioning the ring as I have recommended is a somewhat crude compromise and does cause some increased drag but this is way outclassed by the dramatic increase in power from the seal it helps generate.
I quite agree with your points re. ring and groove flatness and side wear on the ring. This is well known. I suspect the ST pistons “rock and roll” a fair bit exaggerating that very problem but this is real world stuff with STs and what I’m suggesting is as I’ve said a little crude but it works. The performance goes off after a while and you have to do it all again but that’s the high maintenance world of ST 46/60s. We employ the same techniques with our own rings and they produces the goods.

3. Now if it comes to making a new piston, that’s another ball game. I have thought about chroming the liners, making high silicon pistons to much closer tolerances and obviously new properly fitted cast iron rings. I suspect this would even be superior for 2/4 stunt runs than ABC or ABN. But Tigres are old now and I’ve pretty much moved on.

In the meantime for those who want to extract the best performance from the existing ST46/60s, don’t write off what I’ve said on the grounds of perfectly correct theory which applies under more ideal conditions. What I’ve said for STs. works in practice.

Tim

>Ron,
>
>In a perfect world I agree with all your theory. You
>obviously know your stuff and don’t need the reassurance of
>my opinion.
>
>Ron we don’t have an argument here. I’m simply saying what
>works in practice for ST46s and 60s in order to help those
>still using them.
>
>So what are my points?
>1. Honing the liner with even a few minor strokes is a way
>of observing its condition. If it’s got wobbly sides it
>won’t seal properly. My technique of cross hatching simply
>produces a nice even pattern and if the hone marks do hold
>some oil and assist with lubrication and cooling (which I
>suspect but can’t prove) so much the better.
>2.Rings:
>The world of ST46s and 60s is not perfect and compromises
>have to be made to make them go well. It’s interesting to
>note that Saito rings give only a fraction (if any) of the
>trouble you get from STs. This is because I suspect the
>Saito piston is made of better alloy(higher silicon) than
>the ST and is fitted with smaller clearances in the cylinder
>in the first place. The ST piston’s greater clearance asks
>far more of the ring than is ideal, particularly its ability
>to stay in touch with the cylinder wall in spite of the
>expanding forces from the charge which you so rightly
>describe. Tensioning the ring as I have recommended is a
>somewhat crude compromise and does cause some increased drag
>but this is way outclassed by the dramatic increase in power
>from the seal it helps generate.
>I quite agree with your points re. ring and groove flatness
>and side wear on the ring. This is well known. I suspect
>the ST pistons “rock and roll” a fair bit exaggerating that
>very problem but this is real world stuff with STs and what
>I’m suggesting is as I’ve said a little crude but it works.
>The performance goes off after a while and you have to do it
>all again but that’s the high maintenance world of ST
>46/60s. We employ the same techniques with our own rings and
>they produces the goods.
>
>3. Now if it comes to making a new piston, that’s another
>ball game. I have thought about chroming the liners, making
>high silicon pistons to much closer tolerances and obviously
>new properly fitted cast iron rings. I suspect this would
>even be superior for 2/4 stunt runs than ABC or ABN. But
>Tigres are old now and I’ve pretty much moved on.
>
>In the meantime for those who want to extract the best
>performance from the existing ST46/60s, don’t write off what
>I’ve said on the grounds of perfectly correct theory which
>applies under more ideal conditions. What I’ve said for STs.
>works in practice.
>
>Tim

Ron B.
F4Fguy

Tim:

I don't want to argue either,but I just can't agree.

(1)I still maintain,honing is seldom indicated,only when finishing to an oversize or before and after re-chroming. When honing is done it should never be done with a "brake" hone. The only acceptable way is with a controllable industrial hone such as Sunnen or Micromatic. This is the only way to produce a model size cylinder to spec.,especially if you're looking for a small amount of taper. While .001 big at the top won't matter on a 350,it'll kill you on a .60

(2)I have .60s,.46s,and an OOoold .51. I've never had any problems with the stock ST components. The ST piston is a high silicon alloy. Side wear and groove wear is generally not a problem,nor is sealing unless the engine has been run on high castor content oil(50%and up).the problem then is basically ring sticking,in which case you'll get blowby as you describe.

