Hi all, I've recently purchased a 51/52 Plunger B31. I don't know much about it or it's history, so I'd like to do a bit of a service on it. I don't know what grade of oil to use, so any advise as the what is required would be greatly appreciated. I live in Queensland Australia, so things are going to be pretty warm here for the next 6 months, I expect that will influence my choice of oil. Thanks
G'day Thommo, I know that this will raise a few hackles but I wouldn't be putting mono grade oil in ant bike. Have you seen how long it takes to pour when cold? I shudder to think how long it would take to get through tiny oilways and the damage that will occur in the meantime... I'm based in Victoria so although we don't get your heat extremes, it still gets quite toasty so I use Penrite HPR40. It's a 25W-70 oil that has no friction modifiers (good for clutches!) that is designed for Aussie conditions
The FIRST thing you want to do is disconnect the oil lines and put a high pressure hot water sprayer down in the tank. When this engine was first run there was nothing available but non-detergent oils. So there's about 3/4" of crud in the bottom of your oil tank. You have to get that out before running modern detergent engine oils, or they will circulate all that grit over and over until the whole thing is worn slap out.
Wouldn't be a bad idea to fit a small oil filter on the RETURN oil line if you have the money. One from a '75 Norton is easily had new from many Norton sources for under $40US.
On a tight engine a multi-grade oil would be best, but on one of unknown mileage I would tend to prefer a solid weight. Of course, with a solid weight you need to warm up the oil and be careful not to race the engine until you feel the tank start to warm. Also depends upon your driving habits and locale.
Drop by the local Harley shop and see what they use. Your engine oil needs would be much the same as a big H-D. Then go buy the equivilent at the local discount store!