16-05-2021, 08:34 AM
If an engine has stood for a long time the valve chest would become very dry. Nevertheless the degree of scuffing is surprising against cast iron when not much force available.
Brief running would not work oil to the guides. Nevertheless seems unlikely to seize unless an interference developed.
If awkward to remove the valve cover, oil squirted toward the valve head as each is open would find its way down. Valves on moderns with seals must run quite dry.
The guides are 9/32. .2813. For the Mini and predecessors the BMC A engine new clearance was 1.5 to 2.5 thou for inlets and 2 to 3 for exhaust, based on bores up to .5 thou over the exact.
I assume all own inch micrometers, these now being very cheap. (The 25.4 conversion is exact so Metric is fine) Those with lathes can make test pieces for bores. Otherwise a rod can be hammered flat and filed to just enter, then measured. Callipers not sufficiently accurate, despite readout. Drill shafts are undersize.
Guides are less liklely to be damaged if pulled into place. Whatever is used should not contact the inner diameter. Austin inlet valves were originally slightly thicker than the exh. Now I understand same used for both, which means inlet can be a trifle generous clearance.
Normally the reamed guide when fitted still gives enough clearance. New reamers cut slightly oversize so if reamed in place can produce generous clearance esp for inlets. Reamers cut smaller and give better finish if lubricated.
Clearance can be assessed from the degree of rock. By drawing the extreme positions the multiplying factor can be figured.
Brief running would not work oil to the guides. Nevertheless seems unlikely to seize unless an interference developed.
If awkward to remove the valve cover, oil squirted toward the valve head as each is open would find its way down. Valves on moderns with seals must run quite dry.
The guides are 9/32. .2813. For the Mini and predecessors the BMC A engine new clearance was 1.5 to 2.5 thou for inlets and 2 to 3 for exhaust, based on bores up to .5 thou over the exact.
I assume all own inch micrometers, these now being very cheap. (The 25.4 conversion is exact so Metric is fine) Those with lathes can make test pieces for bores. Otherwise a rod can be hammered flat and filed to just enter, then measured. Callipers not sufficiently accurate, despite readout. Drill shafts are undersize.
Guides are less liklely to be damaged if pulled into place. Whatever is used should not contact the inner diameter. Austin inlet valves were originally slightly thicker than the exh. Now I understand same used for both, which means inlet can be a trifle generous clearance.
Normally the reamed guide when fitted still gives enough clearance. New reamers cut slightly oversize so if reamed in place can produce generous clearance esp for inlets. Reamers cut smaller and give better finish if lubricated.
Clearance can be assessed from the degree of rock. By drawing the extreme positions the multiplying factor can be figured.