I had the cam off today to go after yet another tapping lifter. I did this about 3 weeks ago and found the weak lifter and replaced it with a known good used one. The engine really ran a smooth as silk and with no taps, that is until about a week ago and another tap started to slowly develop. Because it had run so smooth and quiet, I got spoiled, so when this new tap started, I decided to go after it.

While I had the cam out today, I thought I should look the lobes over and measure each one. I was surprised to see that there was as much as 1-1/2mm difference from to another, not one was the same measurement, some were only off 1/2 mm, but overall not consistent.

QUESTION:The spare cam I have (pictured below) is as much as 2mm difference. Are these cams well beyond their days, and should I consider a new one? Is my cam causing my lifters to fail?

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What are the cam codes?

Danny

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1984 300SD Turbo Diesel 150,000 miles

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Did you mean cam "lobes" as I indicated, or cam codes? Never heard of cam codes!

There should be numbers (cam code) stamped on the rear of the cam.

Danny

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What is the code for, and what can it tell me? The cam lobes measure between 47mm and 49mm. I would like to know if this measure is still within spec, or allowable tolerances.

why the lobes would be different. i dont think i have ever heard of a car that has different heights normally. i dont see how the lobes could wear out the lifter.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have some problems with the measuring technique.

The use of a caliper, with jaws that are quite far from the cam lobe can give you some errors. It might be a situation where you don't have the caliper directly opposite the tip of the lobe on the bottom side. We've heard of the situation where the 617 cam might not have a constant radius off the lobe.

Try this:

Measure six of the lobes and write the reading down on a piece of paper.
Put the paper away for a day so you can't remember which lobe read what value.

Go back and measure the same six lobes again and write the results down.

Compare the readings.

I'm thinking, due to the inaccuracies of measurement, that the readings will vary by at least 1 mm. In such a situation, you really need a micrometer to get readings that you have confidence in.

Furthermore, it's impossible that the cam lobes have worn randomly by 1.5 mm. So, either the cam was manufactured that way (highly doubtful) or you have measuring errors.

but i have seen several cams in different types of engines that have some lobes worn and others are just fine. when they begin to fail they seldom do it all at the same time. there is a thin chrome plating, when it wears through that the underlying cast iron is pretty soft and it wears quickly. hence some are worn a lot and some are fine. of course if you have one worn you must change the cam... you should actually be able to see the change in color of the material where it is worn through, i believe.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Would you not see some wear tracks of some type, caused by the lifter, if the wear was this great? .060 wear on the lobe is some serious erosion.

I've never seen this much wear unless the cam wasn't getting proper lubrication for some reason.

Are you comparing measurements between intake lobes and exhaust lobes? You might be seeing the difference in lift between intake and exhaust.

How about measuring the small diameter of all 12 lobes? Do you get the same reading for all 12?

Sixto
95 S420
87 300SDL

Brian, my greatest measurement taken was almost 49mm. I then tried the next lobe and it clearly passed between the caliper indicating a smaller distance. I did turn the cam a few degrees either direction within the caliper to make sure. It clearly was smaller in diameter, so too was the next lobe and the next and the next, then I'd get one lobe that closed the gap in the caliper indicating larger diameter. If you don't pass the caliper into the lobe at the correct angle, yes it will not give you correct measurements. I'm pretty sure I measured correctly!

Sixto, I'll look closer at the exhaust and intake lobes. I should mention that the spare cam has 223K, the current cam installed has about 200K. The spare indicates greater wear by 1 mm overall.

What did the lobes look like? Could you see the wear patterns? Was there excessive wear at the tip of the lobe? The numbers that you have, if correct, would reflect serious wear on more than one lobe. If true, this should be evident in the wear pattern. The worn area would be of a different surface finish than the remainder of the lobe.

I would be amazed if there was .060" wear on those lobes. But, I've been wrong before.

I'll measure again and post pictures.

Also, I wonder would a millimeter less of valve opening really effect overall running, or performance, of the engine? I can understand it may run rough if you have varied lobe dimensions, but my engine runs 0 to 60 in around 12 seconds and it runs quiet and smoother than my girlfriends Volvo S70!

I don't think the engine will even notice the fact that the valve is not opening by .060" (1.5 mm.) The engine gets more than enough air for all operating conditions. The only issue is how much air it can get at maximum rack position. In theory, it might run a tad rich at full power, if it can't quite get enough air. But, this would presume that it is perfectly calibrated for the exact amount of fuel at maximum power with maximum available air from full valve lift.

Most of these older 603 engines are running with excess air, even at full rack position, so, they won't smoke at maximum power.