Rod Bearings - Opinions Needed (Engine Rebuilt Forum X-Post)

['76 911S 3.0]

I recently reassembled the connecting rods on my crankshaft and have some interesting characteristics of the rods while on the crank.

Engine is a '79 3.0L, crank was micropolished, magafluxed, and measured all STD on all journal surfaces as well as mains.

Rods measured in spec (resized ~3k miles ago with ARP bolts). Clevite STD coated rod bearings, ARP bolts stretched to spec. No play in the fore/aft direction, no play in the side to side direction. However, the rod seems to rock/pivot when applying a force on the small end. I have read about the side clearance seeming to cause this phenomenon and that it can just be that. In the video you can clearly see the rod pivot on the journal at about the 12 second mark.

The other issue is the bearing alignment in the rod itself. The bearings do not line up with one another across the shells at the parting lines. I have attached a photo (not mine) but same principle.




Any thoughts/suggestions are appreciated.

Link to video:

https://youtu.be/6uu5wA4ucHA

[Ian Comerford]

Have you tried using Plastigauge when assembling? This will give an idea of clearance from shell to crank surface and whether it is in tolerance. https://plastigauge.co.uk/

[Bob Kontak]

Originally Posted by '76 911S 3.0

Rods measured in spec (resized ~3k miles ago with ARP bolts). Clevite STD coated rod bearings

Resized means the bore was cleaned up? That sounds like oversize to me coupled with standard bearings.

I don't like the pic of how the bearings fit together in the rod. There is a protruding edge on the bottom half.

Do what Ian suggests wrt plastigage.

[356911930]

Correct me if I am wrong, but I checked the PET for connecting rod #s from 1975 - 1983 and the con rod numbers do not match yours.

Your con rod: 930.103.015.0R

I found 930.103.015 for about 1974 - 83 I think and something like 930.103.020 for 1984-86 IIRC.

Could be the problem, as the width of the con rod changed along with the diameter of the rod bolts during this time frame.

Hopefully someone with more experience will chime in soon.

Best of luck,

Rahl

['76 911S 3.0]

Copy that, bearings were measured with a bearing mic, bores were measured with a dial bore gauge, rod pins were mic'd and then clearances were calculated and within spec (I don't have my notes handy to give the exact number). I don't really see what Platigauge is going to net me here other than confirm my calculations.

I think the root problem lies with the bearing offset issue. 356911930, I have found those threads and on is where the picture I posted came from. On the previous rebuild I used GT3 yellow bearings. This second go around I am using Clevite coated bearings. Both exhibit the same offset in the alignment of the two halves.

I think my next step here is to grab my original bearings from 1979 and compare to the GT3 bearings I removed this past rebuild and compare. I read somewhere that Porsche changed the width spec of the bearings and that could be the root cause of this perceived offset.

I will plastigauge one of the rods for good measure.

['76 911S 3.0]

Originally Posted by 356911930

Correct me if I am wrong, but I checked the PET for connecting rod #s from 1975 - 1983 and the con rod numbers do not match yours.

Your con rod: 930.103.015.0R

I found 930.103.015 for about 1974 - 83 I think and something like 930.103.020 for 1984-86 IIRC.

Could be the problem, as the width of the con rod changed along with the diameter of the rod bolts during this time frame.

Hopefully someone with more experience will chime in soon.

Best of luck,

Rahl

The PET diagram for SC engines shows that as the part number for the rods:

[Jonny042]

Originally Posted by '76 911S 3.0

Copy that, bearings were measured with a bearing mic, bores were measured with a dial bore gauge, rod pins were mic'd and then clearances were calculated and within spec (I don't have my notes handy to give the exact number). I don't really see what Platigauge is going to net me here other than confirm my calculations.

I think the root problem lies with the bearing offset issue. 356911930, I have found those threads and on is where the picture I posted came from. On the previous rebuild I used GT3 yellow bearings. This second go around I am using Clevite coated bearings. Both exhibit the same offset in the alignment of the two halves.

I think my next step here is to grab my original bearings from 1979 and compare to the GT3 bearings I removed this past rebuild and compare. I read somewhere that Porsche changed the width spec of the bearings and that could be the root cause of this perceived offset.

I will plastigauge one of the rods for good measure.

You're wasting your time chasing a different bearing - I lost count of how many sets of rod bearings I bought and they all had the same fit - the issue was with my rods, not the bearings, and I suspect you have the same issue.

I ended up narrowing the tabs on the bearings so each half shell would sit closer to the center of the rod. Only took a few minutes for each shell.

The picture that you put in your first post is of my rod and bearing. I posted fairly extensively in another thread:

Rod Bearing alignment of edges off

All the information you need is buried in there. Oh and BTW if you've got a bit of side to side play it doesn't indicate a problem, just make sure your bearing clearances are in spec.

I think I put quite a bit of info in my build thread as well, see link below.

['76 911S 3.0]

Originally Posted by Jonny042

You're wasting your time chasing a different bearing - I lost count of how many sets of rod bearings I bought and they all had the same fit - the issue was with my rods, not the bearings, and I suspect you have the same issue.

I ended up narrowing the tabs on the bearings so each half shell would sit closer to the center of the rod. Only took a few minutes for each shell.

The picture that you put in your first post is of my rod and bearing. I posted fairly extensively in another thread:

Rod Bearing alignment of edges off

All the information you need is buried in there. Oh and BTW if you've got a bit of side to side play it doesn't indicate a problem, just make sure your bearing clearances are in spec.

I think I put quite a bit of info in my build thread as well, see link below.

Your thread is very extensive and much appreciated. I'm with you on the rods being the issue, I found a set of Carrillo Rods for a 3.0L in a Super Street article on Ryan's SEMA build with the bearings installed and they appear to be in perfect alignment:

[jons911]

I'll add my rebuild as another data point. I replaced my rods during my rebuild, which means the original 3.2 rods are laying around with the original bearing still in them. I just checked them and the bearings are definitely even with each other. I used Carillo rods with clevite rod bearings for the rebuild and I remember them lining up perfect as well.

[356911930]

Jayson,

Looks like I miss typed, your con rods are 930.103.105.0R not 930.103.015.0R as I typed. Looks like you should have the 930.103.015.0R not the 930.103.105.0R which I see in your video!

I'm not positive this is an issue but I would check it out.

Best of luck,

Rahl