What bearings to choose?

[clipto]

Should I go with clevite or acl tri metal bearings? Just trying to figure out what one to go with.

 

[mitsurage]

I have always used ACL in my builds. No issues yet.

 

[AshyBone]

I've heard alot of good things about tri metal bearings. Also I've heard King bearings are great too.

 

[ed1380]

king aluminum. What I use and recommend.


taken from 3000gt forums

I've been running King bearings since my rebuild ~6 years ago. I've swapped them out once. The rebuild is still going strong after ~30k miles including sustained high rpm roadcourse use.

There are some differences between tri-metal and bi-metal (King and ACL aluminum) bearings.

Points about tri-metal bearings:
The tri-metal costruction has a steel backing plate (for strength) covered by a copper layer (a little more malleable) and in turn covered by a thin layer of lead-tin babbitt. The lead-tin babbitt has a pretty low kinetic friction coefficient so the bearings won't bind easily if they contact the crank.

The downside is that the babbitt layer is VERY thin, meaning it won't last long if there's contact. because the soft babbitt layer is so thin, it also isn't able to embed larger particles which means that foreign hard particles might partially embed, sticking up into the oil flow in the small bearing-journal clearances interfering with oil flow and potentially scoring the crank.

Because of its materials, the babbitt layer is also not able to handle too much heat. The tighter your bearing clearances are, the higher the temp between the bearing and journal. These temps can be significantly higher than the temps you see on an oil temp gauge (if a person even runs one). Thicker oil can exacerbate the temp increase between the bearing and journal and if the temps are high enough, it's possible to melt off the babbitt layer.

If you search through all the available pics of folks who've pulled the bearings on their cars for routine maintenance, you'll find some pics where the bearings are down to the copper layer, but there is hardly ANY evidence of actual contact. These are potential cases of excessive oil temps at the bearing journal interface. When the babbitt layer is gone, there are 2 problems that result. One is that the clearances are now wider than spec and lubrication can suffer, the other is that the copper layer has a much higher friction coefficient so if there IS bearing-journal contact, it can result in a spun bearing very quickly.

Points about bi-metal bearings:
Steel backing with an aluminum based top layer. The top layer is significantly thicker than the top babbitt layer on tri-metal bearings which allows the bi-metal bearings to embed particles larger than tri-metal bearings are capable of. I can personally testify to this.

When I rebuilt my engine I had the block hot tanked after the work done on it. Cleaned out the oil cooler and turbos etc. trying to get every last bit of material from the spun bearing out of the oil tract. Well, I missed some of it. The car ran fine with no problems and about ~7k miles later, I pulled the oilpan off while checking for something else and while the oilpan was off, I pulled the bearings to inspect them. That was when I discovered that a few of the bearings had caught and embedded copper bits that I hadn't managed to get out from the flushing. some of these copper pieces were large enough to have potentially scored the crank, but they didn't. They had all embedded flush to the surface of the King bearings. If they hadn't, I'd probably have been another "My new rebuild just spun a bearing AGAIN" sob stories.

While the engine was apart, I replaced all the bearings with a new set of King bearings.

The top layer of bi-metal bearings are also able to tolerate oil temps 3-4 times higher than the babbitt layer on tri-metal bearings, so you don't have to worry about clearances inadvertently altering because the babbitt layer wore off from elevated temps at the bearing-journal interface.

The downside to bi-metal bearings is that the aluminum based layer has a higher coefficient of friction compared to the lead babbitt of tri-metal bearings. If there is sustained contact at high rpms between the bearing and crank, it will spin the bearing and potentially heat weld to the crank journal trashing the crank.

Obviously, under the conditions that would cause this, a tri-metal bearing would also spin, but to reduce the likelihood of anything like this happening (since it's potentially possible to squeeze out the hydrodynamic oil film at high HP/cylinder pressures and high rpms), I had the King bearing coated with a molybdenum based friction reducing coating.

The company, Swaintech, has some anecdotal info about their moly coating about a Nascar driver who ran 3 laps with zero oil pressure. The car lost oil pressure in the middle of a race. The driver kept going for another 3 laps till a caution flag popped up. He pitted, the crew fixed th issue that caused the loss in oil pressure and he went back out on the track and finished in a high enough position to win the overall cup later that season. I don't know how well the coating would hold up on a 6G72 if it lost oil pressure, but every bit helps. The moly coating is able to withstand temps significantly higher than even the bi-metal top layer.

That's what I've been running for the last ~23k miles. king bearings with a moly coating.

Niterydr used/uses King bearings on his car as well. Pushed it on the dyno till the heads lifted and they were problem-free.


Max

 

[clipto]

Thx that helped alot. Should I use the king xp ones or the standard ones?

 

[nismo2evoawd]

There's a lot of import guys that make good power running a ACL bearing, thats also what i used in my build and worked great.

Good post above.

 

[92AWDHX40]

Ive used both in my builds i, running clevites right now no problems with either over the years.