Advice on Main Bearing Clearance

[Dauner]

Hi everyone,

Need some advice. Rebuilding my 89 911 3.2 with ~212K miles. Assembled my case halves with my new set of Glyco main bearings to do some bore measurements. Numbers came out on the high side of the tolerance. My crankshaft, which has lived a happy life with no signs of wear is more on the low end of the tolerance. My math works out to be ~ 0.0032" clearance. Installed plastigage with crankshaft in place and showed roughly 0.003". I then did the entire exercise with my original bearings. math from bore gauge and micrometer comes up around 0.0029. Plastigage looked like somewhere between the 0.002" and 0.003".

i decided to measure both my original and new bearings to compare using the ball bearing and mic process. I didn't do any excel spreadsheet math, but it appears as though the original bearings are roughly 0.0003" thicker. As a sidenote, the original bearings and the new glyco bearings were thicker at the Tang end. Not sure why this would be, but curiously repeatable. Pic of my notes below. On the original bearings there were several spots that looked "worn" where the finish was slightly worn off, but to my surprise there was no difference in thickness.

Mating surfaces are pretty darn clean. I did not have any machine work done on the case. No evidence of harsh life anywhere that I can see.

Not having owned any other 911s, I don't have a sense of acceptable vs. unacceptable oil pressure, but I did take some pics of tach and OPG both with cold engine and warm engine. This was obviously with the original bearings. Pics are below. I have to wonder if the gap I am measuring now is the same as it was before i took the engine apart.

So now I need to think thru the best course of action, and preferably not one that involves another large outlay of cash.

-Install original bearings and hope I can sell or return the Glycos
-Install new bearings
-Have either old or new bearings coated and use them. Sounds like coating adds ~ 0.0004". Not sure what my target net thickness / gap should be. middle of tolerance?

I still have a positive attitude on my engine rebuild adventure. Things are going slow. Steve at Headwerks in the Twin Cities said he will help me assemble and measure crank and bores to see if my numbers are right, but the fact that the plastigage was close leads me to believe I'm not way off.

Advice greatly appreciated.

Mark

[Walt Fricke]

Nothing wrong with the oil pressures shown in your pictures. One bar per 1000 rpm is very very good pressure, though you really wanted to see what it is when the temp needle is up by the red, or at least at 270 degrees.

It doesn't make sense to put 200K mile bearings back in after going through the trouble of disassembling the engine. If you are concerned that your main bearing clearances are getting too large, by all means have them coated. Some coating shops have coated new bearings on hand, so yours are basically a core and they can deliver quickly.

I don't find, offhand, clearance specs in my Porsche spec book (plus they are in mm). Rather they give a range, same as for the crank journals. So you need to hope some engine builders give you their take on this clearance. And taking your local mechanic up on this makes sense too.

But Wayne Dempsey, our host, in his book on 911 engines (you do have a copy?)opines that 0.05mm is a standard clearance, with the range of 0.03 and 0.088. So 0.0012" to 0.002" to 0.003".

[Dauner]

Thanks Walt.

In my years of ownership I never had the oil temp anywhere near the red during normal or spirited driving. Hottest it ever got was in heavy traffic in downtown Mpls on a 90+ degree day. Once I got to horizontal with the needle, it didn't vary much from there, and even that was somewhat unusual. With that said, I didn't drive it at 5K for extended periods (partly because it had 200K miles on it). Yep I have Bentley, Wayne, and Bruce's book. Will wait to see what others say. Partly I'm looking for an answer on coating thickness, and partly I'm curious if my experiences are typical with a G50 3.2 car that was driven regularly, but taken quite nice care of with no racing...

Thanks

[bpu699]

Find my old threads. All the new aftermarket bearings I bought were thinner than my old, 60k bearings.

Rod bearings from Porsche are fairly cheap, and sold in pairs. I thought the price was per bearing...cheaper than I thought.

My main bearings looked new. I had them coated...it added a tiny amount, but didn’t hurt. I wonder about durability, but they do use the coating in dragsters and it survives...

Your only other option is Porsche main bearings...$700 or so...

