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CenTxRT

Motor died at idle, no compression

Car was idling in the garage, suddenly died.  Not electrical or fuel.  Removed valve covers, everything is moving.  Zero compression on all cylinders.  Does this sound like chain or sprocket slipped?

It's a bitch to take off the front cover on this motor because it has a motor plate so I have to support the motor with a cherry picker.  Sounds like the front cover needs to come off though.

Once again, the cam is turning but the valve timing is suddenly way off.

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So all cylinders have zero compression but you can see the valves opening and closing with the valve covers off?  Even if the chain had broken or slipped SOME cylinders should still be under compression shouldn't they?

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2 hours ago, Speedy said:

So all cylinders have zero compression but you can see the valves opening and closing with the valve covers off?  Even if the chain had broken or slipped SOME cylinders should still be under compression shouldn't they?

Yes all valves are moving.  It's a Manley double roller adjustable chain/sprocket.  The sprocket on the crank is one of those ones that has multiple keyways on it so you can vary the valve timing.  I wonder if it slipped out of the key and then caught again in another keyway on the sprocket.  When it quit there was no engine missing, misfiring or slowing down it just quickly stalled.  Or maybe the cam sprocket came loose.  Looks like the front cover needs to come off. Hopefully it didn't bend any valves.

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UPDATE: Well here's a new one on me: The cam dowel pin is sheared off and the cam sprocket slipped about 70-80 degrees to the retard side. I think the dowel pin can be replaced, so I'll do that and see if it bent anything. It happened while it was idling, so maybe I dodged a bullet.

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UPDATE:

Motor is out of the car.

I have one of those hoses that lets you pump air into the cylinder to hold valves up while you change springs.  I loosened all of the rocker arms so there is no pressure on the valves and shot air into each cylinder.  All cylinders held pressure!  Except for a little leaking past the rings into the crankcase which is normal.  I think I may have dodged a bullet!  I guess I need to fix the timing chain and do a compression test to see what I really have, but this is hopeful!  Advice?  Don't want to pull heads if I don't have to.  ARP head bolts are expensive!

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I would at least do a Borescope to see if you had any piston to valve contact. Hard to belive you didn't bend a valve or something else. These I don't believe are non interference motors.

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I hope you are right there is no damage, but my chain tensioner broke at a very light acceleration and it busted the dowel pin off and bent every fucking valve in the car.

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16 hours ago, Goehner said:

I hope you are right there is no damage, but my chain tensioner broke at a very light acceleration and it busted the dowel pin off and bent every fucking valve in the car.

Goehner, I'm having trouble finding a new dowel pin.  Did you put a new pin on your cam or replace the cam?

 

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UPDATE:

I decided to pull the cam. There is enough wear on it to justify replacement.

I went ahead and pulled the intake and heads tonight.  Take a look at the contact marks and see what you think:

 

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4 hours ago, toofart said:

What did you end up doing to those pistons?

They were about the only good parts left.  Almost every valve was bent, the springs straighten them out when they close, so it looked like they were okay, but no.

Found a spun cam bearing, so we took the pistons and crank out to see if any of them had spun and found a crack in the block!

I found a block at a local wrench-a-part, and it's all at the machine shop getting prepped for assembly.

new valves, valve job, block, crank polished, new cam/main/rod bearings, new cam/lifters, MDS plugs, timing set, gaskets, etc.  had stage 3 cam, going with stage 4 this time.

Intake manifold has no crankcase vent hole on the passenger side so I'm having them mill one.

Hope to get it all back next week so I can put it together.

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52 minutes ago, toofart said:

Wow, quite the overhaul. Did you figure out what's the root of all that carnage?

Well the front cam bearing was the one that spun.  This bearing also oils the chain, so it probably led to the cam dowel shearing and the cam spinning and taking out the valves.

The crack in the block is probably just 5 years of hard bracket racing, and I was lucky we found it because a good block at a junk yard was $210 plus the machine work. The block I found still had cross hatch in it.  It really was a very small crack but it would have expanded over time and caused even worse problems down the road.  I was able to save expensive Eagle heads that had been worked over by B.E.S. and some good pistons, rings and rods and a Manley stroker crank.

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