V8 Cam Issues

[rlees]

Hi Everyone,

I just got a 97 that was not running. I am troubleshooting it now. i got it running but it runs rough, had a couple of bad coils acording to the codes and i talked to the last dealer to work on it. The dealer also said they had a compression concern on 1 cyl. I have driven it up and down the street. I got it in my garage and pulled the upper intake off and went to do a compression test. found the front cyl on the rear bank with no compression, all other between 180 and 200. I just took the valve cover off the rear and found that the cam gear on the exhaust has spun. It looks like the front was just opening which would explain the loss of compression. It looks like the others are all just closed. I am real supprised it would run with no exhaust on one bank.

I have read alot about the cam failures and know that it is an interference motor but i wonder if it is possible to fail and not hit valves. my only concern is that front exhaust. I

My question is regarding removing the cams in the car and replacing the rear one. I think I would probably weld all of them at this time. We have a real good tig welder at work. If I wire the main chain to the large cam gear is it indexed by a key or pin so it goes back in the same spot. If i loosen it from the cam will the tensioner take up more slack making it difficult to put back. I can also mark the small chain to make sure it stays the same in relation to the gears as well. I would rather get this car running than take it apart but I really dont want to have to find gaskets and things for this motor.

Thanks for any help,

Rick

I also have a 92 that i got advise here for. My son has that one.

 

[SHO U UP]

Hi Everyone,

I just got a 97 that was not running. I am troubleshooting it now. i got it running but it runs rough, had a couple of bad coils acording to the codes and i talked to the last dealer to work on it. The dealer also said they had a compression concern on 1 cyl. I have driven it up and down the street. I got it in my garage and pulled the upper intake off and went to do a compression test. found the front cyl on the rear bank with no compression, all other between 180 and 200. I just took the valve cover off the rear and found that the cam gear on the exhaust has spun. It looks like the front was just opening which would explain the loss of compression. It looks like the others are all just closed. I am real supprised it would run with no exhaust on one bank.

I have read alot about the cam failures and know that it is an interference motor but i wonder if it is possible to fail and not hit valves. my only concern is that front exhaust. I

My question is regarding removing the cams in the car and replacing the rear one. I think I would probably weld all of them at this time. We have a real good tig welder at work. If I wire the main chain to the large cam gear is it indexed by a key or pin so it goes back in the same spot. If i loosen it from the cam will the tensioner take up more slack making it difficult to put back. I can also mark the small chain to make sure it stays the same in relation to the gears as well. I would rather get this car running than take it apart but I really dont want to have to find gaskets and things for this motor.

Thanks for any help,

Rick

I also have a 92 that i got advise here for. My son has that one.

I'm pretty sure once the cam slips, there is irrervisible damage that occurs and the head(s) need to be replaced. Hence, the name "interference motor". They are not like the V-6 ones that can break a timing belt and still be usable.

 

[luigisho]

You need to pull the head and look for damage.

 

[Liquid_force]

It seems logical to me that if the slippage was slight that it could be way out of time causing it to run terrible, but not have had valve/piston collision.
Hopefully an expert, or other engine authority can confirm/correct that.

I would find it hard to believe that even if there WERE damage that the entire head would have to be replaced.

I messed up a timing belt replacement on an interference motor once bending 10 of 24 vavles. I just pulled the heads and had the damaged valves replaced. The engine ran fine on reassembly.

However, if the steel valves hit the aluminum pistons hard enough to cause piston damage I would expect the easiest repair would be replacing the engine as a whole.

 

[rlees]

It is a little suprising that it runs. The gear completely freewheels on the cam. I think i may move the cam just enough to close those valve but not open others that might colide and do a quick compression test on that cylinder. If it comes up with compression I think I will try to replace that cam and see if it runs. Is there any way to reindex the gear on the cam and weld it.

 

[ThatShoGuy]

It is a little suprising that it runs. The gear completely freewheels on the cam. I think i may move the cam just enough to close those valve but not open others that might colide and do a quick compression test on that cylinder. If it comes up with compression I think I will try to replace that cam and see if it runs. Is there any way to reindex the gear on the cam and weld it.

i was thinking just like you.. my car ran like it lost 1/2 the motor..

which it did.. my exhaust cam failed.. and the motor still ran and rev.. to bad it trashed the head.. tho i was able to get the heads rebuilt. like 6 years ago. when you could buy head gaskets and bolts right off the dealer shelf..

i just re timed the cam and had it welded all the way around.. cam has close to 35k on it with no other signs of failure.. along with the other 3..

 

[93rev2sev]

Seems to me that if the number one valve won't close, but the rest will...it's bent.