I think I may have lost the timing chain on my 87 250x. The engine spins freely, but the valvetrain doesn't move. There's also some air escaping from the exhaust when I turn the crankshaft, so I'm pretty sure that the piston is moving.

I have a 300EX shop manual, but the info regarding the timing chain is a bit lacking.

Does the camshaft have to come out to install the new chain, or is there a master link on the timing chain?

Any special tools that anyone can think of that I'll definitely need?

This will be my first major engine surgery so I want to be as prepared as possible.

Thanks in advance for any words of wisdom.

 

There is no master link so the cam has to come out. That's not hard. But if the chain broke, it could very well be laying on the bottom of the crankcase. I don't know how you can get it out without taking the engine apart. Anyone?

 

Thanks! I'd assumed that the case cover needed to come off, at least to remove the old chain. I'm more nervous about mucking around with the top end, but I suppose since it's basically dead at this point I don't have much to lose by opening it up and giving it a try.

 

If the cam chain broke then I'd be suprized if there isn't more damage when you remove the clutch cover .. The head should be removed and valves checked if your lucky just 2 will be bent , but possibly all 4 are ..

 

Looks like some good news. I got the valve cover and case cover apart today. The chain is still in one piece. It destroyed the front guide and slipped off of the sprocket on the crankshaft. There's some plastic shrapnel in the bottom of the case, but I haven't found any metal yet, so I guess that's good news.

I think that replacing the guides is more than I'm prepared to tackle, but I found someone local who's done lots of 250x engines and his rates are pretty reasonable. I'm going to disassemble and clean as much as I can to get it ready.

At a minimum, I'll replace the guides and the chain itself since I'm assuming there's a good reason it decided to let loose. I'm also inclined to swap the camshaft bearings too, although the valvetrain looked pretty pristine.

 

You need to do a leakdown before you put this thing back together for good.
If this is an interference engine some valves are going to be bent.