Max wear pistons

[911S_1975]

Hello Pelicans I´m measuring my 1980 3.0sc 9.3 pistons and cylinders and I´ve read that max allowable clearence is 0.15mm but I can not find anywhere max piston and cylinder wear before replacing any of them.

Can anybody help me? Worst case I can buy all new but I don't like to throw stuff that is still fine.

My pistons are 94.975-94.955 at the center and closer to 94.85-94.86 on the edges . are they still ok?

My cylinders are between 95.01-95.025

Thanks guys!!

[911S_1975]

Everytbing is size 0

[Eagledriver]

A new set should have about .05mm clearance between the piston and cylinder. The measurement should be on the skirt of the piston. The piston is smaller at the top where the rings are. Sounds like yours are good.

[911S_1975]

Little detail of what I mean with measuring the piston at the middle and at the edge:

At the middle:


At the edge:

[911S_1975]

Maybe I can just replace pistons with 9.8 mahle ROW new ones.

[Eagledriver]

The piston rocks around the wrist pin. The size at the “edge is less important than in the middle of the skirt. I’m not going to talk you out of new Euro pistons, that’s a great option.

[911S_1975]

Originally Posted by Eagledriver

The piston rocks around the wrist pin. The size at the “edge is less important than in the middle of the skirt. I’m not going to talk you out of new Euro pistons, that’s a great option.

Would you just replace the pistons? or I go for complet piston/ cylinder kit?

[safe]

I would probably just call it good enough or go with higher compression 98mm cylinder/pistons for a short stroke 3.2.

Factors that would influence me: are the cylinders round within spec, did I have piston slap noises before, lastly, the purpose of the car.

[Dpmulvan]

You need to start with a dial bore gauge and get accurate measurements of your cylinders first.
Throwing new pistons in oval or worn cylinders will not help much. Once you properly measure the cylinders, then get back to us with measurements. Difference between A and B at d1 and d 2 should not be greater than .04mm

[Dpmulvan]

Originally Posted by safe

I would probably just call it good enough or go with higher compression 98mm cylinder/pistons for a short stroke 3.2.

Factors that would influence me: are the cylinders round within spec, did I have piston slap noises before, lastly, the purpose of the car.

Guy is trying to save money, bumping up compression gains little compared to displacement, not to mention available petrol, possibility of needing twin plug et.

[targa72e]

Hi 911S-1975

You listed the following.
max allowable clearance is 0.15mm (that is the must not exceed clearance) this is the max piston and cylinder wear before replacing

My pistons are 94.975-94.955 at the center and closer to 94.85-94.86 on the edges . are they still ok?
Edges do not matter. Clearance is measured as indicated bellow at specific location on piston.

My cylinders are between 95.01-95.025

Below is from 911SC spec book. The clearance using your smallest piston listed and largest cylinder is .05mm. This is well under the discard limit of .15mm
This is not too far off the installed clearance for new which is listed as .025mm-.042MM for Mahle pistons and cylinders. So from a clearance standpoint these are fine to use. You still need to measure the cylinder ovality and taper and ringland to ring clearance.




john

[911S_1975]

Hello, thank you for all your answers.
I’ve measured all the cylinders:
1:
a1)95,038 a2)95,04
b1)95,014 a2)95,013
2:
a1)95,032 a2)95,035
b1)95,035 b2)95,038
3:
a1)95,039 a2)95,037
b1)95,01 b2)95,015
4:
a1)95,03 a2)95,033
b1)95,015 b2)95,018
5:
a1)95,046 a2)95,041
b1)95,015 b2)95,025
6:
a1)95,038 a2)95,038
b1)95,014 b2)95,015

Being a and b 90deg offset and 1 upper side closer to head gasket and 2 closer to bottom side.
Cyl2 seem quite funy as there is almost no ovality??

What do you think guys??

[piggdekk]

I'm not an expert, but I think they look ok and probably only need a very light honing. Your second cylinder might have been already honed at some point.

[safe]

Don't hone a Nicasil cylinder.
Its either good or need to be bored/re-plated if oval or maybe just re-plated if round and the plating has been damaged.

[911S_1975]

I don´t know what to think, if I take what Dpmulvan said,they are out:
Difference between A and B at d1 and d 2 should not be greater than .04mm

So what options do I have?, replace all 6 pistons+ cylinders with Euro 95MM 9.8CR ones?
I´ve find them new for 2800€ is that the best option?
What would you do?

[targa72e]

I do not see which cylinder you think is out of spec. Biggest difference I see is on #5 95.046-95.015 = .031 which is in spec. If the ring lands are in spec and piston to cylinder clearance is less than discard I would clean the cylinders with scotch bright, clean pistons and re-use.

john

[911S_1975]

Originally Posted by targa72e

I do not see which cylinder you think is out of spec. Biggest difference I see is on #5 95.046-95.015 = .031 which is in spec. If the ring lands are in spec and piston to cylinder clearance is less than discard I would clean the cylinders with scotch bright, clean pistons and re-use.

john

You are absoletely right, my fault.

One side is telling me it will be just fine, put new rings and just enjoy.
But the other one it is pulling towrds all new 9.8cr pistons & cylinders together with big port head (instead of small ones that I currently have).

Being also cylinderc also close to wear limit wondering also about durability...

Bloody slippery slope..

[piggdekk]

Nikasil cylindres do last very long even when they are a bit worn like yours. For pace of mind you could (I probably would) send them off to replating, matching them with a nice set of high compression forged pistons. In Europe replating runs at around 200 euros/cylinder.

It's a tough call considering the amount of work that goes into rebuilding these engines, but it's really up to You and what you're planning to do with the car. For street use You'd be probably fine for a long time.

[911S_1975]

Originally Posted by piggdekk

Nikasil cylindres do last very long even when they are a bit worn like yours. For pace of mind you could (I probably would) send them off to replating, matching them with a nice set of high compression forged pistons. In Europe replating runs at around 200 euros/cylinder.

It's a tough call considering the amount of work that goes into rebuilding these engines, but it's really up to You and what you're planning to do with the car. For street use You'd be probably fine for a long time.

Do you know any nice place in Europe I can send my heads to be reworked? Same as Cylinders replated ?

I know a nice local engine rebuild shop but they are not Porsche experts at all.