Bearing clearance

[Ol' Ron]

I wrote that book back in the late 80's, after spending most of my building time on racing engines. Published in 1992. Over the past 25 years, I've learned allot about engine building, you can't stay stagment in a field like this. The vast majority of these engines are now used in street applications. However, the bearing load factors have increased by larger displacements and compression ratios. What most people don't realize is the fact that tight bearing clearances create heat with high viscosity oils. Stock clearances of .001/.002 must have a thinner grade oil to prevent this. Today, Main bearing clearances are much tighter in performance engines, I try to get .0025 +/- .0002. Rod clearance depending on he type rod and bearing and following the manufactures recommend numbers . We also have to consider the advances made in the quality of the oil available today. Modern auto engines are small in displacement yet produce a great deal of power, and last hundreds of thousands of miles using a lubricant that runs like water at 200 F. I hope some of the new builders will look into this, there is no reason why these engines can't giver reliable service for 100,000 miles or more.

[GOSFAST]

On just about every Flattie we build we aim for .002"/.0025" on both the rods and mains! We consider this "ideal" for most street/strip applications.

One area we always check first are the main bore sizes AND the rod bore sizes. These numbers will have an effect on your actual clearances. If any of these holes are "out-of-spec" they need to addressed first, before attempting any bearing clearance checks!

The ride in my signature now has (I believe) over 40,000 miles on it and hasn't had a single issue to date. This unit has over 150 HP and over 260# Torque!

Read the P.S. below here, it is important when a crank needs grinding? We will NOT grind any cranks here that aren't included in an ongoing build UNLESS the customer gives us an accurate number, both rods AND mains.

Thanks, Gary in N.Y.

P.S. The one advantage you WILL have grinding the crank to any undersizes over using all new components, is you will be able to pre-measure the rod/main bearings in their respective locations THEN grind the desired clearances directly into the crank. Doesn't get any more accurate when done this way. It does take a very experienced grinder to get the sizes you need.

[Tinker]

Originally Posted by Ol' Ron

I wrote that book back in the late 80's, after spending most of my building time on racing engines. Published in 1992. Over the past 25 years, I've learned allot about engine building, you can't stay stagment in a field like this. The vast majority of these engines are now used in street applications. However, the bearing load factors have increased by larger displacements and compression ratios. What most people don't realize is the fact that tight bearing clearances create heat with high viscosity oils. Stock clearances of .001/.002 must have a thinner grade oil to prevent this. Today, Main bearing clearances are much tighter in performance engines, I try to get .0025 +/- .0002. Rod clearance depending on he type rod and bearing and following the manufactures recommend numbers . We also have to consider the advances made in the quality of the oil available today. Modern auto engines are small in displacement yet produce a great deal of power, and last hundreds of thousands of miles using a lubricant that runs like water at 200 F. I hope some of the new builders will look into this, there is no reason why these engines can't giver reliable service for 100,000 miles or more.

Originally Posted by GOSFAST

On just about every Flattie we build we aim for .002"/.0025" on both the rods and mains! We consider this "ideal" for most street/strip applications.

One area we always check first are the main bore sizes AND the rod bore sizes. These numbers will have an effect on your actual clearances. If any of these holes are "out-of-spec" they need to addressed first, before attempting any bearing clearance checks!

The ride in my signature now has (I believe) over 40,000 miles on it and hasn't had a single issue to date. This unit has over 150 HP and over 260# Torque!

Read the P.S. below here, it is important when a crank needs grinding? We will NOT grind any cranks here that aren't included in an ongoing build UNLESS the customer gives us an accurate number, both rods AND mains.

Thanks, Gary in N.Y.

P.S. The one advantage you WILL have grinding the crank to any undersizes over using all new components, is you will be able to pre-measure the rod/main bearings in their respective locations THEN grind the desired clearances directly into the crank. Doesn't get any more accurate when done this way. It does take a very experienced grinder to get the sizes you need.

thanks, I don't build or own high pro engines, but these make sense. When talking about thousands of a inch, ya have to wonder how much is to little. Oil flow is good.