Crank main bearing clearance
Thread Starter
Pro
Joined: May 2002
Posts: 678
Likes: 2
From: Lengede
Crank main bearing clearance
I’m assembling my 396cc engine at the moment and have found a few things that are out of tolerance. This short block has previously run 8k miles and was built by Nu-Tek, but all parts look okay except the Cola main crank journals are slightly below what is allowed (journals to small) 2.4480".
How much rod side clearance is allowed?
In the repair manual it say .006”--.014”
Mine is using 6” Eagle H-beam rods and Cola 3.875” crank .022--.026”
Is this still okay and if not, how can I correct this???
I also measured the crank main bearing clearance and it’s way more than allowed; it's about at .0033". max. allowed .0028".
Does anybody know of any shop that purposely uses that much clearance for some reason??
I ordered a set of .001” undersize bearing, these should bring the clearance down to a normal range.
For any info I would be very grateful.
Arnold
How much rod side clearance is allowed?
In the repair manual it say .006”--.014”
Mine is using 6” Eagle H-beam rods and Cola 3.875” crank .022--.026”
Is this still okay and if not, how can I correct this???
I also measured the crank main bearing clearance and it’s way more than allowed; it's about at .0033". max. allowed .0028".
Does anybody know of any shop that purposely uses that much clearance for some reason??
I ordered a set of .001” undersize bearing, these should bring the clearance down to a normal range.
For any info I would be very grateful.
Arnold
Burning Brakes
Joined: Oct 2002
Posts: 1,152
Likes: 1
From: Wichita KS
Re: Crank main bearing clearance (vettef6)
That is a large amount of rod side clearance, no way to reduce that much clearance that I am aware of. It can create oil control problems as the oil exiting the journals will spray heavily on the cylinder walls leading to the oil control problem. I've ran up to .018 w/o problem....
Standard clearance for high RPM small block main bearings is .0025 - .0030 the extra clearance of say .0030 provides for a thicker film of oil for high RPM/ heavy load operation. I previously had set my clearance at .0025, during this winters rebuild I set them to .0027-.0030 with the .0003 variation in the bearing shells.
Personally I think the .001 under main bearing you ordered will reduce your clearance too much as you would be .0018 - .0023 make sure you are using a calibrated bore gage & micrometers to take these readings
More bearing clearance = need for more oil volume to keep the oil pressure up which in your case will cause even more oil to spray from the increased rod side clearances onto the cylinder walls
Just my opinion, donÂ’t mess with the big cube motors much maybe some one else will chime in
-Jim
[Modified by superlund, 10:40 AM 2/29/2004]
Standard clearance for high RPM small block main bearings is .0025 - .0030 the extra clearance of say .0030 provides for a thicker film of oil for high RPM/ heavy load operation. I previously had set my clearance at .0025, during this winters rebuild I set them to .0027-.0030 with the .0003 variation in the bearing shells.
Personally I think the .001 under main bearing you ordered will reduce your clearance too much as you would be .0018 - .0023 make sure you are using a calibrated bore gage & micrometers to take these readings
More bearing clearance = need for more oil volume to keep the oil pressure up which in your case will cause even more oil to spray from the increased rod side clearances onto the cylinder walls
Just my opinion, donÂ’t mess with the big cube motors much maybe some one else will chime in
-Jim
[Modified by superlund, 10:40 AM 2/29/2004]
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Re: Crank main bearing clearance (superlund)
That is a large amount of rod side clearance, no way to reduce that much clearance that I am aware of. It can create oil control problems as the oil exiting the journals will spray heavily on the cylinder walls leading to the oil control problem. I've ran up to .018 w/o problem....
Standard clearance for high RPM small block main bearings is .0025 - .0030 the extra clearance of say .0030 provides for a thicker film of oil for high RPM/ heavy load operation. I previously had set my clearance at .0025, during this winters rebuild I set them to .0027-.0030 with the .0003 variation in the bearing shells.
Personally I think the .001 under main bearing you ordered will reduce your clearance too much as you would be .0018 - .0023 make sure you are using a calibrated bore gage & micrometers to take these readings
More bearing clearance = need for more oil volume to keep the oil pressure up which in your case will cause even more oil to spray from the increased rod side clearances onto the cylinder walls
Just my opinion, don’t mess with the big cube motors much maybe some one else will chime in
-Jim
[Modified by superlund, 10:40 AM 2/29/2004]
Standard clearance for high RPM small block main bearings is .0025 - .0030 the extra clearance of say .0030 provides for a thicker film of oil for high RPM/ heavy load operation. I previously had set my clearance at .0025, during this winters rebuild I set them to .0027-.0030 with the .0003 variation in the bearing shells.
