Rescuing an 83 - Piston ring question
12-17-2014, 10:53 AM
#1
Rescuing an 83 - Piston ring question
Hi all,
I have an 83 Blue 944 that I've recently finished disassembling the engine in. The cylinder walls looked in decent shape with no scoring. I've done some searching here and google but only find sporadic info on the subject of changing rings.
I have been reading about not touching the cylinder walls so I understand that. Of course I will be measuring gaps, etc. but I wonder if there would be more of a problem with getting new rings to seat vs reusing the old rings should the gap be in spec.
Before the engine was removed I did get it running and did a compression test. It was fairly consistent across all four but not that high. I do blame my lousy tester not making a good seal. That I discovered when testing my 87 S.
Anyways can someone point me in the right direction?
Thanks!
Chris
I have an 83 Blue 944 that I've recently finished disassembling the engine in. The cylinder walls looked in decent shape with no scoring. I've done some searching here and google but only find sporadic info on the subject of changing rings.
I have been reading about not touching the cylinder walls so I understand that. Of course I will be measuring gaps, etc. but I wonder if there would be more of a problem with getting new rings to seat vs reusing the old rings should the gap be in spec.
Before the engine was removed I did get it running and did a compression test. It was fairly consistent across all four but not that high. I do blame my lousy tester not making a good seal. That I discovered when testing my 87 S.
Anyways can someone point me in the right direction?
Thanks!
Chris
12-17-2014, 01:25 PM
#5
Rennlist Member
With the exception of a few hardore racers etc. in here, I have not seen anyone replace rings "just because". If the compression is good, and you dont have and smoking on accel or initial start up, I'd leave em alone.
12-17-2014, 03:00 PM
#7
Race Car
once the piston comes out of the bore it doesn't matter. The rings seat in their position and once they move they will esentially be like new rings. In fact, I did compression test on my 924s yesterday, 171 even across all 4 on 5th pump at 3200ft elevation.
35k miles ago i replaced ringes and felt compelled to lap the cylinders myself. I purchased the sunnen an-30 paste and "rigged" a hone. I was impressed at how nice the results were and how easy it was to get them. The idea is to clean the old ring material embedded in the cylinder wall out. new rings will then have a fresh surface to seat into. I did find pistons out of spec in my engine and replaced them. Do measure them and visually check for the iron coating wear on the skirts. If the iron is gone and aluminum is visible, chances are your piston is below spec and all that iron is in your cylinder walls.
As the price for new pistons was not realistic, I aquired several sets of same group pistons used and assembled 4 very nice used units. With half a dozen sets of pistons sitting on the bench, I noticed that Mahle pistons had considerably more iron coating missing than Koblschmidt(SP?). I would not combine the two different pistons in the same motor although you are supposed to be able to. Carefully inspect and measure wrist pin tolerance in both piston and con-rod.
I do have a set of NIB 2.7(104mm) Porsche factory pistons.
35k miles ago i replaced ringes and felt compelled to lap the cylinders myself. I purchased the sunnen an-30 paste and "rigged" a hone. I was impressed at how nice the results were and how easy it was to get them. The idea is to clean the old ring material embedded in the cylinder wall out. new rings will then have a fresh surface to seat into. I did find pistons out of spec in my engine and replaced them. Do measure them and visually check for the iron coating wear on the skirts. If the iron is gone and aluminum is visible, chances are your piston is below spec and all that iron is in your cylinder walls.
As the price for new pistons was not realistic, I aquired several sets of same group pistons used and assembled 4 very nice used units. With half a dozen sets of pistons sitting on the bench, I noticed that Mahle pistons had considerably more iron coating missing than Koblschmidt(SP?). I would not combine the two different pistons in the same motor although you are supposed to be able to. Carefully inspect and measure wrist pin tolerance in both piston and con-rod.
I do have a set of NIB 2.7(104mm) Porsche factory pistons.
Trending Topics
12-17-2014, 06:59 PM
#8
Rennlist Member
I tore down my engine at the machine shop. When I went to get rings for it, there were two different sets of rings..one early set and one late..I almost bought the wrong one. On the advice of another shop that dealt strictly in Porsche cars, I was able to secure a set of rings for my 83. Cost about 125 I think. Apparently there was a difference in the Glyco rings between the early 82-85 models. After the 85.5 models the rings changed...what the changes were I do not know..but I was told that there was a difference....Thanks, Tiger 03447