Cam Break In - Tips for Avoiding Wiped Lobes?

Hey all, I have wanted to cam one of my vehicles for some time, and have finally decided to do it to the 1979 Sierra. I bought a Comp Cam Thumpr 279/297, 0.479"/0.465 and Comp hydraulic flat tappet lifters for my 350 that has about 23,000 miles on it.

I am paranoid about wiping a lobe. I wanted to get some of your opinions on maybe how to minimize this risk?? Is there a fail proof way to not wipe a lobe??

I will be of course running break in oil and may even try the spray on graphite for the cam before I use assembly lube on it?

I understand the basic break in processes, I just keep hearing about these weird situations where people still wipe lobes on a cam even after following the break in process. Ive only run stock cams in my vehicles unless it was already done, so I just don’t want to mess it up.

I’ve heard this too and have done a few flat tappet cams lately with no problem. Biggest thing to make sure of is that the lifters are free to spin in the bores when you install them. Whether it be machining issues, oil carbon built up in the bore, whatever, if the lifter can’t spin by hand, you’ll wipe a lob guaranteed.

I’ve just used liberal amounts of assembly lube, cam break in additive and Rotella 15w-40 oil.

I always check and double check my set up to make sure engine fires immediately (all been carb’d motors) and once I see oil pressure I raise rpms to 2000 and rap the throttle every now and again for the 15 minutes or so of break in. That’s it.

I think the reason you hear of so many horror stories now is because people can’t help posting EVERYTHING on their social media. Good or bad. 20 years ago no one had a way to tell everyone about how they screwed something up like breaking in a cam. Now everyone can easily. It’s not rocket science. Just follow the basics, guys have been breaking in cams for the last 75+ years this way and it just works.

good luck

Ben

Ditto what Itali83 said. I have broke in many cams just the same way. High zinc content oil, or break-in additive, and high idle immediately upon fire up.

First make sure your timing is a good enough to get it started quickly, but not so advanced that it runs too hot. Make sure the cooling system is full of coolant and working well.

Lube everything properly. Find someone to assist you so they can run the throttle and you can visually check on the engine at the same time. Hook up a tach to continually check the rpm during break-in. Varying rpm from 1000-3000 for 30 minutes sounds easy until you hear how loud it is at 3k rpm. It will sound really loud with the hood up and you standing next to it, but resist the impulse to let the rpm go down to idle. The 3k rpm won’t hurt anything.

You guys are awesome. I’ve watched quite a few break in videos (at least 20 or 30) and what you all are saying is reassuring. I’m not going to skimp on break in fluid or assembly lube. Good reminder on making sure the lifter bores are good, I watched a demo on YouTube about that as well. I also need to tune my carb. I had it dialed in a while back, I would like it to be on point so that I don’t have any excess cranking situations.

As for timing, maybe you all can help me.... my truck has a crate 350 that a previous owner put in that has confused the crap out of me. It has 2 timing marks so that motor was timed by ear and feel. When I bought it, it was lazy and had the timing WAY too retarded. I bought a piston stop tool to find TDC in #1 and the line in the balancer is right, but it doesn’t line up with either of the tabs. I made my own zero reference mark that doesn’t line up with either unfortunately. I am running a conservative tune on it just because I can’t confirm total timing very easily, I need to really buy more timing tape now that I have my zero spot found, but due to the location of the 2 timing tabs, I wouldn’t be able to read it anyways. I can advance it probably another 6 degrees without it pinging, but I don’t know what the total timing is. I have a buddy who builds Chevys so I had him take a look and he told me that even with my conservative timing, his light says I’m running at 46 degrees. He said that’s not right, there’s no way it’s that high. He ended up doing some math and said I am probably sitting at about 28 degrees total timing.

What would cause this?? I plan to buy a new balancer as well, I am assuming the wrong diameter balancer could be the problem since the line on the balancer is correct according to the piston stop tool?? I also bought a new timing cover and a new timing mark. I’m done fooling with 2 marks that don’t even line up.

Easiest thing for timing to do is that if you have a clear 0DTDC mark you can see and lines up with the mark on the dampener. Just buy an adjustable timing light. You can then dial in whatever degree you want of timing on the light and still line your 0 degree mark up and it’ll be where you want it. No farting around with timing tape, extra marks etc.

As for carb, make sure the bowls are full of fuel before cranking, the idle mixture screws are even. And that’ll get it at least running for you to break it in

timing wise, make damn sure your rotor is pointing to #1 terminal and leave the locking bolt a little loose so you can adjust the timing on the fly. Set your timing light to 15-20 degrees so the second you get it running and up to 2 grand, you can adjust timing to that degree. No worries about vacuum advance or mechanical. Just set it to say 15 degrees when the motor is turning 2000-2500 and that’ll be fine. Then just watch oil pressure and water temp. Don’t shut down for anything unless loss of oil pressure or water temps over 215 or so.
Good luck.

