Main Bearing Clearance

[sjf911]

I was dry fitting my crank and new Glyco main bearings today to measure bearing clearance. I am fitting a used 3.2L crank with standard mains confirmed to my 3.0 case. Using a new set of Glyco bearings from PP I came up with 0.08-0.085mm clearance consistently with both plastigauge and bore gauge. When I swapped my old bearings which have 125K miles back in, I got 0.055-0.06mm clearance. I measured the old bearing shell thickness versus the new and get over 0.0003 inch difference.
So, my old bearings measure in tolerance and my new ones don't. What are my options? Can the new bearings be coated up to standard? Should I source alternate bearings such as an official Porsche set from the local dealer?

[AlfonsoR]

Call up Steve Weiner or Henry Schmidt and see if they can source you a good set of bearings.

I know some of the builders have commented on this forum to stay away from Glyco, but I thought that was for the rod bearings. Perhaps Glyco has quality issues with both Rod and Main bearings.

One alternative I have seen mentioned are the Jerry Woods products.

[earossi]

Hopefully, Steve W. will chime in; but, I can relate that in discussing the rebuild of my 3.6, Steve indicated concerns that quality control, not only from aftermarket, but OEM bearings has been an issue. We were discussing replacing my rod bearings, and Steve felt that the only bearings he felt good about were the Jerry Woods bearings. However, the Woods bearings are incredibly expensive: not so much in comparison to the the cost of building up a motor. But, orders of magnitude more expensive than aftermarket or even OEM parts.

[sjf911]

Thanks for the reply. It looks like the Smart Racing parts are currently unavailable so that leaves me with genuine Porsche or coating if that is even an option. Anyone have a "cheap" source of genuine Porsche bearings?

[AlfonsoR]

I believe you can still get them. Call Steve or Henry or call Jerry's shop direct. Jerry Woods Enterprises - Perserving Porsche Racing History One Car at a Time

The advantage of going with Steve or Henry is that they will clue you in on tips/ tricks/ advise and of course they are always giving free advise away on this forum. It would be nice to pay back a little something in return.... when you can, of course.

[Spenny_b]

Originally Posted by sjf911

I was dry fitting my crank and new Glyco main bearings today to measure bearing clearance. I am fitting a used 3.2L crank with standard mains confirmed to my 3.0 case. Using a new set of Glyco bearings from PP I came up with 0.08-0.085mm clearance consistently with both plastigauge and bore gauge. When I swapped my old bearings which have 125K miles back in, I got 0.055-0.06mm clearance. I measured the old bearing shell thickness versus the new and get over 0.0003 inch difference.
So, my old bearings measure in tolerance and my new ones don't. What are my options? Can the new bearings be coated up to standard? Should I source alternate bearings such as an official Porsche set from the local dealer?

Steve, co-incidentally, Chris Carroll @ TurboKraft has today posted his findings on an engine he's building for Schnele, over in the 930 Super & Turbo Charging forum....he's also found problems with Glyco's, but on the rods.

Have a look on post #55 on p3 of my build thread (linked below)...I've had exactly the same issue as you on the mains, using Glyco's (although my rod shells are ok). I was able to swap them for some original Porsche items. I did exactly the same as you, retrieved and cleaned the old shells (84k miles old) and had far better clearances....the Glyco's put everything out of Porsche tolerance straight away!

Can't remember how much thickness a coating onto new shells will add, but was an option I would have taken had I not had an easy fix solution available to me.

Cheers
Spencer.

[chris_seven]

Having just bought several sets of Glyco Main and Rod Bearings I found this topic quite worrying and started looking for alternative suppliers but the only bearings I could find were ACL rod bearings for a 2.0 litre.

I started to look a bit more closely and found some inconsistencies in some of the published data concerning the 2.0 litre engine.

In the ‘912,911, 911T,911L,911S Spec Book’ and repeated in Wayne’s Book the following sizes are listed:

Crankshaft Pin to Main Bearings 1-7
Shaft Dia: 56.971 – 56.990
Bore Dia: 57.010 – 57.059
Clearance: 0.030 – 0.088

Crankshaft Pin to Rod Bearings
Shaft Dia: 56.971 – 56.990
Bore Dia: 57.020 – 57.059
Clearance: 0.030 – 0.088


Volume 1 of the Workshop Manual on E127 states:

Crankshaft Pin to Main Bearings 1-7
Shaft Dia: 56.971 – 56.990
Bore Dia: 57.020 – 57.059
Clearance: 0.010 – 0.072

Crankshaft Pin to Rod Bearings
Shaft Dia: 56.971 – 56.990
Bore Dia: 57.020 – 57.059
Clearance: 0.030 – 0.088

The Main Bearing Clearances in the Workshop manual are identical to those given in Wayne’s Book for the other 3 Crank designs and the difference in the pin size is relatively minor.

Any ideas which data is most likely to be correct?

[sjf911]

OK, I sourced a ball anvil micrometer so I could more accurately measure the bearing shells. What I found was that the center thickness of the Glyco new #2-7 was perfectly consistent across all 12 halves at 0.0981". My old bearings showed some variation with #3 and #7 showing an average loss of 0.0004", #4 at 0.0001 average, #6 at 0.00005 average, and #2 and #5 showing no difference from new. The edges of the shells showed much more variation both new and old but on average, there was a loss on the old of 5 out of the 6 sets of 0.0001 to 0.0004 inches per shell.
So, we have a new set of Glyco bearings that are almost indistinguishable from a set of original Porsche mains that have 125K+ miles.

Does anyone have measurements of new factory Porsche main bearings for comparison?

