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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Oil Viscosity
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<blockquote data-quote="Matty" data-source="post: 92477" data-attributes="member: 1339"><p>Hi</p><p>I have run my Comet on 20/50 oil for around 40 years- First on Castrol classic 20/50 then - because I can get it cheaper at around £16 for 5 litres-on Millers Golden film 20/50 Classic oil -though goodness knows what I put in it from1956 when I bought the bike till then.</p><p>I have used Millers now for around 10 years with no problems and probably done 40,000 or so miles with it.</p><p>I have rarely changed the filter, but the bike has always used a bit of oil (around a pint in 500 miles) even though the bore, piston and valve guides are in very good order - so most of the time I just topped it up! My Comet by the way has a low expansion piston bored to 21/2 thou clearance and valve guides with oil seals and was run in fairly hard to avoid glazing.</p><p>My contention has always been that any modern oil will be better than the stuff it was designed for before the 39/45 war !!</p><p></p><p></p><p><strong>However I have just seen an article (written in 1986) which says that :-</strong></p><p>Multigrade oils containing polymers are unsuitable for air cooled engines because :-</p><p> They are not suitable for the temperatures in some parts of air cooled engines.</p><p> The polymers rapidly degrade and the oil soon reverts to its thinnest viscosity.</p><p> The 50 rating hot only applies for cooler water cooled engines and the oil is therefore much thinner in a hotter air cooled engine leading to more wear and heavy oil consumption.</p><p> Because the products produced by the engine are held in suspension in modern oils instead of settling out, it is essential to change the oil and filter at around 1,000 miles intervals. My car says 12,000 miles for 5/30 oil and uses virtually none !!</p><p></p><p>Maybe since the article was written the multigrade oils are now very different and better, but certainly I have not had any problems and always find my engine very clean inside and have not had to change mains, big-ends , pistons, etc. for many years.</p><p></p><p>The cams and followers by the way are the original 1952 ones, still work fine and I hardly ever have to adjust the valve clearances.</p><p>Surley the multigrade oil will get where it is needed much faster on a cold morning and this should offset wear to a greater extent than any damage done by other factors.</p><p></p><p>So is all this talk about only using straight oil in our old bikes a load of nonsense now?</p><p>Is there a lubrication expert out there who can say what the real facts are on this.</p><p>Matty</p></blockquote><p></p>
[QUOTE="Matty, post: 92477, member: 1339"] Hi I have run my Comet on 20/50 oil for around 40 years- First on Castrol classic 20/50 then - because I can get it cheaper at around £16 for 5 litres-on Millers Golden film 20/50 Classic oil -though goodness knows what I put in it from1956 when I bought the bike till then. I have used Millers now for around 10 years with no problems and probably done 40,000 or so miles with it. I have rarely changed the filter, but the bike has always used a bit of oil (around a pint in 500 miles) even though the bore, piston and valve guides are in very good order - so most of the time I just topped it up! My Comet by the way has a low expansion piston bored to 21/2 thou clearance and valve guides with oil seals and was run in fairly hard to avoid glazing. My contention has always been that any modern oil will be better than the stuff it was designed for before the 39/45 war !! [B]However I have just seen an article (written in 1986) which says that :-[/B] Multigrade oils containing polymers are unsuitable for air cooled engines because :- They are not suitable for the temperatures in some parts of air cooled engines. The polymers rapidly degrade and the oil soon reverts to its thinnest viscosity. The 50 rating hot only applies for cooler water cooled engines and the oil is therefore much thinner in a hotter air cooled engine leading to more wear and heavy oil consumption. Because the products produced by the engine are held in suspension in modern oils instead of settling out, it is essential to change the oil and filter at around 1,000 miles intervals. My car says 12,000 miles for 5/30 oil and uses virtually none !! Maybe since the article was written the multigrade oils are now very different and better, but certainly I have not had any problems and always find my engine very clean inside and have not had to change mains, big-ends , pistons, etc. for many years. The cams and followers by the way are the original 1952 ones, still work fine and I hardly ever have to adjust the valve clearances. Surley the multigrade oil will get where it is needed much faster on a cold morning and this should offset wear to a greater extent than any damage done by other factors. So is all this talk about only using straight oil in our old bikes a load of nonsense now? Is there a lubrication expert out there who can say what the real facts are on this. Matty [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Oil Viscosity
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