10-10-2017, 06:00 AM
As mentioned before, compression testing only became common when crank handles disappeared. A problem with Sevens is that now many permutations of oversize, head and c.r. An h.c engine with wide ring gaps or broken top rings may give the same readings as a perfect l.c engine. Testing is usually done hot, throttle open. Stock heads seem to have been nominally 1.5 inch deep.
A lot can be discerned with the crankhandle. All compressions should be similar with a a degree of bounce. Sevens hard driven used to be plagued by burned valves every 6,000 or so ; I dunno what the experience is with modern valves, presumably of modern (post 1960) steels. Curiously, whilst burned valves seriously sap power, and may cause a miss when idling, wide ring gaps often seem to have little effect on running.
Until the 1950s and better oils and thermostats many smaller car engines were rebored at 40,000 or so. My car was rebored at this and 60,000 later .010 wear, very rarely encountered now.
A lot can be discerned with the crankhandle. All compressions should be similar with a a degree of bounce. Sevens hard driven used to be plagued by burned valves every 6,000 or so ; I dunno what the experience is with modern valves, presumably of modern (post 1960) steels. Curiously, whilst burned valves seriously sap power, and may cause a miss when idling, wide ring gaps often seem to have little effect on running.
Until the 1950s and better oils and thermostats many smaller car engines were rebored at 40,000 or so. My car was rebored at this and 60,000 later .010 wear, very rarely encountered now.