rebuilding engine

mechanickid

New Member
Aug 7, 2008
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nh
so after a ton of trouble shooting and not getting anywhere i decided to rebuild the engine. ( see Head gasket questions tread )

any thing i should do while i have the engine apart?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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63
up north now
Look at the inside of the cylinder for scoring, scratches, or burn marks. Same for the piston.

If you don't find anything, about all you can do to "re-build" one of these is buy a set of rings/piston, and/or a new cylinder too.

You can't bore them, you may hone one if you are exceedingly careful.

Exceedingly.
 

stuartracing

New Member
Dec 9, 2008
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Gainesville FL.
I just did a top end, if thats what tyou are considering a re build....Alittlec tough to get the rings in the cyl.`s, just take your time...Clean it spotless...OIL the needle bearing around the wrist pin.Port match anything while your in there...,intake port to piston,gasket`s, exh. and intake.....JMO....
Paul...
 

mechanickid

New Member
Aug 7, 2008
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nh
thanks guys.

im a bit new to engine mechanics and the language, where is the "needle bearing around the wrist pin"? what is port matching?
 

stuartracing

New Member
Dec 9, 2008
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Gainesville FL.
If you take the piston off the rod, you`ll see the needle bearins/in a cage...Just oil it up good...If you put the gaskets on their surfaces you`ll see they aren`t a perfect match to each surface....Just match up with a dremil...
Brown around the bottom of the rings is good oiling I beleive...
 

mechanickid

New Member
Aug 7, 2008
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nh
ah! thanks a lot, im going to go put it back together right now.

btw, when i went to robins auto part so get a ngk b5hs spark plug that they said they had in stock, but didn't, so they gave me a bosch equivalent. i asked them if it would burn hotter and they said it may a little. is that bad?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
If it the "equivalent" it should burn the same or very close.
Brown below the rings can be blow by, which could mean the rings are shot.
Some engines don't have needle bearings up top where the rod connects to the piston, some have a bronze bushing.
 

mechanickid

New Member
Aug 7, 2008
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nh
there was only a tiny bit of brown, and the rings were sealing very well.

it was nice to see that mine did have needle bearings.

btw, before i take EVERYTHING apart, do you have to remove the reduction gears to open the case?
 

fm2200

New Member
Nov 16, 2008
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new york city
I never heard of anyone getting away with puttting a new piston into a old bore, because the more miles you have on the engine the piston & cylinder wallls becomes egged and it's no longer round. And I guess it will run, but probably not last very long, BikeGuy-Joe says you can't rebore which is probably true. But what I do know, you must rebore to put a new piston in any engine. good luck with that fm2200