Benton

This could be completely off-base, as I have not had a 911 engine apart, but have we ruled out piston to valve slap as a result of the timing being off? As in, only barely off causing a slap instead of full contact to lock the engine or break a valve?

edit: Now that I think about it, I'm not sure that is the case as it seems it wouldn't be possible for it to happen on multiple cylinders without ingesting a valve.

race911

If we're still thinking it's a lifter........... That low oil pressure at idle thing is odd for just a top end.

OK, I'll throw up something I remember doing at the track one time on a guy's car. (Steve will probably cringe as he continues to read.) This is from the solid lifter days, but there was a noise that we'd now say was a collapsed lifter in the 993 era. Couldn't figure it out. Rocker shaft slid out? No. Valve adjuster broken? No. Broken spring? No. Finally, we took an individual cylinder's rockers off, times maybe 2 or 3 (we'd kind of identified which side it was on), and started the car each time. Bad cam.

Not saying we're looking for a cam issue here, just that taking an individual cylinder out on a one-by-one basis will probably identify what's what.

bobt993

You back dated the cam sprockets. What shim setup did you use on each side since the back dating uses a different set of shims. If these are out of place you chains will not align well and there is not much room in the cam housings. Did you tension the cam chains while doing the timing and use a solid rocker to set the timing?

Mike J

I asked him if he measured the valve/piston clearances all around TDC, he did.

Ponchobroke

I would take a step back and forget about the lifters and oil pressure... If it was not making a racket would you be worried about idle oil pressure?

It could be an ignition problem? Have you isolated one of the distributors and seen the effect of removing a plug wire? Are the distributors (meaning plug wires) in sync? I assume that you may have replaced the wires or at least removed them from the caps... Did they get replaced in the correct position? You (we) could be hearing secondary detonation?

When I did my top end last spring I got a cam 180 out and it made a noise not unlike yours, had a somewhat smooth idle but couldn't rev for beans.

Just my $.02 worth... Good luck...

Like others suggest, I would not run it very long at a time until I decided to start over. Cam timing (indexing) can be accomplished, effectively with the engine in he car...just ask me how I know!!!

Mike J

Yeah, good idea, I was thinking it might be beneficial to have more details on the build and timing aspects - this is why I asked if he has done it before, but there are a few tricks and double check you can do.

One of the reasons I am asking him to listen with a sethescope or screwdriver is to isolate the sound - is it valve train or chains?

He will need to pull a valve cover or two, and run the car. Chain covers might have to come off next...

Cheers,

Mike

Mike J

I guess you did not follow my engine rebuilding thread a few years back - did exactly the same thing, but in my case, the engine would not even start. You actually could start your car which I find strange ... and I also retimed while in the car - its not that hard... as compared to the rebuild anyways.

I would have thought if it even started it would have been way more lumpy than this car. Not sure though, I only have one data sample.

Ponchobroke

Mike, actually I did follow your thread but had to drop the engine, a you did, due a leaky cam gasket. When I put it back together I screwed up and had to dop it again, this time with success.

Mike J

Hey, we are the "backwards bro's"-> Jerry Woods told me that the mistake of timing the second bank without 180 rotation is one of the most typical mistakes. Peter (original PO) confirmed with me via PM about that rotation -> but through text and not being there, I hope it went OK.

Its going to be interesting to see what's up on this one. THe interesting possible red herring is the oil pressure, even if the cams are out, the pressure should not be dropping..

Cheers,

Mike

race911

Count me in the club, too. And yes, I've started one of these three cylinders-on-a-common-crank creations.

Don't think I've ever mixed the cams up side-to-side though. Always been diligent about that from the earliest Bruce Anderson comment about the natural "L" the left cam has with the opposing lobes.

Mike J

Ok, so lets discuss this a bit. Ken/John, when you guys miss timed the cam, did the engine start, and how did it run?

In my case, I could not even get the engine to start, but I suspect if it did, it would be much rougher than Peters (the OP). The ignition would be firing a piston at the opposite side of the cycle than expected.

Cheers,

Mike

Mike J

And the Right being "Rabbit Ears" with the lobes being close together.... yeah, I remember Bruce commenting about that.

race911

This was back in the carbs-on-everything days, so a unsmooth runner on startup would be somewhat expected. Especially with the stupid aggressive cams we all wanted back then.........

Was funny to see that in the book when he finally wrote it. (For those of you who aren't aware, Bruce has pretty much been hospital bound for the past year. For those of you who've maligned him on the Excellence pricing guide over the years, know that he was truly generous with his time in cluing me in to rebuilding my first 911 engine when I wasn't so clued in at 18. My life would be wholly different today if it weren't for him and the Garretson Enterprises gang.)

Vorsicht

Another possibility, yes. I had both cams reground at Elgin and the rockers were reconditioned by Steve.

Vorsicht

I used the original shims as they were. The car is a very early 95 meaning it has the 964 sprocket assemby. The only change I made was the addition of the pins. I wonder how that setup would NOT slip as it seemed to have only a 'friction fit' setup to begin with? And yes, I tensioned the chains with a device exactly like Mike J. used. Yes, I used a solid rocker with the .1mm offset.