HD engine rebuild

bvilleharleycart

hi guys am getting ready to replace the piston , rings and gasket on the top end of our 1976 hd cart. The gasket was leaking really bad under the cylinder and we just couldn't get it to run right. It also leaked oil from the same place. When we got it apart we notice the crank and piston rod look extremely dry. is this normal? The cylinder is fine and not scored ect. so we figure we can just go with standard size piston. I also wondered what I should do prior to installing the new piston ie. hone the cylinder ect. I've also pulled the flywheel and the seals look fine so I didn't want to split the engine. Thanks in advance for any help .

BGW

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Lochlin

I have rebuilt a few of these buggers now though I am far from being a expert. Not sure exactly what you mean by "looks dry." If you mean you don't see any residual lubricant (oil) then yes, I believe this is normal. With the ones that I have done I noticed some minor charring, mainly on the piston, from years and years of use but never anything else. My carts did indeed look dry on the inside.

Do you know what your compression is? Anything less than 90 psi means you have an issue but your planned top end rebuild will likely solve it. That's where I would start regardless.

All the same, I wouldn't monkey with your cylinder if it looks smooth. Rebuild your top end and see what that gets you.

Just my 2 cents.

bvilleharleycart

thanks that helps.

tew45

I have ran carts with compression as low as 75 pounds but it is crying for replacement. If the piston is not galled Just replace the rings and check compression. New rings should check 85 to 90 PSI before the rings are fully seated and 90 to 95 after. Always check ring end gap before installing the new ones. Some rings I have received were too large and needed the gap set. The ring gap can be a little larger than spec but not more than .020. Normal gap is .007 t0 .017 in. Piston clearance is another thing to check on old or new piston replacements.

bvilleharleycart

what about honing the cylinder or de-glazing?

tew45

Any time you install new rings you should break the glaze or slightly hone the cylinder. Also if you use a century hone you can tell if the cylinder is out of round. Probably a set of rings will do depending on condition.

smallblock450sl

Another thing to consider. When reringing and creating more compression, I've found it useually takes a toll on old crank seals. Just because they don't seem to be leaking now, doesn't mean they won't fail after the encreased compression. Sorry, but thats the way 2 cycle's run, ring copression and crankcase pressure. Good luck with your build!

bvilleharleycart

thanks everyone, will take this all into consideration.