Poor compression!

LAST EDITED ON Feb-17-04 AT 11:36 AM (CDT)
 
I recently won two Foxes from u-no-where for not a lot of money - they were a gamble as they were sold as is.

The 35 Stunt is fine - but the Rocket 35 has poor compression - what are the options open to me?

Rebore?

Chrome?

New piston/liner?

What else?

Rgds

Tony

LAST EDITED ON Feb-17-04 AT 11:37 AM (CDT)
 
Buy NEW Cyclinder and sleeves from FOX. about $40 +or- $10

OH THE ROCKET>>>>Frank Bowman with restore.

[email protected]

LAST EDITED ON Feb-17-04 AT 12:24 PM (CDT)
 
I believe I read a note from Mike Ogren that he had used later model 36 P&C sets in earlier Fox 35 4-bolt motors, and had collected a few spare sets. Check with him ( http://www.protech-aero.com/ )

. . and if he's out of spares now, consider using Fox 35 stunt parts. The sleeves are supposed to fit back and forth on the 3 & 4 bolt model engines -- second hand info there -- I've never tried it myself! OK, this is an addition in an edit: I just dropped in on Mike's web site after writing the initial reply, and have just seen that he still advertises having "36X" P&C sets. Only $28 a set.

.

Kiwi

LAST EDITED ON Feb-17-04 AT 12:16 PM (CDT)
 
Thanks to Dan Mrozek and T.Durrill for the following:

The "piston growing" process by heating in the oven process absolutely does work and sure beats having to scrounge around trying to find parts for the older engines. A lot of the old engines, thought to be wore out, could be reserected through this easy to do method of restoration. If you find someone who has some old "worn out" engines, you might be able to obtain them for very little, put them through the "piston growing process" in your oven, and have some good running older engines. It sure worked on my old McCoy Redheads.

I will explain how I grow my pistons.#1-Do not clean it!
#2-Preheat regular oven to 500*and do let it get nice and warm.
#3-Place piston on medal or heavy pie pan.Bake for one full hour.After one hour turn oven off and let it cool on its own.
#4-When cool to touch rub with 3in1 oil,and reassemble engine.If piston has soot just wipe off.Now load that beast with alot of oil and work it into engine.Run engine with26%-28% castor.DO NOT USE RC FUEL!!!After a few runs you should be happy as hell with your revitalized ehgine.I have done STS/Vecos/Johnson/OS Maxs etc.This is a can do project with out any machine help.A little time and Mom's oven is all it takes.
Have some fun and give it a try.

I have just heat treated another Johnson CS and compression is back. The last one I did is still going strong . I find it amazing how smooth it runs. No vibration,a balanced crank is to blame. Now I remember why I liked my Johnsons so well back in the olden days. This treatment will not make them new, but you may get more decent service out of that old favorite. Good time to replace those old gaskets,and clean it up too.

Good Luck..........and good flying!

None of the above, at least at first.

Try running the thing. Use a fuel with a lot of castor.

Sometimes, especially with Fox Stunts and McCoy Redheads, iffy, even poor compression is not a strict indicator of "runnability" or even startability.

True, sometimes you will need an electric (oh, the sacrilege) starter for motors of an asthmatic persuasion. But once they get running...

Currell, I can vouch for that. About 40 yrs. ago my flying buddy had a "worn out" K&B GH 35. We carried a little oil can full of castor oil with us to the field and used some to get it started all the time. Ran pretty darn good once it was running.
I have now "cooked/grown" the piston on that very same engine, and am waiting to see how it does this spring.
Bill <><

Currell is right in his recommendations. Try his suggestions first. I had an experience that supports his post. I bought a mid 1950's Fox .29 stunt engine off the Bay for a reasonable amount of money about 3 years ago. It was clean, but had been run some. The compression was low and I was disappointed and did not expect much performance out of it. Anyway, I put it on a Ringmaster which had previously sported a decent Fox .35 stunt and went to the field. It started right up. What was amazing was I couldn't tell the difference between the .29 and the .35. It turned out to be the strongest stock Fox .29 stunt I've run across. I own 4 others but not one of them runs like this one. I was running it on Taffinder's 5% nitro, 28% castor with a 10/6 Top Flite nylon prop. Actually, you could say, the engine was well broken in but still in its prime. With luck, you may have the same experience............TD

LAST EDITED ON Feb-17-04 AT 02:11 PM (CDT)
 
You never know until you try. I have had motors that I thought were worn out that ran really well once you got them started and they came up to operating temperature. Can't hurt to try running it first.

Jake

After trying to grow the piston you may also try using a tubing cutter and run a shallow cut very close to the top of the piston. This has an effect not unlike rings. The metal displaced from the groove you cut shold cause a tighter fit of piston to cylinder. Don't over do it! You only need a very small groove. If you are going to replace the liner and piston anyway you have nothing to lose.

