Noise from timing chain area

[John C.]

67 L79 327/350 HP engine was rebuilt approximately 18 months ago. Noticed last week a consistent noise from the timing chain area that is directly proportionate to the RPM's. The noise appears to be the timing chain or gear slightly contacting the block or timing gear cover. The noise goes away completely once the clutch pedal is slightly depressed enough for the through out bearing to make initial contact. Using a scope I could detect the noise from the timing gear area while the bell housing was quiet and I believe eliminating the through out bearing as the culprit. The only component which has not been replaced to my knowledge is the harmonic balancer. With the clutch fully depressed the engine sounds perfect at 3000 rpm. Duke Williams and the machinist have questioned the possibility of failed thrust bearings allowing the crank to move excessively so that the timing chain or harmonic balancer come in contact with the cover, curing itself when the crank move forwards once the clutch pedal is slightly depressed. The balancer may be failing but I'm not sure if it would cause this issue. The machinist suggested dropping the oil pan to inspect the crank for excessive movement. I would appreciate any comments if anyone else had ever experienced a similar issue. Thanks John Cianciolo (9728)

[Jim T.]

Re: Noise from timing chain area

John I rebuilt my 64's 327/300 many years ago and the aftermarket cam manufacturer Crower located in San Diego/Chula Vista, CA supplied a round piece of wood that installed in the camshaft gear that would limit the movement of the camshaft forward to the timing cover. I have no idea if you could have camshaft movement which would change the position enough to give you the noise you mentioned.

[Domenic T.]

Re: Noise from timing chain area

John,
The cam follows the crankshaft gear. the thrust bearings on the crank can be tested with the pan on.
Even though the cam follows the crank gear it can't back up because of the cam gear to block fit (cast to cast), like a bearing.
The cam plug at the rear of the engine just in front of the flywheel can push the cam forward if it is installed to far in the block, flush
is the magic spacing for the plug.
Pushing the clutch in will move the crank forward and the cam should follow the movement of the crank.
Could the cam plug be rubbing? The noise can travel thru the cam.
You should be able to check the crank end play with the pan on, a dial indicator works great. That might save removing the pan if it is not the crank.
I have seen the cam plugs push the cam forward when in to far and seen where the cam gear wore the block when they used a teflon button to
hold the cam from hitting the timing cover, but the button was a race set up, not stock.

GOOD luck DOM

[John C.]

Re: Noise from timing chain area

Thanks everyone, I appreciate your help and think I have enough information to evaluate. Thanks again, JC

[Timothy B.]

Re: Noise from timing chain area

John,

Don't rule out a problem with the clutch fork, if the noise stops with clutch engagement that's a indicator of a problem in the bell housing.

[Gene M.]

Re: Noise from timing chain area

John,
Saw this once on a BB. As it turns out the cam lobes were wearing and allowed for the thrust force that normally keeps the cam biased toward the rear to shift around. Normally the gears do that but S%*# happens.

[John C.]

Re: Noise from timing chain area

Tim, the noise is not detectable with a scope at the bell housing but is detectable at the timing cover. I am assuming therefore that its in the front area unless its being transferred. It does stop way before the clutch is engaged as it actually stops once the play is taken out of the clutch pedal when just starting to engage the throw out bearing. All of these components have less than 2000 miles on them with the exception of the harmonic balancer.

Gene, the cam has approximately the same mileage and it is a roller rocker system so I'm in hopes that its not internal to the engine although it could be. I'll inspect this closer this weekend probaly start removing the balancer and timing cover to look for wear unless something else is more obvious. If it is a crank or cam issue, then the next question would be why?

I appreciate all of the feed back, hopefully I'll have some answers this weekend, Thanks again JC

[Joe L.]

Re: Noise from timing chain area

Tim, the noise is not detectable with a scope at the bell housing but is detectable at the timing cover. I am assuming therefore that its in the front area unless its being transferred. It does stop way before the clutch is engaged as it actually stops once the play is taken out of the clutch pedal when just starting to engage the throw out bearing. All of these components have less than 2000 miles on them with the exception of the harmonic balancer.

Gene, the cam has approximately the same mileage and it is a roller rocker system so I'm in hopes that its not internal to the engine although it could be. I'll inspect this closer this weekend probaly start removing the balancer and timing cover to look for wear unless something else is more obvious. If it is a crank or cam issue, then the next question would be why?

I appreciate all of the feed back, hopefully I'll have some answers this weekend, Thanks again JC

John------


When you say "roller rocker system" do you mean that you are using roller rocker arms (which absolutely have nothing to do with the cam and would have no effect whatsoever on the problem you are experiencing) or do you mean you are using a roller lifter-type camshaft and lifters?

[John C.]

Re: Noise from timing chain area

Joe, it is roller lifter-type camshaft and lifters. I think I may have just found the issue though as I see rub marks on the back (engine side) of the balancer. It appears that outer ring of the balancer is slightly rubbing on the front of the timing cover and maybe the rubber is deteriorating. I believe that the outer ring should be flush with the inner ring but this outer ring appears to be offset toward the timing cover by approximately 1/16" and the rubber insulator may be shooting craps. The balancers I just reviewed online appear to be flush so this could well be the problem. Please let me know if this makes sense and thanks for your help, JC

[Joe L.]

Re: Noise from timing chain area

Joe, it is roller lifter-type camshaft and lifters. I think I may have just found the issue though as I see rub marks on the back (engine side) of the balancer. It appears that outer ring of the balancer is slightly rubbing on the front of the timing cover and maybe the rubber is deteriorating. I believe that the outer ring should be flush with the inner ring but this outer ring appears to be offset toward the timing cover by approximately 1/16" and the rubber insulator may be shooting craps. The balancers I just reviewed online appear to be flush so this could well be the problem. Please let me know if this makes sense and thanks for your help, JC

John------


Yes, it's possible that it's caused by balancer ring dislocation. However, if so you should see definite marks on the timing cover. It almost certainly would have rubbed through the paint by now.

As far as the roller lifter camshaft, with this type of set-up you MUST use a thrust button between the cam and the timing cover. It's also highly advisable to use a timing cover with a reinforcement welded or brazed to the center inside for contact by the thrust button. In addition, it's highly advisable to use a camshaft sprocket machined to accept a roller thrust bearing. If the engine lacks the thrust button, it will cause problems just as you are experiencing.

[John C.]

Re: Noise from timing chain area

Thanks Joe for the heads up, I am in communication with the engine builder who I believe in and I'll run these questions by him. I do believe that I'll see the marks on the timing cover as soon as I remove the balancer as the paint should be worn as you indicate just as it is on the balancer. Thanks for all of your help. JC