I say again,ring tension is only required to make initial contact with the cylinder wall. If the ring is not light tight in the bore with low tension,one or the other is out of round,and should not be used until corrected(with an exception;the tips should leak light to a small degree). Sealing problems are(almost)always related to side wear or groove wear,regardless of the engine. If you 're fitted loosely enough to be getting significant side play in the piston,to the point of losing ring support,I suggest the cylinder or piston,or both are worn out.

(3)All the STs I have came chrome plated,if you no longer have chrome,they are worn out. The ST pistons are high silicon. The ST rings are nodular cast iron.

I'd agree that a chromed,ringed engine has a lot to recommend it. My MOKI 61,with the sleeve I made(chromed brass),and a stock piston and ring,swings a 15d or 16d prop with just about any pitch you want to hang on there,and is very docile to tune.

Lastly,everything I've said is "real world". When theory is proven in practice,it becomes "real world". It applies under all conditions,ideal or otherwise. The thing to keep in mind is that these are SMALL engines. A change in groove width of .001 in a Chevy 350 is within wear tolerance,in a Tigre .46 it's about 300% of the original fit.

No hard feelings Tim,just a difference of opinion.

>Ron B.
>F4Fguy
>
>I repeat what I said in my post #10 above. There's no reason
>to hone unless the cylinder is badly worn or distorted.
>Rings will seat just fine on a "glazed" surface.We tested
>surfaces as smooth as 1mu RMSand had no difficulty getting a
>seal.

Well. I'm not convinced on the actual effect (seating, or something else, like hydroplaning), but I can report *miraculous* improvements in run when using a brake cylinder hone to "rough up" the surface of ST46 liner. Not subtle, miraculous, like not being able to get through a pattern, to competitive stunt runs. Ted clued me into this late in the ST46 experience, and it was The Solution to the run issues we frequently had. Note that the "honing" was minimal, as it only took a few seconds (5 or so) of operation either turned by hand, or with a drill at the slowest possible speed. Just enough to remove the shiny spots. Usually, once every 4-500 runs was enough to keep it going.

>
>>Ron B.
>>F4Fguy
>>
>>I repeat what I said in my post #10 above. There's no reason
>>to hone unless the cylinder is badly worn or distorted.
>>Rings will seat just fine on a "glazed" surface.We tested
>>surfaces as smooth as 1mu RMSand had no difficulty getting a
>>seal.
>
> Well. I'm not convinced on the actual effect (seating,
>or something else, like hydroplaning), but I can report
>*miraculous* improvements in run when using a brake cylinder
>hone to "rough up" the surface of ST46 liner. Not subtle,
>miraculous, like not being able to get through a pattern, to
>competitive stunt runs. Ted clued me into this late in the
>ST46 experience, and it was The Solution to the run issues
>we frequently had. Note that the "honing" was minimal, as
>it only took a few seconds (5 or so) of operation either
>turned by hand, or with a drill at the slowest possible
>speed. Just enough to remove the shiny spots. Usually, once
>every 4-500 runs was enough to keep it going.
>
> Brett

Ron B.
F4Fguy

Brett:

I don't question your result,I do question ascribing it to honing the cylinder. I would guess,from your description,that no attempt was made to isolate honing as the only variable. Further,that several other things were done in dis-assembly/assembly. A tear down without cleaning all parts is generally a no-no. You don't say,but I'd guess the ring was replaced. You probably made sure the ring was free in it's groove,even if it wasn't replaced. In addition to the above you probably were running,and continued to run,a high percentage of castor in the fuel. Any or all of these other variables could be the source of the performance drop,and any or all being corrected could have the effect you describe.If I had to guess,I'd go to two,either individually or together;The castor and attendant varnish,and/or ring sticking ,again due to castor.Getting rid of varnish can easily be done with solvent. A further guess on my part,is that with a good all synthetic oil,you wouldn't have had the problem.

