K&B 6.5

Not having much luck elsewhere - Anyone know the size of the rear bearing for the FIRE K&B 6.5 ABC?
Possibly more important, which clearance spec.?

I have no clue. I have always ued Boca bearing as my source for replacement bearing. I tell them what engine & how I will use it. They suggest the bearings. I send them $$$. Also see Ebay for K&B 6.5, bearing for this engine are listed there. I will also check with a speed guy who regularly rebuilds them.

I can look tonight if you need. Should be able to measure and obtain at local bearing house. Use Fafnir bearing with Phenolic retainer so you don't send little pieces of metal through the piston and sleeve when you least expect it.
the bearing should be same as 7.5
Front & rear intake should be same bearing size.

I am looking for 6.5 piston sleeve with some pinch left to it and not pipe timed.

David

>I can look tonight if you need.
>Front & rear intake should be same bearing size.
>David

David - lacking any other reply I might well take you up on that offer!
I don't think front and rear can be the same. The front intake rear bearing is huge, around 0.6"! Can't see a solid shaft rear intake being that size.

Hi Ian
Worked on a restoration project later and harder than I thought!
Hope its ok if I put the measuring off until tomorrow. Just burned out for the moment:8

For the moment I can tell you that the parts from Front intake 7.5 and the rear intake 6.5 will all bolt to each other.
The main difference in the 2 as far as fitting is the case on the 7.5 has bigger bore for sleeve than the 6.5 case bore and of course the head internal is different O.D.

Are you building a F-40?

will measure bearing before getting lost in the monocoque chassis resto.

David

It's probably 5/8 x 1.25 x .25 wide. K&B didn't go in for highly specialized bearings. Class 4 or 5 fit. A non-metallic retainer would be a really good idea, as someone else suggested.

Best bet is to pull the bearing and measure it. I'm pretty sure they press fitted it to the shaft, so the bearing needs to be a fairly loose internal fit.

Ian
Interesting stuff I find here on the FI vs RI engines.

Major assemblies will interchange.
The bearing on the RI 6.5 is captured by the front housing.
The bearing for the FI 7.5 is captured by the main(cylinder) case.

This makes the RI bearing smaller od than the FI!

Ok
Measurements. Did not press shaft out of FI so you will need to measure ID from shat OD.
FI bearing OD= 1.125(not 1.25)
Width=0.25(1/4inch)

The 1.25 OD posted by Phil is probably correct for the RI engine


Anyone have a decent 6.5 piston/cylinder?

Thanks everybody. The problem with measuring the bearing is that I got the engine real cheap, now I know why. There's no rear bearing in it.
It's now confirmed, 15mm x 1.125" x 0.25". C3 clearances.
Not for an F40, but an enlarged 1948 "Weatherman", a fun speed class we have in England. Old design, any unmodded production engine.

Alright!

But please go with Fafiner phenolic or other non metal retainer.

This engine will rev enough to chuck the tabs off of metal retainers
and send them through the top end. Not good.

If you have never seen one of these engines run you are in for big surprise.
8x9 prop, K&B speed fuel= 170-180mph easy on fast Rat(F40).

You have the mini pipe?


Let us know how she goes!

David

Many years ago I ran a K&B 6.5 FIRI and quite a while. One thing to remember this engine is exaust timed for a full pipe, this will run on a mini pipe but they really like a full pipe. MAC mufflers has the header and pipe, at least they did in the past. Second thing to remember they love to rev up, do not over prop them. I ran a Top Flite 9x5 power prop (read thin blade and light weight). I never ran less than 15% nitro, and that was considered on the low side. The engine sounded horrible until it got on the pipe and then it was like a rocket ship. Oh how I loved that engine.
Andy Borgogna

I have (and still do have) many K/B 6.5 engines. None are or ever have been "pipe timed" (i.e. on the order of 180 degrees of exhaust timing). All were made for mini-pipes (OTOO 165 degrees). As opposed to "normal" timing of OTOO 155 degrees.

I suppose there were "pipe timed' liners available, but I don't think K/B ever sold them that way.

Bill

Pipe timed engines were for ducted fan use.
Never saw one in 6.5 but the only 6.5s I have dealt with were RI.
Have seen several 7.5s FI and these were pipe timed for Ducted fan use.

As the 6.5s were intended for rat an F1 where full pipes were not allowed( mini pipes were) I will agree with Bill and his statement.



Ian
Go with the 8x9 no less than 40% nitro and leave it a hair rich.
Trim prop until speed just drops then next prop stop trimming at right place.
Do not break it in rich as piston/sleeve fit will not fit....
Wouldn't surprise me if a 7x10 would work if this is pan speed with drop dolly.

