Flat Tappet Cam failure.....Bad Oil???

[Olivier S]

Hi Everybody!

Spent some time to read your posts, very interesting... Even if hard to translate in french.

Just my 2 cents contribution to your discussion.

Hope you won"t mind nor feel that this is a self congratulation speech. I do not have the pretention to know anything better than all those experienced gentlemen around, and sorry if I expose here common facts, but it may hep?

Just a feedback from a (little) experience in motorsport engine engineering, and also in material studies.

The problem if I understand right is wear on your V8's timing bits.

In tribology, there are several approches concerning wear issues.

The main problem is stress on parts in the interface area and friction efficiency of the interface.
It's something that can be calculated (complicated and not an exact science).

After that there are two solutions (usually the two solutions are employed)

Reducing friction by lubricating.
Dimension hardness of parts in contact according to stress level.

In an engine other factors like friction speed (which can be very important) enters in count.

To make short (and for sure I'm not an expert and not able to calculate it), for classic lubrication (oil between parts), there is a speed limit to maintain the presence of oil between parts. When this speed is depassed, the oil film disapears, and there is a metal/metal contact, which means rapid wear.

One solution wich is employed on race engines (mor thant 10k rpm) for this kind of problem is to coat parts with solid lubricant.

I know that there is a coating called DLC (Diamond Like Coating) which is very usefull and efficient.

Exeprimenting with that would be great, maybe not a solution and deserves to be well studied. This is not cheap, and may only work for particulars applications. As I've mentionned, there must be a lot of thing to be studied like parts speed (depends on rev speed, camshaft law, rocker dimensions, spring rates and so on...)

Would be please to hear from your experiences concerning that.

Olivier.

 

[RG]

In the past two years I have put together 3 sbf's for my projects that have all been mech. flat tappet cams. The procedure I use (borrowed from the Junior Johnson and Yates engine build checklists of the early 90's) coat cams and lifters in spray on graphite lubricant and let dry overnight, coat cam and lifters with cmd #3 extreme pressure lube or isky rev lube, rotate crank 2 full rotations only to set valves before initial startup (you can find tables on doing this for most v8's online). Finally before mounting intake, pour bottle of stp in lifter bores over lifters and in lifter valley.

On initial startup using 10w-30 or sae 30wt. (depending on clearances) VR-1 conventional oil, run outer valvespring only, and circulate oil thru external oberg filter, thru oil accumulator, std. pressure pump (for wet sump), at 2k-2.5k rpm for 30 mins. Change oil and filter again with vr-1, then again at 500 miles to whatever oil you prefer.

Most guys running hi-po engines will run remote mounted oil filters anyways and an oberg and oil accumulator are easily replaced by a standard filter after break-in. Both can be had for the cost of 1 set of hyd. lifters and cam vs. the cost of flat tappet so the investment isn't that big for 1 engine and its a steal if you build multiple engines.

In my experience and after reading all kinds of articles, most flat tappet failures even those occuring thousands of miles later are due to improper break in where the lobe surfaces aren't sufficiently hardened by the initial run-in. If you have access to a dyno you can visually inspect the cam after break-in though most shops will just take off the pan and check the main bearings to verify their oil pressure settings, etc.