Stan.Shaw@Excell.Net

928 rod bearings are all the same.

Update: Per Greg Brown's post below, the above statement is not necessarily true with aftermarket bearings and not true with Porsche bearings (as they come in 3 sizes). Measuring to ensure you have the correct rod bearing is imperative, read below for suggestions.

Stan.Shaw@Excell.Net

All the rod caps I have pulled have a stamped number on them that is the same for the rod. When you reassembly, just make sure the numbers of rod and rod cap are the same, and are adjacent.

GregBBRD

Stan:

Sorry to disagree, but please allow me to shed some light on this subject.

This is actually about as far from a fact as one can get. Not all 928 rod bearings are the same! Porsche may offer only one part number for the "standard" rod bearing, but what comes in the boxes is definately not the same!!! This is one of the small details that separates the rookies from the pros.

The factory used 3 different sizes when the engines were assembled, depending on the size of the rod journals. They were color coded in blue, yellow, and red. They vary in thickness by about .0004". The blue ones provide the tightest clearance and the red ones have the greatest clearance. If you order bearings from Porsche, they will come in a box with 2 shells. The box usually contains either 2 yellows, or a red and a blue bearing. Porsche figures that this will cover most applications, but seldom, this is not the case. Some journals may require a bit more bearing clearance than others, depending on the particular rod size, or which rod journal one is working on. We order a bunch of boxes of bearings and separate them out into the various colors and pick the bearings we need for each rod journal, when we assemble the engine. WARNING: This can be very expensive to do for the "home" mechanic! We order dozens of sets at the same time to "sift" through.

If you order a set of "Glyco" rod bearings from one of the aftermarket suppliers to save money, you will find that this might not be the best decision you have ever made. These are "tighter" than the Porsche "blue" bearings and in most cases, will not provide enough oil clearance, especially on #2 and #6 rod journals.....where more clearance is almost manditory.

You need to be very careful here....get the bearing clearances too tight and you will not have a very good day. In most cases, if you end up with two "blue" bearings on #2 or #6, it is not if you are going to have a bearing problem, but when.

Hope this helps.

greg brown

Nicholbry

WOW! I'm glad you've mentioned that as I am almost to that stage of my project. I've posted this topic here to gain as much and precise information as possible so that I don't regret my still-undecided-decision about replacing the rod bearings (particularly #2 & #6). If I'm going through with this I don't want to screw anything up, of course, and I'll be doing it just as the factory did; hence my repeated inquiries on the topic.

This raises another question though. Since there are different bearings for different rods, would the torque value of 55# ft. be accurate for all nuts or variable torque requirements accommodating the different gauge of bearings?

Regarding your advice about buying after-market bearings for this job, purchasing anything but Porsche parts for a project this sensitive was out of the question anyway .

Terrific piece of information and I thank you for sharing.

docmirror

Ah - time to learn about plastigage, and buy that nice Starrett digital mic. What's this? Metal in my oil? But, but, but I just repaired the bottom end and made it better .

GregBBRD

There are not different rod beaings for different rods....just different rod bearings for different rod journals on the crank, depending on size. The torque value doesn't change on the rods.

Some of the aftermarket stuff works great. Rod bearings are not usually the case, unless your crank is worn from many miles of use....which is why "Glyco" sells "tighter" rod bearings. They assume that the bearings are going to be used on a crankshaft that is used and worn slightly, has been micropolished, etc. They know that very seldom is someone going to use their bearings on a brand new crankshaft. Unfortunately, Porsche cranks don't wear much...which hurts this logic a bit.

Now if you have a Scat crank....

gb

gb

Stan.Shaw@Excell.Net

Hi Greg,

I appreciate the correction. It is early, but apparently I have already learned something today

Mike Frye

Nicholas,

I'm a newbie here, so take this FWIW. I recently did the MM/pan gasket job and asked for WYAITs.

The conn rod bearings were on many people's list, but not all.

How many miles are on your engine? Mine has over 200k mi. and the inside of my engine looks brand new. There was no play or wear evident anywhere so I just left well enough alone.

