Advice Needed On Bearing Clearances

[brn agn]

I am building an iron block 402 (LQ4 block). I am using King Engine bearings on both the rods and mains. The engine will be naturally aspirated and I am aiming for 450 rwhp. I know there are a lot of different opinions on this subject. The factory spec for an LQ4 is .0009"-.0025" on the rods and .0008"-.0021" on the mains. Some recommend following the rule of .001" X Journal Diameter, which means I should be aiming for .0021" on the rods and .0026" on the mains. I would like to hear from engine builders who have built proven street engines.

I am measuring the clearances with a 2-3" micrometer and a bore gauge with .0001" resolution. There is at least a couple of tenths of inaccuracy in my setup, but I am confident that I am in the ball park. Using a mixture of bearings, I have two possible options on both the mains and rods:

Mains:
Option 1: .0018"-.0021"
Option 2: .0025"-.0027"

Rods:
Option 1: .0018"-.0022"
Option 2: .0024"-.0026"

Based on real world experience, what clearances would you run? Am I over-thinking this and either set would likely hold up fine on the street? Thanks in advance!

[Rod]

shoot for option 1 on both mains and rod (closer to factory setting) and get some plastigauge to get a better reading

[Chevelle598bb]

Option 1 is good. I shoot for .0020-.0022 on rods and .0024-.0025 on mains with p series clevitte. I would also use these clearances with your king bearings. I add .0001 or so with h series clevittes.

If you have a mic and dial bore gauge then you would have no need to use plastigauge. Measure it with your mics and you will eliminate possible variables you will have with plastigauge.

[Mike Norris]

For bearing clearances a lot has to do with oil viscosity you are using and what pressure you are trying to obtain.

Newer cars have tighter clearances so they can use 5w30 oil or lighter which in turn takes less horsepower to push and then helps MPG. The better the MPG in a new car the less chance on the manufacturer having to pay, and then charge, a gas guzzler tax.

For me personally I used to do .0020-.0025" on the rods and .0025-.0030" on the mains and use a 10w40, 15w50 or straight 30 weight oil.

Hope this helps.

Mike Norris

[brn agn]

Thank you everyone for your replies. I really appreciate the advice and I feel more comfortable moving forward with my build.