M5X main bearing clearance - second opinion

[Talperian]

Hi Guys,

Looking for input/second opinion on my freshly built M5X main bearing clearance, it's around .0012" all around. All other clearances for the engine are on-point. Engine is assembled and in the car but has not been started yet, i asked my machinist about it and he didn't seem to think it was an issue. He builds a lot of BMW engines for enthusiasts and racers in the area so I want to trust his opinion, but the tight clearance has been bugging me whenever I think about it.

According to the golden rule (.001" of clearance per 1" of journal) and what i've gathered from others with more experience, it is better to have a little looser main bearing clearance around .003" for these cars. (maybe I am overthinking this)

The application/specs of the engine are for reference:
M52 block
85mm bore Wiseco 8.5:1
Molnar 135mm rods
86mm S50 Crankshaft
S54 oil pump/pan/pickup with oil chain tensionor from euro s50b32/s54 installed/pressed into block
S50 head with Supertech +1mm valves and 84lb springs, ported intake and exhaust ports.

Would love to have a second opinion. Since I haven't started the car up, it wouldn't be the end of the world to pull off the caps to change out the bearings, would also like to know what bearings everyone else is using and where i could source undersized bearings. Right now i just have a set of the Glyco standard bearings.

Thanks,

Michon

[Mklock]

That seems to be pretty snug. Still using a 7200rpm limit? Figured .002 was where you wanted to be for an M5X.

Me, personally have never had them that tight. Does not mean it won't work though. S65 and S54 have a tight tolerence I believe like what you said.

Oh, also should note... I've never built a race engine so what the hell do I know about your setup too. Good luck!

[someguy2800]

That seams really tight to me. It's difficult to correct it though unless you can find a set of bearings that are just a tiny bit thinner. How are you measuring the clearance?

[PEI330Ci]

I have had bearings shipped to me from a vendor that were supposed to be the stock thickness, but when installed, we found them to be for 1 step under-sized. Instead of ordering another set of bearings, we sent the crank out to have the journals polished and that brought the clearance back in spec.

Another option is that you get another set of bearings from another vendor. I recommend contacting King Bearings directly to see what they can do.....they are the current cream of the crop. No other bearing manufacturer has product certified by the FAA to be used in Aircraft engines!

[zemaestro]

I don’t know much about dem clarances, but you have one hell of a combo. I think it is the best there is for a 1200 rwhp build, well except for the short rods. Also, don’t forget the ATI damper....7500 rpm is child’s play.

[pbonsalb]

Some S65 are having issues from tight rod and main bearings. I’d follow the general clearance rule rather than go significantly tighter. That seems to be the recommendation for the S65. I’d apply it to the S52 and almost any other motor (unless specific reason based on experience with the motor for deviation from industry standard).

[TheJuggernaut]

That seams really tight to me. It's difficult to correct it though unless you can find a set of bearings that are just a tiny bit thinner. How are you measuring the clearance?

+1 and what are you doing for the fasteners? When I rebuilt mine last year, I didn't have the torque spec for the 11mm ARP mains my motor had and I found a spec from ARP which was 80 ft lbs, and bore gauging the mains at that torque was yielding 8-12 tenths. But I measured more carefully and the bores were ovaling. I calculated the clamp that would be equivalent to the stock fastener diameter/pitch and it would be 60-66. I retorqued and remeasured at 66 ft lbs and got an even 20-22 tenths. Verified with plastigage after.

[pbonsalb]

Good info. So torque with crank out and measure bore. Some have done this with S65 rod bearings and found issues with aftermarket bolts when used with aftermarket supplier specs and had to change those specs.

[Talperian]

That seams really tight to me. It's difficult to correct it though unless you can find a set of bearings that are just a tiny bit thinner. How are you measuring the clearance?

That’s what I was thinking to myself, usually you can find bearings oversized, but not undersized. The clearance was measured via plastigauge after torqueing down a set of stock main bolts.

I have had bearings shipped to me from a vendor that were supposed to be the stock thickness, but when installed, we found them to be for 1 step under-sized. Instead of ordering another set of bearings, we sent the crank out to have the journals polished and that brought the clearance back in spec.

Another option is that you get another set of bearings from another vendor. I recommend contacting King Bearings directly to see what they can do.....they are the current cream of the crop. No other bearing manufacturer has product certified by the FAA to be used in Aircraft engines!

Thanks, I’ll contact king bearings, I hate to tear apart the assembled engine, but if that’s what I have to-do to prevent a failure I’ll do it.

I don’t know much about dem clarances, but you have one hell of a combo. I think it is the best there is for a 1200 rwhp build, well except for the short rods. Also, don’t forget the ATI damper....7500 rpm is child’s play.

Thanks, the application of the car/engine is for a track car, to be further developed into a racecar competing in NASA GTS or another local racing series. Reliability was the primary goal when building the engine, but I wanted to do something a little different than the run of the mill NA e36 racecar with a built m5x, S54, or LS swap. I currently have the stock damper, I don’t plan to rev. the engine past 7200RPM in gears 3-5, perhaps 7500rpm for gears 1 and 2 for low speed corners. The upgraded springs are there primarily for ovverev protection and to just upgrade the stocks, I have heard that the INA 309J lifters can handle 8k rpm with the right cam, so I will be swapping out my stock used lifters for a new set of those prior to startup/break-in. I have heard the RPM range that the harmonics are worst are around 7200-7400rpm, so my rev limit will be set to avoid prolonged time in that RPM range. Special attention is/will be given to controlling heat through ducting to heat exchangers and logging.
A little more info on the engine setup. I am using utilizing the new T4 divided steedspeed manifold, with Tial 44mm WG, and BW EFR8374 with 0.92 A/R turbing housing and IWG, (I understand this should be enough CSA to control boost creep at lower boost settings). Power goal is 450whp with boost controlled to bring torque up but not exceed 450wtq as soon as possible, to create a nice torque, but flat powerband. A ECUmaster EMU Black ECU will be using to control the engine as well as datalog useful data such as pre-IC IAT, post-IC IAT, oil temp., water temp, EGT at each scroll of the exhaust manifold, data sent via CAN to a AIM dash. Here are a couple of pics of the build progress:

