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Valve Train Failure

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I know....I say it over and over again but I still insist that the domed lifter surface is the cause of the cam failures.
Since I grind my lifters dead flat all cam problems disappeared.
The good thing, you can reuse old lifters after grinding.
When a lot grinding is needed to get a good surface then hardening is needed too.

Cheers
Chris
 
swift6 said:
TheSearcherMan said:
As much as you'd like to blame the suppliers, it's really not their fault.
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Gee, let me get out my hankerchief because I think I'm going to start crying for poor unfortunate Moss, et al. :cry: Hey, these guys are businessmen, and if they know something is wrong, they should notify customers. In recent years I have purchased and received lots of crap parts from all of the big three. So, I'm not singling out Moss. I have been fortunate that the defects have been quite obvious, (remember the TR-3 fan with the loose rivets). Not so with critical engine components. Unless you have access to metallurgical testing (which can be expensive) you would never know until you had the unfortunate incident reported here.

Good luck!
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But then you could argue caveat emptor - I bought lifters that were hardness tested for just that reason.

They cost quite a bit more, but then you get what you pay for...

That said, I wouldn't wish a messed up cam on anyone.
 
With most flat tappet cams, the lobes are ground with a very slight fore-aft taper, around 0.002". The lifters are slightly domed. Usually the lifter centers are slightly offset from cam lobe centers. Lifters should have around 0.002" clearance in their bores.

This all works together to promote lifter rotation which distributes the pressure & wear over the entire lifter & cam lobe surfaces.

A flat bottom lifter on a tapered cam lobe would only contact the lobe on the highest portion of it's taper. Contact pressures would be high but the lifter would rotate & work if the parts are hard enough.

A nontapered lobe with a non domed lifter would still have the desirable rotation if the lifter centers were offset & lifter diameters were larger than cam lobe width. ALA mushroom lifters. Old Ford flatheads, maybe some others.

The original engine designers were careful to get a combination of these variables which would give long cam & lifter life.

After market cams & lifters may or may not be correctly designed & manufactured to work together & be optimum.

This is in addition to having correct cam & lifter hardness. Most good shops have a hardness tester with which they can easily check hardness on the Rockwell "C" scale. I personally never install a cam & lifters unless they measure RC55 or greater. It's important to check ALL lobes & ALL lifters. A lot of the aftermarket parts won't pass this test. Don't take the seller's word for it.

Lifters should have about 0.002" clearance in their bores. Check for free rotation & free vertical travel before assembling the rest of the engine. If the lifters don't have enough clearance, hone the lifter bores.

When you first fire a new engine for cam break in, observe all pushrods for rotation. If some are not rotating, a push with your finger to start rotation will usually do the trick. Sometimes several pushes will be needed. If any still refuse to rotate, there is no use in continuing to run the engine. Pull it down as far as needed & correct the problem.

I would check for rotation frequently during the first hours of engine operation. No need to mention proper cam & lifter lube during assembly & using an oil & or additive with sufficient ZDDP.

Just some observations from an old guy who has been building all types of race engines for 55 years.
D
 
Hi Dave,

what you write is an absolute perfect explanation of several cam and lifter designs.

I have cams from about 4 manufacturers here and non of them has a tapered lobe. They are parallel to the shaft axis.

But all lifters you can buy has a very high dome.
End of story is, that the lifters don't rotate properly on most of the cams.

I have NOS lifters from Standard Triumph and they are dead flat. So I started year 2006, after several cam failures, to regrind the lifters to a flat surface.

The best tuning I ever did to that engine.

Cheers
Chris (who has done today some suspension setup tests on the autobahn crossing)
 
MadMarx, it is my understanding, TR6 lifters and cam were flat and not tapered. I would like to know, the 4 cams you have, if you put them side by side, do the lobes line up? The lobe location is what make the lifters spin in a TR6.
 
Thats the problem, the 2 new cams I have, some do not appear to be offset, most are, some way more than others. If you put the 4 cams you said you had, side by side, do the lobes line up?
 
FYI MadMarx is talking about 4-cylinder cams, not 6 cylinder cams, two seperate families of engines (and not just in cylinder count) so I am not sure how accurate the info from one would be to the other. It might be, but it might not.
 
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