Transmission oil

[44knuckle]

Any experience/thoughts of using 50w motor oil versus semi-synthetic transmission fluid for the Harley 4 speed transmissions?

[sirhrmechanic]

Without looking at a manual, I can't say what weight/viscosity is right.

I will note that in the old car world, lots of people use 90-wt High Pressure gear oil in lots of inappropriate places. The high pressure gear oil (that smells like sulpher/rotten eggs) can be VERY VERY bad for vintage transmissions that use yellow metal (bronze) in the gear trains... whether as bushings, carriers, or as bearing holders.

If it smells like sulpher or is a 90-wt EP or modern oil... be VERY wary using it in a vintage transmission or in any application where heavy oil is used. The sulpher will eat yellow metal down into a crumbly zinc matrix/piece of slag. And that's expensive!

Best advice is follow the manufacturers recommendation. They were pretty smart, those engineers. There are 'vintage' oils available for just about everything. It may seem expensive compared to your WalMart brands. But in the long run, oil is really cheap. Vintage transmissions... are really spendy if you have to rebuild them. Don't skimp on oil or try and out-think HD's best engineers.

Just my $0.02. YMMV, offer not valid in Arkansas, as seen on TV, etc.

Cheers,

Sirhr

[Magic]

I'm in Pa where it doesn't get too hot and use nothing less then straight 70wt and have gone to 90 when I was riding more. Been doing ok for 30years that way. To each his own they say.

[Hercumile]

I don't think synthetic is necessary. Using standard 50w motor oil,I've put a quarter million miles on the tranny in my 69 Rigid Shovel without a teardown. Also, when I bought the bike it had 90w in it and the kick starter clutch would sometimes slip. It's not slipped once since switching to motor oil. I wonder if the synthetic might also cause this painful side effect.

[duffeycycles]

If you want it to leak put some Syn in

[BigLakeBob]

Was gear lube available when service manuals were written in the '30s and 40's?

I have some literature on changes of oils as the sd letter designation has changed and have not looked at it for a while, but don't all older oils have sulfer in them? Don't beat me up if I'm wrong. I have also read that oils recommended for diesels have the properties of oils from the past, again I thought sulfer, where modern oils this has been eliminated. My personal experience has been for the last at least 20yrs I've been running 75/90 gear lube in my HD 4 speed trannys, not one negative issue. Oh, the endless oil debate. I tried synethic once, just as Duffy said.

Probably moly or graphite in oil for diesel, does that make sense?

[sirhrmechanic]

Hi Biglake:

Gear lube 'back in the day' would have been 250 weight, 600 weight... there were all kinds of viscosity numbers. For many cars/trucks, gears and transmissions were lubricated with 600. But some transmissions used engine oil, too. Follow manufacturers instructions. They all told you what to use!

This book is also an outstanding resource for translating those old instructions such as "Use Price's Motorine C" or "Duckhams Superior Blend."

http://www.amazon.com/Which-Oil-Choo.../dp/1845843657 Every old car garage needs a copy of this book. (no, I didn't write it.)

All older oils did have 'more' sulfur in them today than most of the highly-refined modern motor and gear oil. But the high sulfur content (and it's probably lots of other 'stuff' in EP oils that, combined, gives that sulfur/rotten eggs smell, not just sulfur is very bad for yellow metal. If it smells very strong of sulfur or rotten eggs, beware using in a vintage transmission/rearend unless you know it does not have bronze in it. If the transmission doesn't use bronze in it... EP won't hurt it.

As for synthetic... it will seep better than traditional oils. If you bike leaked... it will really leak! It also has a property that folks who leave their bikes/cars/whatever sitting over the winter. Synthetic oil won't tend to stick to engine parts... it will run off and return to the sump... and that can leave internal engine parts with less of a film on them and more susceptible to rusting or corrosion. Is this a definite problem? Not usually for machines left a few weeks or months. But if you have bikes that sit un-ridden for long periods... it's a potential to be aware of.

Last, and this may be a problem with some bike engines, is that modern oils have had a Zinc additive removed -- ZDDP. The lack of ZDDP can result in serious cam-follower wear. Cars/bikes with roller tappets... no problem. And I don't know if this has affected the bike world... but lots of older V8's and plenty of engines like Jaguar's that run flat tappets have seen some serious and expensive issues. There are some good ZDDP additives out there. Follow the manufacturers instructions because (here we go again) ZDDP additive in high concentrations will attack yellow metal -- brass, copper and bronze.

Main thing with oil... change it often. Oil is cheap, engines are expensive. Most of it varies only in relation to additive packages. Personally, I use Rotella T in old cars and bikes. But I don't think it's any better or worse than lots of other stuff out there. I use it because I buy it in barrels.

Hope this helps...

[Magic]

I agree with the 90wt the kicker would not engage all the time if the air or engine temp was cold. That does kinda hurt too from what I remember. Been steady with 70wt and all is well. Those 4 speed transmissions were built to last compared to the modern ones.

[Frankenstein]

Just keep in mind that 90 weight gear oil is the same viscosity as 50 weight engine oil. Do a web search to verify,

DL

[harleytoprock]

Just keep in mind that 90 weight gear oil is the same viscosity as 50 weight engine oil. Do a web search to verify,

DL

I agree. So 70wt motor oil is thicker than 90wt gear lube.
The Gl5 rating will attack yellow metals but gl4 will not. It's hard to find Gl4 here in the states so your best bet is motor oil.

[iiggii]

90 wight has always worked.

[T. Cotten]

Folks should remember,

Oil only gets to the main drive gear rollers in a 4speed by seeping past a thrustwasher, and then that's the only way out (until something fails...)
Do you want a lot of oil in-and-out, or not?

This is why the Factory spec'd the same oil for the transmission as the motor.

....Cotten