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I know this has probably been beat to death over the years,but Ill ask anyway as I havent been here!"Back in the Day" when our bikes were made, oils left much to be desired and had little variety.Nowadays with modern metallurgy for our engines,and superior chemistry, should we stick to the manual recomendations that calls for SAE 30? or is 20w50,15w40 acceptable? or as good? anyone have any knowledge of whats best now? i know my last Norton Commando preferred 20w50 over 30 (no wet sumping, BIG plus!)and I beat that thing like a dog!
 

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I run standard dinosaur 20W/50 (sometimes I will actually buy a 4T flavor, but often just good ol' Castrol GTX). Every other oil change, I add ZDDPlus, an additive to put back the ZDDP that they removed from our oil a couple years ago.
 

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Castrol GTX 20w/50 in the Norton.
 

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I always use Silkolene Chatsworth 40, but any straight 40wt oil is great for any Triumph's engine.
 

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Most old bike engines run perfectly well with a hot engine and hot 40 grade oil. Most ( and still many today) bike engines had steel cranks and aluminium conrods. This means that when cold the bearing clearances are tighter than the running clearances and the oil is thicker than is needed, The result is it is very easy to damage a conrod bearing (plain bush type) when cold. The problem is this damage is usually not noticed until summer when everything gets hot and low oil pressure is noticed. So hot running is blamed for ruining bearings, when in fact the damage happened when it was cold.
A multigrade 20/50 oil greatly reduces the chances of oil starvation to the cold bearings so greatly improves their working lives. Many find it difficult to realise that when cold , although you might have high oil pressure, little oil is flowing through the bearings. This oil starvation leads to over heated and damaged bearings even though the motor is still cold.
 

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Wise words, Panda.
TBS, I have used Chatsworth 40 in quite a few of my bikes with good results. Mostly summer riding, I might add.Day to day, all year round you won't go far wrong with a good old 20w/50 mineral oil.
Roy.
 

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My '76 shop manual recommends 20W50. My '66 shop manual says 20W in summer and 30W in winter. Is it fair to say that a '66 engine and a '76 are similar enough to have the same oil requirements?
regards,
Rob
 

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My '76 shop manual recommends 20W50. My '66 shop manual says 20W in summer and 30W in winter. Is it fair to say that a '66 engine and a '76 are similar enough to have the same oil requirements?
regards,
Rob
Yes pretty much the same engine internally all the way back to 1937.
ps I think you transposed the oil viscosities :)
 

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Panda,

Yes I did transpose the 20W and 30W applications. Fingers work much faster than the brain lately.
Thanks for the catch.
regards,
Rob
 

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The motorcycle oil also has more phosphorus/zinc for enhanced wear protection at high engine speeds and high loads
 

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I occasionally use the '4T' flavor of oil, designed for air cooled motorcycles ... but I do not use synthetic oil. I won't turn this thread into a dino vs synth thread ... but there are non-synthetic 4T oils available. My local auto parts chain (Advance) has some (Valvoline, I think) and any motorcycle shop should have a decent selection.
 
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