[Trakrat]

I'm surprised that with ~200k miles, you could take the case apart and NOT have any machine work done. I've always been told that once you take the case apart, it causes the case to 'settle' and you end up being out of round.

I've also read MANY times on here that Glyco bearings are always poor quality and can vary greatly in measurement. Stick with Clevite bearings is what I've understood.... or try to get some Porsche branded factory bearings (even though they are also believed to be Glyco, just with Porsche quality assurance).

[Trackrash]

Originally Posted by Trakrat

I'm surprised that with ~200k miles, you could take the case apart and NOT have any machine work done. I've always been told that once you take the case apart, it causes the case to 'settle' and you end up being out of round.

I've also read MANY times on here that Glyco bearings are always poor quality and can vary greatly in measurement. Stick with Clevite bearings is what I've understood.... or try to get some Porsche branded factory bearings (even though they are also believed to be Glyco, just with Porsche quality assurance).

True, the 2,7 mag cases tend to warp. Not so with the newer aluminum ones.

As I mentioned on another thread, two years ago I used Glyco bearings and they measured out standard. So this undersize issue is a new one.

[Walt Fricke]

The Glyco issue seems to be about their rod bearings. I had just this issue - very premature wear. Others had gotten inconsistent thickness measurements. For rods, Clevite seems to be the safe route, at least until Glyco cleans up their act.

But no one said they had seen this problem with main bearings. This information about their being thinner is interesting. In general, for a race motor you want clearances on the wide end, because it allows more oil flow to deal with the extra heat generated by consistent high RPM operation. These motors tend to be taken apart much more frequently than street motors for a variety of wear issues which decrease performance or longevity. Race motors can also expect to be warmed up before entering the track, or driven carefully for a few laps when practicing.

With a street motor, you want to turn the key and go do what you are doing, at the RPMs and throttle settings reasonable for streets and highways, so by the time you are tempted to wring it out it is warmed up.

So coating Glycos seems sensible. As an example, look at Calico's website.

[Trackrash]

See post #32 here.... Rod Bearing alignment of edges off

Originally Posted by Jonny042

I measured the Glyco mains tonight, and they also seem well made, bus alas they are .0004" to .0006" thinner. Adding .0008 to .0012" to my bearing clearance is not part of the plan.....

They are getting sent back as well.

[Dauner]

Thanks Gordon,

Interestingly, I started that thread as well. I guess I need to go back to EBS and see what my options are. package is opened and has bore gauge witnesses on them.

I really don't want to go down the road of Factory bearing set as it is multiple times more expensive than the Glycos. Hoping I have other options.

Really hoping some others will chime in who have been in similar circumstances with similar era of 911. Again would like advice on target clearance. I know Wayne talks about 0.05mm or 0.002" for Rod clearance. Is that also a good guideline for Mains for a street daily driver 911?

thanks again,

Mark

[bpu699]

Both the mains and rod bearings from glyco were loose. So were the clevites, see my prior posts. I called clevite and they said this was by design, as its a race bearing.

Bought the Porsche bearings, and they were the appropriate thickness (IE. Thicker than the ones I was taking out)...

[Jonny042]

Originally Posted by bpu699

Both the mains and rod bearings from glyco were loose. So were the clevites, see my prior posts. I called clevite and they said this was by design, as its a race bearing.

Bought the Porsche bearings, and they were the appropriate thickness (IE. Thicker than the ones I was taking out)...

I'm in a similar position to the OP, except my mains are (luckily) date coded 2002, and have 10-15K on them. They look like new. with the exception of slight polishing here and there, but more importantly, zero measurable wear, and are going back in. I fully intended to replace them, but the aftermarket Glycos were indeed much thinner and would have resulted in oil clearances out of spec. A bit scary to consider.

[Adrock]

Just as another option for you, I got my bearings from ACL race bearings in Tasmania Australia. They measured up perfectly and well priced too.

http://www.acl.com.au/

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[Jonny042]

Originally Posted by Adrock

Just as another option for you, I got my bearings from ACL race bearings in Tasmania Australia. They measured up perfectly and well priced too.

Automotive Components Limited

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But do they have main bearings?

