School me on camshaft failure root cause

[nicpaige]

I have read many threads on camshaft failures and the many rebuilds associated with the issue. Also some great information on the many things tried in the hopes of alleviating the problem forever. However I have yet to see an explanation as to why this seems to be such a tricky or on the edge process during cam swaps and rebuilds. The 4.0 in my eyes is an extremely durable platform with so many vehicles chugging way past 250k miles on stock components. What is it about changing out to an aftermarket cam that brings these beasts to their knees? Is it the inline 6 format being so long, a lubrication issue, crappy materials in aftermarket cams, terrible spring selection causing excessive pressures? Or all of the above and others I haven't even thought of?

[bigal389]

Nic, from what I understand most aftermarket cams have a narrower lobe width which doesn't help. I have also read that poor breakin procedures or lack there of is a big contributor to cam failure. I have a friend who builds race engines for a living and he is anal about priming an engine before he ever cranks it the first time, he uses the Lucas with ZDDP for lubing all internal parts when he assembles his engines. He also says that if the engine for some reason doesn't start within 5-10 seconds on initial start up he will re-prime it due to the fact that the oil has been wiped from the cam. When he does the cam breakin he will vary the rpms between 2000-3000 for at least 30 minutes and if for some reason he has to interrupt the breakin he starts over.
Al

[SilverXJ]

Contributing factors to cam lobes going flat:
-Improper assembly: dirt, no moly/grey cam lube used on lifter foot and cam lobes
-Failure to break in: Engine not started immediately, long crank times before first fire, no or not long enough break in
-Improper parts selection: springs have to much load, parts binding, crappy lifters
-Wrong oil selection: Low zinc used and no break in additive or break in oil used during break in
-Extended idling: engine is allowed to idle for long periods, very little splash lube to the cam at idle.

Besides those we have the narrow lobes to deal with on most of our after market cams, higher spring pressures over all for performance cams, quick ramp rates which contribute to cam wear and valve train wear.

As for the cam walk issues that a few have i have no idea what the root cause is there.

[nicpaige]

Thanks for the replies. How about this, in your opinion is a camshaft in a 4.0 more prone to break in failure than other flat tappet hydraulic lifter engines?

[jeepxj3]

Thanks for the replies. How about this, in your opinion is a camshaft in a 4.0 more prone to break in failure than other flat tappet hydraulic lifter engines?

'Break' like in 2 pieces? Has that ever happened?

[SilverXJ]

Thanks for the replies. How about this, in your opinion is a camshaft in a 4.0 more prone to break in failure than other flat tappet hydraulic lifter engines?

I don't think it is. If the break in is done correctly with grey/moly lube on the cam lobes and lifter foot, fire on the first start (prime and bleed fuel system, fill all fluids, double check fasteners, set distributor indexing correctly), and ran at 2000-3000 RPM for 30 minutes.

[zjtins]

Talked to my Mechanic (does local race car engine builds). For around 8 years (or more) the forgings/castings are all from China (regardless of manufacturer) and are not heat treated as well as the older cam and crankshafts. The break-in is much longer and excessive forces on the camshaft due to too stiff springs etc. will cause damage.

[SilverXJ]

For around 8 years (or more) the forgings/castings are all from China

That is incorrect. The majority of the cam blanks are made by CMC and EPC in the US

[stroked'73]

Just an observation .....

I notice a lot of cam failure threads mention HP oil pumps in the build.

Any thoughts on a connection there?

[Cheromaniac]

Just an observation .....

I notice a lot of cam failure threads mention HP oil pumps in the build.

Any thoughts on a connection there?

No connection really. Probably just a case of HV oil pumps being used in a large number of stroker builds.
A HV oil pump could cause the distributor gear to wear out prematurely if the oil is too thick and the cold start oil pressure is above 60psi.

[redtnt]

I had a comp cam fail with about 2000 miles on the clock. 2001 gc. It took the front 3 cam bearings out.
When i built the engine i did not like how the small lobes lined up with the lifters. some hit on the middle of the lifters others more towards the rear engine side.
So i decided to try a mopar 229 cam thinking it would b the new design that uses the retaining plate, since mopar shows it for my year jeep. but when i received it it was the old style cam with the button. I decided to try the button again. the only difference being i shaved some material off the button to reduce the spring pressure because oil pressure is at the back of the block pushing cam forward. It just seemed to have to much tension to me but I have built many engines and this is the weirdest failure i have ever seen.
Ive had the 229 cam in now for about 15,000 miles and doing good(fingers crossed). i dont know if it was the cam or the button spring pressure. Maybe its a time bomb.
Hers a good deal on the mopar cam from summit it comes with lifters for 140 +ship, another reason i went with the mopar cam http://www.summitracing.com/search?Sort ... rd=4529229

[SilverXJ]

I decided to try the button again. the only difference being i shaved some material off the button to reduce the spring pressure because oil pressure is at the back of the block pushing cam forward. It just seemed to have to much tension to me but I have built many engines and this is the weirdest failure i have ever seen.

It doesn't work like that. There is no oil pressure pushing the cam forward as there is a hole in the cam shaft journal to relieve any oil from back there.

[Russ Pottenger]

I decided to try the button again. the only difference being i shaved some material off the button to reduce the spring pressure because oil pressure is at the back of the block pushing cam forward. It just seemed to have to much tension to me but I have built many engines and this is the weirdest failure i have ever seen.

It doesn't work like that. There is no oil pressure pushing the cam forward as there is a hole in the cam shaft journal to relieve any oil from back there.

X 2,

Engine oil pressure has nothing to do with camshaft movement. Taper on the camshaft lobes is what moves the cam latterly.


Russ

[Freday2005]

Enginetech now makes cams with a .610" intake and .670" exhaust lobe width. Most aftermarkets use a .500 lobe width that doesnt properly rotate the lifter as it makes contact. Flat tappet lifters are convex and the cam lobes have a slight angle as to otate the lifter as it raises and lowers it. With the narrow contact area and high spring pressures the smaller lobe cams don't have enough rotational force to keep the lifters rotating. Causing them to wipe the cam lobes. Check with enginetech for a cam with proper .610" intake and .670" exhaust lobe widths, reuse your stock cam, or get a mopar purple series cam as they all have proper lobe widths.

[HCE]

Just an observation .....

I notice a lot of cam failure threads mention HP oil pumps in the build.

Any thoughts on a connection there?

No connection really. Probably just a case of HV oil pumps being used in a large number of stroker builds.
A HV oil pump could cause the distributor gear to wear out prematurely if the oil is too thick and the cold start oil pressure is above 60psi.

Actually due to the helical nature of the distributor gears, more force on the gears could work against the tapered cams lobs and button locating the cam. Higher spring pressure could also effect cam location. If that cam lobes get to close to the center of the lifters they will cease to spin and just rub the cam.