[sjf911]

A little more data. I measured the outside diameter of the bearing shells uncrushed. The old shells showed a major axis (edge to edge) of 2.577" and a minor axis (center to center) of 2.555" (avg. of 2.566"), the new Glyco had 2.588" and 2.554" respectively (avg. of 2.571"). This suggests that the Glyco bearings are too long and likely aren't crushing to the right dimensions in the bearing saddles.

[Spenny_b]

Originally Posted by sjf911

Does anyone have measurements of new factory Porsche main bearings for comparison?

Steve, I'm about to do a dummy build on my motor to check valve clearances....at the moment it's closed up just using the thru bolts in order to do a CC check on #1 cylinder. When I disassemble and remove the crank in order to fit the rods, I'll remove one of the new OE Porsche shells and measure the edge thickness.

I only have a straightforward mic and a Mitutoyo digi calliper, not a fancy one like you've just gotten hold of

[sjf911]

Originally Posted by Spenny_b

Steve, I'm about to do a dummy build on my motor to check valve clearances....at the moment it's closed up just using the thru bolts in order to do a CC check on #1 cylinder. When I disassemble and remove the crank in order to fit the rods, I'll remove one of the new OE Porsche shells and measure the edge thickness.

I only have a straightforward mic and a Mitutoyo digi calliper, not a fancy one like you've just gotten hold of

Much appreciated, thank you. It looks like the most important measurement is the outside diameter of the two shells together in two directions 90 degrees apart, I suspect the actual thickness of the shells is not going to differ significantly. I don't think I have a choice now other than to order genuine bearings from the local dealer as these Glyco's are useless without grinding down the edges which I am not willing to try or trust.

[sjf911]

Here's what I'm seeing, crude but reproducible.

Old

New


Old


New

[sjf911]

Well, genuine Porsche saves the day. I picked up a set of "genuine" bearings today from the local dealer and trial fitted them. Every bearing is between 0.04mm and 0.06mm clearance so we are good to go. So much for the "cheap" Glyco. Interestingly, the factory "kit" came with a #8 and 2 #1 sets so I now have a spare of each .

[Spenny_b]

Good, glad you've managed to resolve; sorry, I did think to measure the thickness of the shell material over the weekend, but it slipped my mind to take the measurements as you illustrate above. As accurately as I could measure with the sharp edges of the digi vernier, I saw 2.56mm material thickness, about 1-2mm in from the edge of the shell.

Just looking at the dimensions you show above, with the two halves butted up against each other; is this a meaningful measurement, as the shell pulls-in when pushed into place in the crank cases?

[sjf911]

All of the "genuine" Porsche main bearing shells measured 0.0005" thicker than the Glyco at the center.

[AlfonsoR]

A couple of observations..
1. I think you know, but accuracy of a good dial caliper is +/- 0.001"
2. In my experience measuring these type of sleeve bearings, measuring the OD does not tell much. You can confirm that it should have an oval shape favorable for it to snap into the bore, but that's about it. Two different manufacturers can, and more than likely will specify/design a different oval shape of the bearing shells.

I think you're set on using the new P bearing set, and I would too, but if you want to tell if the Glyco's are indeed too long, what you could do is install them in the case, then do a dry run assembly including thru bolts with either prussian blue the bearing saddles or try to insert a feeler gage at the slit line of several bearing saddles. If the bearings are too long, the case will not completely come together, and you will be able to insert a feller or if the clearance is smaller, see no indication of contact from one side of the case (where you apply a thin layer of blue) to the dry side where you are testing for contact.

http://www.permatex.com/products/automotive/specialized_maintenance_repair/rebuilder_aids/auto_Permatex_Prussian_Blue.htm

[sjf911]

Originally Posted by AlfonsoR

A couple of observations..
1. I think you know, but accuracy of a good dial caliper is +/- 0.001"
2. In my experience measuring these type of sleeve bearings, measuring the OD does not tell much. You can confirm that it should have an oval shape favorable for it to snap into the bore, but that's about it. Two different manufacturers can, and more than likely will specify/design a different oval shape of the bearing shells.

I think you're set on using the new P bearing set, and I would too, but if you want to tell if the Glyco's are indeed too long, what you could do is install them in the case, then do a dry run assembly including thru bolts with either prussian blue the bearing saddles or try to insert a feeler gage at the slit line of several bearing saddles. If the bearings are too long, the case will not completely come together, and you will be able to insert a feller or if the clearance is smaller, see no indication of contact from one side of the case (where you apply a thin layer of blue) to the dry side where you are testing for contact.

http://www.permatex.com/products/automotive/specialized_maintenance_repair/rebuilder_aids/auto_Permatex_Prussian_Blue.htm

I installed all 3 sets (old, new Glyco, and new Porsche) in the case torqued to spec with and without the crank and did both outside micrometer to dial bore gauge clearance and confirmed with Plastigage. I agree that the outside measurements do not correlate although the relative circumference of the old is less than the Glyco yet with the same material thickness gives better measured clearance. The best clearance is with the Porsche bearings which have a consistently thicker shell in the center measured with a ball anvil outside micrometer. As measured using both Plastigage and differential dial bore gage, the Glyco's are out of spec on this crank/case combo.

[AlfonsoR]

I'm certainly no expert and hope my comments do not come across as critical, just relaying my experience. I think you're on the right track and you seem to have be proceeding with reasonable caution.

Good luck!!

[TT Oversteer]

Just curious what the cost from the Porsche dealer was for the main bearing kit. Did you also have problems with the Glyco rod bearings and order them from the dealer as well? Was it readily available or did you have to order it?

[sjf911]

The quoted cost for the kit from Porsche which included a #8 bearing was $860 but they ended up charging me $750 (about $800 after tax) so it was about $350 more than what you would pay for a complete set here as you have to order the #8 separately. The Glyco rod bearings I got through PP are spot on so those will be going in the engine.