The same engineer suggested unbolting the conrod and checking for wear/damage with a view to replacing the bearing. Now I have seen there are different thicknesses of replacement bearings shells to ( I assume) account for wear such as I may have. He suggested this should be an easy thing to do and check... he's experienced I am not
As your engine is relatively new, the big end journals should still be on standard size, and if your lucky and caught it soon enough. You may be able to get away with just replacing the big end shell bearings (after polishing the big end journals).
However the condition of the big end journals is going to determine if this is a viable solution. If they are scored you may end up needing a crank grind on the big end journals.
Finally I would suggest replacing the big end shell bearings on the other cylinder whilst your in there.
My questions to the enlightened is ..... is is a relatively simple thing to unbolt the conrod via the open side of the crankcase.
Yes, I have done this myself on numerous occasions, however as your engine is installed in a narrow boat, you will not find it particularly easy.
Then is it a matter of checking the surface as well as measurements of the shaft the conrod bearing clamps to. If there is not real wear replace the shell bearing with like for like ....
Yes and Yes, Standard journal size would be 2.4975/2.498" if we were dealing with a genuine Lister CS engine, but more importantly is ovality of the journal. More that 0.002" out of round and your into regrind territory.
If there is wear replacing the shell bearing with one to compensate for the wear?
Yes, upto 0.0060" undersize. However, be sure to specify a Lead / Indium bearing for the top half bearing shell, because if you fit a white metal version you will knock out he big end in no time.
Obviously if the crankshaft surface is damaged too badly i expect that it is the crankshaft out to have it build up and turned back to spec?
It will be ground to the undersize (in 0.010" increments) at which the journal cleans up at.
Why not take it back to Redshaw's for some corrective surgery (that is if your not to far away)