Bearing clearances

[adrianphu123 73]

Hey guys

 

What bearing clearance would you guys recommend for mains and rods?

 

Its for a 250 crossflow reving to 6000rpm

 

thanks

adrian

[slydog 7,873]

2.5th rods 3th mains orrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr just jam em in there and live with it cos xflows don't rev anyway LOL

[Nath 1,975]

2.5th rods 3th mains orrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr just jam em in there and live with it cos xflows don't rev anyway LOL

Not with that attitude!

[slydog 7,873]

Don't worry mine rev's with 2.5 and 3th...

 

[ando76 4,354]

Yep 2.5 and 3 is what I set all my race motors up with but they run 25-50w fuchs mineral oil.  I'll be trying something different on the mad scientist engine - tighter tolerances and thinner oil - just for shits and giggles and because the motor will not see consistent high revs like my race motor builds. 

[adrianphu123 73]

i usually run HPR30 20W-60 so 2.5 and 3 sounds the goods. Thanks guys

[slydog 7,873]

So with the new engine you will run Fuchs or if you can afford it PM50 cos it's better then Penrite. Or conversely give it oil changes ALOT more often then you normally do. 

[adrianphu123 73]

Just curious, why do you run half a thou more on the mains compared to the rods?

[ando76 4,354]

Bigger bearing with more surface area contact than the conrod bearings and the crank can get some side load so a bit of extra clearance helps stop picking up the bearing and allows the oil to take the load.  also gives a better cushion if you like.