ATF is basically 10 weight motor oil. I have run 100% atf in a V8 engine before, it cleans sticky lifters and the detergents really clean the engine. Ran it for a few days, drained it out, and it really brought some crap out with it.

Will quieten down sticky lifters and such. Won't hurt a thing, none whatsoever.

 

I would imagine that with the Harley engine, things would get noisy once the viscosity lowered from the ATF and you'd check your oil thinking it was low, only to find it was overfull!

 

ATF that is used in auto transmissions is pumped under pressure unlike the primary in the bike. It's more of a driving force for the clutches but serves to lube the transmission too, just not as good as something that was made for the primary.

 

I ran the cheapest 10w40 fossil oil available at Wal-Mart ($1/qt.) in my '96 RK for >100k miles and had no problems related to the oil. I did change out the clutches at 65k even though they had quite a few more miles left on them, and replaced the chain at around 80k IIRC, as it showed a little wear and primary chains are cheap.

I've been using Castrol GTX 20w50 (fossil oil) in my '07 since new. The primary was completely disassembled last fall for a tranny mainshaft bearing replacement with 32k miles on the clock. Everything looked good: Chain, tensioner shoe, clutch disks, and bearings. Nothing was replaced, and since clutch action is perfect with no creeping or slippage even with 255 cams installed, I think this is a good testimony for this oil and I'll keep using it.

 

Wouldn't you have to replace the sprocket and clutch basket when you replace the chain? I'd expect the new chain to wear badly on the worn sprocket teeth.

 

Do you have an automatic on your HD?
Primary needs a better OIL it has chain and a wet
clutch but it is no an automatic

 

I will have to go with 1stSgt on this one.

 

Naw, I don't always agree with the manual, especially since financial interests are at hand written by the Moco. There are better oils than Harley recommends, as we all know, but thinner oil like tranny fluid isn't gonna be one of them. There are certainly improvements that can be made...look at what they put on the new bikes for TIRES for instance. Only now I see they have a contract with Michelin, so that's an improvement - even the Moco can learn.