john73bb

I've got some funny noises in my engine. I started by disconnecting the alternator, power steering and water pump belts, noise is still there. There is a knocking noise coming from somewhere. I could hear, with my stethascope, at the timeing chain cover but not on the heads, block, valve covers, etc. so I figured it must be something in the timing chain area.

I pulled the water pump and harmonic balancer, and pulled the timing chain cover. I notice that when I crank the engine over, the timing chain sprocket moves in and out about 1/16 inch or so. The bolts holding it to the cam seem tight, and the allen head bolt I could see through the timing sprocket sprocket is tight.

How much movement is too much?

Thanks,

John.

dually4wd

With a hydraulic cam, the lifters will keep it from walking, so not much to worry about there. It sounds to me like maybe the chain is loose and hitting the inside of the timing cover. Check for marks; you may as well replace the chain anyway while it's apart.

john73bb

The chain only has about 5K miles on it. I don't see any markson the sides of the cover, but there are several marks where it looks like the chain has scraped the inside front of the cover. I don't think the chain is loose (how much deflection should there be on the chain?). What would allow the sprocket to move forward far enough to score the timing chain cover? In one place it looks like it is scored .020-.030"

marky mark

When we rebuilt my motor we installed a cam button even though it wasn't a roller cam. After about a thousand miles I started hearing a noise like yours coming from the timing cover. Turns out the cam button was hitting the front of the timing cover when the motor warmed up. Luckily no damage done. Had button removed and no more noise.

I know this doesn't fix your problem but does show that cams can and do "walk" both frontwards and backwards (had another one do that- ate into the block!). Perhaps you can get an after market timing cover and/or a slightly thicker gasket to give you more clearance. Also, look at front cam bearing to be sure cam has not moved off the bearing. Also, if possible take a peak at the lifters and make sure they are lining up close to the center of each cam lobe and not off to one end which would indicate cam movement.

Best of luck!

Regards, Mark :flag :chevy

john73bb

I have no space between my timing cover and my water pump now, so I don't know if I could put a different timing cover on or not. Although a nice chrome one might be a good idea :)

I was hoping not to have to pull the intake manifold, but I may have to. I will pull off the timing chain this evening and see what else I can see. There must be something that is different since I didn't have this noise before. Come to think of it, it all started about the time I replaced my valve springs with new ones from Comp Cams. Hmmmm :confused:

marky mark

john, that's an interesting idea that perhaps the new springs are the culprit. Not sure if you changed cam & lifters at same time or if springs you installed were stiffer or weaker than ones on beforehand. But, it could have some merit as springs would seem to create tension on the pushrods which in turn put pressure on the lifters & cam. This is just a guess but maybe you've discovered something here.

Any engine "Gurus" care to de-bunk or confirm this theory about "cam-walk'???

Regards, mark :chevy