IMG_20171230_133131.jpgIMG_20171230_133200.jpgIMG_20180103_174835.jpgIMG_20171230_133214.jpg

+1 and what are you doing for the fasteners? When I rebuilt mine last year, I didn't have the torque spec for the 11mm ARP mains my motor had and I found a spec from ARP which was 80 ft lbs, and bore gauging the mains at that torque was yielding 8-12 tenths. But I measured more carefully and the bores were ovaling. I calculated the clamp that would be equivalent to the stock fastener diameter/pitch and it would be 60-66. I retorqued and remeasured at 66 ft lbs and got an even 20-22 tenths. Verified with plastigage after.

Fasteners are stock main bolts. I talked to a couple folks who have built M5x motors and they didn’t seem to think there was an issue with using the stock mains, ARP bolts are used of course with the Molnar rods, and ARP head studs to clamp the head and block together.

[TheJuggernaut]

What was the torque when they were plastigauged? What was your stock bearing color? The block has a paint dot near the front main I believe, which is the factory stating what size bearings you have. They have white, green and yellow, which are all slightly different size. This is one of the problems with using an aftermarket bearing source - they don't have this kind of range, they are all one size. And not all the same. I can't remember now but I believe the stock Glyco size were closer to yellow, the KS I used are green size.

I'm not an engine builder but not sure I'd worry too much about 12 tenths, it's still within spec. I'd just make sure the torque value is correct because as I said before, if you torque more than the block was honed at, you'll distort the bore.

[dburt86]

King offers bearings with a slight under size that might work well for you. In my LS, we put them at .003 on the mains. Full season later, my machinist asked me if I even raced the car

[Talperian]

What is the journal size on an LS? TIS specifies Radial crankshaft bearing play to be between 0.020mm and 0.058mm for M5X. That equates to between .0007" and 0.0023" for the bearing clearance.

Maybe i'm picking the fly shit out of the pepper on this one, just makes me nervous!

[MikeE36]

FWIW I run stock size Kolbenschmidts at .0022" on both rods and mains. That spec seems a bit tight, although I believe that is still within BMW's spec, which is a fairly wide range IIRC.

Mike

[Talperian]

What was the torque when they were plastigauged? What was your stock bearing color? The block has a paint dot near the front main I believe, which is the factory stating what size bearings you have. They have white, green and yellow, which are all slightly different size. This is one of the problems with using an aftermarket bearing source - they don't have this kind of range, they are all one size. And not all the same. I can't remember now but I believe the stock Glyco size were closer to yellow, the KS I used are green size.

I'm not an engine builder but not sure I'd worry too much about 12 tenths, it's still within spec. I'd just make sure the torque value is correct because as I said before, if you torque more than the block was honed at, you'll distort the bore.

At the time i didn't know as much and just ordered a set of "standard" Glyco's, sounds like they are yellow from what you are saying. Yes my clearance is still within spec. Mains were fully torqued during honing. I may have another issue though...I thought the main cap bolts were reusable, but apparently they are torque to yield?

King offers bearings with a slight under size that might work well for you. In my LS, we put them at .003 on the mains. Full season later, my machinist asked me if I even raced the car

Thanks, I may contact them to see what my options are. I little looser clearance would be nice.

FWIW I run stock size Kolbenschmidts at .0022" on both rods and mains. That spec seems a bit tight, although I believe that is still within BMW's spec, which is a fairly wide range IIRC.

Mike

Thanks for your input Mike, yes it's tight but per TIS is still within spec. I talked to my machinist again and he again stated he has no concern over it, i guess i should trust him.

Anybody know if the main cap bolts are reusable? I thought they were so I reused them, but apparently they are torque-to-yield?

Thanks,

[gdavid]

They are recommended to be replaced but I reused mine. I Have a hard time believing that those bolts are permanently deformed with a such a relatively low torque. I replaced the rod bolts with OEM.

[MikeE36]

Thanks for your input Mike, yes it's tight but per TIS is still within spec. I talked to my machinist again and he again stated he has no concern over it, i guess i should trust him.

Anybody know if the main cap bolts are reusable? I thought they were so I reused them, but apparently they are torque-to-yield?

Thanks,

I have reused mine a few times without any problems. It's recommended to replace them, but I haven't had any issues.

Mike

[Talperian]

They are recommended to be replaced but I reused mine. I Have a hard time believing that those bolts are permanently deformed with a such a relatively low torque. I replaced the rod bolts with OEM.

I have reused mine a few times without any problems. It's recommended to replace them, but I haven't had any issues.

Mike

Thanks guys, I talked to my machinist again and he said he reuses them all the time, for the same reasons mentioned above. Also, reassured me about my main bearing clearance. I'm going to run it for a season and check bearing clearance, will report back, hopefully with no tears.

[Tulok]

Thanks guys, I talked to my machinist again and he said he reuses them all the time, for the same reasons mentioned above. Also, reassured me about my main bearing clearance. I'm going to run it for a season and check bearing clearance, will report back, hopefully with no tears.

Have you torn down yet?