Flat tappet Cam Failure theory's.

[MrBeachcomber]

Originally Posted By: Garak

...Even back in the Chevy small block days (with high ZDDP oil) there were major issues of excessive cam wear. All our fleet vehicles had the issue. Could they have been poorly sourced? An engine design issue?...

Seen many a SBC in the shop with worn lifters/lobes on the #1 and #2 cylinder positions since these were the last to receive oil from the galleries especially during the late 70's and early 80's when the emission-controlled engines ran much hotter than the engines of the 60's. Seems like sludge/crud build-up in the oil galleries would choke down the amount of oil available to splash lubricate the lifter-lobe interface. No amount of ZDDP would have prevented this type of failure.

On a side note: When I ran my SBC in B Production racing in the 70's, we had to use factory cams. All the SBC cams were ground at Flint, MI. Chevy advised all racers to degree the cams using the #1 piston's intake lobe and then check the phasing of the exhaust lobe for accuracy. After degreeing the cam, we also checked the timing of #6 cylinder both intake and exhaust to determine the accuracy of the cam across the board. (Had to chuck one or two cams over the years, but for the most part, these factory cams were pretty accurate.)

The racing cams were broken in using light weight valve springs with plenty of black moly lubricant on the lobes and the seats of the solid lifters as well as a quart of GM's EOS in the crankcase along with the low ash 30W racing oil. After about 30 minutes of run time barring any problems, you were set to go for the rest of the racing season after installing the correct springs and setting the lash. (Of course you had to change the oil and cut open the oil filter for inspection just to make sure.)

I used the same cam & lifters for about five years before I replaced it with another factory racing cam (2nd design).

 

[punisher]

I can remember in the 70s and 80s when I would buy cams, I shopped Isky almost exclusively. I pulled a couple of those cams out (from SBCs/BBCs) for either rebuilds or swaps, and every cam was as perfect as you could expect, even the lifters were still convex.

Over the recent years there has been an influx of foreign castings/billets that do have some questionable metallurgy. Cam blanks from certain suppliers are a c**p shoot. You can find internal components like cranks and rods made overseas, China and India being two majors, that range from decent to absolute trash, same for cams/cam blanks. I think another problem is once you get away from the big cam OEMs, machining and finish can vary as well. The good stuff is still out there, but in comparison the garbage has increased as a percentage of the overall product. If you cheap out, be prepared for garbage metallurgy, improperly finished cams, improperly crowned lifters etc.

 

[MarkM66]

Originally Posted By: Tim H.
Originally Posted By: MarkM66
Just had a comp xtreme 286 flat tappet cam go flat in a 468 BBC I built.

I built the engine years ago......

but I skipped removing the inner valve springs....


And you wonder why it went flat...


Huh? I pointed out why it went flat!

 

[MarkM66]

Originally Posted By: rodinator1234
MarkM66

Just out of curiosity how much spring pressure did you have? Over the nose and on the seat.


I don't know, I lost the paperwork from the machine shop. And I now no longer care.

To me, the added trouble to "TRY" to get a flat tappet cam to work is no longer worth the potential savings. In my case, and with many others, it cost WAY more after having to go through the whole thing again.

When you build a high end show car, what's a few more hundred.

 

[rodinator1234]

I agree, I wouldn't build a flat tappet motor. My friend just put together a pretty nasty BBC, with a flat tappet, I tried to talk him out of it but couldn't. I hope it won't wipe the cam, he's runnin something like 140 off the seat and 370 over the nose. That's quiet a bit of spring pressure. We did the proper break in procedure but you just never know anymore.