I thought the timing setting for a 930/16 (U.S. spec 911SC) with an SC cam is 1.1 mm, no? I overlap spec a different thing than the number used for timing the cams?

I have a 930/10 and I am getting ready to put in SC cams reground by camgrinder to 964 profile, and the timing setting accd to JD is 1.26 mm.

Gunter, your make shift mechanical tensioner for the right side is brilliant. I have been sweating how I would do that side, and now I know. :)

Bentley 152-10 Overlap Tolerance for stock cams:
930/04 0.9 - 1.1 mm
930/07 or 930/16 1.4 - 1.7 mm
Confirmed by Wayne's book 207
930/10 RoW is given as 0.9 - 1.1 mm

If JD says 1.26 mm with 964-profile, go for it.
You'll find it difficult to get a precise setting, that's why Porsche gives a tolerance.
I believe the difference from one hole to the other with the small pin is 0.2 mm??
When you do the cam timing, go around 3 times re-checking.
Don't set the tension on the chain too tight with the temporary set-up.

Silly question time...

Wayne's book shows removing the heads and cam housing as a unit. Is it necessary to take out all the rockers and cam in order to seperate the heads from the cam housing? Wayne's book only speaks to a full rebuild.

HI yes as 6 nuts are under the rockers.

regards mike

Thanks Mike... it was just a thought.

I have confirmed that the pistons and valves did touch. Any comments on the likelyhood of stretched rod bolts based on the photo?

http://forums.pelicanparts.com/uploa...1166975523.jpg

Lee:
The cam tower has to be seperated from the heads anyway to replace the bent valves.
Give us a picture of the valves so we can see the damage.

When removing the rockers, keep the shafts and rockers together and mark them for location, i.e. #1 IN & EX etc................

Cam tower removal is next on my list. Is there a way to remove the valves without a valve spring compressor?

Valve removal is not very succesful without a valve spring compressor,but if your SURE that the valve is ruined,you could use the socket and hammer method.A couple of good raps with the hammer on the socket placed on top of the spring retainer cfan due the trick.However if the valve is not hurt you could scar the valve stem. By the way looking at the picture....this is why I told you checking the valve to piston clearence is SOOOOOO important!!!! Tim

It's interesting to look up into the heads. I can't really tell that the valves are bent. I can see marks in the carbon buildup where they used to sit and compared to where they sit now, they aren't off by much. I can't even see any marks on the valves.

You indicated earlier that you had significant compression loss; some valves are bent.
You need a valve spring compressor. Don't damage the valve keepers (Collets) you'll have to re-use them.
So, you buy a compressor, then what? :rolleyes:
You cannot just throw in new valves.
Why bother spending the money? You don't have the equipment/experience to do the heads.

Bring the heads to a shop with Porsche-experience.
The seals have to be replaced.
The springs will be checked on a test stand.
The bent valves will be replaced with new ones getting a 3-angle grind to mate with the seats (Concentricity).
Valve seats and guides inspected/replaced.

If you try to do this on the cheap, you'll be sorry later.

What was the cam timing before you took it apart? :confused:

That's definitely my plan. I'm anxious to see the valves so I can get your opinion on whether or not I need to replace the rod bolts. How much of a challenge is it to replace the rod bolts without splitting the case?

I'm not sure if the machine shop is open tomorrow, but I'll have the heads in there as soon as possible.

What was the cam timing before you took it apart?
:confused:

I don't currently have the gauge and Z block. I've read the procedure from several sources and it seems to make sense. I hope that knowing the previous cam timing wasn't critical. I thought it was more a matter of curiosity.

Is a fair amount of carbon build up typical of these engines? Seems the valves hit more carbon than they did piston.

It would have helped in determining if it was correct in the first place and equal on both sides. I would have waited and checked it.

There is always carbon build-up.

The severity of the impact between piston and valve is a factor in deciding on the rod bolts.
For that, you need to look at the depth of the mark on the pistons and the bend on the valves.
Do all 6 pistons have marks?
Post a clear picture of the worst marks on the pistons and the bent valves after they come out of the heads.

