ACL Race bearings "X"

[DoyoFCT]

ACL offers a race bearing with an additional .001 clearance for oil, but is still a STD. size bearing. Here's a quote off of their tech talk section, but they do not elaborate on the pros/cons of this additional clearance. I'm building a mostly race car, but will see occasional street use.

Q Some of the ACL Race Series bearings contain an X suffix. What does this mean?

A The ACL Race Series Bearings that contain an X suffix have an extra +0.001" oil clearance over a STD sized bearing. These bearings are only available in the STD size.

I'm curious if anyone can tell me the benefits of these bearings, or any downsides to having the additional oil clearance.

 

[Cesar]

I remember my first 4g63t build. I have a crank that was polished and after being measured with a micrometer, was on the loose side of the spec. One machinist told me I should perform a radius grind and use underside bearings. I refused since I wanted to keep the hardened surface.


Another machinist told me that if the crank that was going to see abuse from forced induction or nitrous, it could use the extra cushion of oil (assuming you have appropriate pressure and oil weight).

recently I spoke to another machinist and he said the extra clearance isn't necessary. He also didn't say a looser clearance was a bad thing.

try it, and let us know.

I think good pressure is the most important. even if clearances are out of spec, the motor should last as long as temperatures and oils are properly monitored.

 

[assault187]

I have been looking into this myself. I am working on a rebuild and I am undecided of which ACL bearings I want to run, between the STD size and STD w/ .001 additional oil clearance.

I was told, when using the bearings with the additional oil clearance, that it is good for those who dont run B/S's with increased oil pressure to bring the high oil pressure down a bit closer to a normal value. He had also told me that its not really for the daily driver/street driven car either but told me to contact my machinest and ask their opinion.

now my car is daily driven and see's alot of weekend street abuse @ 500hp. I also have the balance shafts removed and I was seeing 80 + psi oil pressure by 3000-4000 rpm and I run full syn 5w30 oil and always have, so I figured I could benefit from the extra oil clearance but wanted some expert opinions before I buy the bearings.

Any more input??

 

[bpestilence]

Smokey Yunick, in Power Secrets says that high power race engines need more bearing clearance due to the massive force of the crank on the main bearings, to prevent crank-on-babbitt contact. But.... He also says that the downside of this is more wear during startup because it takes longer to develop the dynamic oil film. Personally, I would keep the clearances of everything in the engine as tight as possible without interference. If your last set of bearings showed a bit of copper, you might want to loosen the clearance, otherwise I would stay with STD.

 

[420a-t]

Has anyone else heard the pros/con of these bearings since the last post? I put some in my motor, and was wondering what weight oil to use and such. I was thinking either 0w-30 for oil to get to the bearings and everywhere fast, or on the other hand, 20w-50 so there's more cushion between the bearing and the crank.

What should I run?

 

[TSIfreek]

Get the standard bearings. Keep bearing clearance between .002 and .0025 on the crank and rods

Has anyone else heard the pros/con of these bearings since the last post? I put some in my motor, and was wondering what weight oil to use and such. I was thinking either 0w-30 for oil to get to the bearings and everywhere fast, or on the other hand, 20w-50 so there's more cushion between the bearing and the crank.

What should I run?

Engine oil weight is determaned my many things but the biggest is the bearing oil clearance. I like to run our motors a little loose at the above specs and use a 15/40 regualr HD diesel oil. Keeps the bearings and the oil cool.

 

[420a-t]

Get the standard bearings. Keep bearing clearance between .002 and .0025 on the crank and rods



Engine oil weight is determaned my many things but the biggest is the bearing oil clearance. I like to run our motors a little loose at the above specs and use a 15/40 regualr HD diesel oil. Keeps the bearings and the oil cool.

Why should I have gotten the standard bearings? What's the pros and cons? I had my motor put together to spec for the clearances, minus the .001" extra clearances for these ACL bearings.

Thanks,

Josh