Just after some feedback/advice from the senior/experienced forum members about the following... Recently, I rebuilt a number of ZXR250A & C carbs so I can test different jetting and airbox configurations. As part of my testing of said carbs, I have been testing them on a ZXR250 engine that I have had sitting around for some time. My issue is actually with the engine. It has compression across all cylinders (see below), but it is at the lower end of what the manual recommends. The engine starts and runs fine (a little noisy), but it blows a lot of oil smoke as you get on the revs and the hotter the engine gets the more smoke it blows. I Pulled the pipes off and there is a LOT of black oil in the exhaust track of the head. I changed the oil and filter before testing the carbs I also topped up the radiator. I have tried a different set of pipes, but the result is still the same. the smoke is constant and more pronounced when the revs are applied. It doesn't seem like it's sucking oil when the throttle is shut as there isn't a big expulsion of smoke when the throttle is reapplied. due to my novice mechanical standing, I'm not keen to pull this engine apart, but I guess if the consensus is that it needs new rings (and/or a bore hone), then I will do that. I won't really know what the bores are like until I pull the head off. I have a bore scope, so I might stick that down there first. Thoughts?
It's going to be rings and valve stem seals mate. Compression rings will be sad and the oil control rings will be worn beyond limits. Would wager that the bores are glazed up as well. Valves will all need lapping at least but preferably cut along with the seats and then lapped. That means doing clearances too, and then cam chain tensioner, and then... on it goes.
Thanks for confirming that Adrian. I had a bad feeling I was going to have to go down this path. It's a little noisy, so top end sounds like it needs a fiddle as well as checking the cam chain limits. Anyway, by the end of it, I should have a happy little motor.
