Mandatory parts renewal for 3.2?

[El_Mecanico]

Took apart my engine and the question is what parts do I need to replace. I know bearings are a must but what about the chains and sprockets? Car has 115k and everything looked great including pistons and cylinders. The only thing I found out of wear were the intermediate shaft bearings.

Andy

[Flat6pac]

Thats because everything is still good as long as the oil pressure is still good. 115K is just broken in. Replace the chain ramps, the intermediate shaft bearings, reseal, send the heads out to be freshened up and put it all together for the next 115k.
Bruce

[Walt Fricke]

Rod bolts. Rod bolts. Rod bolts. Porsche also says the rod bolt nuts should be replaced. Not clear to me that the nuts will have been stretched beyond their elastic limit, but that's the advice one usually gets. These bolts are the weak link in this motor. Even better would be to use ARP or Raceware bolts, which are stronger than the Porsche bolts. But the stock bolts are fine for street driven motors held within the factory rev limit.

If you are cheap like me, you could consider reusing most of the gaskets if they seem in good shape. The only stuff which can't be reused in the sealing department are the little O rings on the case through bolts. Those are always mangled.

The machinist who freshens the heads will certainly check the valve guides for wear - at least if you ask him, as now would be the time to replace any which are worn out of spec.

Bruce - my chain ramps have never looked worn. I've occasionally broken one of the plastic clip parts on disassembly or reassembly, and so had to replace. What has been your experience?

[Flat6pac]

Walt, I find that the ramps get too brittle and as you say the clips break on removal. Not like the days of yore when you would find a broken piece of rubber tearing up the gears and chain but an inexpensive safety replacement.
Bruce

[500_19B]

I am in the midst of a similar journey: 3.2 with 108K. The impetous for the tear down was valve guide wear, but I elected to seperate the case too, as I was doing the labor...

Like you, I found the intermediate bearing (aside from the valve guides) were the only parts that showed visible wear. In your case I would certainly have the heads fully done with new valve guides. There are some much better guides available today that will have great longevity.

As suggested above, I am going with ARP con-rod bolts and nuts. Although new stock bolts should be OK for the way I expect to drive this car, I could not stomach leaving a known weak point unattended to.

The other significant "upgrade" I am doing is Supertec head studs. Although none of mine were broken, the lower studs on the 3.2s are Dilavar and some experienced hands suggest that they don't take well to a second torquing. I'm not sure if that is proven or not, but in general those studs have a checkered record. A minimal approach might be to change out only the exhaust-side studs with stock steel studs. A next step up might be to refresh all 24 studs with new steel stock studs. In my case I decided to replace all 24. The cost of Supertec ($660 from Pelican) versus stock ($440) was a small enough delta that I elected to go with Supertec, which are overkill for my situation.

[El_Mecanico]

Is it common to replace the chains and sprockets for the 911? It is for most cars. Just want to make sure how many miles should you have before renewing them.

[Walt Fricke]

El Mech - I think you are going to find a variety of opinions on this one.

The high end race shop guys are unlikely to let an engine with any kind of mileage on it out of their shop without replacing these parts. The risks to their reputations are too great. Just about any shop is going to ask you to consider doing this, for the same reason.

Guys with motorcycle backgrounds seem to know a lot about chains and chain gears, and they tend to want to replace this stuff. Of course, their chains run out in the dusty, wet atmosphere, not constantly bathed in clean oil.

Cheapskates like me look at our gears to see if they seem to have, by whatever yardstick we think we have, excessive wear. Especially on the sides of the teeth, which I think comes from a bit of out of parallelism (or a lot). I also am at the point where my stock 3.0 and three race motors are all my own handiwork, for better or worse. So I have a more or less accurate estimate of how many revolutions these assemblies have had to survive. I can't imagine a need for change at less than 100,000 miles absent engine abuse for a street motor.

Changing the cam gear is, of course, no problem as it is off anyway. The idler gear is a bit of a puzzle to me - does it really matter if it is somewhat worn, as long as it keeps tension on the slack run of the chain? But it too is easy to change.

The IS gears are, in my experience as a home brewer, a pain to change. First off, the pullers I have (cheap stuff) tend to damage the gear on removal. Which isn't all that bad if you are going to replace them anyway. But not quick and easy. Then I need to do the freeze/heat thing to get the new ones on, and cross my fingers that they drop all the way on at first blush, as I don't have a press to complete the job.

It is said that you can check how the chain is working with a fairly simple test: with the chain around the gear, see if you can lift the links in the middle. If you can, chain and gear are not matched. And, I suppose, all of the pulling will be on the last tooth rather than distributed, which maybe acccellerates wear?

One thing you will hear is to replace them all together, the theory being that they wear in together, and replacing one will mean a bit of a mismatch with the others.

Porsche did one interesting trick with these, though. Because the 2:1 reduction is accomplished via the intermediate shaft, it appears that the ratios chosen cause both the crank/IS gears, and the chain to chain gears to end up with different faces contacting each other all the time, and so only every X number of revs do the same teeth on the gear to gear contact come together, and only every Y revs does a particular chain roller enter the same gear pocket. This is said to even out the wear.

One slightly reformed ex-motorcycle racer of my acquaintance thinks that uneven wear is the reason why sometimes, when timing the cams, you find the dial indicator to give slightly different readings from one pair of crank revolutions to the next.

[El_Mecanico]

Walt,

Do you think installing a new chain and keeping the existent gears would be and issue or just leave them alone?

Andy

[hcoles]

if changing the cam chains consider using the non-split chain since you have the case split. It makes me nervous thinking those small (I mean tiny) "E" clips are all that are standing in the way of disaster.

[Walt Fricke]

Andy

If this were a 100K mile plus motor, I might persuade myself that I was seeing enough chain wear that the chains should be replaced. And what the heck, replacing the gears too wasn't alllll that much more expense, now that I was in there, etc etc. But I'd consider what others suggest, as long as they give reasons and so on.

I really have no data on how much the chain wears (stretches) versus the gears wear, and how much those values, on our engines and not on motorcycle exposed drives, really matter. How much is OK?. Cam timing, for instance, falls within a range. How much wear does it take to move it outside that range (which can just be reset anyway)?

About my first engine work on a 911 was the Carrera Tensioner job, and as part of that I replaced the chain (engine still in car) because somehow that seemed the thing to do, everyone mentioned chain wear, etc. Looking back, I think that was probably a needless expense.

If the chain and gears are really worn, the tensioner has to extend farther. But I don't know of a standard spec one could use to measure this and say "go" or "no go." Maybe someone does? It isn't the extension that matters - the tensioner will do its job all the way until the left side idler arm hits the top of the chain housing.

I had good results from my split chain. Still have them in the "used but look OK' parts collection. Positioning the clip so its closed end faces the direction of rotation is recommended. But I'd not use them on a split case rebuild. In the unlikely event you decide you absolutely need to replace the chain outside of a full rebuild out in the future, easy enough to break the old unsplit chain.