main and rods clearance

I have been reading about the main and rod clearances, it seems the standard is .001 for every inch of crankshaft. What would happen if the rods and mains had to much clearance such as .004 or .005?

Pretty much irregardless of journal diameter, .0025-.003 is ideal for clearance. There are some places where a slightly tighter or looser clearance can be beneficial. The looser the clearance the lower the oil pressure is going to be.

What makes .0025 to .003 ideal regardless of diameter?

Adney Brown has a lot of good info on the many reasons why, maybe he'll chime in here and list them all.

Above that you have failure issues, But thier are applications like top fuel that run much looser tolerances but very thick oil and 200# of oil pressure (and destroy bearings every pass).

Below that in a perfromance application you can have issues too, you need oil for cooling and tigher clearances do not allow sufficient flow. (Depends on oil used also)

Its all about the application, but .002 to .003 is pretty good for most everything performance.

BradB wrote:What makes .0025 to .003 ideal regardless of diameter?

In a race engine, bearings should be considered a "consumable" part and use whatever clearance makes the rest of the parts live and work consistantly.

There is NO WAY to get a 20 year bearing clearance education condensed into a few sentences; the bottom line is it has to do with the flexing of all the other hard parts at the power levels which they are to run along with balance of oil film strengh and the amount of oil cooling needed as it flows through the bearings.

rmcomprandy wrote:

BradB wrote:What makes .0025 to .003 ideal regardless of diameter?

In a race engine, bearings should be considered a "consumable" part and use whatever clearance makes the rest of the parts live and work consistantly.

There is NO WAY to get a 20 year bearing clearance education condensed into a few sentences; the bottom line is it has to do with the flexing of all the other hard parts at the power levels which they are to run along with balance of oil film strengh and the amount of oil cooling needed as it flows through the bearings.

That's why it's important to use a machinist with a good track record. The auto rebuilder down the road may not be your best choice. The higher cost associated with "race engine" builders comes from their vast knowledge of building these motors. I couldn't even tell you what our clearances are. I told him about the combo and what I do with it and he machined it and put the short block together.

I don't trust (ANYBODY)but myself,even though my machinist is a good friend and a sponsor.I really don't feel anyone will take as much extra time w/my engine than me. I just went through a BBF engine for a friend that he had a so called (Pro) to build. His clearances were .0015 on the rods and .0175 on mains. And alot of other subpar clearances inside.

edited stupid me.. for got about the cylinder bores

hows this one? about to pick one up

http://www.shopwiki.com/_Mitutoyo+511-166,+Dial+Bore+Gage,+2+-+6+X+.0001?o=1032325863&s=3885&

I was just curious what too much bearing clearance would cause. I assume it would wear the bearing out faster on a 400 - 500 hp engine that only turns 6,000 rpm max using 50 weight valvoline racing oil. Am I correct on that assumption?

It would wear the bearing faster, high enough oil pressure would be more difficult to maintain, it would knock some at low speeds and make less power ... and probably some other "not so good" stuff I haven't thought about.

Damn "WHATBUMPER".....that is some serious trust there.....I don't trust anyone as they are human.....I measure everything they do...then I get up in the middle of the night and measure some more....lol..........D

devildog wrote:Damn "WHATBUMPER".....that is some serious trust there.....I don't trust anyone as they are human.....I measure everything they do...then I get up in the middle of the night and measure some more....lol..........D

The guy is a machinest for a nascar team so I think he is pretty good. If his motors will last hundreds of miles at 9000rpm I think it will be fine for some 5 second passes. He also builds turbo and nitrous motors for some of the fastest cars in the nation so he has some experience too.

I could measure stuff but the last bracket engine he machined for us that we put in another guys ride just topped 2000 passes. (We pulled it a part and put standard bearings in at 1500 passes for insurance purposes.) It is only about 450 horsepower but it has held together. Yes, the number of zeros is correct.

He gives us a digital print-out of all of the measurements and we checked it a long time ago on another engine and everything was exact so we just believe him now.