ptuomov

I have questions about 928 main and rod bearings. Specifically, this is for a 1987 928 S4 with stock crankshaft and aftermarket rods, all in good condition and in standard sizes.

- What are the materials used in the OEM bearings?
- Are tri-metal bearings available?
- Are coated bearings available off the shelf? I am thinking products such as Clevite's TriArmor
- Do off the shelf bearings have oil grooves?

Thanks in advance for your help.

GregBBRD

Main bearings are only available from Porsche....no other choices, so all your questions don't really apply. Rod bearings come either from Porsche or Glyco.

No idea what Porsche actually specs their bearings out. They certainly have a steel backing, with a mid copper layer, and some sort of softer lead/tin material on top. No coated bearings, you have to do this yourself..although it will be tough to maintain proper bearing clearance, with a coating. The main bearings are 200 degree grooved bearings.

ptuomov

GregBBRD -- Many thanks for your response.

Choosing from one option greatly simplifies matters.

Follow-up questions, both for you and others:

A person I spoke to over the phone a couple of days ago recommended 270-degree grooves. In your opinion, is there a reason why a 270-degree groove would be superior to a 200-degree groove? If such a reason exists, why wouldn't the factory use 270-degree grooves as well? Is there some kind of tradeoff here?

Are there known issues with clearance if bearings are coated? From www.swaintech.com: "Though the coatings will add a slight film thickness, it would be unusual to need to make a clearance provision for any of the coatings." This gives the impression that for typical application the clearance is not an issue.

Venturing to a different but related topic, namely crankshaft oil passages. There is a lot of great information here at rennlist.com about how to modify the crankshaft oil passages. My question is which shop would you recommend for this modification? I am looking for reasonable pricing and high quality control.

Are there other modifications to the stock 87 S4 crankshaft that would materially increase the reliability of the engine at, say, 7000 rpm producing 100 hp per cylinder? For example, would diamond like coating of the journals be effective and, importantly, cost effective? My assumption is that it would not be particularly effective or cost effective.

My personal prior is that it is relatively difficult for any individual or even a small firm to beat the factory designs, and therefore the actually beneficial modifications to stock engine are relatively few and far between. People on this forum have decades of experience and cumulated evidence on what modifications actually produce a demonstrable benefit. I'd very much like to tap into that info!

Vilhuer

Search archives for "crank drilled like chevy". Lots of info why factory crank design is no good for high revs.

ptuomov

Thanks for your response as well.

Yes, I did search for "drilled crank" and found a lot of useful information. The consensus seems to be that drilling the crank helps with the oiling problem if done correctly. This leads me to a question to the broader group: Does anyone know a machine shop near Boston that does reasonably priced, high quality work AND that has experience with drilling 928 s4 crankshafts according to the consensus blueprint?

Also, on of the posts mentioned some perceived difference between the Glyco and Porsche rod bearings. Is there evidence of either one being superior? Also, is it worth it to machine a longer groove into (either one of) these bearings?

Thanks again for the help.

ptuomov

I stumbled on this bearing failure diagnostics manual while surfing the web. It was useful for a complete novice like me.: http://www.clevite.com/publications/CEB-1-1208.pdf

worf928

No. I wish I did. I will have a crankshaft needing the same treatment in the near future.

Doc Brown, do you do the drillin' in-house?

ptuomov

I looked up the Glyco bearings on the web. The product description implied that these are bi-metal aluminum bearings, although it was not 100% clear. Are "genuine" Porsche bearings also bi-metal aluminum or are they tri-metal copper?

Rob Edwards

I don't have definitive proof (or knowledge) of the metallurgy of the Porsche bearings, but I recently tore down a '91GT motor that was rebuilt in 2002. The main bearings were Porsche replacements (as that's all that's available). Due to some overzealous application of loctite (I'll post the pics tonight- the damn motor literally had Loctite atherosclerosis) some of the oiling channels to the mains were partially blocked, leading to excessive wear on the mains. The posterior surface of the thrust bearing has an area (on the left half-shell, at about 10 o'clock) that is copper colored. I ASSume that means there's a copper layer in ther somewhere?


Dunno whether the rods bearings were Porsche or Glyco - the 2nd picture is a part info stamping on the rod bearing. Is that a Porsche # or a Glyco #? They were in pretty good shape except for #5, seen at left in the first picture.

RyanPerrella

i believe Porsche rod bearings would have the Porsche "P" in the triangle, when it doesnt then i suggest they are glyco.

Rob Edwards

Like this Triangle-P on the thrust bearing?

RyanPerrella

thats it

all genuine porsche parts carry that mark SOMEPLACE

Rob Edwards

Here's what too much loctite 574 will do to your cradle oil passages. The lower pic is AFTER I cleaned a bunch out of some of the crevices. I spent a good 3 hours cleaning the block and cradle.

RyanPerrella

very good point

your supposed to paint this on, like with a paint roller. Ive seen most people put an entire line across each passageway and that must have been what was done here. There should be just a very light coat, it should cover the aluminum but it needs to be rolled on, THATS IT

ptuomov

Glyco rod bearings for 1987 928 S4 are bi-metal aluminum. Those I belive are inferior to tri-metal copper bearings. Frustrating.

See the chat with a vendor:

2:33:45 PM Chris: Welcome to Live Help! How can I assist you today?
2:34:37 PM Tuomo: Are Glyco Rod Bearing Set 1978-1995 Porsche 928 (W0133-1616564) made of tri-metal copper or bi-metal aluminum?
2:36:06 PM Chris: these are metal aluminum
2:36:36 PM Chris: bi-metal
2:36:47 PM Tuomo: Thanks. That settles it.