Tore down the '85 motor I am using as a replacement for the '83 in my recent car, found evidence that all intake valves are tapping the pistons - TAPPING, not Bending. The motor ran when we pulled it, but sounded like a diesel. The bottom end looks beautiful - almost upset I pulled it apart.

I dod not have a chance to verify cam timing before we pulled the flywheel off of the new motor. The cam sprocket is loose, will rotate back and forth without turning the cam itself. The belts were very oily - bad front seals.

My opinion - timing slipped enough to allow very light contact, causing the diesel noise. Timing slipped either from belt stretch from oil contamination or was placed on the sprockets a tooth off.

Any other ideas? Everything else looks good.

 

'the cam sprocket is loose'
99% sure that's your problem. If it can turn without turning the cam, then that will mess with your timing badly. Even if the gears are all lined up, the cam probably won't be.

Looks like you'll be changing intake valves. They probably won't seat right after that kind of abuse.

 

Tapping means timing is off no matter if its a loose sprocket or timing belt. Do you see a shiny spots on the piston? If so, then you will need valves.

 

Use the head and cam off of the 83. The cam pulley and cam keyway on the 85 are most likely shot. Get a replacement cam from a later 944. Has longer duration on the exhausts.

 

I was going to pull the cam apart tonight and get the whole story, but I have to work on my Suburban first. I am figuring on new intake valves, there are "almost shiny" spots on each piston, just from the intake valves. I realize the timing is off, just don't know the exact reason - did the cam loosen up and start hammering the valves, making the situation worse, or was the belt timing off, causing the valves to touch? Only the Shadow knows, now!

I do have a good head from the '83, plus access to other bits and pieces.

When you say "later 944's have longer exhaust duration" what years are you talking about?

 

85.5 and newer. The one's with the more modern dash. When you take the cam pulley off of the 83 you will find the slot in the cam and pulley elongated. The only way to fix it is to have the cam and pulley slots enlarged at a machine shop for a larger woodruff key. $$$$

Takes being off just two of the timing belt teeth to crash the valves.

 

Unfortunately, we removed the flywheel before I could confirm proper belt timing, so I will never know exactly if the belt was off. The '83 has good valves and cam, but has a broken stud in the cam housing (one of the fuel rail bolts was broken). I will just swap the '83 cam and sprocket into the '85 head (cam housing) and swap out the intake valves from the good '83 into the questionable '85 and get everything cleaned up at the machine shop.

 

Overrevving can cause the valves to kiss the pistons as well due to valve-float. Also worn-out leaky liifters and cause a delayed valve lifting motion that's not what the cam intends. There are numerous harmonics at various RPMs where the valve's motion and velocity are not as optimal as can be...