Some Leyland 4/98 engines had 5 ring pistons.

For tractors they left the bottom ring off, but for the early JCB back hoe loaders the fifth ring (an oil ring) at the bottom of the skirt was fitted.

I believe that the fifth ring was fitted on the more stationary engine of the two applications to prevent oil coming up past the other four rings as the JCB application ran a little cooler.

My understanding is that the fifth ring reduced the horse power slightly (some say by as much as 5H hp).

Maybe bedding in a tractor with a dyno attached to the PTO or ploughing was easier than bedding in a JCB so they added a fifth ring.

Must have something to do with glazing a liner on a diesel engine.

For stationary air cooled petrol engines, I would guess the opposite is true in that the airflow is negligible. Maybe they rev much slower and therefore don't heat up as much.

I wonder if the old rotavators with the M20 engine had an extra ring.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

If you use the piston in a motorcycle engine I would never fit an extra oil ring.
Why should you ? It would make your piston run dry. One on top is enough.

I wonder if m21 engines were also used for stationary work.

['It would make your piston run dry']...

['I ran them with the lower oil ring fitted and they performed perfectly well...Ian']...

As per my original post, I have run this type of piston without any problems and with the 'skirt' oil ring fitted...

Unfortunately I didn't take any note of whether oil consumption was reduced..Ian

email (option): ian@wright52.plus.com

AEC 9.6 ltr engines had an extra oil ring on the bottom of the pistons. When London Transport used the engines in their RT buses they left off the bottom oil ring because of drag and loss of BHP. In the RT bus I was involved with there was not a bottom oil ring fitted.

M20 engines were used in hundreds of stationary applications, particularly post WWII when there were thousands of surplus engines available for scrap metal prices.
Stationary engines tend to run at a single speed for hours on end, particularly when used on a pump or saw bench.
These engines are generally run at peak torque so they run quite slow, even by M20 standards. Using a diaphragm carb which was vacuum governed.
And no when used stationary they retained the oil quill feed through the crank.

Genuine BSa stationary engines post WWII also had end fed cranks and it has always been a mystery to me why all of the motorcycle engines did not run end fed cranks.

Any time you see an M20 with a short solid lever on the decompressor it has come from a stationary engine.
The really good thing is they will regularly have a platform style horse shoe magneto from a pre WWII ( thus obsolete & cheap ) on them which is where all my early BSA got their sparks from

email (option): bsansw1@tpg.com.au

I'm getting close to having a new cylinder liner fitted and bored and was cleaning up the used standard hepolite piston I'd like to use. There might be a few issues with it and I would like some opinion on weather I should use it. There are some scuff marks in the top land on one side and they look worse in the photo than they are.



There is some light corrosion that came off with a light sand with wet and dry and again the photo makes it looks worse, it feels perfectly smooth.



Lastly there is some galling in one pin boss.



So should I use it? Keep in mind quality M21 pistons are rare even more so here in Australia and I have been burnt (pun intended) with a pattern piston overheating.

email (option): spacemonkeym@gmail.com

Bump.
Any opinions?

email (option): spacemonkeym@gmail.com

Assuming the ring grooves are OK width wise I would use it...Just carefully ease out any high spots in the gudgeon pin bore...

The piston appears to be suffering more from light corrosion than wear and that is largely cosmetic...

As the cylinder is being rebored for clearance to match the dimensions of the piston that will take account of any wear on the thrust faces...

A new set of rings, clips and a good/new gudgeon pin should complete the job..

Out of interest, Triumph T140 circlips are dimensionally the same as BSA clips and are easier to source...

I once built an M21 engine from 'the best of the best' second hand parts I had lying about in my workshop store and used it for the daily commute to work for about 8 years with just regular maintenance...

I'm pretty sure that frequently, in the search for mechanical 'perfection', many useable parts are consigned to the scrap bin...

I think as time goes on the ever declining availability of original parts may change that attitude...Ian

email (option): ian@wright52.plus.com

Cheers Ian.

And yes attitude changing.

email (option): spacemonkeym@gmail.com