Flathead engine oils

Before I have been advised to use Penrite HPR 50 in my WLA, but noticed on the label, not recommended for motorcycles.Not sure why this is.
Would Pentrite HD Oil 50-70 be more suitable. High viscosity multigrade, high zinc, non friction modified ect.
Any experience out there on flathead engine oils????
Thanks Keith

You need to use an oil that is formulated for the service, which is an air cooled engine. IMO, any oil formulated for liquid cooled engines should not be used. There are many makers that make good motorcycle oil but none is cheap. You'll end up paying for being too economical in the lubricants you use.
I wouldn't even do that to a lawnmower engine.

I've put any old oil in lawn mower engines all my life, it does 'em no harm... Nothing does.

For old air-cooled motorcycle engines, different game. I used Duckhams Q 20/50 in my old 45 for years, and it's still in use now with its current owner. These days I use a special straight 50 mineral oil sold for classic bikes, there are several brands around. Personally, given the actual mileage bikes like that do, and the distance they cover between oil changes, I don't think it matters much what you use as long as it's the right grade and type.

Straight 50 hinders cold-weather starting but th days when I worried about that are long gone....

Pentrite HD 50-70 is what I use
made for Pre Evo Harley's

Rod

Sorry that i'm not up to date on all oils out there but there are alot of oils available that put hd into their names and it has nothing to do with their service duty.
It seems that should be a good choice but to use a multi grade oil in an air cooled engine, it must be formulated for the service.
I hear of guys using Rotella and others mixed with stp or Lucas oil stabilizers but i'm not that much of a gambler.

What is wrong with the synthetic oil you can find at any motorcycle shop? They have all the good stuff in them unlike automotive oils. That's what I run in my high performance VW bug engine.

the age old oil debate. synthetics i believe would lube well but they tend to run out of old motorcycles with porous castings like the harley has.i don't like aircraft oils myself as they are designed to run in an engine at low steady rpm and constant oil temp.some oils are marked not to use in a motorcycle engine as most modern bikes have a wet clutch. all that being said(and remember,it's only my opinion) i like penzoil racing 50wt. for all round use.it's high zinc etc...just like the old time motor oils.

Well that should be true, if it's labeled for "racing only", "off road only", then it should have the good stuff in it.

Harley sidevalve motors have a small oil supply pump. So they are very dependet of the weather temperature. So consider viscosity and operating temperature when choosing oil. I have been using 10W-40 oil successfully for 15 years (wheather rarely more than 25 deg. celsius). With low cylinder wear. The higher viscosity you choose, the less oil will flow to the rod and pistons. There is no use in heavy oil when it is only flowing to the cam chest.

sidewinder..i agree about the viscosity. even with 50wt. you really need to warm the motor up good before riding as the oil really moves slow when cold. on the wla's the manual said to throw in a quart of kerosene in cold weather to thin the oil down.the 20w40 or 20w50 is probably a good choice for colder weather. with multi-vis oils remember that the oil doesn't thicken when hot... it's 20wt.with the properties of the higher number.summer in the states gets quite hot and the 20wt. tends to run out on the floor easily.the flatheads are low performance engines and are very forgiving as to oil choices.

Heavier oils, and synthetic oils especially, I believe, have much greater shear strength than light oils. So, just for the sake of debate, you might speed up oil delivery a bit with a light oil, but you lose some shear strength. More quantity, less quality. ??

Having said that, I suppose it could be true that roller bearings don't require the shear strength that a plain bearing engine would.

I tend to lean towards heavier oils, I'm just not convinced that lighter oils flow that much faster, or that it makes that much difference with a roller bearing engine. I think our imaginations tend to get carried away thinking that heavy oil flows like gear oil or maple surup. With plain bearings, I think that's probably more true, or more important, to get oil to the rod and main bearings faster. Synthetic 20w50 seems like a good compromise for me...but the last time I had a 45 was back in the straight weight days, and I'm just now putting a big twin flathead together...so I've not tried it yet. But that's what I'll start out with.

I don't know if it's true, but I've been told that a Harley lower end can run quite a while with the oil pump out, without being damaged. I don't think the pistons and rings would like it though! ?? Don't know if that's true.

I'm thinking that it was suggested to add kerosene to oil WAY back in the day, when people were using side car rigs in very sub-zero temps. I bet that not too many antique Harley riders are going for joy rides or on runs when it's below freezing, ten degrees out, 20, or even 40 degrees out for that matter. So I'm not too sure that lighter oil for colder weather holds true for us flathead enthusiasts.

