I was wondering if anyone could explain to me how a cam goes flat, in saw a freshlt built, new motor. I've heard it happening, but not that often. I just don't know what has to be out of wack to cause that. Again, if anyone could explain this whether it happend to you, or someone you know, that would be great. Thanks!
HBjet
Shoulda put some viagra in the break in oil. LOL!
I've heard it can be caused by lack of improper lubercation on initial start up. Scoring the lobes and lifters that in turn causes further wear until they are basiclly flat. Others that I've heard is improper valve spring pressure (too high).
Boy I know this one. Learned the hard way. The cam and lifter are designed to make the lifter spin as the cam turns. The cam lobe is ground on a slight taper, and the lifter base is spherical ground on about a 80 inch radius to match the cam lobe taper. This puts the contact point off center causing rotation. If either part is incorrect or the lifter is tight in the bore, it wipes out. And yes, if you are running a flat tappet cam with high spring pressure, some builders use lower tension springs for break in. And of course, lots of moly cam lube.
I think the most common cause is improper break in. The cam lobes get most of there oiling from oil that slings on them from the rotating crank assembly. That is why you should keep rpm at over 2000 for the first 30 minutes of run time, if you idle during the high friction breakin time, the lobes may not get enough oil on them to keep from wearing. Lifters (non roller) must rotate in the block also. A lot of guys will drive old gummy lifters out of a block with a screwdriver and score up the bore walls enough that the lifter cant turn freely, which is certain death for your cam. Always check the be sure the lifters are completely free to move in their bores before you start to assemble the motor.
I had an engine eat a cam during break in once. It was in a boat that was new to me and a newly rebuilt engine. I had the timing set right, fuel in the float bowl, moly lube on the cam, etc. The engine started immediately ran 10 sec. then stopped. So I put more fuel in the float bowl. Then it started immediately ran 10 sec. then stopped. More fuel. After four or five times of this I checked and was getting no fuel from the tanks to the fuel pump. The aluminum fuel pickup tube had come loose from the fitting and fallen into the tank so it was not picking up fuel. By then the cam was scrap. This entailed a complete engine dismantle and reassemble. The grit had even got into the wrist pins and had to be pressed apart and reassembled.
The boat couldn't have run the way it was and the pickup tube must have fallen off since the previous use.
Moral, Flat tappet cams have a critical break in period when they need to be flooded with oil at 2500+ rpm. High lift cams exaggerate the problem. GO ROLLER !!
I'm with R C. My motor builder told me that the only thing STP was good for was lubing the cam lobs. Brake in was real inportant. He also said if you every take the lifters out for any reason( like check them out) put them back in the same hole. Originally posted by rivercrazy:
Shoulda put some viagra in the break in oil. LOL!
I've heard it can be caused by lack of improper lubercation on initial start up. Scoring the lobes and lifters that in turn causes further wear until they are basiclly flat. Others that I've heard is improper valve spring pressure (too high).
many ways putting old lifters,yoo much spring pressure,not enough lubication,or improper break in(too low idle not above 1500).A good thing too do but a pain in ass is too use soft springs to break in then go back after break in and install the proper springs.I myself have never had a cam go flat and have even used the same lifters on the same cam for rebuilds(all lifters were put back in their orinal position)done this many times.
HB, the guys gave you a wealth of info already,but I put my two bits of info as well.GM [sorry Froggy,no bashing here http://free.***boat.net/ubb/biggrin.gif]had a lenghty problem with their cams going flat at the rear banks, in the early eighties on thousands of camaro berlinettas ,due to oiling problems.Mercedes had a similar problem almost in the same timeframe [who copied who?].Mercedes fixed the problem under warranty ,by plugging [?] 2 of the 5 oil supply holes with setscrews .I thought only Olds had oiling problems before http://free.***boat.net/ubb/wink.gif.There was another info about GM frontwheel drive cars, I only learned about ,because a friend of mine ran a transmission shop.GM sent out a service bulletin to dealers to make a notch 1 1/2 inch above the oem marking on the dipstick to fill with more fluid,because these trannies mounted sideways had a problem with the fluid rushing up on the side when turning sharp at speed, prematurely burning up .There're a host of problems manufacturers don't brag about.
this is not a chevy /ford answer but it is a problem inherant to chevy's especially 350cid, the more correct definition is "soft cam" and it was a little known recall on 72 - 84 350's, it is most notable by a rough idle and usally hits on the center lobs of the cam it was due to a improper heat treat to the cam, in todays world of "roller profile" cams it is becomming more frequent to all makes as the spring rates that are required to handle the aggressive profile of the roller cams is more than metal of the cam can survive this will be even worse on a boat motor that spends it's life at higher rpms, the best solution is to not go crazy with your cam selection with todays roller profiles a .500" lift cam is just about the same as the old flat tappet at say .600" lift not to mention the reduced drag adds several ponies as well, the other thing to watch out for in preventing this is stay with a small ratio rocker like 1.5:1 or 1.6:1 this will reduce the stress on the cam and give you many happy hours of service. The best advice I can give anyone is work to release the power that you aready have in your motor instead of tring to make it make more power by adding things, due the things that make it easier for the motor to run like going full roller on the valve train and spend time in the oil pan to reduce paracitic drag like having the crank edges sharpened so it slices though the oil splashing about the pan and a windage tray is one of the best things you can add.
Crazy, Something another old motor builder told me,(Dave Zuchel). (not sure of the spelling) After you brake in the cam and you want to brake in the motor put it all the way to the wood and hang on. Originally posted by rivercrazy:
Shoulda put some viagra in the break in oil. LOL!
I've heard it can be caused by lack of improper lubercation on initial start up. Scoring the lobes and lifters that in turn causes further wear until they are basiclly flat. Others that I've heard is improper valve spring pressure (too high).
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