DanD

Pulled my 86 turbo apart.

Compression reading on the 2nd cylinder was 121 dry and 143 oiled. The cylinder has a good amount of scoring. Not terribly deep, but enough that I can feel it with my finger.


This motor is completly original.
I happen to have a second block in similar condition. However, it has been bored out 1st oversize.

My thinking is that I can bore engine #1 to 1st oversize, (do the necessary sylicone block lapping procedure) and then pull the pistons out of engine #2 and end up with a decent rebuild. Add, rings, bearings, etc as nessary.

Link to thread about #2 engine

The funny thing is that the headgasket was perfect. I thought sure it was gone.

Another question, can I use a bare NA block? Swap in my turbo engine guts?

vetblack

That scoring doesn't look to bad. It is hard to tell by the picture, but run your finger across the grooves to see how deep they are. A cetain amount of not to deep scoring is OK, and not out of the oridinary (especially on #2).

This block/cylinder looks much beter than your other one. If the grooves are not to bad, I would just ring the pistons (along with the other standard items, ie bearings etc) and put it back together.

Good Luck

rage2

Is there a reason why #2 would score more than the other cylinders? My stock block also has light scoring on #2 (way less than this).

Mike B

What shape are the oversize pistons in? If they are good I would agree with your plan. Might as well do it right especially if you already have the expensive oversize pistons.

DanD

I wonder if the scoring is due to high boost. I did run this engine up to 18psi for a while. And occasionally up to 21psi. No head gasket damage though.

The other thought I had was either a lean or rich air/fuel ratio.

I'll pull the pistons out of #2 today and check them out.

My feeling is that the biggest question is if the bores on #1 measure even or not. I may have to rent a mikcrometer (sp?) and see to see if they are egg shaped. Does anyone have some tolerance figures for that?

Anyone know about the N/A block?

Thanks for the comments.

m42racer

Get the Block sleeved. Then you will have no further problems. There is a reason its always # 2. Stick with the DI liners as they are much harder than the Chrome moly type. If you have scoring as bad as the pic shows, the Pistons will be damaged beyond use. Do it properely now, and take no chances with used parts. Ask the professionals their advice, as they know what can be reused and what cannot. The problem is A/F or Head sealing. The problem with # 2 going is very simple, but an overlooked area direct from the factory. Some on here know what I am talking about. Call Neil @ PD 949 646 7461. He will tell you. Its a $ 5.00 part ( not there), causing a $ 1500.00 problem.

m42racer

My mistake in last post. The problem IS NOT A/F or head sealing!!!. Its somethging else, which PD have found, and others have not.

rage2

OK, so what is it?

tazman

I was thinking the same thing!

David Floyd

Me too

DanD

I have $5, the problem is I don't have $1500...
If you know the answer, please spill...

Sleving is out. Can't afford the sleves much less the pistons to go with it. So, it either gets put back together with minimal $$ or gets parked..

I have no problem throwing rings and berrings in it and driving it another year, then tossing the engine and getting another one. Maybe by that time I'll be able to afford a sleve job.

Keeping 2 951s running is sometimes a bear...

lejams

I believe the $5.00 part m42racer is talking about is the front dowel pin on the crank. The blocks are machined for the dowel, but the dowel wasn't installed by Porsche. But I don't think the fact that Porsche left this out necessarily justifies the problem with #2. It could be the problem and maybe P.D has confirmed this, but so far this sounds like a theory.

I'm about to have another engine put in my car due to failure in May.
After burning a valve on #4, when we popped the head we discovered the real nasty was on #1 and not the infamous #2. A complete surprise, because prior to burning the valve the car was running absolutely great.

You can see the pics below which I think clearly show detonation. You can see it in the dish of piston of #1, and if you look closely at the top of the cylinder wall where the scoring is, you can see pitting there too. The other strange thing is that the scoring travels all the way through to the top of the squish area. How does this happen?


Cylinder #1 - Firewall side of tower scored
http://forums.rennlist.com/upload/po..._022_large.jpg

Detonation on piston #1
http://forums.rennlist.com/upload/89...14_large_2.jpg

#4 - Burned valve
http://forums.rennlist.com/upload/89...31_large_2.jpg

m42racer

PD found the problem, that most have not or are not prepared to share. I think most didnt even see it.

Take a look at your girdle. Its doweled at the rear and not at the front. Its drilled for one at the front but not installed. Then the girdle is held in place by studs with less dia than the holes in the girdle. If you expect the crank and girdle not to move you are mistaken. The first Piston to lose its clearance with any moveemnt is the 2nd one. Once the second dowel is installed, the girdle needs to be line bored to make round again. Take a look. If you have the 2nd dowel installed you will be the first. A very scary thing to expect the girdle to be help by clamping force only.

lejams

Why would #2 be the first to lose clearance and not #1 instead. Many problems have been attributed to #2 rod bearing receiving insufficient oiling which have lead to bearing damage and ultimately clearance issues followed. And others have experienced success by drilling the crank and flowing more oil.

Interesting enough, I chose not to install the front dowel due to the fact that Porsche elected not to install it, however, I did something under my builders advise that Porsche also did not do and this is to replace the solid portion of the main bearings with another half grooved section to complete a full grooved bearing. The idea is to flow more oil along the crank to supply more oil to the rod bearings. I'm trying this as opposed to drilling the crank or installing the pin.

tazman

Thanks for the info even though I don't know enough right now to understand what you are talking about Some day I will be researching rebuilding my motor and this will be in my notes for it!