Hi,
In my experience, when those machines were current, it was considered good money wasted to throw away good oil just because "it was black" to replace it with fresh oil which would "be black" itself in a couple of hundred miles. Owners would perpetually top the oil up rather than change it causing premature wear, and as the timing side bush wore the oil was lost because of excess clearance rather than be pumped through to the big ends. Hence big end siezure. It always seemed to be the drive side that siezed, which was logical since that side got the least amount of oil.
A50's and A65's suffered similar maladies and, like the A7/10 got the reputation as rod breakers.
I have experience of examples which were neglected and ones which were looked after. A person I was in contact with bought an A10 with a sidecar which had always been run as an outfit with over 100K miles. It was a little rough, always having been kept in the street, but as it was the man's sole form of transport apart from his bicycle, and because lube oil was free to him (he was a maintenance fitter in a large factory, I worked in the same factory) he used to change it regularly when on night shift. He bought a new Ford Escort Mk1 when it was just a Ford Escort (the Mk2 had'nt yet been seen), because the Mrs was getting a little wide in the hips and was experiencing some difficulty getting in and out of the sidecar. She could have worn it as a coat if he had taken it off the bike!
It lay outside his door for about 6 years after he bought the car, then he sold it to my friend who also worked there and who decided to "restore" it (pot of black hammerite and a two inch brush) and at the same time, decided to re-bore it as it was smoking a bit , being on it's original bores and pistons witch had been disturbed once at 70k miles for new rings.
He asked my opinion about the bottom end, which he was convinced should be beyond redemption. I measured the big ends and found about 1 thou ovality in the journals with the major diameter 2 thou undersize, and similar wear on the timing side main. I recommended new standard shells which were fitted with a piece of one-and-a-half thou shim steel under the shells of the big end caps. The old boy made him a new timing-side bush a couple of thou undersize to suit the crank, from a piece of phosphor-bronze (same as original, I think), turned on a centre lathe and finished with an adjustable reamer. I assembled the bottom half for him with a new driveside bearing, and told him to change the oil every 2 to 3 thousand miles. he moved to England shortly after, and I was surprised to see him about six years later with 50K more on it. Apart from new valves and guides when he was "across the water", he had not touched it. What really did surprise me though, was that he had re-finished all the painted parts, re-built the wheels and re-upholstered and refurbished the sidecar. It was hard to believe it was the same outfit.
I knew an A65 which broke the drive side rod before 30k, the fella had been boasting that he just pours it in, it runs out all over the road. Then he said they were "soft", and they all had bottom-end problems.
I also knew (not well) of three racing outfits, and another more closely. the fella I knew better was using secondhand engines (he had a couple for the racer) plus a Lightning, I think with a Watsonian Monza for the road. He spent about £120 at the time for a roller bearing timing side conversion when a new 250 Suzuki onl cost about 4 times as mutch. Not that he'd broke a rod - he was just afraid he might.
If the bearings are not already nackered, thin oil is ok in my opinion.
A.
