straight 40 v's 15/40

If an engine is designed to run on 40 grade oil then the thinning process when the oil is heated has been allowed for. Oil ideally should get heated to about 80 deg C on every run to dry out water vapour and the like and also to thin out which allows the engine to run with the least friction. New multigrade will be at the same viscocity as straight oil at this higher temperature. Roller bearings don't actually need thick oil as the balls need to roll over the very hard track and not be impeded or caused to skid with too thick an oil. Engines with plain bearings as they age are often treated to thicker oil by their ownersto maintain oil pressure and to quieten the running a touch with the bonus of the engine burning less oil. So if oil is of suitable high quality then the very thin film that coats the bearings track and rollers is sufficient to stop metal to metal contact and as said earlier, the balls or rollers are very hard and revolve rather than scrape together....Les

The newer 15W40 oils will also have better detergency to keep pistons clean and to keep piston rings free and also better dispersancy to cope with sludge and stop it blocking oilways. It will almost certainly give better wear protection to highly stressed components such as cam and followers.

Also remember that there is no guarantee of performance quality for the monograde oils, just the suppliers say so.

I feel I do have to point the following fact out. Old engines have very highly stressed cam followers due to the fact they have quite a small surface area unlike modern car engines that have much larger area. Whereas modern oils have reduced certain anti-wear additives (chiefly ZDDP) to avoid air pollution modern cars cope very well with this reduction, old classic engines still require a good dose of ZDDP to ensure a decent low wear rate on the highly loadedsliding parts like cam followers or tappets. I think the highest level was in the API rating: SG as after that the level was reduced considerably.

To ensure low wear I would choose a modern oil that is designed for classic engines generally these are at least an API rating equivalent of SF...... I like the Millers range myself....Les

This story of the deleterious effect of reduction in ZDDP levels and enhanced cam/ follower wear is frankly a load of cobblers whose perpetuation is intended to promote the sale of classic oils. Modern oils do not rely only on ZDDP's to provide wear protection under severe contact conditions and so the reduction in concentration of ZDDP to preserve the catalytic converters is compensated for by alternative catalytic converter friendly alternatives such as Boron compounds.

They are required to pass fired engine tests for cam and follower wear that are even more severe than those in use at the time of SF etc.

I think the major factor is that multigrade oils require a full flow filter to allow them to clean the oil properly. Straight 40 & 50 oils work with the filters used in our engines.

I do not think one should use a modern, high detergent oil in an old engine that does not have a good particulate filter. The detergent oil will carry the 'muck' around expecting the filter to take it out. If you do not have such a filter then the 'muck' is presented to all the bearing surfaces.

Safer to use a 'classic' style oil like the Morris Golden Film range.

If you have a rebuilt, clean engine (washed crankshaft) then a modern detergent oil is fine as you will replace it once a year, and the engine will remain very clean.

I used to run Castrol GP (20 W 50) in my Dominator. I'm reassembling it at the moment, after a long 'rest'. What oil will be good today? I parted the crank to clean the sludge traps, cleaned oil ways, have fitted a Commando oil filter plate, behind the gearbox. With a filter....

Paul

Previously norman_lorton wrote:

I do not think one should use a modern, high detergent oil in an old engine that does not have a good particulate filter. The detergent oil will carry the 'muck' around expecting the filter to take it out. If you do not have such a filter then the 'muck' is presented to all the bearing surfaces.

Safer to use a 'classic' style oil like the Morris Golden Film range.

If you have a rebuilt, clean engine (washed crankshaft) then a modern detergent oil is fine as you will replace it once a year, and the engine will remain very clean.

Paul, I can tell you that 20-50 works well in twins and if you have a rebuilt engine or using a spin on car type filter I find this works better than straight oil. (Much easier starting)

However, depending where you are riding, I find nothing better than SAE 40 in my singles with a top up with SAE 30 in the cooler months. The 30 also comes in handy if you run out of 20 for your primary chain.

I seem to remember Mike Pemberton trying out 15/50 or something like that in a single and had to return to straight oil.

There are good modern 20W50 oils available but I know of nothing better than Mobil 15W50 unless it is their 10W60. Both are available from Opie Oils.

