Welcome to Modern Mopar Forum

Register now to gain access to all of our features. Once registered and logged in, you will be able to contribute to this site by submitting your own content or replying to existing content. You'll be able to customize your profile, receive reputation points as a reward for submitting content, while also communicating with other members via your own private inbox, plus much more! This message will be removed once you have signed in.

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.

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

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.

20190708_111609[1].jpg

20190708_111620[1].jpg

Share this post


Link to post
Share on other sites

 

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!

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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?

 

Share this post


Link to post
Share on other sites

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:

 

20190717_194411.jpg

20190717_194418.jpg

20190717_194506.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now