Seized engine - what could it be?
 

Hey all, looking for some help with what's hopefully not a permanent problem. A while back I started an engine rebuild on my 1988 944 with the help of a few other 944 enthusiasts: rings and rod bearings in the bottom end, and a full head rebuild. A couple months ago I finally got the engine back in and everything hooked up...and it wouldn't start. While attempting to troubleshoot the no-start issue, the engine locked up. Literally it was cranking just fine one second, and then "click". Wouldn't crank anymore. I suspected the starter, so I took that off, but I can't turn the crank by hand. It had oil and wasn't making any strange noises when I cranked it. I have the cam tower off right now and everything looks good with it. Head looks great too, no dropped valves or even cracked retainers.

I know it could be a spun rod bearing, or maybe the rings weren't installed correctly. But I'm almost positive it's not either of those, so I'm hoping there are some other things I can look into without pulling the engine again. Any suggestions? Balance shaft maybe? Flywheel stuck somehow? Bad oil pump leading to dry bottom end? Thanks in advance.

Edit: Forgot to mention, when I pulled the cam tower off, I noticed that the timing belt was loose. Loose enough that it could've jumped timing, which would explain my no-start issue...but tight enough that I still had to pry it off. Maybe a factor? I had checked timing just a few hours before and it was fine.

can you rotate the engine by hand in any direction? if you can go reverse you may have jumped timing and it is stopping against the valves. however if you can go neither way then it would be best to pull the head first and inspect the cylinders

did you make sure that all timing marks...not just on cam but also on flywheel...were lined up properly at the same time?

No, it can't be turned in either direction. I'll pull the head if I have to since the cam tower is already off anyway. And yes, the timing marks on the cam gear and the flywheel lined up. Impossible to check now since the crank won't turn.

when you pull the head, look into the cylinder bores to see if there's any evidence of gouging along the cylinder walls. The next step would be pull the oil pan, undo the rod bearing caps and see if you can push the pistons up. When you find one that won't, that'll be your issue, plus you can check the rod bearings and after that, the crankshaft bearings. When you put the bearings in did you use an assembly lube on the bearings? That prevents damage until the oil pressure comes up and lubes them.

Yep, used a generous amount of assembly lube. Can the oil pan be pulled without dropping the front suspension / crossmember? That's how I changed the rod bearings once before.

I wish you could. I replaced the rod bearings and oil pan gasket and dropped the cross member and suspension to get to it. The suspension needed new tie rod ends and all the other rubber boots replaced anyhow. Wish I had a 3 piece cross member. I figured you were planning on pulling the motor again. Good luck.....let us know what you found.

You could have the bearing shells in backwards