250sx Top end rebuild

[diamondstealth]

Guys, I picked up a 250sx that had the top end tore off already. I've never rebuilt one of these 4-strokes. He said that the machine was kinda slow in 4th, and 5th, so thats why he tore it down. Piston looks ok, so i just ordered rings and a gasket kit. Whats the steps i need to take to line up the cam with the crank, or anything else i should know?? Valve lash specs? Thanks Guys.

:beer

[225dx]

If the machine was slow in just 4th and 5th, it probably wasn't the top end. It was more than likely the clutch. When they start going bad, the higher gear you go the worse it slips.

[225dx]

Oh yeah, welcome to the boards. :welcome: :beer :TrikesOwn

[diamondstealth]

Thanks for the welcome. I knew it was probably in the clutch, but the top end was already tore off this thing when i bought it. I don't have a clue as to how to set the cam up.

[225dx]

Get the piston TDC with the T mark on the flywheel at the timing mark. Put your cam in with the lobes facing toward the bottom end. Now look at your cam sprocket, you should see a circle around the edge somewhere, put your sprocket back in and line that circle up with the mark around the inside of the head. Put everything back together. That should make it run. It may need a little fine tuning but this will get you running.
Wes

[Huffa]

Get the piston TDC with the T mark on the flywheel at the timing mark.
Wes

He's correct but you also must have it on the compression stroke. You can tell if you do if both valves have freeplay in them where you check the gap. If one is tight you must rotate the camshaft sprocket so the mark comes around again.

Now that I re read Marks thread, putting the cam lobes down (like he said) is the same thing what I am telling you but now you know why they must be down.

[diamondstealth]

Thanks Guys, Hopefully it works out that easy.

:w00t:

[TeamGeek6]

Before putting it back together, pour a little alcohol or other thin solvent in the valve ports and see if it leaks past the valve faces. I always lap them (valves and seats) if the head comes off, its cheap insurance and not too hard to do. Also, it cant hurt to check the head and deck for flatness with plate glass. Thick piece of glass makes a pretty good, cheap surface plate.

[diamondstealth]

Smart Thinking, I'll have to take the head to my car engine guy, because i don't have a handlapper at home. If anyone knows, whats the correct procedure for adjusting the valves on these engines?