My dad has a 1975 Harley. Both the manual and the service manual he has for it list:

Special Light 58
Medium Heavy 75
Regular Heavy 105

Obviously these aren't SAE grades, so being a past oil geek I set about trying to find out what these corresponded to. I searched the net, found a good post on BobIsTheOilGuy, but nothing absolutely definitive.

Then I remembered American Pickers and the old oil cans they sometimes collect. So I went to eBay and checked there, and after a lot of digging, found my answer:

It seems some of the older cans, notably some of the ones that list the Harley number type in addition to the 3 different Harley word weights, actually have the number on the back, and on the top of the can. And, most importantly, actually have the SAE grade on the top of the can as well. Below is the cross reference:

Special Light 58 = SAE 20W (you read that right, twenty weight)
Medium Heavy 75 = SAE 40W
Regular Heavy 105 = SAE 60W

Now I don't know if Harley eventually modified these SAE weights against these three categories down the road, but at least in the age range of my dads bike, this is what they intended one run.

Just wanted to post this here for anyone running older Harley's and wondering what oil they should go with. I think I'm going to try and convince him to go with Delo 400 15W-40 once his Harley 50W oil is used up.

Chuck

 

Chuck, those numbers, 58, 75, 105, are the SUS at 210F for the oil.

58 is a 20 weight, not 20w
75 is a middle SAE 40, not 40W. There is no 40W viscosity.
105 is a heavy SAE 50, not 60W. There is no 50W or 60W viscosity.

Ken

 

That is what a poster on BobIsTheOilGuy was claiming, and I don't necessairily disagree. My post though is backed up by what Harley (or in some cases, AMF) has stamped themselves on these cans of old oil. Who am I to argue with what they themselves have stamped on there?

I'm still going back and forth on buying the Medium Heavy 75 can that had SAE 40 on it, shaking it up real good while warm (wrap it in electric blanket perhaps?), ruining its value by puncturing the bottom, and taking an oil sample to send into say Blackstone Labs.

While the add pack (what would be observable on the cheapo analysis that is) would be interesting, what we could see would be the cSt that Blackstone does, and I'd pop for the TBN just for the hell of it to see what the starting TBN was on oil that old.

It's oil right? I'd think other than addpack seperation, the oil itself should still be the same cSt today as it was back then?

Chuck

 

This subject somehow got back into my head, and having nothing else to do tonight (yes, I have no life), I searched eBay againi for perhaps some better deals on the 75 type. I've got some messages to sellers out, but, I wanted to post here on something I ran across:

Someone on eBay is selling an AMF vintage quart can that has the 3 word types listed as normal, with the numbers listed. What's different on this one is, what is on top of the can.

On top of this can, there is:

90 - B
SAE - 50

This would mean there is now a 4th number type, type 90, and it corresponds to SAE 50.

This number type is not listed in either of my dads AMF books for his bike.

Chuck

 

OK, another update:

I found a decent price on a 70's era AMF 75 number type quart can. Should arrive here in the next week or so. Going to warm it up good, shake it up good, puncture a hole in the bottom metal plate, and drain the oil. Will take a sample out of that and send for oil analysis. This will give us the cSt of the oil (I'll look for a place that can do SUS as well), which should put this to rest once and for all.

Chuck