Personally I think the .001 under main bearing you ordered will reduce your clearance too much as you would be .0018 - .0023 make sure you are using a calibrated bore gage & micrometers to take these readings
More bearing clearance = need for more oil volume to keep the oil pressure up which in your case will cause even more oil to spray from the increased rod side clearances onto the cylinder walls
Just my opinion, don’t mess with the big cube motors much maybe some one else will chime in
-Jim
[Modified by superlund, 10:40 AM 2/29/2004]
For the rods, besides the oil control problems associated with large rod side clearances, you can have the rods twist on you under high loads.
At work, we sent main clearances to .0030 maybe a little tighter for a street motor. If you put 1's on there your clearances will be too tight and you'll probably be replacing bearings in short order. What brand of main bearings are you using?
What kind of rod bearings are you using? Is the chamfer on the outside of the rod journal larger than normal? You might need an H-spec bearing for the rods, has a larger chamfer to go with a race prepped journal chamfer.
[Modified by JCAIRE2, 12:57 PM 2/29/2004]
Thread Starter
Pro
Joined: May 2002
Posts: 678
Likes: 2
From: Lengede
Re: Crank main bearing clearance (JCAIRE2)
Jim, why did you go from .0025 to .0027-.0030??
I'm going to see if I can get the main clearance set to about .0023-.0027 by using only the upper half or both halfs of the undersize bearings. I've done this before on my 350cc 400 hp engine for all bearings and it works great, 15k miles so far. We do this at where I work, the largest engine plant in the world, on all engines. We have 4 different sizes for rod and main bearings and mix these accordingly.
The main bearings I used for measuring were new Federal Mogul std. 7081 CHBL / 522T.
The rod bearings are new Clevite 77 CB-663 H / 03C12CD1
Arnold
I'm going to see if I can get the main clearance set to about .0023-.0027 by using only the upper half or both halfs of the undersize bearings. I've done this before on my 350cc 400 hp engine for all bearings and it works great, 15k miles so far. We do this at where I work, the largest engine plant in the world, on all engines. We have 4 different sizes for rod and main bearings and mix these accordingly.
The main bearings I used for measuring were new Federal Mogul std. 7081 CHBL / 522T.
The rod bearings are new Clevite 77 CB-663 H / 03C12CD1
Arnold
Burning Brakes
Joined: Oct 2002
Posts: 1,152
Likes: 1
From: Wichita KS
Re: Crank main bearing clearance (vettef6)
Increased bearing clearance as car is driven less on the street these days & more on track / ORR events at sustained high RPM operation. Wanted more oil film thickness, sucked some air into oil pump last season - scored some bearings. Had a Canton road race oil pan, did not help-pan cannot trap oil that is not there (oil was pumped up into the top end).
Planned to install an oil accumulator but ran out of time, thought I could sneak / get by with out it, ran some long 1 mile plus sweepers at 115-125 MPH. Car continued to run well found the problem during winter tear down / inspection...
Use Clevite “H” series bearings as well, oil was Mobil-1 15-50. This season going to try thinner viscosity synthetic oil to speed / improve oil drain back times
Yes mix & match bearing shells as needed during assembly; I feel anything over .0025 should be fine.
Planned to install an oil accumulator but ran out of time, thought I could sneak / get by with out it, ran some long 1 mile plus sweepers at 115-125 MPH. Car continued to run well found the problem during winter tear down / inspection...
Use Clevite “H” series bearings as well, oil was Mobil-1 15-50. This season going to try thinner viscosity synthetic oil to speed / improve oil drain back times
Yes mix & match bearing shells as needed during assembly; I feel anything over .0025 should be fine.
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Re: Crank main bearing clearance (vettef6)
The main bearings I used for measuring were new Federal Mogul std. 7081 CHBL / 522T.
The rod bearings are new Clevite 77 CB-663 H / 03C12CD1
Arnold
The rod bearings are new Clevite 77 CB-663 H / 03C12CD1
Arnold
Too bad you have H's on the rods already. Maybe you could call eagle and see what they have to say, also the crank manufacturer and see what they recommend.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Crank main bearing clearance (vettef6)
Are you saying you have .022/.026 rod side clearance?
