top end rebuild

[dpitt]

I'm about to rebuild the top end of my 96 Cr 250. Couple questions: Do the rebuild kits come with instruction manuals? Is there much more involved than just tearing it down and putting it back together with new parts?

 

[Moparman1539]

I got alittle set of instruction when i did mine..

It was pretty seasy, pretty much taking it apart and putting it togeather.. or thats what i did.. But apparentually you are supposed to check your ring gap, and piston clearence..

i didnt do that and my bike runs GREAT.. but i might have just been lucky.. But it is pretty easy, and remember, NEVER install dry, coat the piston, and cylinder with a little 2-stroke oil.. And befre you put everything togeather clean your cylinder very well with (well.. people say warm soapy water.. but i used a whole can of break clean, and a high powered air gun..)

Have fun..

 

[Filthy_McNasty]

and remember, NEVER install dry, coat the piston, and cylinder with a little 2-stroke oil..

On that we definitely disagree. I've been installing my top-ends dry for 30 years. I only oil the bearings.

 

[DLHamblin]

On that we definitely disagree. I've been installing my top-ends dry for 30 years. I only oil the bearings.

I'm between you two, I oil up the rings and put a small bit of oil around the skirt area (and the bearings of course!).

I will bet this topic will generate a lot of differeing opinions on the wet vs dry :nod:

 

[mkelly04]

On that we definitely disagree. I've been installing my top-ends dry for 30 years. I only oil the bearings.

Do you do it dry so the rings will cut better?

On my last 2 2-strokes(kawi) the service manual recommends a light coating of oil on the cylinder.

The service manual for a yamaha 2-stroke I rebuilt for a friend said the same thing.

 

[Moparman1539]

My shop and Clymer manual told me to put a thin layer of 2-cycle oil on the piston, rings, and cylinder... And grease on the bearings.. So thats how i did it..

Yeah.. i guess everyone will have their own opinions..

 

[76GMC1500]

I work the oil into the piston ring groves and wipe the cylinder down with it. I have absolutely no idea why somebody would install a piston dry.

 

[wake_rider]

On that we definitely disagree. I've been installing my top-ends dry for 30 years. I only oil the bearings.

I've always applied a skim coat to everything. I just like to play it safe and if it fouls a few plugs getting broken in, I dont' care.

 

[Filthy_McNasty]

If there is enough oil in the fuel to lubricate the engine when it's running, why would you think it won't perform it's lubricating duties after a rebuild? Within a few seconds of running, everything will be lubed.

 

[IndyMX]

When you do a fresh rebuild, you are starting with parts that have NO lube at all on them...

I'd feel much better about that first few seconds of running time on a fresh build if there were at least a little oil in there.

 

[CRazy250]

just lightly coat the cylinder with whatever oil you mix in the gas. i dont see why not?

 

[wake_rider]

just lightly coat the cylinder with whatever oil you mix in the gas. i dont see why not?

Absolutely. The argument of "it will only run dry for the first few seconds" is terrible. Just take anything nickel plated and run a knife blade down it, see if it scores the plating. Rings have sharp edges and as soon as you run them down the interior of the cylinder without lube, you're causing scoring and future issues that could have been avoided just by taking an extra step.

 

[mox69]

If there is enough oil in the fuel to lubricate the engine when it's running, why would you think it won't perform it's lubricating duties after a rebuild? Within a few seconds of running, everything will be lubed.

Why lube? Because a "few seconds" can be the difference between getting 5 hours out of the top end or 25....

A few seconds is about 50 crank revolutions. Take and move the piston w/ rings up and down inside the cylinder 50 times with no oil. Take before and after pictures :)