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3hw piston help


TimKearney

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Hello, does anyone have a Triumph 3hw piston they could measure for me please?

The bike I'm rebuilding has a non standard 72mm piston fitted.

i need to source a larger replacement, but don't know the correct pistons dimensions to cross reference with.

Even better would be if someone has encountered and solved this issue before?

Any help is much appreciated.

 

Thanks,

 

Tim

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As it looks you are on + 0.80 oversize with a piston of 72 mm. Standard bore on a 3HW is 70 mm , so it will be difficult to find a bigger oversize piston as 0.80 is really the maximum oversize you can find.

Even if you tray to go over 72 mm the cylinder wall is getting really thin.

 

Guy.

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Hello Guy,

 

Thanks for replying, as far as I have ascertained, the maximum oversize Triumph piston was +40thou.

So your information is useful, thanks. It's possible to buy 72.5mm pistons for a range of modern bikes.

I'm confident the barrel I have will stand having 10thou removed from the wall thickness.

My problem is......I don't have an original 3hw piston to compare the one in my engine to.

So I don't know wether it gives the required compression ratio etc. I would rather not go to the trouble of working this out.

I hoped someone on here could give me the gudgeon pin to crown dimension of a standard piston. This will hugely assist me

in my search for a modern oversize replacement, if that makes sense?

 

Thanks again,

 

Tim

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Tim did you buy one of Brian Tillin's 3HW front brake rods? Can't remember if it was you. If not, I'll email you his phone number. He's a Triumph singles guy, and might be able to help you with the info you need. Ron

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Hi Ron,

 

No that wasn't me, I'm doing very little to the rest of the bike until I know

i can source all the engine parts. Although I do have a set of John's fork spindles and bushes on the way.

Thanks for that chaps number btw.

 

Cheers,

 

Tim

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Tim did you buy one of Brian Tillin's 3HW front brake rods? Can't remember if it was you. If not, I'll email you his phone number. He's a Triumph singles guy, and might be able to help you with the info you need. Ron

 

Ron

It was me who purchased the brake rod and very good it is too, I can recommend Brian if anyone else needs one but I do have a standard piston if you still require any info Tim, please let me know.

 

Steve

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