23-06-2018, 09:09 AM
It is hard to imagine a reconditioner guessing bores more than .0015 out of size, and then only over. Split skirt pistons soon collapse to some degree anyway. And if c.i. rings do not bed well initially (but not scuffed) they apparently come right with use in reasonable time, even with current oils. Rings supplied here were generally pre gapped and had a coarse finish which soon disappeared so gaps were not absolutely minimal. Apart from that the big variations in oil use are a mystery. Some oil was lost under the block but would never amount to a pint in a long day trip! A little leak makes a big mess.
The situation with pressure fed engines is entirely different.
The advice from two ring manufacturers, based on plated rings, pressure fed engines, filters, is to warm up with brisk idle (possibly radiator masked) then accel and decel a few times at medium rpm with generous throttle. Change oil early, at not more than 200 miles. With a jet fed Seven the start up speed likely less important.
Costs seem not to matter nowadays but can pour oil through a filter and reuse.
I guess the total detritus after a rebore would approximate about 1/20 of one Dynamator tooth in 50 miles!
l looked up some old notes. Reconditioners and others were caught with a lot of Seven parts in the 1960s. Set of pistons with rings L2.10s! Rebore work L4.10. ( I produced the block out of a business briefcase which amused the staff) New b.es. L6. Seems cheap but a tradesmans wage at the time was well under L20. (And a now $1.5m house was L5,000!)
Whereas now buy oil in packages, it was then usually bought from service stations by the pint in own container. So top ups usually also done at service stations pint at a time as no price saving doing at home. Hence owners became aware of consumption in terms of miles per pint. Topping oil was very much part of the attendants job. Basic grades about 1/9 pint. However as my car used a pint per 50 miles and worse at one stage it about matched the petrol ! Despite oil use, with the early head it never faltered, although following motorists often did, until they could see.
It is a pity to bore a Seven block more than necessary. It was common to centre the machine on the wear. The consequent slight shift in crank degrees is nothing.
The situation with pressure fed engines is entirely different.
The advice from two ring manufacturers, based on plated rings, pressure fed engines, filters, is to warm up with brisk idle (possibly radiator masked) then accel and decel a few times at medium rpm with generous throttle. Change oil early, at not more than 200 miles. With a jet fed Seven the start up speed likely less important.
Costs seem not to matter nowadays but can pour oil through a filter and reuse.
I guess the total detritus after a rebore would approximate about 1/20 of one Dynamator tooth in 50 miles!
l looked up some old notes. Reconditioners and others were caught with a lot of Seven parts in the 1960s. Set of pistons with rings L2.10s! Rebore work L4.10. ( I produced the block out of a business briefcase which amused the staff) New b.es. L6. Seems cheap but a tradesmans wage at the time was well under L20. (And a now $1.5m house was L5,000!)
Whereas now buy oil in packages, it was then usually bought from service stations by the pint in own container. So top ups usually also done at service stations pint at a time as no price saving doing at home. Hence owners became aware of consumption in terms of miles per pint. Topping oil was very much part of the attendants job. Basic grades about 1/9 pint. However as my car used a pint per 50 miles and worse at one stage it about matched the petrol ! Despite oil use, with the early head it never faltered, although following motorists often did, until they could see.
It is a pity to bore a Seven block more than necessary. It was common to centre the machine on the wear. The consequent slight shift in crank degrees is nothing.