Oil viscocity

Hi Paul,

Without wanting to open another can of worms re oil choice I would be just using the latest spec 20W50 multigrade oil for your climate. Here in Oz I use Penrite HPR 50 in my machines (including my FergusonTEA 20 tractor) with great results.

I have attached  a couple of photos of a suitable factory maintenance manual for you. These regularly turn up on a well known auction site.

Note that the dimensions for the rear chain are incorrect.  Should be 5/8" x 1/4"

If you are not able to locate one I could possibly photocopy mine for you.

Send me a personal message

Try Andover Norton. They have Maintenance Manual and Workshop Manual in stock.

Search this site if you want to read hundreds of opinions on oil. I suggest you do your research late at night if you suffer from insomnia. It should cure you.

Just note that, if you have a pressure gauge on yours (the early ones did), don't be surprised if you see next to no pressure when it is warmed up. That's perfectly normal, and Norton quickly removed the gauge to set owners' minds at rest.

Hi all, The engine number on my 650SS is 18SSM/116188/P. Anyone able to tell me what the 

M and the P stand for? 

I think todays oils are so far removed from the 1950,s offerings  and the model 7 is so understressed that almost anything  could be used. Castrol do a 20/50 XL that came out very well in a recent test . My 99 is  running 10/40 fully synth  ( it comes free !)  without any issues other than it seems to get used a bit more quickly than expected. When I have to start paying again I will look for the Castrol.      A 650 with M and P in the no  ?, perhaps a Mercury based motor built at Plumstead?.  

This is just a guess but I would think that the P would stand for Plumstead (where the bike was assembled) but I have no idea what the M would stand for other than for Meridan where the bike (or engine) might have been assembled

Mike.

Mercury engine numbers would all start with 650SS/129***/P  

Most were built in 1969 at Plumstead just before it closed for good.

I cannot think of a reason for an M in any Norton 650 engines.

116188 would put this 650 in a 1966 period.

Another guess ?,  perhaps this was an experimental engine with modifications that would  later find their way into general  production ?. 

First off I reckon that it's always best to use oil in an engine and worms in the garden - just my personal opinion. 

From around 1965/66 Norton Manuals were recommending SAE 20/50 for all twins, as you can also see in Roy Bacons book "Norton Twins".   One even mentions Castrol GTX.  You don't say what year your Model 7 is, but from 1948 - 1952 the oil tank needs 6 pints and from 1952 onwards,4 pints. The tank shouldn't go below half full, nor above 3/4 full. 

Back in 1964 we used Duckhams 20/50 - pretty much when it first came out because "new" is better eh?  LOL!  I could wind my 1959 '99' round the clock to the stop - an indicated 120mph so probably about 100mph actual!  If the multigrade oil was the slightest bit unsuitable that would have shown up in a nasty way!

Against my usual practice I'm attaching a digital copy from my collection of manuals - not copied by me.  Hope it's useful.  

I had an N15cs which I had to change the oil in Toledo in Spain in July 1970. The manual said SAE50 Grand Prix Castrol. I remember in 40 to 45degree C temperatures one could get a nasty burn on the oil tank heat -shield. It was a job to find it in Spain! Honestly I think that Universal Farm Oil is OK for most old British engines. Only use Mineral Oil, and keep away from Synthetics, as they only suit piston clearances of half a thou.

That used to be Agricastrol 40 which I happily used in my 99. The modern equivalent is Tractor Universal 10W 30 which is probably a bit thin for Norton twins. Great for primary chaincases and forks though. Oh, and tractors.  

Now that the weather is getting warmer  10/40 is a bit too thin,  I have some classic 40  but I'll save that for the Ducati ,so XL 20/50  it is. Not that the 99 will  notice.