brg2290

I have a '78 SC, the motor (~145,000 miles) of which is currently lying disassembled because of 2 broken head studs.

Yesterday, I met with the technician performing the work to talk about pistons/cylinders and camshafts. From this discussion, I came away with the understanding that his intention is to reinstall the Mahle pistons as they were removed, without re-ringing them.

I stated my interest in JE pistons. My car's compression ratio is 8.5:1, and the possibility of using JE's 9.8:1 set intrigues me.

We also discussed the camshafts today. I expressed a desire to explore a 964 or SC sport grind.

With this background, here are my questions:

1. Generally speaking, is it folly to reinstall Mahle pistons with 145,000 mi. on the clock without re-ringing them, given that a set of rings are only about $100.00?

2. If I use the JE 9.8:1 pistons, do I need to make any subsequent alterations? (I'm aware that the higher compression ratio might necessitate stronger valve springs, and I'm hoping that the higher compression ratio will not require twin-plugging to avoid detonation.)

3. If I use the JE pistons, do I have to be concerned about valve clearance?

4. Regarding the cam grind, and assuming the JE piston install, what would be an appropriate specification. (I am leaning in the direction of the 964 grind.)

5. Lastly, I have read (How To Rebuild And Modify Porsche 911 Engines - Wayne Dempsey) that reconditioning the rockers is recommended if the camshafts are to be ground. After a visual inspection, the technician performing the work on my engine stated that there was not sufficient wear to necessitate rocker arm reconditioning. So, my last question is, should the rockers be sent out with the camshafts for reconditioning simply as of course, or is it a legitimate savings to reuse minimally worn rockers on a reconditioned camshaft?

Any other pertinent thoughts and suggestions are greatly appreciated.

Thanks, Gary S.

DGaunt

Yes, Re-ringing would seem a good idea at that mileage.
When I was building my 2.7, I was advised that the limit w/o tein plugging was 9.5:1. I went with JEs and they are forged rather than cast and 100 gr. lighter. Plus they are SOOOOO pretty!
I suggest you discuss your potential mods with Jon at EBS. You wouldnt want to put in too much compression and require expensive (avgas) fuel for the street.
Higher compression will not rewuire heavier springs, but a more agressive cam may well.
Don;t forget to do the bottom end and check cam chains etc. while youre in there. Bottom ends cost peanuts "while you re in there."

Peter Zimmermann

1. Are you planning to use your CIS fuel injection?
2. Do you want to go faster, regardless of cost?
3. Do you have restrictions caused by smog equipment requirements?

Pete

brg2290

Gents, thanks for your replies.

Dave,
I will follow your suggestion and call Jon @ EBS tomorrow. Good point on the timing chains...we're going with the hydraulic tensioner upgrade kit.
As far as the bottom end, I watched yesterday as the technician manually smoothed the main bearings with a fine emory cloth or the like, and popped them out of their saddles and cleaned underneath. Unlike the intermediate shaft bearings, the main bearings still had their coating intact, with no shiny metal showing through. I asked him about replacing them, and he said his intention is to re-use them.
Also, he has reattached the rods to the crank (using new rod nuts and bolts), but I don't believe that he used new rod bearings. It may be after the fact, but I will check with him tomorrow. I'm also sure that he did not replace the rod bushings.


1. Yes, sticking with CIS.
2. No, not regardless of cost.
3. No. No longer required to emissions test.

Peter, I wonder if your #3 question is pointing in the direction of SSI's. My plan is to budget for engine internals first, and then SSI's either now or later, depending on total expenditures.

Peter Zimmermann

Yes, SSIs make for a nice improvement. Also, NEVER EVER re-use main or rod bearings!!! You're there, replace them! Unfortunately for you, if the rods are back on the crank, and the old bearings were used, you will have to buy ANOTHER set of rod bolts and nuts - they are "use once and discard" parts! About re-ringing, that depends solely if your piston/cylinder set measures within published factory wear tolerances. All (6) must be measured per the factory manual, if your technician doesn't have the correct tools to do it find a machine shop that can. Cams: Stay with stock. Compression: You won't realize a substantial benefit from an increase unless you switch to radical cams, carbs, etc. Going fast (performance increase) is always done with a package. In the old days guys would put "S" pistons in a "T" motor. It didn't do much because they didn't port the heads or use "S" cams.
Pete

Camgrinder

If you use the 9.8 JE pistons, use 964 cams. If you stay with your factory piston use the stock cam or the Sport Sc cams.

r911

I'm surprised Steve Wiener hasn't posted about the JE's. He is telling street car owners to avoid them, since at least the last couple of months. Search and you'll find his posts on this. My guess is that the Gamroth organization has seen some cars come back or has other info re longevity on these things. I have a set in my car as of about a year ago - we'll see if they last longer than I do....