Ben

Great stuff, thank you so much!

Is there such thing as a hardened lifter? In one of the YouTube videos that I watched, the guy mentioned that if your lifter has a line machined all around it, it’s a hardened lifter? Mine do not have that line, does that matter?

Since your truck is a 79, the orginal engine would have used the 12:00 balancer/timing cover, Dorman 635-510 is the for the new cover, and make sure to get a balancer that matches the cover, so have both be 12:00 (looking strait down from the water pump) or the 2:00 cover/balancer, and make sure to get the right size of balancer, both my 350's are 8" balancers, but ymmv.

my 76 with 2:00 timing tab

my 79 with 12:00 timing tab


For break in, follow the mfg's recommendations on proper prep, most agree with a regular style assembly lube on the bearing journals and to put moly lube on the lobes. Check lifter preload with the intake off, and make sure all the push rods are properly seated to the rocker and lifters to avoid having one fall out during break in. recheck your steps and double check little things like hoses tight, throttle cable set right, things tight, etc.

Yeah I have the 12 and 2 o’clock tabs. I will say that my 0 mark that I made falls on the 2 o clock tab but at like 12 degrees ATDC notch.... that’s why I can’t read timing tape because the indicator completely covers the top of the balancer at my TDC mark.

I have an 8” balancer currently, how can I confirm which tab is correct? What if my motor needs the 2 o clock tab? I know nothing about it. It’s definitely a lower compression motor. Something like 8:0:1 or 8:5:1, I think it’s just a 260hp crate, but I don’t know the details. That’s why I haven’t bought my balancer yet, I wasn’t sure if it was correct or not..

The engine it self does not (or crank rather) does not dictate which timing tab it uses, all that matters is that the timing tab matches the appropriate balancer. For example I could swap my 76 and 79s balancers and timing covers and both will read just the same.

There is a possibility that the outer ring on the balancer has slipped and that is why you have a wacky reading, when checking timing you do disconnect the vacuum advance and plug the port?

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@79dentside,

Fix the engine problems before you even start putting the new cam in. All those timing problems with the tabs and all that crap, fix all that before you put the new cam in. Otherwise you'll have to do all the tab business by hand. Unless you still have the old cam in then do all the correcting before you put the new cam in.

I have broke all my cams in at 1500 rpm. That's plenty high enough, besides, like has been mentioned here already to follow the manf. instructions and you'll be fine. If your engine was starting okay before, it will start this time. All these other details like correcting the timing and all can be done later since all you need to be concerned about is 20 to 30 minutes time. You can do all the carb. ajustments and timing adjustments later.

Just start the engine and let it run. You can take a small screw driver and turn you idle screw up to 1500 rpm and just let it run. If you don't have any way to see what rpm you're at then get a old tach and hook it up temporarily. It's important to see what rpm you are at. Don't be scared. As long as you've lubed it according to manf. instructions it will be okay. If it was back firing and the timing is all out of whack, and carb. stumbling and all that before, then you've got to correct all that before you start it obviously. Don't try to fix that while you're trying to break the cam in.

If the old cam is still in the motor, fix all the running problems before you put the new cam in! That way you will know all the timing and carb settings are correct. Then put the new cam in, let it run and for 20-30 min. Then you can start with setting the total timing and all that other stuff for the new cam. Don't try to fix the engine with the new cam in with everything different from the old cam.

Good call. Yep, truck is still in running order, the parts are just sitting in the garage. I’ll look into the timing deal, that is a wise idea. As for the carb, I think I got it where I want it.

I agree with Raider, get it running correctly then do the cam upgrade. As others have said it is not hard just use additive or break in oil and keep the rpms up. Though I didn’t see anyone mention about using a priming tool to get oil circulated before starting. I went to autozone and did the free rental of a priming tool, or if you have an old distributor hanging around you can mod that to work. I thought I had wiped a lobe due to a stupid mistake but I readjusted and it worked out fine. Your right though all I heard before was go roller or you will wipe out the cam! Roller would have been great but for the extra money was not an option for me. Good luck!

Everyone covered it all. Except I will add, long heat cycles. Trailer queen, or just ran for short periods of time, not good. Drive it, at least for a few, long heat cycles to harden the lobes.

A Zinc Oil Additive is important for a fit tappet lifter engine. They modern oils don’t have zinc because of catalytic converters. There is some debate on the necessity of Zinc only for break-in of if it should be uses on every oil change.