I did a 4x4 service on my truck. 6 speed manual with a manual transfer case. My engine makes just over 500hp at 800ft/lbs torque. And yes, that's just more than the stock clutch can hold. I figure if it's okay for my truck trans and transfer case, then it must be okay in the primary. Had some left over so I thought I'd try it (Amsoil OE synthetic Multi-Vehicle) in my primary. Works as advertised. Clutch feels good and no big clunk into first gear. If it's cold, I pull in the clutch for a few seconds before I put it in first. That big cluck is mostly gone. The truck trans doesn't have any sun/planetary gears either BTW, and the transfer case had a big assed chain in it, so these arguments are moot to the nay sayers.

 

you have to go back to the engineering!
when designed, the engineer spec out the best option for lubrication in consideration of gear cut angles, clearance, bearing type and shear. a gear oil has hp additive to cushion the gearing and keep a film on the gear where as atf is not designed for that type of service. also, it has been said that gears chew up the molecular structure. also one has to deal with temperature issues, yep atf is more hydraulic in nature and will take quite a bit of heat but it does thin out and if it did not have anti-foaming agents, destruction is in short order. what happens when lube gets entrained with air, looses it ability to lubricate and heat will ensue. then there is the lube system, splash vs pressure. in an automatic, the pressure system is what makes it last, ensures constant lube and cooling, splash does not.
who has worked on old dipper rod engines??? get the picture, they usually handle small power and low speeds and they do not last long and the older machines used a soft bearing material, remember poured bearings, saves the crankshaft. when they rifle drilled the rod journals and pressurized it, the bearings changed and capability of the engine improved and lasted longer.
so there is a lot to think about.

 

There’s gears in the primary? (Sans the starter gear)

 

Saw an interesting post about Primary oil and its relation to the famous shift clunk.
I am running M1 4T in the primary and the clunk although never went away did become less. OK, I change fluid again but only had M1 v-twin 20W-50 so I put that in. First I thought that it was my imagination but the Clunk did increase. The post talked about how 20W-50 can cause just a little more drag on the clutch plates than the 10W40, It was not harming the clutch but did bring back the clunk. Could be why Harley switched out from using SYN 20W-50 from their primary. too many complaints about the clunk returning. I will be going back to 10W-40, anyone else notice any changes in clunk vs. oil weight? and yes W stands for winter I am referring to 40 vs. 50 50.

 

 

Another convert

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Yes, type f. No super special brand needed

 

 

On my 03 RK - 95" w/ cams, compression & headwork I ran Dexron ATF in the primary for 150K miles. At that time I put in a Barnett extra plate clutch and a AIM lock up , I now have about 200 K miles and am still on the original primary chain & comp sprocket. - Eastcoast Jim

 

My owner's manual for my 2002 Ford F-150 pickup truck's 5-speed manual transmission specifies full synthetic ATF. Amsoil recommends their Amsoil OE full synthetic Multi-Vehicle for my truck and that's what I've been using with great results. This Amsoil ATF meets the Dex/Merc spec's which seems to go against a lot of this forum's members who recommend Type F instead but they don't say why. I've been watching Delboy's Garage videos and he recommends ATF (he doesn't specify a particular brand or type) instead of the V-twin motor oil in the primary because of its anti-foaming ability. It appears to me that the Amsoil OE Multi-Vehicle is a good choice. If it works in the truck's manual transmission, it seems that it should work in another manual transmission which is also splash-lubricated.
I'm in the process of buying a 2003 Sportster 1200 and the first thing I plan to do is change all the fluids.