David

PS
Bill probably knows more about these K&Bs than anyone I know
So if he say something different listen to him!

>It's now confirmed, 15mm x 1.125" x 0.25". C3
>clearances.

I have a set of these if you're interested. They are new take outs because I use bearings with polymite plastic retainers supplied by Randy at the K&B factory. The part # on the bearing is 902YR8 if that helps the front one is R6.

I race the 5.8 which uses the same bottom end. A couple of things I can tell you is if you're going to go full bore with this thing the first thing you'll need is a billet conrod. Also the front case bolt holes should be bottom taped then get some 1" 4-40 shcs with a 1/8 grip lenght and cut them to length and also use lock washers.

The drive washer needs to be machined down around the OD at the front where there is no knurling so the prop can grip. The 3/8" knub on the collet that sticks out can be ground off and the stud should be loctited and torqued into the shaft with a double nut for tightening. I use a longer stud, just make sure it's a high grade alloy.

So much more, no time.

MM

What Randy is saying on 'Grip length' is the smooth part under the head of bolt or in other words non threaded.
This move the stress riser of the start of threads out of the shear plane of the joint. Also makes for better fit of the bolt to the bolts bore in front housing.

Never blew a rod but did break the crank pin off our first one on about the 10th flight. This was in late 74 early 75.

Once again, thanks everybody. LOTS of GOOD STUFF here, I shall follow all this advice.

I have a few old rat race wooden(?) 8 x 9 props left.
We arn't allowed performance enhancing exhausts on Weathermen, so may have to run open exhaust, - lots of noise, bit less speed?
Regarding running in, this may be too late. My worry is that it may already be run out. But it doesn't look too bad.
I've established the head bolts are retapped 4BA. The front housing may also be due for similar treatment.
Weatherman has fixed u/c.
I recall when these engines were in use over here several years ago, loose crankpins were a problem.
Anyone make bullet proof rods? I guess the 7.5 DF engine will have a solid rod?
I do have RI motor also, for a full blown speed model in due course. First I have to discover if I can still get round a pylon!

I new the man who did the development for K&B on the 6.5 there were two distinct version the Formula 1 racing engine, RIRE this was timed for a mini pipe because AMA did not allow full pipes in Formula 1 racing. The other engine was a FIRE this motor was timed to a 180 degrees and was intended for a full pipe, this was the engine I had. Sorry to say the F1 engine was over shadowed by the highly modified ST .45X that Dave Shadel made famous and from engines by Dubb Jett, the K&B F1 engine never quite lived up to the later engines. I flew mine on a Bill Evens 540 Simitar, and lord I wish I could remember the name of the guy who built it, he was really upset when I told him what fuel and prop I originally used. The compression was set up for more nitro and whole lot less prop.
The K&B 7.5 was purely a ducted fan engine with a Perry carb and Perry pump for fuel delivery. It too was designed for a full pipe and mucho revs. My flying buddy took the 6.5 off his Simitar and replaced it with a 7.5, that was nothing short of insane.
Andy Borgogna

The FI engines were used in all applications and were not constrained to F1.

K/B (young John Brodbeck) sent me samples of both the 6.5 and the 5.8 when they first appeared. I found that the FI version was superior to the rear intake in every test I made. That is until the crankshafts started to break across the pressed-in crank pin. I used them in both Fast Rat (6.5) and Slow Rat (5.8).

And NONE of these engines were timed for a full pipe.

Breaking FI crankshafts was a continuing problem until 1980 when Bill Wisniewski took all of my broken samples back to K/B after the NATs and figured out what the problem was. When he sent me back the replacements, I never had another failure in the following 4 years that I competed using them.

Not saying that pipe-timed liners didn't exist, but the engines from K/B that I had/have were/are not pipe timed.

I have nothing to say about the 7.5 since they were not used (legally) in anything that I flew back in those days. Nor can I speak to something K/B may have produced in the last days of their existence. My use of K/B stuff pretty much ended when we dropped the fuel allowed in CL Racing to 10%: I was pretty much off into F2C then and never really tried to pick up the game after that.

Bill

Bill
out of curiosity what year did the fuel drop to 10%?

I know over a few short years we dropped from 4-5 pilots down to 2 in Fast Rat and unlimited fuel.
Last event I was involved with was Houston at the middle end of 75 when Bobby and Stubbly flew of for 1st and even with just the 2 in the circle it was tough on them, both wising the end would come and not caring who won!LOL

Not sure if the FI was available when we got the 6.5, Did hear that the FI was better than the RI but never wanted to believe it could be with less supercharging(crank case) compression ratio. I do know the disk could be troublesome and fail but never had one fail.
Known for my hard head though...

