I just finished installing a Comp Cams K kit last weekend. Got it fired up and broken in (30 min at 2000-2500 rpm). Shut it off, changed oil and filter again, and then ran a test run. My timing light went south on me and I went by ear. Not good I know but all I could do. She drove pretty good and smooth, knowing I needed to tune the timing better.

I drove the truck to work today for the first time with the new cam and halfway here (about 8 miles) started running pretty rough and hearing a tapping noise. I am not looking forward to tearing this down again. What signs can I look for to confirm what is going on?

The engine is a 66 390, fresh heads with stainless valves and the matched springs from Comp, timing chain and cam/lifters. Edelbrock RPM intake, Holley SA 670, 30 over pistons, C6 tranny.

Any tips would be great.

 

Adjustable rockers?? Could have a few loose? Is the noise up top or bottom end??
Pull valve covers and do a quick check for any rocker with excessive lash. This will nail down the noise. If adjustable, then just re-adjust. If non-adjustables.....there is something wrong.

Is there a rash of valvetrain failures around here?? This is not a good thing.

 

i think we will see more cam failures with the new sm rated oil it has very little zddp.

 

Stock rocker shafts. Non adjustable. I haven't been able to troubleshoot, still sitting here at work, sweating bullets. Almost sounded like a slight exhaust leak, with the tapping noise that is, the one that is hard to find?

 

I think you're on to something here, what kind of oil were you using Scamardo?

 

For the break in, I used Havoline 10-40. After break in, I changed to Motorcraft 10-30.

 

this has probably already been decided previously but what oil has the most zinc in it?

 

Put a hammer handle on valve cover and ear to end of handle. It will help pinpoint the noise. If it's that light of noise...doubt it's bottom end. Sounds valvetrain related.

Or just pull cover and feel around. The loose one will tell the tale.

 

One that has the diesel "C" ratings, later than CF. Usually this means the latest, which is CI-4. The 4 on the end means it's for 4 stroke diesel engines. They are also usually also rated with the "S" ratings, so you'd see one with the SL / CI-4 ratings, usually in 15w40 grade, although some manufacturers make them in 10w30.

You'll never see a dual rated SM / CI-4 oil, since the anti-wear additive was Zinc Dialkyldithiophosphate (ZDDP for short) was severely reduced. What happens, is when the oil gasses off, it takes some ZDDP with it. This fouls up the catylitic converter (which you dont have). So the API reduced it to a bare minimum level for the SM grade. As it turns out, flat tappet cams really rely on this additive for protection. Diesel engines require a much tougher oil, and thus still have plenty of ZDDP. Ever wonder why diesel engines seem to last longer? There's your answer.

Do you remember if the Havoline and the Motorcraft that you used were SM rated? I would suspect that they are.

 

Hey Scamardo, this sounds WAY too familiar to me. 390 rebuilt with Crower cam. Just as in your case, my break-in went fine, changed oil, drove a few miles - everything seemed good. Then --- tap tap tap, that came and went, came and went and then came back with a vengence. Ended up with a wiped cam, bent pushrod(s) and beat-to-death lifter(s). The machinist says it was a "soft" cam but I don't know. From what I can gather from all of the experts here, it was probably set up wrong. I am very interested in what you find out and I hope it is nothing more than an exhaust leak or a collapsed lifter. Good luck.
jor

 

I will check the oil ratings when I get home.

I installed myself with the help of some friends. I know I got it right on installation with the exception of setting final timing. Could I be so far out (advanced) on timing that this would happen? Like I said, I drove it before today and she was real smooth. I don't even have 100 miles on it yet.

Thanks for all the tips folks. I appreciate it. Hopefully the boss lets me off early so I can get into it today.

 

Uh, if you bent pushrods, that's not just wiping out a cam lobe. You have some other interference in the valve-train that bent the pushrods... and wiped the cam with it.

Do I hear an echo in here?

Seems every time someone wipes a cam, they have bent pushrods. Wiping a cam lobe might loosen up the rocker-arm/pushrod, but would it normally bend a pushrod? Was the pushrod still seated in the lifter and rocker arm, or was it laying loose and obviously molested?

 

It does sound like a valvetrain problem. One other thing to consider. Did you measure and get the correct length pushrods? If you use the nonadjustable rocker arms, it's difficult to get the proper lifter preload. Depending on the condition of the heads, you might even need to run different length pushrods in different positions to get the proper preload. When I did my 390 I attempted to install the nonadjustable rockers....after much frustration at attempting to get everything right I opted to purchase adjustable rockers...it makes it so much easier.

 

IF the pushrod started to fall out, getting caught in the wrong position when trying to open the valve might cause it to bend?? Just a thought?

 

I think the bend occurs because of all the extra lash when the lobe is severly damaged....

Scamardo.....what grind are you running....?