You mentioned oil pressure and someone (MrMerlin?) mentioned that low oil pressure could have an effect on the bearings, they won't cause it. If your low pressure issue hasn't affected the bearings already (and your car doesn't have 300k miles on it) I would personally not suggest messing with them at this stage.

Also, look up Jim Morehouse and get his CDs before you go in. You sound like someone (like me) who would greatly benefit from the info and the searchable WSMs and PET program. After the Rennlist membership, absolutely the best money you will ever spend on your 928 IMO.

Good luck with this!!

M. Requin

Greg, Can you order Porsche bearings by size/color code? If so, would it make sense to mike the crank journals and then order bearing shells to fit? I would assume plastigaging everything before final assembly to be sure everything is OK (and knowing how to mike the journals properly - I think this is another area that might cause a beginner some trouble if they don't know which axis to mike, or have much experience with micrometer use). And thanks for your very useful post.

Nicholbry

My apologies, in advance, for drawing upon so much knowledge and then backing away from the Rod Bearing replacement . My car only has 69K mi. and, although many have given me confidence enough to proceed, I think that it would be best for me to avoid surgery this complicated as the results of doing it incorrectly would be catastrophic. I started down this road after reading several threads here from people who decided to do this coinciding with the motor mount and oil pan gasket replacement. Up until the last few replies here, I was probably going to move ahead; however, now we have gotten into the topic of micrometers, Plastigauge, and different gauge of bearings for different journals or wear. I'm putting the brakes on there.

Even though I have decided against doing the Rod Bearings, I believe this to be the most comprehensive on the subject of Rod Bearing replacement for the 928 on Rennlist. So, all is not lost in your efforts to help. Someone will surely benefit from the collective knowledge assimilated here. I would suggest keeping this topic going if there is more information to share.

Thank all of you for your warranted concern. I love my 928 way too much to risk it's demise to my inexperienced hand.

Respectfully,

M. Requin

At 69K, with no lower end knock, I would say you have made the right decision. Good luck, keep us posted, and you're right about the thread- it will likely be useful to others in the future.

GregBBRD

All the bearings come under one part number, which is 928 103 143 15. You have to sift through these and hope that they are sending a variety if bearings. Lately, all of the 928 bearings I've ordered have been coming in the "yellow" size. Occasionally, a box will show up with a red and a blue, which is good. The 911's have been coming with one "red" and one "blue". I guess they figure that one of the smallest bearings, mixed with one of the largest bearings will average out and work just fine.....I don't use this logic and separate them out in different sizes. You can obviously end up with thousands of dollars in bearing, by doing this. I've never seen a box with two "reds" or two "blues", BTW.

Porsche bearings have gone crazy in price. Each Porsche rod bearing HALF for a 928 retails at 28.00 each. Each 911 rod bearing HALF is $43.00. It takes a few dimes to buy a couple of sets and then pick out the size you want. In 2002, a set of 911 main bearings was $150.00, retail. They went up to just a bit over $300.00 in 2004. They are now $1187.00 per set, retail. Not a bad return on an investment...too bad I only bought 10 sets and used them when the price doubled.

The price makes people use the "secondary market" Glycos to build engines...although they are not even close to being correct. The Glyco main bearings for the 911's have the old design thrust bearing, that Porsche quit using in 1986. Glyco doesn't furnish a set of late 928 main bearings....only Porsche.

Anyway, I guess the point is that you can never assume anything. You need to measure things and try to get parts that are correect for your individual application.

We never use plastigage. We measure the crank journal for size, measure the torqued rod with the bearing installed, and subtract the two to find out what the bearing clearance is. This is the most accurate way to do this.

gb

M. Requin

OK, this grasshopper needs some illumination... I have rebuilt many many many bike engines, a few autos, and have always relied on plastigage. In a few instances I miked the peccant parts, usually because I suspected abnormal wear, but never, if memory serves me, found any problem with the plastigage measurements. That said, I am no expert, so I really would like to hear why you don't use plastigage! Your answer will go in my (mental) toolbox... And just one other Q: do you use telescoping internal gauges for the torqued rod bearing, cylinder bore mike, or internal mike? Thanks for taking the time to deal with these minor points!