The tests we ran were designed experiments to determine the effect of individual variables. There's absolutely nothing different about model airplane engines that would make them unique. We ran two and four stroke engines ranging from Briggs@stratton,Outboard Marine,and Stihl,to Rolls-Royce and Chevrolet/McLaren Can-AM V-8s.

>I don't question your result,I do question ascribing it to
>honing the cylinder. I would guess,from your
>description,that no attempt was made to isolate honing as
>the only variable. Further,that several other things were
>done in dis-assembly/assembly. A tear down without cleaning
>all parts is generally a no-no. You don't say,but I'd guess
>the ring was replaced. You probably made sure the ring was
>free in it's groove,even if it wasn't replaced.

Actually, when it was done under controlled conditions in the shop, it was cleaned properly. Never replaced the ring at the same time - because one thing you learn very quickly is that once you have a good ring, you don't ever replace it, because good rings were in such short supply.

But when we did it at the field, it was as quick-and-dirty a job as you could imagine. I recall taking an attempt and redoing it in the time it took for the second flight to come up. Engine out, head and backplate off, liner out, rough up in about 15 seconds, wipe off with a paper towel, put it all back together, engine back in, do the official.

I could have been varnish, or some other effect, but we attributed the improvement to eliminating shiny spots on the liner. It didn't help anything if there were clear indications of cross-hatching over the entire relevant part of the liner (i.e. above the ports).

I would also add that this is an illustration of the vast amounts mickey-mouse fiddling we used to do all the time to keep engines like this running competitively. Soon as something came along that didn't require this, me and everybody else dropped them like hot potatoes. I for one am not pining for the "good old days" where you carried 2 spare motors and a big box of parts, brake cyliner hones, etc. I currently have one copy each of the RO-Jett and PA, and I ran my PA with no backup for 6 years with no mantainence, and no concerns that it was going to crap out on me unexpectedly.

> In addition
>to the above you probably were running,and continued to
>run,a high percentage of castor in the fuel. Any or all of
>these other variables could be the source of the performance
>drop,and any or all being corrected could have the effect
>you describe.If I had to guess,I'd go to two,either
>individually or together;The castor and attendant
>varnish,and/or ring sticking ,again due to castor.Getting
>rid of varnish can easily be done with solvent. A further
>guess on my part,is that with a good all synthetic oil,you
>wouldn't have had the problem.

That's true. At least some synthetic eliminated the ring sticking in the groove problem. Ed Southwick got me on that one.

Hey Dave Simons,
You reading this?
Tim.

Tim,
Brian and I were exchanging letters the last couple of weeks lamenting the good old days with some of the stump pulling ST 60's we used to have. I think that Brian had 7 of them that were always in various states of rebuild to keep the kind of power he needed. I think I had 5 at one time. I'm most interested in this thread as I'm trying to get a couple of really good ones ready for a another model I just about to start on. Maybe I should start thinking about a Retro like Dave.
Alan

Hi Tim,
Yep, just lurking, cant contribute as what I know about ST60's could be written in large print on the back of a postage stamp! Good thread though, lots of useful stuff. Agree with Ron about ring gaps, better too much than not enough & side clearance is the critical thing.

Seems like there is an opportunity for someone to make ABC, AAC or plasma replacement P/S kits, anyone tried?

I'll have a modern ABC setup any day.

>Hi Tim,
>Yep, just lurking, cant contribute as what I know about
>ST60's could be written in large print on the back of a
>postage stamp! Good thread though, lots of useful stuff.
>Agree with Ron about ring gaps, better too much than not
>enough & side clearance is the critical thing.
>
>Seems like there is an opportunity for someone to make ABC,
>AAC or plasma replacement P/S kits, anyone tried?
>
>I'll have a modern ABC setup any day.
>
>Cheers, Dave

Ron B.
F4Fguy

Dave:

Keeping the ring free is,perhaps,even more important.Every time I,ve experienced overheating and or loss of power with a Tigre(or any other ringed engine for that matter),I've found a stuck,or sticky,ring.Left unattended,this leads to local heating from lack of ring sealing,varnish on the sleeve,and further buildup of varnish in the ring groove,in a worsening spiral.The solution,for me,was to eliminate castor from the fuel,and go to all synthetic. In a ringed,double ball bearing,chrome cylinder engine,why castor?