With regard to the use of Modern oils in old engines, the job of the detergents is to remove deposits and, by surrounding them keep them in suspension. They also neutralize the acids formed by oxidation of poor quality oils and by contamination by blow-by gases. Dispersants keep sludge and soot in suspension and stop them blocking oilways etc. Modern oils, such as the above, do this much better than the so called Classic oils.

Filtration is desirable for any engine, but absence does not, I believe, make the use of modern oils inappropriate.

I would honestly be interested in hearing of cases where damage has ensued from the change to a modern oil.

Flushing is always a good idea.

P.S. Other high quality oils are available.

The story from 30 years ago is that the viscosity improvers in multi-grade oils get chopped up by ball and roller bearings. So stick to mono-grade oils in trad English singles.

I used to run 40 W high detergent in my BSA Super Rocket, with a filter. They like mono oil due to that silly timing side bush

It gets complicated.... Vincent people are heading to wide range multi-grades, due to cold running oils. Some are even going to 10 W 60

Paul

Previously charles_bovington wrote:

There are good modern 20W50 oils available but I know of nothing better than Mobil 15W50 unless it is their 10W60. Both are available from Opie Oils.

.

Previously paul_standeven wrote:

The story from 30 years ago is that the viscosity improvers in multi-grade oils get chopped up by ball and roller bearings. So stick to mono-grade oils in trad English singles.

I used to run 40 W high detergent in my BSA Super Rocket, with a filter. They like mono oil due to that silly timing side bush

It gets complicated.... Vincent people are heading to wide range multi-grades, due to cold running oils. Some are even going to 10 W 60

Paul

Previously charles_bovington wrote:

There are good modern 20W50 oils available but I know of nothing better than Mobil 15W50 unless it is their 10W60. Both are available from Opie Oils.

.

Permanent viscosity loss due to viscosity modifier degradation , either by oxidation or by mechanical shearing , is not a problem. For many years lubricant specifications have included tests where the oil is subject to very high shear stresses for extended periods and the minimum values demanded for approvals exceeds that needed to ensure adequate engine protection. The relevant test methods are backed up by extensive field testing over up to 30,000 miles drain interval and under severe operation conditions and in a wide range of vehicles.

Rest tranquil in your beds, all is well.

Just a heads up.

If you are a user of Classic Multigrade oils then my recommendation is Millers "Classic 20w50" nowseamingly being sold off cheaply by OPIE OILS on Ebay....I bought two 5 Litre cans of it....was tempted to buy three to get an extra 5% discount...Chatted with their excellent tech man Colinsays the ZDDP content is well over the 1000PPM level. It is also only midly detergent which helps in old engines as they burn more and cause ash problems. Detergents help safeguard against sludge but if you are worried about circulating debris, then I would suggest the only really abrasive stuff is ferric in nature rather than carbon which surprisingly can act as a lubricant. Fitting a powerful sump magnet and an additional dangling Neodynium ring magnet in your oil tankfrom a wires should mop upthe ferric debris. Morris Golden Filmoil looks to be a good product too.

As regards 10w 60 multigrade oils.... the 10w cold end viscosity is still thicker than the 60 weightspec theoil works at when at running temperature so no worry as being too thin when cold.....it just makes starting easier and less oil pressure blow off when cold resulting in more oil actually getting inside the engine crankshaft and crankcase and lubing the bores right from the start. A further advantage is less wear and tear on the poor old oil pump which doesn't have to shift treacle thick oil when cold.....Les

PS...I'm not suggesting using the modern 10W 60 oils (I'm sticking with classic types) as this wide range viscocity is usually a synthetic oil but if you feel these are OK I was just explaining some advantages with multigrade oils....not forgetting that we change our oils with very low mileage intervals so shearing is no problem...if it ever is...Les

PPS...Oh yes, one problem using multigrade oil is wet sumping. Thinner oil will of course run through the gear pump that much quicker. In practice I don't find this a problem unless the bike is left unused for several months where the best way is to reduce this is to simply run off the oil from the oil tank drain plug into a clean plastic 4 pint milk bottle (add a label of date drained off) and keep it if the used mileage makes it worthwhile cost wise...It only takes a minute or two...Les