Bearing crush

colin1928

colin1928

Well-known member
Hi can anyone tell how much bearing crush for mains and con rods engine is 8BA any info welcome
I believe it should be 0.004 - 0.005
I have read the instruction that come with the bearings no mention of crush checked most of my books can not find anything
 
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Working with my machine shop we usually end up with .0015" to .002" Seems to work out quite well. I always check all with plasti gage.
 
colin1928 said:
Hi can anyone tell how much bearing crush for mains and con rods engine is 8BA any info welcome
I believe it should be 0.004 - 0.005
I have read the instruction that come with the bearings no mention of crush checked most of my books can not find anything
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If you are attempting an online search, the word "crush" may not turn up what you are looking for, the normal specification term is "clearance". .004 - .005 would be way to loose. By the way, these numbers are normally given in inches, not millimeters (sure you already knew that, but just to be on the safe side). Think 4tford has the correct clearances and I agree, check it with plasti gage.
 
JSeery said:
If you are attempting an online search, the word "crush" may not turn up what you are looking for, the normal specification term is "clearance". .004 - .005 would be way to loose. By the way, these numbers are normally given in inches, not millimeters (sure you already knew that, but just to be on the safe side). Think 4tford has the correct clearances and I agree, check it with plasti gage.
Click to expand...

Crush and clearance are two different things, not different names for the same thing,
If you want to find out about bearing crush, look up bearing crush. It's where the bearings are slightly over half the Rod or main bore. They sit a tickle proud of the caps before torque down. When you torque the cap, the bearing shell is forced hard into the bore, making it fit real good.
This is a simplified explanation. To show that it's different to clearance.
Martin.
 
Normally the bearing catalogs had the bore of the main bearings and the bore of the connecting rods listed in them ( the crush was engineered in ) you would then check Main bearing with a dial bore gauge and for rods a Sunnen AG-300 Precision gauge (Arnold Gauge). Sunnen Gauge below.

Regards,

Brian

HillsboroRaceEngines325.jpg
 
scooder said:
Crush and clearance are two different things, not different names for the same thing,
If you want to find out about bearing crush, look up bearing crush. It's where the bearings are slightly over half the Rod or main bore. They sit a tickle proud of the caps before torque down. When you torque the cap, the bearing shell is forced hard into the bore, making it fit real good.
This is a simplified explanation. To show that it's different to clearance.
Martin.
Click to expand...

I have been rebuilding engines for over 50 years and that is the first time I have heard crush used that way (or if I have I forgot, which is more likely). I understand what it is, just never thought about it. Because main caps or rod caps are torqued to spec when they are bored or honed to final size isn't it automatically taken care of? Seems like this would be an engineering factor that would be designed into the IDs and bearing sizes, correct?
 
I've not heard much about crush in automotive engines but have a lot of experiance with aircraft engines that do. Lycoming has two different types of bearings for their opposed engines. The lower horse power slower rpm engines have high crush bearings that have a relatively thin bearing shell thickness. The high horsepower & high rpm engines have heavy (thick wall) low crush bearing shells that are also pinned in the bore to keep them from shifting around. Both crush a bit but the thin ones are designed to crush more than the thick ones.

This is all designed in to the individual applications and there is no adjustment of the "crush" that I am aware of.
 
I used to cut bearings for years back in the 60-70 we used to get semi bearing and could cut any size you wanted, the bearing are about .001 thinner on the sides then in the middle, when you torque them down in the block or rod cap they squeeze together or crush. You can't check that with plastic gauge you have to use a mic. If you talking about clearance .002 is about right for a stock engine. My brother used to go out on the road and turn a rod journal on a truck that had spun a rod bearing with a portable crank grinder, he would call me with what size and I'd cut a bearing to fit it. That's a dead occupation now. Walt
 
Walt Dupont--Me. said:
I used to cut bearings for years back in the 60-70 we used to get semi bearing and could cut any size you wanted, the bearing are about .001 thinner on the sides then in the middle, when you torque them down in the block or rod cap they squeeze together or crush. You can't check that with plastic gauge you have to use a mic. If you talking about clearance .002 is about right for a stock engine. My brother used to go out on the road and turn a rod journal on a truck that had spun a rod bearing with a portable crank grinder, he would call me with what size and I'd cut a bearing to fit it. That's a dead occupation now. Walt
Click to expand...


Yup x2

R
 
JSeery said:
I have been rebuilding engines for over 50 years and that is the first time I have heard crush used that way (or if I have I forgot, which is more likely). I understand what it is, just never thought about it. Because main caps or rod caps are torqued to spec when they are bored or honed to final size isn't it automatically taken care of? Seems like this would be an engineering factor that would be designed into the IDs and bearing sizes, correct?
Click to expand...


Have a look at the clevite link, or Google it, there's info out there that can explain it far better than me. There's far more to it than you'd believe.
Martin.
 
Interesting thread, learned allot. The clearance if a stock bearing is also designed for the oil viscosity. This .0015/.002 is why a thinner oil is necessary to improve flow through the bearing for cooling. Racing engines have larger clearances (.0025/.003) and thus a thicker oil can be used. You might re think 20/50 oil for a street engine.
 
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