bearing clearances

[crashing_sux]

I just dropped the last of my parts off to my engine builder today and talked with him about clearances. I know stock the clearances get looser as you move from one end of the block to the other, but he said he'd be setting it up with race clearances (.400) since I have a high volume pump and that I should run 15-50w Mobil 1 in there after the breakin.

Is this common? I thought people were moving towards slightly tighter clearances and more like a 30 weight oil even in race motors now, (hell, even Nascar doesn't run over 30w anymore)?

I was also curious about him running all of the bearings with the same clearance, instead of loosening up as you move down the block like GM did. Still, since I am having this motor rebuilt after only 10k because the last builder installed the bearings too tight I'm inclined to go along with what he says, just wanted to run it by you guys to see if anyone has any input.

 

[jwaller]

Re: bearing clearances

why are you using a high volume pump with a sump as small as ours?

I normally use 10-30 for breakin and 5-30 for normal running.
I also set all the cleanances the same from front to rear, gm also has bearings in 0.001 increments.

 

[crashing_sux]

Re: bearing clearances

A high volume pump was in the engine when I bought the truck, but in searching old posts the only reference I have seen to someone actually draining the sump was a post where Myclone mentioned it happening on a truck spinning 8k with a high volume pump. Since I'll never spin 8k it didn't seem like a problem with me.

The bearings are Kings, not GM's. I didn't even realize people rebuild engines using GM bearings, I figured they always went with Clevite, King, and Fed stuff.

 

[nightdiver]

Re: bearing clearances

Id say .0030 is fine but .0040 is too much. I would even say that .0035 is more than it should be .

We made my engine with .0030 and it runs fine till now. Oil pressure is 65 psi cold and 35 hot(195*F)
I use 20/50 oil

 

[JuStBlAzIN]

Re: bearing clearances

why are you using a high volume pump with a sump as small as ours?

I normally use 10-30 for breakin and 5-30 for normal running.
I also set all the cleanances the same from front to rear, gm also has bearings in 0.001 increments.

so a High Volume mellings pump is not recomended?

 

[crashing_sux]

Re: bearing clearances

Just spoke with the builder again today, I completely misheard him. He'll be using .0022-0023 clearances on the mains. I talked with a SyTy vendor who recommended .0026 and the buick and ls1 guys also seem to like right around .0025 so my builder seems in the ballpark.

I allready had a high volume pump but it is being replaced by a new one since the old one had bearing material circulating through it. The new pump will also be a high volume pump, with the bypass blocked off. I plan on blocking the oil filter bypass as well and just making sure I have a filter that can hold the pressure, seems like a K&N, Mobil 1, or Pure One will take the pressure with no complaints.

 

[cloneman315]

Re: bearing clearances

what is the advantage of blocking off bypass?

 

[myclone]

Re: bearing clearances

what is the advantage of blocking off bypass?

None on a street motor other than adding heat to the oil. I dunno why ppl still do this :shrug: . Blocking the filter bypass(es) is ok if youre careful about beating on the motor when its cold but blocking the pump bypass is for crazy loose clearanced track only motors.

 

[cloneman315]

Re: bearing clearances

oh ok i think my builder has it covered but i was just curious

 

[crashing_sux]

Re: bearing clearances

My builder suggested blocking off the pump bypass but I can't see any good reason to do it. I'm going to ask him not to. Blocking off the filter bypass can keep crap from circulating through your motor, say a bearing grenades and starts clogging up your filter. Normally your filter would clog up, then the bypass would open up and you'd never know what happened, and that crap would circulate through your motor. With the bypass blocked off instead your oil pressure would drop, and you would know to take a look at your filter. Worst case scenario, it starves the motor for oil, I'd still rather have this happen than have debris circulated through my engine and turbo.

 

[nightdiver]

Re: bearing clearances

Do not block off the pump.
The gear will get damaged soon and the hp it robs is A LOT.
You can shim it but dont block it. Come on ....its the V8 pump for a V6.
I blocked the bypass on the block and let the oil filter adapter bypass valves as it was. I just cleaned everything
I use a Hvolume pump with a normal pressure spring