82 911 SC 3.0 pistons and cylinders

jess p · 08-18-2016, 05:31 PM

Hi Everyone

I'm finally getting around to restoring my 81 SC. The engine is an 82 that I picked
up from an add for sale. When I picked up the engine the shop, non-Porsche
mechanics told me it's from a customers car and all they said was it was worn out.
I got the engine for $2000. I did a compression test and got 162 psi on all
cylinders except one which gave 152.

I've decided to rebuild the engine, after removing one bank I found there was a
little play in each elephants foot and the rocker arm bushings look a little worn.
There was average amount of carbon buildup but overall the engine isn't bad. I
do not know how many miles the engine has. I have a nice set of webers and a
backdated exhaust from an early 70's 911. The cylinders say Mahle but I'm not
certain if they are allusion or nikasil. I've started buying parts like rocker bushings
from our host and I'm ready to spend what I need to bring this machine back to
life. Please advise me what to do with the p/c. Can they be bored and JE's put in
or should I just buy new original p/c. Thanks in advance

arbita1 · arbita1's Garage

Try the magnet test to confirm if they nikasil. You should know that first before moving to the next step.

Sent from my iPhone using Tapatalk

jess p · 08-18-2016, 06:01 PM

I checked the inside with a magnet, slight magnetic pull.

Mark Henry · 08:13 PM

The 3.0 has a head gasket ring machined in the cylinders so I wouldn't overbore it.
Feel the top of the jug wall to see if has bellmouth, Nikasil doesn't wear a ridge like an iron cylinder, but will feel more like a wave if it's worn. This also should be measured with a bore gauge if it's out of spec it will have to be replated.
If you still want to go oversize you'll need to find a set of 3.2 jugs, have them bored and plated. You can use Alusil or Nikasil cores for this.
Slight magnet pull means nikasil, but on the 3.0 you can also do a fin count, I forget the number so do a search in this forum.

911 adjusters have slight play in the joints new.
The 81 (or 82) SC engine will have small ports on the heads, unless it's a ROW (non US) spec engine.
The stock pistons on a US spec engine are low CR so JE's would be a bump up for those webers.
But then HP it's a slippery slope as those JE's should have a new set of cams and you will have to rejet the carbs, put in bigger venturi's....mo' money.

tom1394racing · 08-19-2016, 07:54 AM

Your pistons and cylinders are Mahle Nikasil. They can be checked and possibly reused with new rings. PM me if you would like to follow up on this.

jess p · 08-21-2016, 08:09 AM

With Mahle Nikasil cylinders is it OK to skuff the cylinders.

Forrestkhaag · 08-21-2016, 02:03 PM

I too am rebuilding an 82 SC and have secured a nice set of Webers and PMO intakes to install. After i tore the thing down to every nut, bolt, and part (all carefully bagged and labeled) I have a real nice in spec crank, rods that weigh within a gram across the board, mains that look brand new, and cams with one lobe with an oil stain on it. So off to Webcam for a regrind and rehardening to address the Weber tweak, etc.

When I bought this stock 82 3.0, I was told by a very reputable Porsche dealer of many many years (who sold it to me for 1K including everything including a fairly new clutch and nice new flywheel but no intake system) and that the engine needed a top end rebuild to address worn out valve guides. I was therefore unable to do a leak-down with reliable results as ya'll know... So i am most interested in assessing the conditions of my pistons and cylinders / of which i know very little.

Maybe tom1394racing could help me clarify how to proceed in terms of trying to avoid buying new ones by assesssing what I have / my goal is a fairly reliable basically stock 911SC for my 914-6 conversion.

tom1394racing · 08-21-2016, 03:36 PM

Quote:

Originally Posted by Forrestkhaag

I too am rebuilding an 82 SC and have secured a nice set of Webers and PMO intakes to install. After i tore the thing down to every nut, bolt, and part (all carefully bagged and labeled) I have a real nice in spec crank, rods that weigh within a gram across the board, mains that look brand new, and cams with one lobe with an oil stain on it. So off to Webcam for a regrind and rehardening to address the Weber tweak, etc.

When I bought this stock 82 3.0, I was told by a very reputable Porsche dealer of many many years (who sold it to me for 1K including everything including a fairly new clutch and nice new flywheel but no intake system) and that the engine needed a top end rebuild to address worn out valve guides. I was therefore unable to do a leak-down with reliable results as ya'll know... So i am most interested in assessing the conditions of my pistons and cylinders / of which i know very little.

Maybe tom1394racing could help me clarify how to proceed in terms of trying to avoid buying new ones by assesssing what I have / my goal is a fairly reliable basically stock 911SC for my 914-6 conversion.

You can PM me for more info.

Mark Henry · 08-21-2016, 03:38 PM

Quote:

Originally Posted by jess p

With Mahle Nikasil cylinders is it OK to skuff the cylinders.

There is two camps on this, some say no just clean them, others have used different methods to hone their cylinders.

You still need to measure them, I don't care how good they "look".

de-glazing nicasil cylinders - a new approach?

Forrestkhaag · 08-21-2016, 05:21 PM

I will PM Tom to confirm what I have and continue to learn from the sage advise herein... cheers

jess p · 08-21-2016, 07:15 PM

When all is said and done I would hate to put this engine back together and it burn
oil or smoke because I went cheap on the P/C . I'm basically rebuilding the
whole car with new suspension pan, trans, front and rear suspension, fresh interior
and paint. I would hate to have to drop this engine again.

On a side note I have not measured the bore and Pistons yet although I do have
the tools to do it. What I did was removed the rings from the piston and put the
piston back in the bore in the correct orientation. I tried to see if there was any
play by rocking the piston and I could rock it to the point that I could make a
tapping noise. Now I realize Pistons will expand as to some degree the cylinder
will too. At this point I'm leaning towards just getting new P/C because I want
to drive this car for some time. My plan is to use an earlier 915 with the 7/31
ring and pinion with backdate earlier exhaust and 40mm webers. I'm not looking
for crazy power or performance. That's what my 930 slant is for. But with this
SC it's just for cruising, trips to the coffee shop, etc.

I'll thank everyone for their advice

al lkosmal · 08-21-2016, 08:47 PM

I may be interested in your Nikasil cylinders.

930cabman · 08-21-2016, 11:16 PM

Have you checked the piston/cylinder clearance? and follow with how is the finish? any cross hatching? Ring grooves?

Do your homework to get it right, I would not cut corners if you can help it

Mark Henry · 08-23-2016, 12:12 PM

The Mahle pistons are quite tight tolerance, whereas the JE's are sloppy till they warm up. All has to do with the expansion rates of the material used.

My opinion is send them out and have them replated and sized to the pistons you will be using.
If staying stock size pistons you can use the jugs you have for replating.
If you want to go bigger sell what you have and buy a set of 3.2 core jugs, for replating alusil jugs will be fine.

If you want to price out a new set of Mahle's be prepared for a tad bit of sticker shock.

Personally if you have the coin and want a nice set of oversize P&C's I'd look at LN Engineering, pretty sure you can get them through our host for the same price.
Porsche 911 3.0 100mm Nickies inc. 9.5:1 JE Piston set - Porsche 911 1978-98 - Aircooled Nickies - Products LN Engineering