cam chain and tensioner question

[jimtash]

I still get an intermittent tapping noise right at the front area where the cam chain is located along with a light miss. I put another tensioner in it a while back and it went away but now has returned. And along with that, there's a loud pulse upfront in the exhaust manifold area that's most noticeable highway cruise in 5th gear. Louder than usual I should say. Power feels OK but not as smooth as it should be. A lot more harshness than the engine should make.

Tonight I find this post on here and he was experiencing the same thing.

http://www.shoforum.com/showthread.php?t=40033&highlight=exhaust+pulse

This is exactly what's happening:

Anything's possible, you'll need to open it up to see for sure, but the lack of power coupled with a chain tensioner failing causes a "snapping" of the chain timed with the firing pulse, which aggravates the stretching (no tension, FIRE, snap into place, repeat thousands of times on your way to work).

Every time the noise happens in mine, it coincides during a firing event which ends up sounding like a slightly dead cylinder and then a slight pop in the intake follows. This is at idle. And during cruise, the slightly out of time exhaust cam is what's causing the louder pulse note. It's not in synch with the other exhaust cam. Make sense? And I should've caught it before but that rear exhaust cam might be off slightly relative to the intake.

These chains were installed on this engine which sat for who knows how long before being rebuilt. Could they've stretched from it? And what is the best way to check them to see if they're in spec? I don't think it's the tensioner causing the noise this time but the chain itself. And the cause of the slight intake backfire the engine was having because of the exhaust cam being slightly out of time.

 

[rubydist]

I don't think the cam sees any "snap" from the cylinder firing - the valves are shut at that point. However, there is a "snap" on the cam every time the valve lobes go from rising to falling on a particular valve - the cam wants to retard as it is pushing the valve open, and then advance as the valve is going closed. Same kind of pulsing on the cam, but for a different reason.

The simplest way to check the chains for wear is to remove them, and see how much they will "bend" side to side. The only way they will have side to side slop is due to clearance between the pins and bushings internal to the chain. Typically, if a timing chain will move side to side more than the width of the chain in each direction, it should be replaced.

Typically, we do not see timing chain wear to excess in these engines, but a bad tensioner for an extended time could have caused excessive wear on a chain.

 

[jimtash]

When I replaced the tensioner on the rear head, I rotated the whole assembly to make sure everything was lining up properly. And the rear cam was off ever so slightly. I had to wiggle the crank to get the cam position tool to seat. Should've caught it then and that's probably been the issue all along with the intake popping noise. Especially considering the cam sensor is ran off that cam.

The chains that are on this engine have around 90k miles but it had been sitting for years stored in a garage. I'm starting to wonder if that affected them. The inside of the engine was coated in a heavy varnish as well.

 

[SHOtimer]

I agree with rubydist....I'd take a closer look at the tensioners. The chains will not go 'bad' from sitting.

Doug

 

[jimtash]

I replaced the front chain today and it's running a lot smoother. Whereas before a vacuum gauge needle would bounce around 1inch hg, now it holds steady at 20inch hg. Maybe the chain came off a half link or was stretched? Took both tensioners off and they are fine. Cleaned out the holes and made sure they moved freely. Realigned everything up on both heads and it seems OK now. No strange noises either.

 

[rubydist]

its pretty easy for the chain to move a tooth or two when you are replacing the tensioners. one must be careful to keep that alignment correct.

 

[jimtash]

But would is cause a noise coming from that area that coincides with a miss? Not sure what happened with it because I remember using the white chain links to time it to the cam sprockets and rotated the engine around a few times to make sure everything was lined up. Even made sure with the cam holder tool.

Pleasantly surprised at the vacuum gauge reading. Plugs have a nice tan color to them and it idles smooth.

 

[rubydist]

no, the noise would be something else - like the bad tensioner, etc.