Mac,
I just read the whole thread again.
I empathise with Bob. I reckon he is just about spot on with his comments.
I would answer Matt (
I for one would be interested in finding out the actual long term results in running a listeroid with 20:1 compression ratio.) by saying : Read the Lister manual.
They designed it, they knew, they recommended against operating the engine above 1/3 load while the COV was screwed in.
I am led to believe that early examples had bearing trouble. This led to the adoption of the larger crank (larger bearing area).
The Indian 'copiers' apparently know better. Metallurgy, fuels and lubricants have certainly improved vastly since the engine was designed originally but the same will still hold true, I am sure.
We do not know the actual numbers or times but rest assured those recommendations were not made without reason.
I would think the Lister engineers were looking at a life, before major failure, of something like 20+ years. I would think that modern-day buyers would think that if it lasted 10 years before major failure it would be long-lived. It is all relative to what else is available.
This also flies in the face of Craig who reckons the stresses are less at higher compression ratios. Power is a function of torque and rotational speed. It is the torque component which dictates the strength requirement of the crank (and thus it's size). In this case, as I mentioned above, the crank may well have been up-sized due to loading on the bearings being the stress 9failure) area and had little to do with the mechanical strength of the shaft.
Also he needs to compare 'apples with apples'. I have Peugeot XUD engines which push out about 60 HP naturally aspirated, at around 5000 RPM. They idle (virtually no output power) around 750 which is more than full rated speed of a 6/1. They have 5 main bearings, full pressure lube, one small (relatively) flywheel, not two hanging outboard at each end of the crank, and are multicylinder. Just not comparable.
I agree with bob - if it starts, runs smoothly and burns properly (no particulates) it is OK at the lower compression ratio.
If you have a 6/1 why try to make it into an 8/1?
Regards, RAB
