Is this Squash Band effect??

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I bought an Aeromarine .21 cat the other day that came with a K&B .45 engine complete w/red carb and a water cooled header. The motor looks and feels as though it has barely been used. The compression is great.

I was considering trading the motor for a .21 so I opened the head button to check the quality and noticed some shinny aluminum around the top of the piston. Furthur inspection of the head button shows as though the two may have been touching. Odd that there was no head shim. I thought all K&B motors are supplied w/at least one??

Any how, there is no "junk" or crap to do damage in the motor which is good. What are you guys raising the head clearance to to run 50%?? Is .008 good??

Overall the motor is rated as a keeper.

 

[TimD]

I'd be checking the rod and also the wrist pin / pin bosses in piston for going out of round. That goes hand in hand with a piston touching the head.

 

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The rod and pistonare good t go. What do you mean the "pin bosses" is that the name of the pin that slides through the piston to hold the rod? If so it rools smootthh!

 

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Here is a picture of the top.

 

[TimD]

The pin bosses as I call them are the parts of the piston that the pin sit's in - they can wear "out of round".

If the piston looks like it has been hitting the head then the parts I mentioned before really get damaged pretty quickly.

How does the head button look?

 

[Grimracer]

Looking at the Pic i would say that the head space was too tight an the motor run to lean. The missing chucks on the top of the piston is from detonation. Looking at the piston you can see the witness marks of the detonation to the circumference of the head squish area.

The fuel the guy was using could have also been a factor.

Grim

 

[topfuel443]

agree with Grim, definately detonation.

Grim YGM

~ James

 

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The head button is not as bad but has similar marks. The guy I bought it from said he only used it twice. Unfortunately he runs that crappy Omega fuel. I agree w/the detonation part. I'm shocked w/all the K&B motors I have I don't have a single shim for this motor.

Any of you have some to sell??

 

[MarkScott]

BD,

I've got some shims laying around and will check to see if any are for the .45.. Only motors I have are K&B, so I'm sure there are some around. I'll let you know when I get home tonight.

Mark..

OB Nut Racing..

 

[izitbrokeyet?]

Maybe it's Just me....but I've never had any good results running a K&B 7.5cc less that .11 without increasing the combustion chamber. Also, looks like detonation to me, so I'll have to agree with the "too tight" folks.

 

[GTR]

Hi Guy's

I remember reading on one of the boards somewhere that K&B 45s should never run less than 0.012 because of the sloppy and inconsistent fit of the crankpin/rod/gudgeon pin. I think they even suggested to go out as far as 0.015. Apparently if you try and run too close you can end up with the piston and head trying to occupy the same space - not good.

GT ;D

ps. Rodney I would take the piston out and try and clean the top with wet-n-dry paper. This sort of rough surface/damage will lead to more detonation.

 

[izitbrokeyet?]

oops that was .011" ;D

where's Ben Stein when you need him?

 

[izitbrokeyet?]

Another point that I think you’ll find interesting:

I’ve owned a bunch of K&B from 3.5 thru 11cc and I can’t ever remember having a stock K&B that would deck down to .008” without some cutting (not even on a 3.5cc). I’m told the air cooled SS .21 head will let you squish down to about .008” without a shim if you get lucky when you buy it (I’ve never had that type of luck). Looking at the picture you posted, I guess that someone cut the bottom of the liner lip to decrease the intake duration (that’s good on a K& B) and maybe raised the exhaust to 180?

In any case, it doesn’t look like anything that cant be taken out with some 1000 paper and a lapping plate using “figure 8” laps.

 

[MarkScott]

RCBOATS2,

Sorry man, all I have are two shims... And I have four 7.5 (2 IB and 2 OB)... Need to make them work between the four.. Got plenty of the 3.5 shims!

Mark..

 

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Thanks everyone for the good advice. I'm gonna wash it up good in my parts cleaner machine and then do like you guys said and clean the piston with some fine wet sand paper. I did find one shim that is .012 so I'm good to go there.

Outside of the ugly detonation discoloring the motor has got great compression and yeah it looks like the timing has been changed. I'll let you guys know more on that later.

I bought this with a Cat but there's no way this .45 and .21 Cat combo are gonna work. I've seen a dozen guys try to put a big motor in these little boats with no luck. They always blow over.

My goal is to get this cleaned up and either trade it for a .21 or just sell it to get the money and buy a .21 that will fit. I missed a good green head CMB .21 package on ebay about two weeks ago. It had a the .21 CMB pipe, spring, header a good looking motor and I think, I think it had a motor mount. It sold for $117.00 that's pretty **** cheap. I hurts when you simply forget to bid. Bummer days.