I've agreed a $10 refund with the seller!

My gas cooker only goes up to gas mark 9 which I believe is 475 degrees will that do?

Tony

Tony,
Give it a shot at 475* for 1 hr. Let it cool to room temp by itself.

I have a 1960 Rocket that is in outstanding shape except it is a little down on compression. I am going to run it before I do anything to it. If it doesn't work, I have an extra 35 Stunt pis/cyl that looks like it will be a perfect fit.

Bill <><

Whether the piston grows or not you might consider switching to 25% all-castor fuel, as someone mentioned above. Even a little synthetic can "clean" your iron piston and that is opposite of what you want. Running all castor will allow a varnish buildup on the piston which usually will increase compression.
It could be that running on synthetic after using all castor may have contributed to the lost compression. Give all-castor a try, nothing to loose and compression to gain.
Perhaps you have already tried this.

George

BTW. Baking the piston with oil still on it may provide a two-shot improvement. First the piston growing, second, the varinsh buildup created from the oil.

For no particular reason I swapped the heads on the Rocket and Stunt - the Stunt head was ok on the Rocket but the Rocket head on the Stunt would not turn over - seems like the baffle was hitting the top of the cylinder head - the Rocket head has a slant plug!

Tony

Tony,
I am not familiar with the variants of the Rocket, but I know there are several. My '60 Rocket has a standard plug set up, and is red.
I would like to have a Rocket 40.
Bill <><

>I would like to have a Rocket 40.
>Bill <><
>
The Rocket 40 is a good choice for porky ships that already are drilled for a Stunt 35. Just make sure the insert is in the venturi, and use one or two more head gaskets.

I did this on a $coted Sterling Hellcat. The Stunt 35 on it was not man enough for the avoidupois.

The Fox Redhead 40 is...

Thanks for all so far - I will indeed give it a run before carrying out any surgery!

How do I get the liners out?

Tony

LAST EDITED ON Feb-20-04 AT 10:37 AM (CDT)
 
Tony,
I believe that the safest method is to remove the head and put the edge of a glow plug washer (copper) in the edge of the exhaust port and turn over on compression stroke. If it has years of running on castor, a slight warming of the case will help break the deposits of castor between the liner and case.
Bill <><

I thought the Fox had 'shrunk-in' liners - use a lolly stick to pop up the liners usually!

Tony

Tony,
I think it is just that after a lot of running with castor fuel of the right content, the sleeve gets stuck by "varnish" build up. They usually are a pretty good "slip fit" when new/clean.
Bill <><

I have a Fox 35 stunt and a McCoy 35 both with poor compression both bought on ebay. Neither engine will come up to full RPM with a 10x6 prop using 10% nitro fuel. Every time I turn the needle in very slow the engine RPM's pick up until at a certain RPM then the engine dies. The engines will turn a 9x6 prop full RPM just fine. I figure I have 3 choices, new piston and sleeve, smaller prop, or a different fuel. I switched fuels the engines both turn a 10x6 prop and run fine on 15% nitro fuel. If the engines ever get so they won't run on 15% nitro I will switch to 20% nitro. Easy fix for $3.00 extra per gallon of fuel. I am also adding 5 oz. of caster oil to a gallon of 16% oil fuel to get 20% oil.

LAST EDITED ON Feb-20-04 AT 11:02 AM (CDT)
 
Gary,
Just a note: Fox Stunt 35, McCoy, K&B Green Heads, etc., need AT LEAST 25% CASTOR. If they are worn, they need even more. Fox Superfuel is/was 29% castor. They really do run better and last longer on this type of fuel.
Bill <><

Gary: If you think your motors have low compression now, go ahead and run them on your planned 20% oil. It will get worse...

You want, as said before here, at least 25% oil.

Dump 12 ounces, not 5, in your existing fuel. Currell

I know oil increases compression. Maybe my engines will run on 10% nitro if I run them 25% oil instead of 20% oil. Its worth experementing to find out. The guys I sometimes fly with use 21% oil so I decided to do that too. I know the old engines need more oil the new engines are RC and the only fuel the hobby shop sells in 16% oil. All the RC people use the 16% oil. Whats the deal with that??? Is 16% oil because the engine is RC flying on and RC airplane lower RPM or is it the newer engines?

Gary,
Two things will allow you to use less oil, ball bearings and modern construction (ABC,AAC,AAO).
Upping your RC fuel to 25% will provide enough lubrication for the iron/steel and sleeve bearing setup. Using ALL CASTOR 25% fuel may gain back some compression.
Using less will work but don't complain if your engine wears out prematurely.
Folks on this thread have provided some very good information and tips. Which to use, if any, is still your decision. Good luck.