Background Info:

I have a '74 260Z that I transplanted the block and head from a '81 280ZX into a few years back. Regarding the head, I took a new ISKY stage II cam (with matching springs and lash pads) down to my local NAPA machine shop, and had them clean and rebuild it. They said the rockers were in good condition, and there was no reason to get new ones..

After the first 1 or 2K miles, my head started making alot of noise, so I thought I should check the valve clearances. Cold and hot everything was fine. Then it starts gettting really loud. So loud that I don't even want to drive the car anymore, so I think maybe there's a stuck valve.

I was in the process of rebuilding a MN47 to replace my P90, and got to a point where I could remove the live head. When I did so, and took off the cam towers, the wear on the rockers jumped out at me. The pattern is really pronouced on the rear cylinders, and almost vanishes towards the front. The lobes on my cam near the back are very sharp, whereas they are more rounded at the front.

I'm guessing the rockers and cam are trashed now. Ideas or suggestions?

Sounds like the cam towers weren't line bored or shimmed properly. And yes, it does appear you're gonna need a new cam and hardware....

Frank

Sound like the machine shop was wrong. If your not going to replace the rockers, then have them resurfaced. The rule of thumb is a fresh surface on both sides.

you really should replace the rockers with that much wear..

looks like you weren't getting enough oil and/or were running too hot. is your cam internally oiling? if not, were you running a spray bar?

Background Info:

I have a '74 260Z that I transplanted the block and head from a '81 280ZX into a few years back. Regarding the head, I took a new ISKY stage II cam (with matching springs and lash pads) down to my local NAPA machine shop, and had them clean and rebuild it. They said the rockers were in good condition, and there was no reason to get new ones..

For the record, I don't think this was the fault of the rockers. The fact that it is worse from one end of the head to the other is extremely weird, makes me think the head was warped or the cam was bent or something. Very funky, never seen that one before...

Thanks for the input, and sorry about the picture quality - my camera is next to worthless for anything close up and the colors are terrible, hence the black and white. I definitely plan on doing this right now.

The head had to be corrected when I took it in, but they said the amount shaved wasn't an issue. Regarding overheating, the vehicle did overheat between the rebuild and current situation. Perhaps that is partially to blame as well.

I wasn't entirely comfortable taking the head to this shop since it's not something they normally work on (ie. not a Ford or Chevy), but I had little choice since I had virtually no experience at that point.

The rocker geometry looks to be way off toward the pivot. How much was shaved from the head? Did someone do a wipe test on the rockers and cam lobes? They say to never use rockers from a old cam on a new one, and even when they are reused on the same cam, it is imperitive to keep the rockers and lash pads in the order that they were removed. Keep us up on your progress! Guy

I agree with eracer1999. Do your cam and head have the same oiling style? Is the cam internally oiled? If you bought the cam for a 260, it should have been externally oiled via a spray bar. The '81 ZX head would need an internally oiled cam. From the picture, it almost looks like oil starvation.

Voila......I think you guys nailed it! Good detective work. Oil makes things run slicker and cooler.

everyone, thanks for the insight on this.

I took apart 3 L heads this weekend and I discovered why my 260's original E88 head sounded so loud before I transplanted in the L28...the very first valve was bent! I have enough heads laying around to make something work. I'm kinda looking forward to getting some street idle back too.

But now I need to investigate this lack of oil problem.