DanD

Actually, it's not more flow but the problem is that under high RPMs the oil has to flow against the centrifical force. So the builders are cross drilling the crank so that the oil flows downstream, not upstream.

That's an interesting fix suggestion. Does the oil flow thru the main bearings then to the rods? Would more flow to the mains mean more to the rods? It seems like more to the mains would mean less pressure to the rods.

Anyone know about that early NA block? Is it the same as an 86 turbo block?

lejams

I'm in over my head quick here, but my understanding is the concept is more flow thru the main bearings on the crank and into the rod bearings. As far as the change in pressure to the rods, etc. I can't comment. The builder I'm using is a guy named Gary Elledge in Atlanta. According to people he has built for and tracked on Road Atlanta, this has been a good remedy.

Porsche did some peculiar things such as leaving the front dowel out, or installing a half grooved bearing, etc. According to Elledge, some Porsche's are doweled as m42 describes the 944 should be and some have full grooved bearings as I think the 928 does.

DanD

Here is some more info for those who are information hungry.

Renegade Archives click on Engines interior

This may be way more than most people want to know. But, I found out the early NA block may not have a necessary Oil Feed line. Figures I should look at my own website...

m42racer

The original question referred to the scoring in the block. If some one can tell me how the Rod bearing affects this I would love to know. The failure of the Piston bores in # 2 bore is directly contributed to the girdle moving. There are many things that Porsche did that make no sense. For those who wish to continue to do the same mistake, do not install the dowell. For those who wish to eliminate the problem. lock down the girdle and stop it from moving. This movement could also contribute to many other failures. With over 200 FT/Lbs of torque on these cranks and the only thing stopping the crank/girdle from moving is clamping force and "hope", we all should be thankful more problems have not appeared. Add more torque from higher boost and your in for wild ride. Look at the parting line between the block and girdle. The fretting marks from movement are all over it. For sure the oiling system is another problem, but this problem if solved from more oil etc, cannot be expected to stop the girdle from moving. Once locked down, the main bore needs to be line bored to ensure it is round, concentric and straight. As I have been told many times by my engine builder, " there are those that see it wrong and can fix it, and there are those that cannot see it at all".

Chris White

Hi Dan – the difference between the turbo block and the early NA is more than you might think. The oil tap for the turbo is the obvious (and easily fixable) one but the ‘important’ difference is that the diameter of the main oil galley in the block was greatly increased form the early blocks (pre 86) to the later blocks. I don’t have the tec reference in front of me (I am on vacation in Santa Fe!) but I think the galley went for 6mm to 10mm. That’s a huge difference.
Lots of other good info on this thread! It was interesting to go back through your archives and see a lot of familiar names….ahh, the good old days!

Chris White

TonyG

DanD

Put it back together and run it. Then while you're still enjoying your car, build another short block.

This is much better than letting your car sit for months and months, etc...

You'd be surprised at how good the car will run with cylinders like that.


PS> I'm having a new short block built as we speak. And well over 3 liters I might add...

TonyG

DanD

"….ahh, the good old days!"

Hey Chris, Good you hear from you. You probably are in that archive somewhere...

BTW, Just to give credit to Claus Groth, He created that document (and almost all the others as well), and allowed me to place it on my rennlist website. Thanks Claus!

"Put it back together and run it."
Tony,
That is definatly one of my options. I have about a year before my Son turns 18 and then we'll begin some double duty track days in earnest. So, I'll need to have a solid machine to endure the punishment of 2 driver weekends.

lejams

Again, I'm in over my head quick, but I'll repeat what I understand. Ultimately, when a rod bearing burns, one affect will be less oil being projected onto the cylinder wall, thus damage, scoring... etc. particularly when under higher boost/more stress.

Don't mistake me for trying to wear the hat of an expert. Like yourself, I like many owners of the 951 who are suffering these failures are trying to understand what is causing the problems to find the right remedy, and discussion as it is, the girdle moving is not necessarily proven "the culprit" or better said necessarily proven the only culprit. I think this would depend on how much movement we are talking about. Other than oiling or rather the lack of it, to the rod bearings, the other well known familiar culprit is detonation. We all know detonation can work on rod bearings which can affect damage to cylinder walls. Back to square one, most of the time detonation seems to be a tuning problem, which seems to be a big problem for so many 951 owners.

