E: Engine Oil Viscosity

[greg brillus]

I just thought I might mention about different grades of oil and the effects it can have on our engines. After the rebuild of my Rapide last year, and after the first 500 miles I changed the oil and filter. Ordinarily I have mostly used a 20w/50 mineral oil, but this time I opted to use a Penrite 20w/60 that had added Zinc for better protection of the cams and followers, so I gave it a try. Since the rebuild I have noticed that the engine has been more difficult to start, but the main change had in reality been the change of cams, from original Mk 3's to some type of Mk 2, I say that because I have no idea as to their origin, Only that their specs match most other Mk 2 cams giving about 0.385" lift at the valves. With this newer oil I had chosen, I noticed that it is definitely thicker, and it appeared to me that when kicking the engine over that it felt as though it had wet sumped, as I could feel the extra drag as the engine tried to rotate. The only thing was, that if I removed the sump plug that only about 150 Ml's of oil would drain out, so hardly a wet sumping problem. So with the new engine at about 1200 Miles now last Thursday I changed the oil/filter, and used a 15w/40 mineral oil for Diesel engines. Started the engine after I first primed all the oil ways and filter chamber, and on the Saturday the wife and I headed off for a local bike rally where we clocked up about 100 miles or more on the Saturday stopping here and there for a toilet stop and for lunch. I guess over the weekend I must have started the engine 7 or 8 times, and it basically started first kick every time, and I noticed how much easier the engine spun over considerably quicker than with the heavier oil. It is surprising how much extra drag is imparted within all the roller races and to some extent from the piston skirts to the cylinder walls. Before this my level of frustration was climbing rapidly as nothing is more annoying than trying to start an engine on a newly rebuilt bike that you and everyone else around you knows should not be that difficult to start. After last weekend, I could not have been happier with how it started, because when it is running, it really goes very well. Interesting results.............

 

[Albervin]

Was that Penrite Enduro, Greg? Been using that for a few years now and happy. A few of the fellows down here use the Diesel oil so interested in your comments.

 

[greg brillus]

Hi there Alyn, I don't believe so, It is just a HPR 30 mineral. I have been using 20/50 weight oils in all older machines for many years with no bad effects. I only chose it for its zinc content, but even using it in my oil can which i use a lot, I could tell straight away that it was a much heavier oil. Probably fine in a brit parallel twin like a Norton or Triumph, but I think the drag is more obvious in a roller bearing crank especially with four bearings. I had almost convinced my self to go to coil ignition to help the problem, but it seems the thinner oil definitely allows the engine to spin over faster. I know Diesel oils keep the insides of an engine much cleaner and I believe they also contain zinc to help with the heavy loads imposed on the reciprocating parts of a Diesel engine. Cheers................Greg.

 

[Len Matthews]

Morris's Golden Film 20/50 is my favourite.

 

[Garth Robinson]

Hi there Alyn, I don't believe so, It is just a HPR 30 mineral. I have been using 20/50 weight oils in all older machines for many years with no bad effects. I only chose it for its zinc content, but even using it in my oil can which i use a lot, I could tell straight away that it was a much heavier oil. Probably fine in a brit parallel twin like a Norton or Triumph, but I think the drag is more obvious in a roller bearing crank especially with four bearings. I had almost convinced my self to go to coil ignition to help the problem, but it seems the thinner oil definitely allows the engine to spin over faster. I know Diesel oils keep the insides of an engine much cleaner and I believe they also contain zinc to help with the heavy loads imposed on the reciprocating parts of a Diesel engine. Cheers................Greg.

Greg,Could it be anything to do with your magneto?There was some talk on here a year or so back about the need to re-magnetise magnetos in order to get the best low speed spark.I use HPR 30,and have done for years,but I have coil ignition. The motor is very well worn,but does seem to be a first or second kick starter.

 

[greg brillus]

Hi Garth, Yes at first I thought perhaps the magneto could have been an issue, I am using one of the newer BTH magnetos which are a type of CDI unit, rather than a conventional type and they do need a certain amount of rotational speed to generate a decent spark. That is why my thoughts were to change to coil ignition, but the use of a thinner oil is allowing the engine to spin that bit faster.........My knee is all the better for it too.

 

[Bazlerker]

I use Pennzoil 50wt racing oil in the summer, switching to Brad Penn 30wt in the spring & fall. I also have a magneto recently completely overhauled by Spyder Technologies (Ottawa, Ont.) ..There is no doubt in my mind that magnetos need all the help they can get in being "spun" over as quickly as possible - a perfect magneto less so, however using a thinner oil to assist a weak magneto is foolish as it endangers the engine..

 

[bmetcalf]

Some feel our cool running engines benefit from less viscous oil.​

 

[Bazlerker]

There's a delicate balance isn't there...sufficient viscosity vs thin enough to flow to all parts of the engine quickly. Because I dont know very much about it - I tend towards a conservative point of view on the matter..

 

[vibrac]

Because the oil company was paying the bill I belive I know one place they used inappropriate oil. The Montlhèry 24 hours record attempt, and we all know what happened then...