Molykote 321 on Main & Rod Bearings

[Gordo2]

I'm going to coat my bearings with Molykote 321 this weekend.

I've read threads with Henry S. recommending cleaning, a light 600 grit sanding & spray.

Any other tips - heat curing or otherwise?

Thanks

[Gordo2]

I went ahead and dry film lubricant coated my main and rod bearings today.

Background:
- 3.2L engine had ~ 30k miles on a rebuild done by the previous owner. I'm upgrading the engine upper half and decided while I'm at it, I ought to check on the bottom end/replace the bearings. As I researched the project I found the new Glyco bearings are hit or miss for quality - lots of recommendations to re-use bearings over buying new. Based on this, I decided to re-use my ~30k bearings, but to coat them with a dry film to help with start-up and run-in. Henry Schmidt from Supertech recommended Molycoat 321 in a few Pelican threads - So I went with it.

Coating process:
Started out by cleaning - sprayed the bearings with carb cleaner to get the oils off. Once cleaned, I lightly scuffed the bearing surface with a 600 grit wet sandpaper (bowl of water on the side). My bearings seemed to have some sort of original coating remaining on the surface - which the 600 sanding removed:

Left bearing as removed, right bearing lightly polished with 600 grit sandpaper:


Once they were lightly sanded, I thoroughly cleaned the bearings again with clean wipes and alcohol to prep for the Molykote. I taped off the backside of the bearings. Not sure this was required, but I saw it recommended on another bulletin board: theory being that you don't want the back of the bearing coated with slippery stuff - check.



Once I had all the bearings prep'd I placed a few on a screened spray bench surface (recommended by Dow) and sprayed each bearing, one at a time.



A quick shot of Molykote, was all it took for each bearing, rotating the can to direct the spray across the bearing surface. The stuff goes on quick and pretty thin - so you need to keep the spray can moving / not hitting one spot more than a moment or it will run. Runs don't seem that concerning, flip the bearing over so it doesn't puddle in the center and the Molykote seems to even out pretty well. I only over-sprayed and had running on my first bearing, after that, I had the hang of it and the rest went on smooth.

Here's a shot of one of the bearings as it dries:



Seems like good stuff / a worthwhile step for my rebuild - time will tell.

Gordo

[tocobill]

For what its worth ... We use this type of dry film Moly out on ship all the time. Usually on any metal to metal surface where there is a chance of galling. The coating works very well then it is lightly buffed. This "buff" brings the surface to a slick polished finish and removes any of the extra moly that might be left on the surface that will wipe off. It can be applied and buff in several coats. A horse hair brush works best but a clean natural cotton rag will work well too.

[Kemo]

If Henry uses it..im all ears. I will be in my 92K mile engine in the near future and would prefer to re-use the Rod and Main bearings. Any more info on this product? I have been trying to research a bit on this.

[jpnovak]

Steve, We should talk about coatings.

[jpnovak]

I do not have any experience with these particular coatings. I do have experience with other DFL (dry film lube) and TBC (Thermal barrier coatings). They are a great addition to our older combustion engines. There are many places to put them and they do make a difference.

[Kemo]

Jamie, check your phone

[Gordo2]

Hey,

I'm wide open to more spraying

Considering thermal barrier for the piston heads and/or skirts - interested in other's thoughts.

[Kemo]

it seems the molykote is a dry film lube right? combine that with some thermal coats on the cylinder tops and heads? we just need to find the right product. if anything, its an interesting topic...

[KTL]

What kind of sticking power does the 321 have? I'm curious if its just a coating that rubs off or not.

Curious to know how much build it has. Bearing clearances are quite close. A desired main clearance is 0.0030" for a racy engine. Not too hard to build that up with a coating and close that clearance to much less.

I'm not saying Henry is wrong for recommending the use of it. Just curious what flexibility there is in using it. Meaning, if you've got a fat clearance and you want to close it up, or you've got a tight clearance and better not treat them with anything.

Do some research and you can have a set of bearings done for you for pretty cheap. Swain Tech does a set of 6 cyl rods for $35 and mains for $41. Obviously a can of 321 is a lot cheaper than that.

[tocobill]

It does rub off to an extent. The whole point of polishing after you spray it is to take the extra top coat that will rub off and leave the slick polished finish. If you do it twice it does build up a bit then re-polish.

[AlfonsoR]

I think you're taking a big chance coating the bearings with a $3 rattle can. I would guess that companies that mass produce these, spend millions of dollars getting the babbitt to a consistant thickness to ten thousands of an inch or less.

