Over size pistons

Racing K Models

Over size pistons

Postby twowrench » Mon Feb 22, 2016 3:04 pm

Hello
I am looking for a set of pistons etc for my KR project. My cylinder`s measure 2.905, I know thats HUGE. The cylinder`s came with one (1) Hepolite/Heplex piston #13047 and is a +.030 I can`t seem to find any info. on them and would like to use the cylinders and not sleeve them back to stock. Dose anyone have a line on anyone making BIG piston`s for the K`s without having them specially made.
I appreciate any and all help.
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Re: Over size pistons

Postby thefrenchowl » Mon Feb 22, 2016 4:23 pm

Hi and welcome...

You can't have much meat left in the spigots or between piston and inlet valve...

Looks like someone thought this would be a good idea and then gave up...

If it was my engine, I would source new cylinders/pistons within tolerances (KR max was +.040, 2.790 nominal...) rather than spend untold $ on pistons that I won't know before hand if they can work in such conditions...

Cheaper in the long run...

Bye for now.

Patrick
Flat Head Forever
https://web.archive.org/web/20071011184353/http://www.harleykrxlrtt.com/index.htm
I'm the one who has to die when it's time for me to die so let me live my life the way I want to...
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Re: Over size pistons

Postby EKHKHK56 » Mon Feb 22, 2016 5:09 pm

I too have a set but wasn't able to match them to date. They may be obsolete? I've heard they are possibly British Flathead pistons or even Indian. Those must be thin in the sleeve like Patrick mentions! I just ordered sleeves from LA Sleeves and went back to Std. The overbore on the KRs was limited to keep the engine displacement within the 45" rule. Std bore was 2.747" from the factory. The KR book mentions overbore to .045" to stay in class "C" rules. So .050" over would be cheating. So like Pat said .040" is it as that's the closest std oversize piston. The book says max overbore is 2.792" Erik K
Last edited by EKHKHK56 on Wed Feb 24, 2016 3:21 am, edited 1 time in total.
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Re: Over size pistons

Postby hayleyl » Mon Feb 22, 2016 5:31 pm

At 2.905 the structural integrity of the cylinder wall near the base is seriously compromised. I have a set of KH cylinders that have been bored and someone has ran them at maximum size, both cylinders have cracked just above the bottom cooling fin. I suggest sleeves or new cylinders. JE Pistons will make pistons for you to custom specs - but you'll certainly pay for the service. Cheers Hayley
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