Forum

[Alan R]

>>>>>>>>>>>>>>>>>>>>>>>>>> this being a Technical Forum I thought this might be appropriate ?? }----------------- ----------------------------- YABBA---DABBA---DOOOOOOOOOOOooooooo !!

[geoffro]

Oil's cheaper than metal, make your own mind up.

[Presto]

Oil life and abilty is far greater than is often thought. Especially in an understressed engine like the Bullet. I have never heard of an engine failing because the oil was 'too old', but I've seen many where the oil level was too low or was contaminated with water.

[Frank]

I can't quite understand this idea that the Bullet engine is under stressed. Whether an engine is under stress or not depends on design, materials, build quality and use it is put to. A Honda Goldwing, for want of a better example, may be deemed as being under stressed spending it's life plodding along country lanes at 50mph. A Bullet is not in that catergory and by the tales of early bearing failures, pistons breaking up etc etc contained in these pages it seems to confirm that it is indeed under a lot of stress. However frequent the oil change and however high quality the oil is you can probably never compensate for this, but at least you are off to a good start. You may be able to attribute failure due to contaminated or insufficient oil, the evidence is there, but it's a lot more difficult in the case of poor quality or old oil. Best to stay on the safe side with frequent changes using good quality oils.

[Presto]

There is a point beyond which engine components and materials are liable to fail – as engine speed increases so does stress and fatigue damage (‘fatigue’ as in ‘metal fatigue’, implying structural damage caused by tensile cyclical loadings, forces that tend to pull the material apart).

Stress loading rises as the square of the engine speed and ‘fatigue life’ rises by that figure to the 5th power 1.

An engine running at 11,000 rpm is subjected to around 3 times as much fatigue damage as when run at 10,000 rpm – that 3 fold increase in fatigue damage is the consequence of only one tenth increase in rpm at that engine speed.

If a wider variation in engine speed is taken into consideration, the comparative increase in stress and fatigue damage, as engine speed rises, is staggering.

3,000 rpm could be regarded as a ‘sensible’ engine speed for a Royal Enfield Bullet. 3,000 rpm will give a road speed of around 50 mph in fourth gear. A gentle tweak on the throttle will take the engine speed to 4,000 rpm, not high by any standard. However, that small (1.35 times) increase in engine speed subjects the engine to a 13 times greater level of fatigue damage compared with 3,000. Rising to 5,000 rpm means 201 times increase in fatigue damage.

Fatigue damage increases 1,024 times when engine speed rises from 3,000 rpm to 6,000 rpm; from 3,000 rpm to 7,000 rpm stress fatigue increases 4,000 times; from 3,000 rpm to 8,000 rpm fatigue damage is 20,000 times greater, and with an increase from 3,0000 rpm to 9,000 rpm there is a 60,000 times increase in stress damage.

Using the engine up to the designer’s recommended rev limit, engine materials and components are able to withstand those stresses. But, as these figures show, stress is related to rpm and the Bullet engine is more lightly stressed than an engine that revs at say 12,000 rpm. Stress produced by friction between moving parts also rises with increased rpm; i.e. the longer the engine runs the more it will suffer from wear caused by friction.

[Norm]

Presto, we had a member prove this a few years ago, he was in Perth on the other side of Aus and he wanted to get back to Melb somewhere about 3,000ks I think, and with what he believed a failing floating bush. He made it back to Melb sitting on about 40kph and crossed the Nullabor with a section there 90 miles straight without a bend in it, dead straight. Very slow trip but he made it. He is heading back over there on Sunday but this time on a 612, should be a bit quicker

[Frank]

Presto, my hat is tipped to you, not only in recognition of your in depth knowledge but also for your speed of typing! There are plenty of bikes out there that are built to rev far higher than the Bullet and yet can cover vast amounts of mileage under this stress. Mathematically the Bullet at 3000 rpm should be under a lot less stress, granted. However it seems, and my argument is, that even when used within it's parameters the component life is not anything like those of other machines designed, built for and used at sustained higher revs. So, mathematics aside, in reality, which one is under the greatest strain?