That's a lot but, unfortunately there isn't much you can do about it. It's going to cause a lot of oil to be thrown on the walls, so you'll definitely need to run standard tension oil rings.
Wouldn't cause me a lot of concern though, if you run the Speed Pro SS 50U oil ring set.
Be sure to index the rings correctly for best oil control.
There are differing views on bearing clearances. Some like 'em tight, others, loose.
I prefer .003 to .0035 on the mains and .002 to .0025 on the rods. On small journal rods I like the high end of the spec.
Jake
[Modified by JAKE, 5:17 AM 3/1/2004]
That's a lot but, unfortunately there isn't much you can do about it. It's going to cause a lot of oil to be thrown on the walls, so you'll definitely need to run standard tension oil rings.
Wouldn't cause me a lot of concern though, if you run the Speed Pro SS 50U oil ring set.
Be sure to index the rings correctly for best oil control.
There are differing views on bearing clearances. Some like 'em tight, others, loose.
I prefer .003 to .0035 on the mains and .002 to .0025 on the rods. On small journal rods I like the high end of the spec.
Jake
[Modified by JAKE, 5:17 AM 3/1/2004]
Thread Starter
Pro
Joined: May 2002
Posts: 678
Likes: 2
From: Lengede
Re: Crank main bearing clearance (JAKE)
Jake,
yes that’s what I measured.
I just called our engineers from development & research and they told me, and that is what I also think, that the rod bearing clearance is responsible for how much oil is going to be thrown on the walls, as you say, and not the rod side clearance.
We have on our V10 cyl. engine even a larger rod bearing clearance than mine: .024-.028
BTW, I have Speed Pro rings but I don’t know which ones. I indexed the rings just as SRP suggested. The ring gap is set between .022-.026. That’s they way I bought them; I think that should be okay.
I only drive on the street and not on a track but nonetheless we have on most of our Autobahns no speed limits.
Arnold
yes that’s what I measured.
I just called our engineers from development & research and they told me, and that is what I also think, that the rod bearing clearance is responsible for how much oil is going to be thrown on the walls, as you say, and not the rod side clearance.
We have on our V10 cyl. engine even a larger rod bearing clearance than mine: .024-.028
BTW, I have Speed Pro rings but I don’t know which ones. I indexed the rings just as SRP suggested. The ring gap is set between .022-.026. That’s they way I bought them; I think that should be okay.
I only drive on the street and not on a track but nonetheless we have on most of our Autobahns no speed limits.
Arnold
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Thread Starter
Pro
Joined: May 2002
Posts: 678
Likes: 2
From: Lengede
Re: Crank main bearing clearance (superlund)
Increased bearing clearance as car is driven less on the street these days & more on track / ORR events at sustained high RPM operation. Wanted more oil film thickness, sucked some air into oil pump last season - scored some bearings. ...
Use Clevite “H” series bearings as well, oil was Mobil-1 15-50. This season going to try thinner viscosity synthetic oil to speed / improve oil drain back times
Use Clevite “H” series bearings as well, oil was Mobil-1 15-50. This season going to try thinner viscosity synthetic oil to speed / improve oil drain back times
couldn’t get back to you any sooner, it took me some time to get all this info together. I asked the engineers of all of these manufacturers to give me information pertaining their main bearing clearance, rod bearing clearance and rod side clearance.
Here are the tolerances measured at 68°F and also the remark that enlarging the bearing clearances will bring you nothing but LESS hydrodynamic pressure and more oil spraying all over the place!!!!!!
.........................Main b. clear.//Rod b. clear.//Rod side clear.
Volkswagen .........0009-.0017//.0009-.0017//.008-.016
Volkswag.Diesel..0010-.0020//.0010-.0020//.022-.026
Audi.....................0009-.0017//.0009-.0017//.008-.016
Bentley................0009-.0017//.0009-.0017//.008-.016
Bugatti.................0009-.0017//.0009-.0017//.008-.016
GM.......................0008-.0020//.0013-.0035//.006-.014
All engines except the diesel have their max. Hp at or over 6000 rpm
Volkswagen up to 450 Hp
Volkswagen Diesel 330 Hp
Audi up to 450 Hp
Bentley 560 Hp
Bugatti 1001 Hp
Arnold
[Modified by vettef6, 7:41 AM 3/4/2004]
[Modified by vettef6, 7:43 AM 3/4/2004]