Comparatively, the coating applied with rattle can is going to be much less consistent due to the simplicity of the spray system, the geometry of the shell (small radius that you would want to follow to keep the coating consistent), and the possibility of human error due to manual application, muscles getting tired, etc.


Just my 2 cents, good luck.

[911pcars]

Originally Posted by AlfonsoR

I think you're taking a big chance coating the bearings with a $3 rattle can. I would guess that companies that mass produce these, spend millions of dollars getting the babbitt to a consistant thickness to ten thousands of an inch or less.

Comparatively, the coating applied with rattle can is going to be much less consistent due to the simplicity of the spray system, the geometry of the shell (small radius that you would want to follow to keep the coating consistent), and the possibility of human error due to manual application, muscles getting tired, etc.

Just my 2 cents, good luck.

+1. Sounds like the Parkering process applied to new/rebuilt cam lobes - temporary until the lube system is at full operational mode. However, cam lobes are a high-load application and cam lobe oil clearance isn't quite the same as the space between journal and bearing (.0015-.003"). What's wrong with moly engine paste, engine oil and engine cranking to build oil pressure? For some, I suppose it's another layer of protection.

Sherwood

[KTL]

Yeah Calico's CT-1 bearing coating is 0.25 to 0.3 mil (0.00025-0.00030") and that's pretty hard to apply with a spray can? It's intentionally super thin because bearing clearance are really tight. 0.002" to 0.003" doesn't give you much room to play around with thicknesses applied by eye.

Really the bearing coatings are just extra insurance. Took this from Swain's website. Swain Tech Coatings’ PPM™ solid film lubricant is a thin, tough coating applied to bearing shells to reduce friction and improve the wear life of both the bearing shells and journals under normal operating conditions. However, it is when operating conditions are less than ideal that PPM™ really goes to work. If there is a cold start, oil starvation or any other situation where the primary lubrication is less than ideal, PPM™ will provide a solid film of lubrication to prevent a catastrophic failure.

Honestly I would like to see how my last engine would have looked in the crank area if I had spent the $80 for PPM on the bearings........... Might have saved me a crank replacement, rod rebuild (one replaced), cam housings, camshaft repair, oil coolers, etc. etc. blah blah blah.

[Gordo2]

Originally Posted by AlfonsoR

I think you're taking a big chance coating the bearings with a $3 rattle can... human error due to manual application, muscles getting tired, etc.

Dude - it was a $35.00 can and my calibrated arms are huge

From one of the NASA studies that I read before I went forward with the job (I'm a research junkie):

"It is difficult or impossible to apply dry-film lubricant with a uniform thickness on internal surfaces and radii."

Though you would think the pro's have some sort of wild, super accurate application gizmo - I kind of doubt it. Sprayed, dunked or screened at the cyclic rate.

Meanwhile I don't doubt the big guys like Calico inspect some % of product for conformance to specs - be it application thickness, adhesion or other.

Gordo

[AlfonsoR]

Hey Gordo, you never know, maybe it will make the engine run for a couple of hundred thousand miles. I would be interested in knowing what your bearing clearances will be. I hope you can take the time to post them.

[robcf]

I work for an OEM and a few years ago in an engine plant. There are two mainstream methods out there for coating journal bearings (and piston skirts): spraying and screen printing, the latter being more accurate. Spraying has a few inherent issues which have been touched on here, primarily overspray on the backside of the bearing shell.

In both cases the bearing manufacturer will study then optimise their process to control the coating thickness to the part specification, periodic inspections will measure the process for drift and correct when necessary.

In your instance (myself included) the only opportunity to conclude that the bearing coating application was successful is if the bearing never fails, however, the opposite is also true.

[afterburn 549]

My only concern , Did Henry say 600 grit? thats ruff stuff !

[Lapkritis]

People polish cranks with 600 grit - pretty popular for race engines that people want to be a little loose and fast. I tend to go a bit finer in stages.

This picture has me concerned about the bearing due to what appears to be damage on the top left:



I probably wouldn't run that guy if I can catch a fingernail on the edge.

[KTL]

And some people may not realize how seemingly crude the polishing method is.....

https://www.youtube.com/watch?v=V82WnutmFAk

Most would be quite surprised to see the polishing is done with a giant belt sander! But it works.

Note that he does each journal basically the same number of revolutions so it keeps it same from journal to journal. Also note how much he says it takes off the crank. One to two tenths? That seems like a lot in bearing clearance numbers. I gotta measure my recently polished "new" crank that just came back from the shop & see how much it changed before & after. Might actually need to coat my bearings to close up the clearance!