Pictures- Cylinder Damage, Root Cause?

John Herrst · 07:17 PM

Attached are some pictures of the damage I found while overhauling my '86 951. The bearings all looked good and the car was a non-smoker. The previous owner had an overheating problem so I suspect that caused the damage. However, I am curious why all four bores were damaged in the same quadrant. (Exhaust side rear) The number 2 bore and piston has the most damage but the rod bearing looks great with 170K on it.

Has anyone seen damage patterns like these? Could this be caused by detonation? My engine was cutting out on overboost before I tore it down.

Anyone have extra pistons? used is OK

Thanks,
John

porschepatron · 05-08-2002, 05:13 PM

I also have an 86 going through a full rebuild. Garrity Repta at Performance Auto Works is doing all my machine work. 102.25 bore with custom rods and JE pistons. As you may already know oem oversized pistons are a rarity and super duper expensive if you are able to locate a set. There are a # of tuners out there that will be able to help you out in this dept. Pics arent showing up either.

Mike B · 05-09-2002, 11:12 AM

Hi John...I'm half way through doing the same thing you are starting...I tried finding pistons cheap but had no luck...Finally bent over, grabbed both ankles and bought the oversize 100.5 mm pistons for Porsche....Youch!...In my quest I did find a set in Florida at another place for $1252 US...Not to bad really and Ian (hint, hint) did have them in stock...email me if you need the info...

John Herrst · 05-10-2002, 05:40 AM

I have the pictures working now.

The damage on the side of the #2 piston I have been told looks like detonation. My engine did cut out on overboost a few times before I tore it down. What do you think?

porscheboi928s/c944t/n · 05-10-2002, 10:50 AM

Re-sleeve the block to a nickasil parts and labor is between 7 to 800.00
then get a JE piston to match ur existing rod...Just my IMHO...

porschepatron · 05-10-2002, 08:52 PM

WOW, that piston is really chewed up. I think detonation is possible but unlikey. As you said before it would overboost and cut out. The dme lockdown should have safegaurded against the detonation problem thats why its there. What did the plugs look like? How about the head of the piston? I would lean towards service neglect from what I see in the photos (infreqeunt oil changes and overheating). I have to admitt Ive never seen a piston that marred before so that would be my educated guess. The damage here has been over a lengthy period of time the scars dont look fresh to me and the I seriously doubt the detonation took place during the few times you overboosted before the rebuild. Expect to drop some money into this puppy. So what are you trying to build here track, stock, or spirited street?

John Herrst · 07:42 PM

There were no signs of damage to the faces of any of the pistons, they were evenly black but not heavily carboned. The plugs we all a light brown ash. The previous owner had an overheating problem. In fact, both thermostats were missing; the water pump and radiator were shot when I bought the car. There was some sludge when I tore it down. Running cold probably did not help and the crank is not pristine ether. I put 3K on it last fall after I fixed the obvious problems. The engine ran very strong and did not smoke, except for what was burning off the exhaust from the rear main leak.

I am researching my options. Boring out the block and new pistons can cost more than a used engine. I have not found anyone to sleeve the block yet. Also, I am looking into obtaining the correct hone from Sunnen and smoothen out the bore to bring back some silica lining myself.

I am really getting hooked on these cars and am starting to look for a second one. An 87 or 88 in silver. This one is going to be a streetcar with occasional strip and track visits. A fellow I work with (Mr. Fast & Furious) is building up a twin turbo V6 Stealth AWD AWS to about 450 hp and I do not want to get beat. Due to the fact Mr F's car weighs 3800 pounds and that model gearbox is junk I think I have a good chance with MAF and a K27. Nothing like some friendly competition.

Thanks for your input.

John

wolfrpi · 05-16-2002, 11:41 PM

I have a near mint used 86 engine (short block) for sale (forged rods in 86)

John Herrst · 05-21-2002, 03:42 AM

Send me the info...

lordgrommit · 05-22-2002, 11:52 PM

Mike is Ian doing some kind of sexual favors for you or something you pimp him all over the place. Here Rennlist about half your posts have Ian in them ?

Matt

Mike B · 05-23-2002, 03:20 PM

Funny...Actually No...Pimping would imply I getting some sort of kickback (I wish) and I'm not...John was looking for pistons and I tried a pile of places and found only TWO that had them in stock...The dealer $$$$ and Ian...Thought I would save him the trouble of doing what I had just done...Now if Ian has a good looking sister...