Before everyone is all over me:Yes,castor gives "some" added protection at extreme temps. The answer however is not "add more castor". The answer is "avoid the overheat by running the engine well within it's design parameters". A stock Tigre is perfectly capable of running a 12.5/13.0 x 4.5/5.0 without over heat with the right venturi. If you keep the ring free it's very reliable.The only real problem with the Tigre(.60&.46)is availability of both engines and parts.

As an aside here,all the Tigres I have are still running the same P/C/Ring that came with them.

I agree,I'd like to see someone produce some P/C assy's,but I'd rather have an ABCR(ring)setup.Properly set-up,with the correct oil,this would be as user friendly as it gets.Broken in is broken in,no "break it in the way it's going to be run".Another thing I'd like to see (not just for Tigres)is availability of "standard over-size" parts such as rings and pistons.

OH WELL!

>As an aside here,all the Tigres I have are still running the
>same P/C/Ring that came with them.

My one remaining 46 is still running the original piston/ring/liner. I had other engines were there were literally 40 or 50 different rings. Ring #51 was a good one, then never changed it afterwards. Good rings last a long time. Bad rings last 20 flight and no point in trying to break it in.

>I agree,I'd like to see someone produce some P/C assy's,but
>I'd rather have an ABCR(ring)setup.Properly set-up,with the
>correct oil,this would be as user friendly as it gets.Broken
>in is broken in,no "break it in the way it's going to be
>run".Another thing I'd like to see (not just for Tigres)is
>availability of "standard over-size" parts such as rings and
>pistons.

I really don't see the need for a ring. Regular AAC systems are dead reliable, don't care much about running temp, and last for nearly ever. And best of all, not even the possibility of unexpected or rapid changes (from unseating, sticking, gap rotating (Tigres weren't pinned - no problem with a perfect ring with 0 gap at running temp, but inconsistent otherwise as the gap went from place to place).

I have had *zero*, nada, nonexistant, nyet, etc. problems, unreliability, inconsistency, anything, resulting from AAC/ABC setups. A ring just seems like another variable that we don't need.

Yes Brett I know what you mean.
ABC/AAC give amazing consistency and longevity but from what I've seen (in the same motor)they run a little differently and perhaps not quite with the desirable characteristics of a top original. Let me explain:
A friend of mine has a GMA AAC ST60 (now a collector's item). It took a power of running in and whilst it runs extremely consistently it seems a little dull or lifeless compared with a good ringed version. I know that doesn't sound very technically objective but I don't know how else to describe it. It just doesn't seem to have that ST "sparkle" which excites the pilot and turns the pattern into a "YES".
Other friends have plasma 46s. Initially they would not run satisfactorally if they were set like a traditional good 46. They just didn't make the low down grunt. Run them faster with less pitch and they give very consistent results. They do run an ST 4stroke but only at considerably higher revs. Now this may be OK or even better but it's not the same.
I suspect the ABC/AAC/Plasma setups need to run a little hotter to get into the sweet zone.
I know the word "ring" has associations of grief, inconsistancy and high maintenance but I don't think it has to be that way. I quote again the case of Saito where the closer fit of standard piston in the liner compared with STs allows the benefit of rings to shine.

So that's why I suspect the best set-up might be a chromed liner, high silicon piston close fitting in the liner with a ring, as it may be the way to achieve the best runs with minimal running in and the capacity to run well over a greater range of temperatures.