[Jonny042]

Originally Posted by Jonny042

But do they have main bearings?

Answered my own question, they do not. But according to ACL they are on the list for development, but without an ETA.

[Dauner]

Jonny042,

OP here. I ended up getting GT3 RED bearings from EBS racing, as recommended by Don. They are in the neighborhood of 4 to 5 tenths thicker. Just installed in my case and with bore gauge measurement minus crank journal I'm right around 0.0021" clearance which is just a tad less than with original bearings. I think all is good. Bearings very affordable as well. Also, my confusion on varying bore with the bore gauge answered as well do to some Pelican searching. Bore is narrowest 90 degrees out from parting line and opens up as trend toward parting line. I didnt know that. I assumed bore should be perfectly round. Thanks everyone... Mark

[Jonny042]

Originally Posted by Dauner

Jonny042,

OP here. I ended up getting GT3 RED bearings from EBS racing, as recommended by Don. They are in the neighborhood of 4 to 5 tenths thicker. Just installed in my case and with bore gauge measurement minus crank journal I'm right around 0.0021" clearance which is just a tad less than with original bearings. I think all is good. Bearings very affordable as well. Also, my confusion on varying bore with the bore gauge answered as well do to some Pelican searching. Bore is narrowest 90 degrees out from parting line and opens up as trend toward parting line. I didnt know that. I assumed bore should be perfectly round. Thanks everyone... Mark

I looked for GT3 bearings online but was unable to find them. Do you have part numbers? I know there are other sizes (colors) available too.

Pardon me if I missed it, but what did you end up doing for rod bearings on your 3.2?

[Dauner]

I don't know part numbers as I'm here at work, but I don't think you will need them from me. If you call Don or any of the sales consultants at EBS racing, you should be able to tell them your engine, and what you are trying to accomplish, and they can get the right ones to you.

I ended up returning the defective Rod Big End Glycos that had the edges not aligned, and purchased Clevite 77's. Scroll to the last post in the thread I started, which is referenced higher up in this thread. My Clevite 77 bores were highly repeatable, gaps right in the sweet spot and the completely unofficial test of letting the rods swing down from vertical on the crankshaft was medium speed and similar between all rods. FYI, I also returned my Porsche rod bolts and went with the ARP ones. I missed that this is non-negotiable. Wayne even states it in the footnote of that particular section. also bought a JEGS stretch gauge, which worked reasonably well. required more torque than the spec to get the required stretch, but that sounds somewhat common.

[bpu699]

Originally Posted by Dauner

I don't know part numbers as I'm here at work, but I don't think you will need them from me. If you call Don or any of the sales consultants at EBS racing, you should be able to tell them your engine, and what you are trying to accomplish, and they can get the right ones to you.

I ended up returning the defective Rod Big End Glycos that had the edges not aligned, and purchased Clevite 77's. Scroll to the last post in the thread I started, which is referenced higher up in this thread. My Clevite 77 bores were highly repeatable, gaps right in the sweet spot and the completely unofficial test of letting the rods swing down from vertical on the crankshaft was medium speed and similar between all rods. FYI, I also returned my Porsche rod bolts and went with the ARP ones. I missed that this is non-negotiable. Wayne even states it in the footnote of that particular section. also bought a JEGS stretch gauge, which worked reasonably well. required more torque than the spec to get the required stretch, but that sounds somewhat common.

The clevites are looser than Porsche bearings, just so you know. They are the same tolerance as the glyco's. I was surprised. When I called clevite they said the tolerances were set looser, as its considered a race bearing. Just be aware of that, in case you were worried about oil pressure. I bought clevites and had to return them. Used a micrometer to measure them, and they were thinner than the bearings I took out, by .0005 or so...

[Trakrat]

Originally Posted by bpu699

The clevites are looser than Porsche bearings, just so you know. .

Just to verify... are you talking about main bearings or rod bearings?

[bpu699]

Originally Posted by Trakrat

Just to verify... are you talking about main bearings or rod bearings?

Rod bearings...

Never saw clevite main bearings. Just glyco, and Porsche.

Clevite makes main bearings for a 911?