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when are 3/4 grooved main bearings needed for bbc ?

General engine tech -- Drag Racing to Circle Track

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badbug3
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when are 3/4 grooved main bearings needed for bbc ?

Post by badbug3 » Tue Nov 19, 2019 2:47 pm

I was told by a reputable engine block builder that he recommended i use 3/4 groove main bearings to insure plenty of oil flow to rod bearings. I notice that clevite dont even make that bearing. I see where king and acl offer that bearing. Ive never used anything but clevite bearings in all my motors with no problem so i wonder if its just hype or what?

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by Warp Speed » Tue Nov 19, 2019 3:06 pm

badbug3 wrote:
Tue Nov 19, 2019 2:47 pm
I was told by a reputable engine block builder that he recommended i use 3/4 groove main bearings to insure plenty of oil flow to rod bearings. I notice that clevite dont even make that bearing. I see where king and acl offer that bearing. Ive never used anything but clevite bearings in all my motors with no problem so i wonder if its just hype or what?
Pure hype, and comes from a low understanding of oiling systems and how they work.

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by rp930 » Tue Nov 19, 2019 4:32 pm

MythBusters

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by GARY C » Tue Nov 19, 2019 5:00 pm

I prefer the 3/4 on my SBC's from a mental perspective but I have run both with nitrous and have never seen wear on either.
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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by Walter R. Malik » Tue Nov 19, 2019 6:40 pm

Some main bearings today are not even HALF groove but, only 160 degrees of the upper.
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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by modok » Tue Nov 19, 2019 7:56 pm

3/4 groove....... as compared to what?

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by superpursuit » Tue Nov 19, 2019 8:39 pm

modok wrote:
Tue Nov 19, 2019 7:56 pm
3/4 groove....... as compared to what?
Full circumference groove.

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by digger » Tue Nov 19, 2019 8:57 pm

i've seen some inline 6 builders prefer 360 vs 180 to ensure rod bearing oil supply. I'm interested in the myth behind it

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by modok » Tue Nov 19, 2019 11:59 pm

Ok, so....270 groove bearing in a v8? that's wierd


clevite studied it, and concluded 220 degrees of groove was best compromise. I agree.
If 220 degrees isn't enough for you, go full groove.
The 3/4 groove thing does not make sense for a v8, IMO

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by modok » Wed Nov 20, 2019 12:07 am

BTW show me a bearing with 3/4 groove.
probably 2/3 groove if you measure it

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by mag2555 » Wed Nov 20, 2019 6:33 am

Will the be for circle track or Boat useage?

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by Circlotron » Wed Nov 20, 2019 7:18 am

A groove might feed oil to the drilling in the journal for more degrees of rotation but it reduces the load bearing capacity of a bearing considerably. Think of how a bald tyre so easily loses contact with a wet road, then you put grooves in it and it cuts through the water and makes contact with the road again. Just the ticket for tyres; bad news for bearings.

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by ptuomov » Wed Nov 20, 2019 7:44 am

I think the load bearing logic is why “they” nowadays groove a little less than 180 degrees of the bearing shell and all of it in the upper shell.

Are there some special considerations with BBC that would make grooving more than the top shell a smart idea?

People are down on cross drilling the mains, too, but for a low rpm engine it may not be such a stupid idea, it only causes issues with high rpms by my logic.

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by ClassAct » Wed Nov 20, 2019 1:51 pm

There are times when a full groove bearing is needed. To just say is stupid or not needed in a blanket statesman is foolish.

If the oiling system is inefficient then a full groove bearing will put some oil to the rods all the time.

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Re: when are 3/4 grooved main bearings needed for bbc ?

Post by russxr67 » Wed Nov 20, 2019 4:33 pm

ClassAct wrote:
Wed Nov 20, 2019 1:51 pm
There are times when a full groove bearing is needed. To just say is stupid or not needed in a blanket statesman is foolish.

If the oiling system is inefficient then a full groove bearing will put some oil to the rods all the time.
Agreed, particularly when the crank oil timing is incorrect, it can bandaid the issue.

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