1979 911SC piston and cylinder question

[mdwracer]

In looking at P/C's for a 1979 engine rebuild still on CIS injection, I see stock comp US spec and the Mahle Euro 9.8 to 1 spec and I would opt for the Euro set with the added compression and they are a bit cheaper... Seems logical , any reason to stay lower US compression? Euro Comp seems all fine with 92-93 octane pump gas?
My last question is what is the added benefit/differences on the Euro Mahle "Nickies" listed on Pelican in comparison to the traditional Mahle Euro (both are 9.8 to 1 and both are Nickasil style?)

Thanks,
Mike W

[Kemo]

I was in your shoes not too long ago on my 81. I opted to have my Alusil cylinders sent out for Nikasil plating at EBS and matched up to some 9.5:1 JE pistons. Worked out real well for the price about $2000 if I remember right. If I were doing it now, I would talk with Henry at Supertec about the 3.1 package with 964 Cam exchange.

However, if you want to stay stock the 9.8 Mahles are a quick way to get going and you could probably sell your set of P&Cs to offset the cost. I dont think there is a performance benefit to the "Nickies" but they are very well made from what I hear and L&N just makes good stuff.

hope this helps....

[cmcfaul]

My only caution with the 9.8 cr is that the heads will be resurfaced as part of the standard top end rebuild. This increases compression a bit. 10.0 (where you may end up) is probably just a little too high for single plug. 9.5 JE's would be just a bit safer.

Chris
89 Carrera

[mdwracer]

ThankYou for the infomation, it helps a lot... I quess I should explain more of the reason for rebuild...
Car is a 1979 that my Dad bought new and it had head stud problems at just over 20k miles, engine disassembled and repaired reusing everything including engine bearings, pistons and cylinders, etc. It got the tensioner upgrade and air pump system removed at stud replacement. Car has around 100k miles and is stock other than SSI's and muffler.

Car has oil leaking and smoking when driving at hard acceleration. I have verified no crankcase ventilation restrictions and feel the leak is where the cylinders meet the cam tower(s) esp on drivers side and think maybe some blow by is making the situation worse?
I def need to repair and reseal the towers and probably time for pistons and cylinder at 100k miles... Thoughts?

Thanks again, Mike

[Trackrash]

Sounds like you will need to address the cylinders/pistons. IF you have Mahles, AND they are in spec, you can just deal with the pistons. JEs as mentioned may be your best choice in that case.

If you have KS alusils, then it is probably time to upgrade, and I think you know the options. IF you are set on NEW pistons and cylinders, IMO the '80+ SCs had 9.3 CR and would be a no brainer.

I have not heard of Henry's 3,1 exchange, but that could be the way to go.

[mdwracer]

And I want to clarify smoking is from oil leaks at tower area and NOT at tail pipe.

[Turbo_pro]

Here's one option that looks interesting.

Remanufactured 911SC 3.1L pistons & cylinders

[Walt Fricke]

What are the leakdown values?

It is unusual to have leaks from the head to cam carrier seal. The orange goo does a good job usually.

The most likely leaks, at least on my motors, are from the rocker shafts.

The cylinder to head joints ought not to leak (if they do, suggests the combustion is eating away at the mating surfaces, and might show up in the leak down, perhaps as bubbles in the leaking oil).

The cylinder bases ought not to leak - weep a bit maybe, but not leak.

I'd suggest you thoroughly clean the engine in the car, including pulling the valve covers and getting in there and cleaning and observing where leaks seem to come from.

Then use talcum powder on the clean surfaces, or a fluorescent black light dye in the oil, and see just where the leaks come from.

Pump gas premium is often 91 octane. That's really not enough for 9.8/1 CR over the long haul. No knock sensors or spark retard systems on these cars.

The smoke may well be oil dropping on the headers.

[Kemo]

thanks Turbo_pro for the link...this is the 3.1 kit i was referring too earlier.

210HP is a nice way to get around town in an SC

Originally Posted by Turbo_pro

Here's one option that looks interesting.

Remanufactured 911SC 3.1L pistons & cylinders

[Kemo]

also, I wanted to add, that I had some oil leaking from what appeared to be the base gasket. once I pulled the motor, I found that a few of the head studs had loosened for one reason or another. so, checking my head stud torque at every valve adjustment is part of my PM.

[coomo]

I have good set of 78sc pistons and cylinders if you want them.Came from perfect 100k motor.We have gone to 3.2ss with "Moritz" Mahle from EBS 98mm cylinders.

[MichaelSJackson]

mdwracer,

I'd follow Walt's advice; instead of rushing to buy parts. Not only will you get a clearer understanding, but a little more time to think about your path forward.

[mdwracer]

Thanks for everyone's input, plan is to do some leak checking and fact finding before engine comes out and I'll report back...
Mike

[r lane]

Machine your cylinder heads only if absolutely necessary. Usually they can be lapped in with no problem. If machined, all have to be dead on as the cam housing must sit squarely.