Coated Rod Bearings for 6G72?

[Drweldin]

Calico used to carry them, but site says they are all out of stock...anyone know of a vendor selling them?

[bluemax_1]

Do what I do, buy King bearings, send them to Swaintech to be coated. End result, better than anything you can find on the market, and cheaper than a set of OEM Mitsu bearings.


Max

[Drweldin]

Thanks for the reply Max...
That's pretty much exactly the route I was going to go.
How do you pay for the Swaintech? Their ordering system seems a little antiquated from what I can tell.
On a side note: Bruce (Parts Dinosaur) says the ITM bearings he sells are re-branded King's....which makes sense
since they are both "Made in Isreal"...any thoughts? BTW I already ordered a set, so I can report back. Are there any
clear identifiers on the Kings that would validate?

[bluemax_1]

Yeah, King bearings are all stamped with the King logo on the back, and will have King's part number stamped on the back too.

As for paying Swaintech, yeah their system is old school. I just print out their order form, list what I want coated, pack the items with the order form and ship it to them. They'll usually call and confirm prices over the phone, I pay by credit card, they ship 'em back.


Max

[Drweldin]

Max,
I know we got into this discussion a while back on 3Si, but can't remember - what does the coating do in terms of imbedability?
And you talked about burnishing being involved...is that a requirement?

[bluemax_1]

The coating doesn't actually affect embeddability, that's a characteristic of the bearing's construction.

With trimetal bearings (OEM, Clevite etc.), the bottom layer is the steel backing, followed by a layer of copper lead alloy and topped with a very thin babbitt layer. The Babbitt is there to provide an anti seize layer. The copper lead layer has a much higher friction coefficient, which is why contact between the crank journal and the 'copper' layer can result in a spun bearing very quickly. It also allows for embedding of very small particles (generally silicon dioxide or sand/dust, ingested from poor air filtration or leaks in the air intake paths) that could otherwise score the journals and bearings and interfere with the fluid hydrodynamic layer which is supposed to support the crankshaft. This babbitt layer is very thin (0.0008") so it can't really embed larger particles. The copper lead layer is much harder and doesn't really embed anything very well.

Bimetal bearings on the other hand, use an aluminum tin alloy over steel backing. The aluminum tin alloy layer is several times thicker than the babbitt layer in trimetal bearings and can embed significantly larger particles. The King bearings that saved my rebuild embedded a piece of copper approximately 1/8" across (along with several other smaller bits of copper) from the previous spun bearings that wasn't completely flushed out of the system during the rebuild. I only found out several thousand (problem-free) miles down the road when I pulled the oilpan to inspect something else and decided to replace/refresh the bearings while the bottom end was apart. The biggest piece would have been more than the babbitt layer in a trimetal bearing could embed. It would have scored the bearing or journal (or both) and potentially caused another spun bearing within 300-500 miles (which I've heard of too many times on this platform).

The moly coating layer doesn't affect the embeddability of the bearing beneath it. I chose to go with moly coated bimetal bearings to try to get the best of both worlds, with the superior embeddability of bimetal bearings and their higher temp resistance (aside from the oil coating the walls of the cylinder, the hottest temps the oil sees are at the bearing journal interface) and the low friction of the moly coating. Bimetal bearings on their own have a higher friction coefficient in the event of bearing journal contact than the babbitt layer of trimetal bearings, but if the babbitt layer is worn off (or melted off if the babbitt sees higher than 400f), the copper lead layer has a far higher friction coefficient than even the bimetal bearings aluminum tin alloy layer. Lose the babbitt layer and you're going to spin a bearing shortly (your bearing oil clearances just changed by 0.0008" AND contact with the crank journal means the copper lead layer is much more likely to get 'grabbed' by the journal).

As for the burnishing, nah, you don't need to do that. It will generally happen when you run the engine anyway, and the coating is only 0.0002" thick. Burnishing it can reduce that to 0.00005" to 0.0001"


Max

[Drweldin]

Stupid question, are all King's (6G72) Bi-metal?
as usual, thanks for the info...
Also, is there any issue with installing bearings to plastigage, then sending them for coating as to get an idea of pre-coated clearance?

[bluemax_1]

Stupid question, are all King's (6G72) Bi-metal?
as usual, thanks for the info...
Also, is there any issue with installing bearings to plastigage, then sending them for coating as to get an idea of pre-coated clearance?

Yes, all the 6G72 King bearings are bimetal (I'm not sure they even make trimetal bearings).
As for plastigaging before getting them coated, that's what I did


Max

[Drweldin]

What did you do to make sure the bearing went back to the rod it was gauged to?

[bluemax_1]

I bought 2 sets of King bearings and tried them both. They all gaged out at about .00017" - 0.00018". After coating, they all came in right about 0.00015"


Max