I havn't done it so I can't be sure but that's the way I would start as a best guess. Someone else can do the experimenting with STs because as I have said I've sort of moved on BUT it's worth a thought for future new engines which may be aimed at lower temperature running eg. larger capacity non piped 2strokes.

(By the way Alan R. I would make no apology for still running STs as despite the ring thing and the 60's tendency to gallop in the wind they are still an amazingly good motor and in the right hands are competitive at the highest level. I can't believe I've still got 7 of the wretched things!!)

>Yes Brett I know what you mean.
>ABC/AAC give amazing consistency and longevity but from what
>I've seen (in the same motor)they run a little differently
>and perhaps not quite with the desirable characteristics of
>a top original. Let me explain:
>A friend of mine has a GMA AAC ST60 (now a collector's
>item). It took a power of running in and whilst it runs
>extremely consistently it seems a little dull or lifeless
>compared with a good ringed version. I know that doesn't
>sound very technically objective but I don't know how else
>to describe it. It just doesn't seem to have that ST
>"sparkle" which excites the pilot and turns the pattern into
>a "YES".

Well, if the only difference was the AAC liner, then you might be on to something. Based on many examples. I would be willing to bet that there are a lot of other changes, too - like greatly reduced compression ratio. Might want to check the head clearance and baffle height and see. I would also anticipate there might be excessive liner taper - which would lead you to believe that it had to run at higher temperatures.

None of these things are really related to the AAC liner design - more like a particular implementation with some fairly significant other changes. I can't say I have cared - at all - for the GMA ST60s with rings that I have had reason to come in contact with, either, and power was certainly an issue.

How does a your best ST60 compare to, say, a muffled PA or RO-Jett 61? That's a much more valid comparison. "Sparkle" shouldn't be an issue, that's for sure!

If you just like ST60s, then that's of course fine with me, but I think you are attributing differences to the ring vs. AAC that are the result of other issues.

You could be quite right Brett. That's why I have qualified my opinions with words like "best guess" and "I suspect".
As usual only time (and money)consuming testing can really replace suspicions with facts.
Interesting thread this. I only wish we were all around a table having this discussion face to face.
Cheers,Tim

>You could be quite right Brett. That's why I have qualified
>my opinions with words like "best guess" and "I suspect".
>As usual only time (and money)consuming testing can really
>replace suspicions with facts.
>Interesting thread this.

Short version - I know for virtually certain that there's a lot more different on a GMA motor than the liner design - and just the kind of different that has a huge effect on the run characteristics (good or bad is a matter opinion).

Brett you are quite right about the standard GMA 60 aac setup. Actually the one I'm referring to was re worked to standard ST60 timimg and head clearence by Brian Ea for Dennis Percival. Should have mentioned that but it was several years ago and until you mentioned it I had forgotten the original differences.
Tim

I missed out on the Plasma P/Ls but if anyone ever scomes up with another "good idea' conversion for the Tigers, I'll be in line for 6 '46' sets and 4 '60' sets! Just let me know.

People keep saying that Tigers are "unavailable" but I never seem to have any trouble buying nice examples. eBay has nice Tigers every week! (I've sold a few myself.) Whats up with that?

BIGS

PS: If anyone has an unused Plasma set-up please contact me. I want one!

While I have no objective test results to offer, when it comes AACR setups, the ringed piston in a Saito 56, running in a chromed aluminum cylinder, seems to be nearly bullet-proof.

Unique to this design and/or manufacturer? Possibly, but I don't think so.

And certainly not justification for changing what works so well in many two-stroke and PA-specific engines.

>While I have no objective test results to offer, when it
>comes AACR setups, the ringed piston in a Saito 56, running
>in a chromed aluminum cylinder, seems to be nearly
>bullet-proof.
>
>Unique to this design and/or manufacturer? Possibly, but I
>don't think so.
>
>And certainly not justification for changing what works so
>well in many two-stroke and PA-specific engines.
>
>Dan

Dan
That's exactly the point. I think with good engneering we have both options (ringed/lapped)open to us.
Tim