And, I could be wrong. !!

krazy ken

you have to take everything posted on here as opinions and not the last word. like i said flatties are very forgiving. the synthetic might stay in the motor better if the cases are painted inside to seal them. is glytol still availabe ? rustoleum red primer stays in our car engines fine.. maybe that would work as well.we always ran straight weight in our wr's and kr's but we only ran 2 quarts at a time and they only ran 6 to 10 laps on a dirt track and we drained all the oil at the end of every racing day. as a testimony as to what you said about the low oil needs of a roller bearing engine the kr's ran a quarter speed oil pump instead of a half speed so as to keep oil from loading up the bottom end and dragging on the flywheels.

Ooops my engine is all together, but I bet painting or coating the inside of the case would be a great idea. Probably lots of high tech coating available for that purpose. Or, as you mention, some good old Rustolium Red.

Well I have no experience putting synthetic in a old Harley so I don't know how it will work. I do have a Bug with a HP engine in it, and a BMW "R" engine motorcycle, and they, both being aluminum cased, air cooled engines do great with synthetic. But I do imagine the castings are a bit superior to 1940's casting technology and metallurgy. !!!

[Pa]

glyptol is still available at generator and electric motor specialists. It is also available at industrial suppliers such as MSC Industrial Supply Company. I prefer fosil oils for air cooled machines. Even small engine repair oils are adaquate for daily runners. Synthetics, in my opinion are fine after an engine has been put through a thorough breakin period. I have heard horror stories on using synthetics before breakin periods with roller bearing skidding due to to low of a friction to turn the rollers.

Yep I agree that's something to think about, and I usually break my engines in with a good dino-oil. Certainly won't fire up the UL for its' first time with synthetic.

I suppose there is good reason to change oils regularly.
I run my 45 about 2000 miles a year, and I like to change oil every 5000 miles, so my oil ends up a few years old.
Any advise on this.
Thanks Keith

I would think you'd want to change your oil at least once a year, I'd do it at 2000. If you live where there is four seasons, the temp changes during winter and spring would/could cause some condensation...although I suppose a hotter running air cooled engine will burn that off. If you park your bike in the house, or live in a very hot climate I suppose it wouldn't be as important. Still, I don't like going over 3000 on a hard run air cooled engine, and usually change oil in the spring no matter how many, or few miles are on it.

I've always run automotive oil in my bikes, from nitro 70 in the old days, to Castrol 20-50 nowadays. The knuck has over 70k miles, as does the 65pan. Bores are still serviceable, and bottom ends are tight. I do run the H-D canister filter and the tiny power steering cooler as an oil cooler. I'm sure the specific additives for mcy use are useful, but I guess I've been lucky with good oil that's filtered and changed at 5k or every season.
I like multi vis as it does start easier in cold weather, and is readily available when on the road. I've run pressure gauges on some of my machines over the years, and don't see any difference in oil pressure at operating temps, so I guess that new fangled multi vis technology must work.
Of course, oil is one of those things that everyone has an opinion on, and all this only proves I'm no different!
DD

Good choice Dick. 20-50 oil is racing oil and contains additives that standard automotive oil (10-30, 5-40, etc) doesn't have. I think the racing oil additives have more to do with removing the condensation and other combustion debris from the short run time racing engine than they have to do with lubrication and there may also be more zink. Racing engines and air cooled engines benefit from the mix. If you go on-line you can find a vast amount of information on oil. Its all about the additives. Any oil you buy today has got to be tremendously bettor then the stuff that was refined back in the day when your flathead was new. By the way one of the best oils for air cooled engines is diesel engine oil ( I just can't bring myself to putting the cheapest oil at the tractor supply store into my bike ). Of course this is all just my opinion and your results may vary. Just one more note; if you heat 50wt and 20-50 to operating temp there viscosity is the same.

I may be wrong, but I believe that although 20-50 and 50 weight oil will have the same viscosity when new, or fresh, that the 20-50 will break down faster, and as it does will lose viscosity and shear strength a little faster. So, might want to change the multi-grade oils a little more often than the straight weight oils.

The diesel oils are indeed good, but very expensive. I still think that the motorcycle oils are the best bet. But I could be wrong!