Steve Weiner-Rennsport Systems

Gary:

Wise words from Mr. Zimmerman and you would be well ahead to heed them,...

Raising the compression in a CIS motor without being able to richen it up in the 4000-6500 RPM range is asking for big trouble. These things run too hot as they are and that simply adds to the problem.

If your expectation is that your rebuilt engine ought to last another 100K miles, then don't reuse many parts and stick with Mahle P/C's.

JE pistons are a fine choice for the race car folks who freshen up their motors every two years or less. The rings simply do not last long due to the piston design/shape and the larger piston-to-cylinder clearance these require.

A "rebuilt" engine is only as good as the parts that are used inside of it and if you reuse the items you are talking about, its not really rebuilt,.......IMHO of course.

I fully understand economics as well (or better) than anyone here and I simply choke when I see what things now cost, but there is no cost savings when deciding to "recycle" the 145K engine parts you currently have. You'll simply do it ALL over again in the near future and where is the economy in that?.

brg2290

randywebb and Steve,
I appreciate the insight...I had no idea there is longevity issues with a JE / street combo.

Steve and Peter,
Points well taken regarding main bearings, rod bearings etc. Communictation with the technician has actually been a bit of a challenge. When teardown began, I photocopied Bruce Anderson's engine rebuild checklist and faxed it to the tech., asking him to record the values of measurements taken so that I could see the criteria for reusing, reconditioning or replacing parts. Much to my chagrin, I have seen no evidence that he is employing this method. It has been very hard for me to question his expertise, as I am new to Porsche ownership, and his business card claims 35 years Porsche experience, In-Factory trained...etc. I guess it's time (past time) to have a serious discussion.

Camgrinder, thanks for your input. Looks like I'll be sticking with the Mahle 8.5:1, so I guess it will be the factory or sport SC grind.

Gary S.

DGaunt

Interesting about the JE pistons. first I've heard of it. When I put mine in, I felt the piston to cylinder fit was at least as good as the Mahles they replaced. OTOH, the car did run a bit hotter, but no sign of leaning out and a Carerra oil cooler has got it running cooler than it ever did.

Gues the bottom line with the "35 year" expert, is, what kind of warranty is he going to give (in writing) against the 'rebuild'? The answer should tell you what is really what.

jet911

I have dealt with two "Factory Trained" independent mechanics in my life. One was years ago (1975) when I took an MGB motor in for a rebuild. That turned into a disaster (and started my home wrenching adventures), and that schooling cost me a couple grand only to have a main bearing spin causing it to throw a rod. The second was two years ago when I did a rebuild on my 915 tranny. This guy is german, "factory trained" blah, blah, blah. Well after dropping and reinstalling the tranny five, yes five times in four months, and $4 grand later, I said enough is enough. I had all bearings and syncros replaced, etc., etc. The tranny still does not shift as well as when I took the car in, except for down shifting into first, the reason I took it in (second syncro was shot). As far as I'm concerned, any moe can put on a card "Factory Trained" or go to a print shop and have a wall certificate made. What factory were they trained at - Nucor steel factory? :-). Anyway that's my story and the words "Factory Trained" to me holds zero weight.

Good luck and listen to Steve and Pete, they know their stuff...

bones

Hope everything turns out ok but I'd be worried if I was you right now. However when evrything hopefully does turn out ok , having stayed with stock cams and the Mahle pistons (with new rings for god's sake) why don't you fit early heat exchangers or SSIs and a Triad 2 in 2 out exhaust couple these mods with a CIS to EFI kit and you could be looking at a noticeable performance increase.

Peter Zimmermann

Gary: My two-cents worth regarding your technician; YOU are going to write the big check TO HIM. You have every right to ask him anything that you want, and he has an obligation to answer your concerns, petty or major. If his arrogance outweighs his professionalism, or if he doesn't have the right answers, have your car towed home and get your engine to someone who will respect you as a customer.
Pete

Steve Weiner-Rennsport Systems

Gary:

I'd unconditionally "second" what Pete just said. Its your dime(s) and you have every right to demand competance.

Hetmann

I had my engine rebuilt a couple of years ago and my experience was the exact opposite of yours. My technician presented me with the deluxe estimate that replaced everything with top of the line parts. After some discussion, we agreed on what to replace and what to reuse. Rebuilds are a line in the sand, but it only make sense to replace wear items like bearings and rings while the case is split. You don't want to do that again anytime soon.