Until there is established mileage, data, etc. I will not accept that the missing dowel/girdle movement is the primary cause for so many of the failures on #2 or for that matter other tower damage. Yes, I can see how it could be a problem, or part of the problem. but it's not an absolute answer, not yet. Commonly, many engines have only one dowel. Perhaps the machining in the block for the second dowel relates to how the block is mounted for boring etc. I think this is a fair argument for why Porsche and many others built this way.

As for the damage on cylinder wall #1 on my engine which I thought perhaps was relative to DanD's, being my HG was also in perfect cond., I thought of something which I hadn't before. It should have been obvious as many times as I've looked at my engine and the pics, but I think some of the material that has been detonated from the surface of the piston was displaced to the cylinder wall thus offering an explanation as to the scoring starting at the very top of the tower. it could have been splattered around onto the cylinder walls and piston itself and dragged, I dunno. I'll know fully when I can take it apart.

adrial

OK, now does anybody want to explain the exact location of the dowels? What needs to be done to install the front dowel? Does the crank need to be removed or can it be done with the crank still on the car?

Thanks,
Adrial

TonyG

adrial

remove the crank girdle and you'll see one dowel installed. Also, you'll see the holes for a second dowel on the other end, but not installed.

Installing the second dowel is trivial. But you have to line bore your main journals afterwards.

TonyG

DanD

I'm guessing that if you line bore it, you will need to have oversize main bearings. Are these available?

So if you don't line bore it, what's to say that you don't put it back in the same spot that the girdle was before adding the pin.

I'm speculating here...

Do you suppose that Porsche engineers, assemble the crank then tightend down the girdle after the crank is firmly in place? I'm trying to figure out their strategy here...

m42racer

The answers here are simple. I am not an engine expert, but I can pass along the info I was told. Take a look at the girdle for size and strength. The Torque produced by these engines with this girdle is just simply scary! All engines with a girdle have 2 dowels. I do not know of one that does not! In fact, most engines with caps are dowelled, and some even have 4 bolts holding the cap down.

Jim, if you think this needs to be tested to be sure, better line up those blocks. Not trying to be funny here, but there are some very smart people helping us now, who have way more experience than most at Porsche. Yes I will say that! Just because its Porsche so what, it still comes down to people. If the people at Porsche are dumb, then Porsche is dumb! Thats my logic. why don't you get a Torque wrench set at 300 FT/Lbs and attach it to the Girdle and start turning. Thats what your Crank is doing to the Girdle. At 5000 RPM, you better beleive its moving. When problems arise in engines, each problem is addressed and fixed. Fix the Girdle problem, then address the others. Just don't leave one problem just because it seems to not be associated with every fault. But, it is your call.

As for the Main Bearings, no there are not oversizes available. The Girdle is decked then re line bored back to the standard size. Once the second dowell is installed the Girdle needs to be line bored as the bearing housings have gone out of round.

I am not an expert here, but I can relay the info I was told. Even the 911 cases which have 2 dowels at the rear move. The fix is to put one at the front of the case, and some even dowel each main web.

Why was the dowel left out? Its either a mistake or cost savings. I believe it was a mistake, as the effort and cost was incurred to machine both the block and Girdle. Porsche seems very content to use full circle Main bearings on the front of the crank. Maybe this is why. but these bearings distort and move.

Steve Lavigne

It would seem that the block would need to be decked as well. Is this the case?

Bill

Interesting stuff.

While adding dowel pins would certainly be a good thing, I am not so sure that it would cause cylinder scoring. The piston is meant to move in its bore. If the piston is abnormally rocking in the bore, the piston skirts should show abnormal wear. In fact, it is the job of the piston skirt to keep the piston from abnormally rocking in the bore. If the girdle is moving that much, I think the larger impact would occur to the crank, its bearings and saddles.

From the picture, I see an awful lot of carbon build-up on the piston. I would bet with that much carbon on the piston dome, there is also some on the rings. Carbon is just like sand, especially on aluminum bores.

Carbon occurs from incomplete or improper combustion. Like the grandma that only drives 1 mile to the store and back. When the engine is cold, fuel is enrichened to aid drivability. If all that rich mixture is not burned, you get carbon deposits. So Dan ask yourself, do I drive like a grandma at times? Short trips that do not allow the engine to warm. How is your fuel ratio? running rich. Do you use additives to reduce carbon (Chevron Techtron)?

As stated so often on this board, a proper fuel curve keeps a lot of nasty gremlins away.

Also, oil squirters to the bottom of the pistons would help. Like the ones used on the 968. More oil on the cylinder walls reduces friction.

MarcBaker27

doesn't the one piece #1 main bearing acts as the dowel at the front,