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Discussion Starter · #1 ·
After refreshing the head on my 91 900 turbo and completing a T5 swap I attempted to start the car today. After cranking for a couple seconds the engine seized abruptly. I knew something failed and it was no bueno. I tried turning over the engine by hand with a wrench and I couldn’t. I pulled the valve cover and sure enough- user error left and right. The intake cam sprocket bolt was never installed or was at least missing, and the sprocket itself fell off. My question is am I wasting my time trying to reset timing (I loosened the cam caps to relieve valve spring pressure) and try again-
Or should I just pull the head now to see how bad it is?
 

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Well, I want to have a good laugh at your expense but a very similar thing happened to me... Or, rather, I did something similar to myself. So I won't.

After fixing the problem and verifying everything I could from the outside, I did a leak down test to ensure the cylinders would still seal, and then once I got reasonable leak down values I did a compression test. Everything came back fine and I've been running that motor for a couple years.

Jamming things up was a worse symptom than I had, but I wouldn't give up hope. At low engine speed, there is a reasonable chance the cams rocked back into the closed position rather than sending the the valves into the piston, so I'd at least explore that possibility before tearing it all down again. Just be sure to inspect everything you can carefully - especially the timing chain and guides.
 

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Discussion Starter · #3 ·
Well, I want to have a good laugh at your expense but a very similar thing happened to me... Or, rather, I did something similar to myself. So I won't.

After fixing the problem and verifying everything I could from the outside, I did a leak down test to ensure the cylinders would still seal, and then once I got reasonable leak down values I did a compression test. Everything came back fine and I've been running that motor for a couple years.

Jamming things up was a worse symptom than I had, but I wouldn't give up hope. At low engine speed, there is a reasonable chance the cams rocked back into the closed position rather than sending the the valves into the piston, so I'd at least explore that possibility before tearing it all down again. Just be sure to inspect everything you can carefully - especially the timing chain and guides.
Yea I totally get the laughing, it sucks but it’s comical. I expect the worst and hope for the best but thanks for reminding me to use the scientific method I honestly didn’t think of a leak down right away.
 

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Yeah, I've done a LOT of heads on c900s and this time I forgot to torque down the cam bolt. Luckily the only damage was murdering a cam sprocket's key. I guess a first time for everything.

I would try to account for that bolt - if it's stuck around the crank sprocket it would be a problem. If it made it to the sump it's probably not the end of the world, but you might be able to fish it out through the turbo oil drain hole. But, hopefully it's on the bench somewhere wondering why it was forgotten.
 

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Discussion Starter · #5 ·
Yeah, I've done a LOT of heads on c900s and this time I forgot to torque down the cam bolt. Luckily the only damage was murdering a cam sprocket's key. I guess a first time for everything.

I would try to account for that bolt - if it's stuck around the crank sprocket it would be a problem. If it made it to the sump it's probably not the end of the world, but you might be able to fish it out through the turbo oil drain hole. But, hopefully it's on the bench somewhere wondering why it was forgotten.
Lol my guess it’s hanging out among other old fasteners. I’ll get back to it later this week. Looking into the timing cover area I didn’t see anything out of order. FWIW the clearance between the sprocket and the face of the valve cover/gasket isn’t enough for it to back out completely. And it didn’t get sheared off in the cam..
It’s just a good old case of the lights are on but nobody’s home. It’s a good reminder that there is a bit more going on here coming from the other Swedish tractor world of the Volvo b230ft far more forging engines timing wise. When I back out the chain tensioner and look down there with a light while I rotate the the crank I’ll know for sure.
 
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