Castrol 20w-50 in a '74 MKII?

Dan1950

Dan1950

1974 MK II Roadster
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Seeing as how I live near the Canadian border and the vast majority of my riding will be at moderate temperatures on rural roads and highways in the Adirondacks, I am considering running Castrol 20w-50 in my 850 Commando.

I had good results when I switched from 60 (summer) and 40 (fall/spring) straight viscosity oils to Castrol 20w-50 in my 86 inch '64 Panhead stroker.

I especially liked the multi viscosity oil in spring and fall when temperatures could fluctuate significantly from daytime to evening riding. Thick oil robs power and doesn't really help the engine IMO.

Of course that was in a fully roller bearing engine right down to the lifters. Given the flat tappets and insert rod bearings in the Norton, should I reconsider running multi viscosity oil?
 
20w50 was the recommended oil from the factory, and I think you'll find that most of us have stuck with that. My buddy runs straight 50w in his combat (not sure why), and we're in Connecticut so we see a decent range of ambient temperatures.

However, Castrol has fallen out of favor because over the years they've changed formulas to keep up with emissions requirements and the level of zinc that we need for flat tappets has been reduced. There is a thread here about oil tests done by Jim Comstock that rates them by cam wear, and it's pretty revealing.

My personal favorite is Valvoline VR1 20/50.
 
I am about 2 hours west of you in Ontario. I run Castrol GTX 20/50 in my Combat, along with a quart of Lucas Oil Stabiliser. I have experimented with other oils, but settled on this as the best performer - very consistent oil pressure, good hot idle oil pressure, low oil consumption, reduced valve train noise, and little to no metallics on the drain plug magnet.
 
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Castrol 20w-50 GTX is all my '74 mkII has ever had...... I live in South Texas too. I do dab in a little of that zinc snake oil since the resurrection couple of years ago.. Its amazing how it seems to quiet things down somewhat... then this could just be imagination on my part, but I'm easily pleased.
 
Hello Dan1950

Castrol do a 20w50 oil in the UK called Castrol Classic XL 20w50 which tested well in Jim Comstock's test. I have used this in my bike.
I'm not sure that this is available stateside although one that is available is a Castrol GTX Classic 20W50 which mentions high zinc but was not tested by Jim.
It has a different formulation to Classic XL.

If I was you I'd use one of the 20W50s available that also tested well, e.g. Royal Purple HPS 20w50 or Bel-Ray EXP 20w50 4T. All imho.

As an aside most of these oils will change formulation over time even though the 'brands' remain! There are a range of GTXs available today, e.g. see Castrol-GTX

Back in the day (1970s) I knew a good sidecar racer (top 10 TT finisher) that although sponsored by another oil company used to put Castrol GTX 20w50 in the other company's cans. He always said he obtained better engine wear and the oil pressure held up well. Good to see that some - although not all - of Castrol's oils still performed well in Jim's tests.

Andy
 
jbruney said:
Castrol 20w-50 GTX is all my '74 mkII has ever had...... I live in South Texas too. I do dab in a little of that zinc snake oil since the resurrection couple of years ago.. Its amazing how it seems to quiet things down somewhat... then this could just be imagination on my part, but I'm easily pleased.
Click to expand...
What is your favorite snake oil?
 
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jbruney said:
Castrol 20w-50 GTX is all my '74 mkII has ever had...... I live in South Texas too. I do dab in a little of that zinc snake oil since the resurrection couple of years ago.. Its amazing how it seems to quiet things down somewhat... then this could just be imagination on my part, but I'm easily pleased.
Click to expand...
Thats essentially what I run in my classic mini with pushrod engine and GB sharing same oil. Add in some zinc additive to it. For my Commando I was running Valvoline VR1 when I was able to find it locally at a Walmart for $2 a litre! Now I'm using BelRay EXP as it was highly rated by the Comstock tests and I can get it for less than $11 per litre from Fortnine.ca.
 
850 I use ZDDPLUS. May or may not be good but hasn't hurt anything... also add a little Marvel Mystery Oil for a grin into both fuel and oil... Have always loved MMO anyway.... next I'll paint myself blue and cavort around the oak trees to ensure my bases are covered.
 
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