Geoffrey

I finished the disassembly and inspection of the engine tonight and I'm very happy with what I've found. I am glad that I took the engine apart and didn't run it longer, although it would have run another season (about 30 hours) with little issue.

When we disassemble a 100hr 964 stock race engine (Cup for instance) there is considerable wear on the main bearings. We found we had issues with rod bearing failures so we no longer use Porsche rod bearings, but rather an aftermarket race bearing developed for the C2 engine. We usually see a lot of piston wear due to the weak connecting rod and heavy Mahle piston.

Here are some highlights I thought you'd be interested in.

1) Main bearings in the case. The main bearings look very good with a little wear on the thrust side of the #1 bearing. There is also some wear on the #8 nose bearing which I didn't replace from the original core engine. I will replace it this time. The main bearings are standard Porsche bearings. I did pay close attention to the crankshaft end play when I assembled the engine.

2) Piston dome. The piston has little to no carbon, no signs of detonation (even without knock sensors), no piston to valve contact from an overrev. The piston is black due to the 93 octane street fuel run through this engine.

3) Piston Skirts. The RSR race pistons have a graphite coating on the piston skirt to reduce friction. Normally due to the rocking of the pistons, the coating is worn and the pistons are worn through the finish on the piston. These look almost new and were unexpected. Looking at the ring lands, the rings were still sealing well. Often the piston peans over the wrist pin from being hammered so much. In order to remove the wrist pin, you have to clean up the edge of the piston bore and heat the piston with a heat gun. These wrist pins came out very nicely.

4) Rod Bearings. This engine uses a GT3R rod bearing which is a coated racing bearing, not a street bearing. It has a black coating on it and is tougher than a standard bearing. You can see that the rod bearing has begun to wear through the coating in the center. The GT3R crankshaft has improved oiling over a standard crankshaft. I did not "cross drill" this crankshaft like many people do with the street crankshaft.

Porsche917K

That is so cool!!! The technical info you provide to this forum is incredible Geoffrey!

PAOLOP

+1

Paolo

Wachuko

I always wonder, if I was to rebuild my engine, what part list should I use? I mean, with the experience you have using this engine on the track, the modifications you have done, the fact that you still run it on street 93 octane gas, etc. All the areas you have found where the stock parts could benefit from improvements or replacement... How should I rebuild a 964 to take advantage of all these findings and have the most reliable and bullet proof engine... for the street, not track.

Maybe an overkill, I know, maybe just keeping up with maintenance for street use is enough to have this last 200K+ miles... but I always dream of the close-to-perfect 964 street engine...

Anyway, back to normal programming...

Geoffrey

For the steet I'd simply blueprint the engine using stock parts with the exception of valves, valve guides, valve springs, and valve spring retainers which I'd get aftermarket ones.

garrett376

And aftermarket rod bolts? For less than $300 seems worthwhile...

Geoffrey

Yep, I forgot about those since I haven't seen a stock one in so long

Wachuko

Thank you! So no changes to the bearings, rods, and oil pump?

Geoffrey

Well, I would use the aftermarket racing rod bearings, but that is it

Geoffrey

Recently I spent some time disassembling and measuring the 9M heads for evaluation. These were preproduction heads from Colin that he had used for development in his engine prior to installation on my engine. Further, they had a machining flaw where the bottom fin was undercut by mistake rather than being solid like the current production version. Prior to installation in my engine, I resurfaced the head for a cylinder to head surface, I did a new valve job using my preferred valve angles and seat widths, I replaced the springs with ones for my application but reused the valves, retainers, and locks. Basically, these were just thrown together with minimal modification from Colins use.

1) As I would have expected, the valve seal is still good and not leaking. There is some wear noticable, but that is to be expected in the racing environment. The valve guides have a similar amount of wear as the racing valve guides we've been using here. Nothing abnormal here and if you wanted to reuse the valves you probably could. As a practice, I don't reuse valves since they are inexpensive enough to replace.

2) I measured the cylinder head surface on a flat plate. In a normal Porsche head, the head will warp between the intake and exhaust stud by several thousandths of an inch. The 9M heads had no measureable warpage, even with the production flaw. The surface will need to be cut, but only a few thousandths to clean up the mating surface.

3) Ahhh, no ceramic liner to worry about. However, I am considering experimenting with a ceramic coating on the exhaust port of the new heads.

In all, I'm very happy with the performance and longevity of the 9M heads and can highly recommend them, especially as the availability of used 964 heads is reduced. Pricewise, a used set of 964 heads is now approaching $2500, porting is another $1200, valve job is $5-600, resurfacing is another $500, guide replacement is another $300 with guides costing $125. That adds up to approximately $5225 for racing preparation. Colin's heads are $7356 bare with valve guides, valve seats cut ready for valve installation. Seems like a pretty good value to me.