Visit The Dirt Forum for More Information

Author Topic:   CAM WENT FLAT
Dirt Roller

Total posts: 9
posted May 29, 2002 10:32 PM
I installed new solid cam and lifters last week and cam went flat after first heat race. Yes I followed proper break-in procedures. It was .508 lift with "Z28" springs. Any ideas to why it went flat so soon? Any input is welcomed.

Dirt Administrator

Total posts: 5556
posted May 29, 2002 10:36 PM UIN: 16262997
Spring pressures?

Dirt Freak

Total posts: 499
posted May 29, 2002 10:55 PM UIN: 23443678
I have allways run flat tappet cams and from time to time i will loose a cam from lobes going bad. I run heavy springs and dont allways pull the inner to break in but when i do they break in fine. Now the last one i did i used the oil lifters and left the inners in and it was fine. The oil lifters have a hole in the bottom that oils direct to the cam threw the lifter.

Dirt Maniac

Total posts: 135
posted May 30, 2002 12:29 PM
As a converted drag race engine builder, the solid cam/lifter combo has given me fits, being used to rollers. Granted, we're using roller-like profiles, big lifters, and pushing everything to the max, but it has still been an expensive learning experience. Here is some of what I've learned, other people may have much different opinions, and you should listen to them also. Block restrictors are bad news, as are lifter valley standpipes, no matter what the magazines say. I want as much oil on that cam as I can get, and I'll live with the "horsepower loss"! Synthetic oil is bad news with solid cams(Flame away!). The Winston cup boys spend a whole lot of time making cam tunnels that completely submerge the cam in oil, and also have rigs that break in the cam and lifters outside the engine.
The Z28 spring is a generic name for a type of spring that there are several versions of. It doesn't have an inner coil, so you can't remove that for break-in, so that complicates things. Sometimes, when they are shimmed to get a decent seat pressure, you could be close to coil bind, even with "only" .508 lift. If there was anything restricting the proper rotation of the lifter in its bore, this will do it too. Proper rotation is a must(found this out the hard way), and lifters should be disassembled and have the upper and lower edges of the oil relief chamfered and polished, and have proper clearance in their bores. Lack of rotation can also be caused by an improper fore/aft cam position.
Once a cam does go flat, it loads up the bearings with all kinds of crud, and a complete tear down is usually in order.
I've heard people say: "Sometimes they just go flat.", but I have always found a reason on the ones I have dealt with.
I also have a bunch of very aggressive cams for sale, most just missing 1 or 2 lobes!

Dirt Full Roller

Total posts: 51
posted May 30, 2002 06:54 PM
I keep a set of lower ratio rockers to use to break in the cam. Takes some of the pressure off those lobes until things are seated. If your running 1.6s then break in with a 1.5.

Nova 73
Dirt Roller

Total posts: 23
posted June 02, 2002 10:39 AM
Speedway is selling a set of 1.3 rockers for breaking in new motors,this seems to me to be easier than removing the inner springs and then reinstalling them after break-in.Anyone have any experience with these?

dryslick racer
Dirt Roller

Total posts: 8
posted June 02, 2002 03:12 PM
We run our lifter valley "plugged off" and have never lost a cam. One of the most common causes of cam failure is lack of connecting rod side clearance. The oil that is sprayed from between the rods is what oils the camshaft as the rods swing by the cam. The lifters with the hole burned into them will probably cover up the problem and could not hurt anyway.Make sure you are running oil restrictors with a solid lift cam.

Dirt Forum Racer

Total posts: 87
posted June 02, 2002 10:28 PM
The "Z28" springs were commonly referred to as the valve springs that came on the 302 chevy smallblocks from 1967-1969. They have decent seat pressure but weren't really meant to be used on a cam with over .500 lift. The 30-30 Duntov cam that came in those engines only had .447 lift provided the valves were set at .030 and .030. You may have been a victim of "coil-bind", especially if any of those springs are shimmed for increased seat pressure. If the springs are binding you have several options you can go with. Check with a local shop that reworks heads to see about having them machined to accept larger springs or even going with a slightly longer valve will give springs a little more travel, provided that they are strong enough to maintain the seat pressure you need. Hope this helps!

Dirt Freak

Total posts: 467
posted June 03, 2002 09:52 PM

On the subject of lifter rotation ....... It is common to see stock block's and bow-tie block's with the lifter bore's machined in the wrong location (centering the lifter on the cam). You should have your machine shop check for proper lifter bore location .

Everything else that monster spoke about I agree with , other than the synthetic oil issue . We have used Mobil 1 or Royal Purple in every engine that we have built since 1992 . We have noticed a dramatic decrees in valve train wear on both flat tappet and roller engines .

Another thing you might try next , is to use the Crower Cool Face lifter's . They have a small EDM hole in the face of the lifter that pressure feed's oil directly to the cam lobe . We have noticed on some of our extremely radical 2bbl cam's , that this lifter has helped even more on the wear issue . I use this lifter in every solid lift flat tappet engine that we build . A few of our customer's are still running the same cam and lifter combo after 4 season's of racing . We also run no restrictor's to the top end , and no stand pipes in the lifter valley on a wet sump application .

As for valve spring's , the "Z-28" spring is a joke . It does not have enough open or closed pressure for any modern flat tappet racing cam ! All too often I get customer's who come in and talk about the great cam they just bought , and the set of "Z" spring's to go with it . At that point I immediately know that the person who sold these spring's to the person , has no clue what they are doing . If you must use a stock diameter spring , then use the Vasco spring . Generally I will set up this Vasco spring at 145lbs seat pressure , and it will go 340lbs on the nose with a .525" lift cam .

As for cam's just going flat . I have seen this before , and testing will usually show that the cam in question was a bad blank to start with . I most commonly see this with cam's that are ground in the Memphis area (not to name name's


Hendren Racing Engines
Rutherfordton , NC

Back to the Archives