Is my 100-4 cam shot

[kurts100]

Several months ago I asked the forum about a louder than normal noise coming from the rocker shaft assembly. The car only has about 1500 miles since the engine was rebuilt and the rocker shaft was also just redone. Several of you thought that I may not have broken in my camshaft when new and that it may be the problem. Well, I finally got a dial indicator and measured the cam lift taken from the top of the push rods. My measurements in inches were, starting at the front of the engine, .284,.282,.282,.282,.284,.284,.281 and .281. Can anyone tell me if that is in the normal range for a stock cam for a '54 100-4 or is it worn?

Thanks for the help,

Kurt

 

[Dave Russell]

Hi Kurt,
It's hard to say if the cam was ground that way or is very slightly worn. Some cam grinders are not as precise as they claim. Nothing to worry about at this time. OTOH, I'd keep a check on it & see if it continues to change. If it does, there's a problem.

I had one that measured about the same variation. When I pulled it out, the cam & lifters were showing the first signs of failure.
D

 

[kurts100]

Hi Dave,

Thanks for the quick response. So those numbers seem fairly normal? I'm now going to take the side inspection panel off and check the tappets, pushrods and cam lobes. Still not sure why I'm getting such a loud tapping noise. Almost like the valve clearances aren't adjusted properly, but they are. How about the cam bearings. Could they be causing the problem? Again, they only have about 1500 miles on them.

Thanks for the advise,

Kurt

 

[glemon]

Just wanted to add something, didn't know if you had read about the new reformulated oils that have less of an additive that aids in prolonging cam and tappet life.

Most modern oils now have reduced levels of ZDDP, especially on a newly rebuilt motor you want to be sure to use a specialty oil that still has the stuff, or GM EOS additive. More at:

https://www.ttalk.info/Zddp.htm

Since this article was written I think the diesel oils have been reformulated and are not so good for our cars either.

 

[Dave Russell]

Hi Kurt,
Attached is a pic of two lifters.
The front one shows a light circular wear pattern which shows that it has been rotating as the cam turns. This helps distribute the pressure over a larger surface.

The back one shows a trough pattern through the center with raised edges. An indication that it is no longer rotating, & it's built in crown is gone. It also shows pitting in the center, the first signs of metal fatigue failure. The corresponding cam lobes showed similar pitting.

Cams are usually ground with a slight front to back taper on the lobes, the lobe centers are slightly offset from the lifter centers, AND the lifters are ground with a slight crown in their centers. ALL to promote lifter rotation which prolongs cam & lifter life.

If you actually have a couple of thousandths cam wear & the grinder did not make the lobes undersize, it's likely that the lobe's intended front to back taper has been removed.

The bottoms of the lifters should have a very shiney surface with a barely detectable circular pattern.

Your best first check is to remove the valve cover & observe the upper push rod ends for rotation with the engine at a fast idle. If they are all rotating, the intended geometry is still intact to some degree.

Sometimes on a new cam & lifters it's necessary to observe for this rotation & actually give the non rotating push rods a little help with your fingers during the first start. The lifters may be too tight in their bores, or the cam or lifters incorrectly ground. Hopefully they will take over the rotation on their own. If they don't, they are doomed to a short life. I've known fussy mechanics, myself included, to replace a new cam & or lifters to correct a non-rotation situation on start up.

I personally think that my use of the "new" formulation of Valvoline Racing Oil" with reduced ZDDP, the street legal variety, as opposed to the "Not Street Legal" formulation contributed to the beginning of my cam failure. I'm now using the same oil "VR1 Racing 20-50 street legal" along with 16 ounces of GM E.O.S. with each oil change. so far, in the first 1,200 miles on the new engine, the push rods are still rotating & the valve lash has not changed. I also think that some of the synthetic oils are too slippery for the cam to get rotating traction on the lifters & may prevent their rotation.

Since there are so many varying opinions on this issue, to each his own.
D

 

[kurts100]

Thanks Glemon and Dave. I'm definately going to be changing my oil and using the additive you both mentioned. I'll also check to see if the push rods are rotating. Maybe the cam is fine and several of the tappets are bad.

Dave, just curious if I have to replace a tappet can I just replace the one or should they all be replaced and also if a tappet is replace should a new pushrod also be fitted or can I use the old one?

Thanks again,

Kurt

 

[Dave Russell]

Each cam lobe & tappet wears in to a slightly different condition/contour. Once a set of tappets have mated to a particular cam it's very risky to interchange them. Thus the advice to always reinstall the tappets in the same locations that they came from on an old cam. Old tappets on a new cam are a sure receipe for disaster.

Your best chance would be to replace all tappets if any show signs of distress. I go so far as to have all tappets checked for a hardness of RC55 or better. One soft tappet can ruin an engine. Surprisingly, replacement tappets are not always uniformly or sufficiently hardened.

The old pushrods should be fine if none are bent. You can make a fixture with dial indicator & check/straighten any bent rods which would obviously interfere with tappet rotation.
D

 

[kurts100]

Thanks again Dave. Appreciate all you advise. I'll let you know what the results are.

Kurt