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Author Topic: Engine rebuild  (Read 565 times)

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Offline OddInTheForrest

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Engine rebuild
« on: June 27, 2022, 10:38:25 AM »
Hello all

I recently got my hands on a HQ336FR, small clearing saw. It is in dire need of a total rebuild, as the engine seems to have been ran without oil.

It has a 38mm piston (585998302). My question is : 

Can i fit any odd 38mm piston from say a Hq135 or 137 chainsaw? They seem to look more or less the same. 

Has anyone tried? A chinese knock-off piston for one of those saws would set me back 20usd, but a original 38mm one is just over 100usd here in norway.

Best regards

Online JoshNZ

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Re: Engine rebuild
« Reply #1 on: July 02, 2022, 02:15:39 AM »
I think people would generally say use the correct part no. and not interchangeable, the dimensions/tolerances might be subtlety different in ways you don't notice.

But if they're not different, then it will work.

Would have to measure piston diameter, gudgeon pin diameter, ring slots (get rings to match piston), distance between gudgeon pin and crown, length of skirt, diameter of skirt (I think they make the crown slightly smaller as it runs hotter/more expanded), etc etc all critical dimensions that could mean anything from running funny to grenading itself if not right.

Offline joe_indi

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Re: Engine rebuild
« Reply #2 on: July 04, 2022, 04:30:25 AM »
How bad is the damage? Could you upload a picture? Maybe you need to consider a possible repair of the existing piston as option A

Offline OddInTheForrest

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Re: Engine rebuild
« Reply #3 on: July 20, 2022, 07:18:24 AM »
I ended up buying a new cylinder and piston after hours of work. 

Just one of those engines I guess. I was not able to get the proper compression in the cylinder no matter what I did, so i had to bite the bullet and get OEM parts :)

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