I think a 6.5 RI hold current F40 record set in last few years.
Haven't kept up on recent events


I think that should probably be ST X40 not 45X as pylon was limited same as Rat to .40(6.5)Have never seen 45X but been out along time.
The 2 X40s I have have both had the chrome on the liners fail on first run. Very nice looking heavy paper weights!!

So for F40 I currently have very tired 6.5 and 2 paper weights with one new airplane.....

So what was the fix for the crank pin? I want to check my engines because, we still race them (5.8 on suction).


MM

David, the fuel drop was made in 1984 after the Reno NATs. Stuff was just getting out of hand. The lower nitro helped for a while. Ultimately the very best Rats were back to their speeds from the high nitro days, but Goodyear and Slow Rat never made it that far back. Close, but not quite.

As I recall, the FI became available in the later 70's. The 6.5 first showed up in 1976 (from memory, perhaps a bit faulty). I know I ran a 6.5 the first time at the Dayton NATs in '76. Had just received it and had no time to figure out what it took to make run. Was blowing plugs so bad that I kept adding shims until it stopped. Had .036" head clearance but it still was godzilla-strong! Rusty Brown flew for me at those NATs.

Walt, Bill W. told me that they took all of my failed parts and found that they suffered from machining errors. The circular cut which created the counterweight on each side of the crank pin area wasn't centered properly in the crank web. He said that on some of the cranks, the remaining material that was hidden underneath the packing band was paper thin. He also told me that they made a change in the material that he cranks were made from. That's all he would say, but I never had another failure after that, and I suspect that anything produced after about 1980 would be o.k. And I can't believe ANYTHING we could do today using a 5.8 on suction and low nitro would stress the crank like we did with the Slow Rats at 13.2 and 60% nitro!

Bill

Long winded tonight........

Godzilla fits Bill!
Mine was known as King Kong...

Did some checking on date of last Nats I flew in-1975 so that places our 6.5 late 74-early 75.
At the end of 75 this 6.5 was the only one I ever saw. Others were running STs and OS(or Enya?)and couldn't touch King Kong.
Have no idea where this engine came from as Bobby just showed up with it one day. Suspect my dad who was good at spending money and making calls and deals was the silent culprit.
Was winter time for sure I remember sitting in front of the fire place
De-Buring, radiusing and fitting it.
Called John B and told him there was no way that piston/sleeve was going to work--must be defective or sumtin? Once he stopped sputtering and laughing he educated me on pinch..cool idea.

Other stuff I remember:
We did not put any air onto engine--completly enclosed with oly a 1/8th inch dia. hole in front
The massive amount of fuel burned did the cooling.

Never ever did I let it run peaked out--if it did I had Bobby hit the shut off. I truthfull was afraid that something bad was going to happen with it peaked. actually was kind of scary.

1 new K&B 1L plug every heat. element would be mangled at the end of heat

1st-2nd flip hot starts--EVERY TIME!

Toward the end of tank as it would lean out a little was passing others ever 3-5 laps. How Bobby managed? Stub and others worked with him on passing.

Ian
on the props. Dug out the old Rat prop box.
What I find are untouched 8.75x8.5 Revup pylon racing/speed series 400
never used.
I find on same brand/series that size was sanded off in balancing.
it appears to be an 8x9 or 8x8.5
The prop on my F40 and useless(new paper weight) X-40 is a 8x8.5
>Also find the F40 prop hand marked 8x9=7 3/8X10
Hard to read back of prop, looks like 176.4mph. This prop is from the first F40 event we ran end of 75 and the last time I pitted it(quit flying)in Houston.
My memory was a real fat rich run that came in a little about 1/2 way through. We did win rat and F40 that day.

Bobby went to Nats to race, I went for combat. Girl friend drug me off and Bobby got help from others who decided they knew best(Jim Ong, Darrel W, Ron Jacobs) who changed to a fiber glass 8x8 prop, changed to some odd plug(glowbee?) and no telling what else. They never got it started.
I think to this day Bobby is still upset with his disappearing engine boy.
The engine disappeared at Bobby's dads house.
Ron wound up with that airplane and Darrel's.
Ron called one day and was going to throw it all away as he was moving so I picked them up with Rons also.
Ron kept his engine. Darrel's O.S was there.
Ran across Bobby and gave his airplane to him and the other 2 to Darrel.
Best I could do.

picture of useless X40.
Sure would like to find good piston liner for 6.5 I recently picked up


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