The machine shop has the heads. They gave them a quick inspection and said that as far as bent valves go, they would rate them a 2 on a scale of 1-10. I'll post pics when I get them back.

Meanwhile... IF the pistons and cylinders don't end up coming off, is there anything that can/should be done about the carbon on the pistons?

Rating 2 meaning 10 is really bad and 0 is no damage?

Use a brass wire brush or a soft steel one; they come in hand-held, and round version to be mounted in a drill motor.

Rotate the pistons to the top, brush and clean.
Very important: Blow out any residue with compressed air.

If you can, find out the type rod bolts you have from PO?
ARP? OEM?

leeh dont used compressed air on piston tops. use a shop vac. no need in blowing crap all over. if compressed air is all you got tape off all open cavities so no crap can get in any openings.

Correct. They felt like it was a very light hit based on what they saw.

I believe that the bottom end of the engine is all original. Records indicate there are about 55K miles on the engine.

Lee

For what little it is worth, were this my 55K mile engine, I'd have the bent valves replaced, the good ones (surely there must be some) touched up along with all the seats (all this done by the shop), and I'd put the thing back together and get back on the road. New cylinder/head sealing rings, and a set of new valve cover gaskets, along with a couple of other ones, and you are back in business.

Hard to tell just from pictures, but the carbon doesn't look all that bad. Some carbon is normal. Clean it off and it will just come back. Sure, if you are doing a full rebuild you will clean most everything off. But why waste time and worry about some carbon particles escaping yolur vacuuming? Yes, if you do removal at TDC, and then clean up the debris, and then move that piston down, you should be able to get all the little bits off the cylinder wall now exposed. If your heads are at the shop and you are itching to do something, no harm. The shop guys will probably bead blast the carbon out of the heads. But folks run these engines out to 200K and more without ever removing a head.

Rod bolts earn their keep at the TDC where the exhaust valve is closing and the intake is opening. The air in the chamber presents little resistance to the rising piston, so about all that prevents it from trying to fly right through the head are the rod bolts. On the compression stroke you have 120 or more PSI slowing the piston down. In your case you had valves slowing things down a bit, bending them in the process.

I have most of a set of exhaust valves whose stems were bent into an S shape (not quite as amazingly dramatic as ones recently posted here on PP, but that same general shape) due to hitting 1st instead of 3d upshifting on a track. Twice. After adjusting various things externally, in my ignorance I drove the car for almost two years after that. The bent stems sawed nice grooves into the guides, and the valve heads did a reasonable job of sealing thereafter. Eventually I pulled the heads and had things fixed (this was before I owned a leakdown tester or understood the valve/piston relationship that well). Kept driving. Eventually one of the new valves had its head fall off, trashing the engine, but its bottom end was just fine when I pulled that apart.

But you have to make your own call on how worried you will be versus how deep into the engine you go. I'd be more inclined to wonder what the overrev did to the rod bearings than to the rod bolts, since it is the bearing that takes the stress at BDC with little to cushion it on either cycle. At most I'd pull one rod to check its bearing, and replace just those two rod bolts when reinstalling if it looked OK. That means just pulling one cylinder and piston off, greatly reducing the work. I did this on a race motor once where only one valve was bent (and one guide broken) due to a broken spring. Bearings looked fine, so back together it went (Raceware bolts just got torqued instead of stretch gauged, but it has held together just fine).

A shop checks valves by removing them from the head and chucking them up in a lathe or a valve grinding machine (which is a small single purpose lathe) and spinning them. You can see one that wobbles immediately, even if it is only a little wobble. I suppose this could somehow be measured, but no one bothers since functionally only zero wobble is acceptable, and they either wobble or they don't. I've tried this in my drill press, but I'm not sure that is closely enough centered to give the right information unless there is a pretty good bend. But your 2s obviously are ones with clearly visible wobble, just not as bad as they have seen. 2 or 10, they go into the scrap pile just the same.

Walt Fricke