What do I do?

I have the teflon scraper setup, but have cut the teflon to provide alot more clearanced against the fillets than was suggested.

I also provided alot more clearance near the rodbolts.

My real concern is making sure that I get the best of both worlds - not alot of oil around the crank, but also enough oil sprayed and splashed at the pistons and bores.

The fuel I am using is not going to be very lubricating, so I need to make sure I do not forget this point.

Mike Simard suggested a new thread - just when I was thinking about this.

My bottom end is nearly completed, but I can still change certain things.

 

Thanks for starting this thread. There are some things I'd noticed about Porsche rod bearings and it's been hard to bring it up without it being buried. We can all agree that crank scrapers and windage devices are a good thing and aerated oil is bad so there's no need to sell that idea again given all the attention the topic has been given recently.

I was surprised when I measured the shell thickness on an original '87 rod bearing. It was the exact same thickness at all points with absolutely no eccentricity near the parting line. That and the fact that Porsche rod bearing clearances are on the tight side could be a problem and I wonder if it's a big factor in failures.

Eccentricity refers to a bearing shell being thinner at the parting line. That allows for the connecting rod to stretch under extension load and not squeeze the journal. In a high performance engine that can be a factor. The Porsche piston and rod mass is also unusually heavy which compounds the problem. Modern aftermarket bearings have eccentricity designed into them and it can be measured, something like .001-.002" thinner at the edge. I don't know what the current crop of available Porsche bearings are like but if they have no eccentricity I wouldn't use them in a racing engine, I also wouldn't use those tight clearances.

The bearing's clearance determine how much oil flows through the circuit. More oil flow also has a very measurable effect on bearing temperature. A tight fitting rod bearing is hotter and delivers less oil to the cylinders and wrist pin.

As a practical example, I've run an engine with loose rod bearing clearance, .003-.0035. On track the engine had a head gasket failure and the oil became frothy, pressure had dropped off and I assumed it was toast so I kept driving of course
A teardown revealed rod bearings that looked just fine, IMO a tighter claearnce would not have fared as well. The downside to looser bearing clearnces is low oil pressure at idle. If you ever sell your car to a non-gearhead they will think something's wrong.

 

On the clearances issue, or somewhat related, Glyco bearings have a different side profile at the edge of the bearing than do the porsche bearings I installed. One was "less wide" than the other at full contact. I think I have pictures somewhere.

I made the clearance at least 002 on all bearings - under plastigauge they were all over 2 thousands. Closer to 2.5. Hopefully that will help in the long run.

Question:
Is a large separation between the crank and the pan a more important characteristic than a scraper taking oil off the crank?

 

The rod side clearance is the primary source of piston pin oiling. Obviously the rod bearing clearance has something to do with it but the side clearance is your control point. I don't know what rods you are using but aftermarket rods generally have more side clearance built in. If not enough you can always machine the rod sides to increase it.

Hammer

 

These were 85 rods. I will check the side clearance.

 

Charts!

 

Looks good to me.

 

Has any one ever had any problems using a crank scrapper/windage tray in regards to lack of piston oiling?

 

I don't know. I tried googling this morning, but I didn't find anything yet.

 

So we may be worried about a problem that does not exist?

Greg

 

IMO you guys have no need to worry about a lack of cylinder oiling when using a scraper.
The term 'scraper' is a misnomer, it's not like a squeege that wipes the crank dry, it's more if a windage shield that just pokes into the crank area.
I would worry more about wrist pin oiling anyway before cyliners oiling but that's just a hunch.

 

Is the wrist pin oiling not handled by the oil holes behind the oil ring groove? And then the holes in the small end of the rod?

 

Correct, it is oiled by the hole in the pin end of the rod. But look at the hole & imagine how efficient that is. Obviously through the years it has proven to be adequate in most engines for street use. But a lot of companies have experimented with direct pressure oiling coming up through the rod bearing feed because it wasn't adequate in hi-performance applications so there must be some reason for that.

Hammer

 

I guess I have to start a whole 'nuther car with "What I know so far, NOW" instead of what this car is, which is "What I thought I knew then,"

 

BTDT. I don't mind admitting that I've learned quite a bit about 928's since I've joined this list.

Hammer