Auto Racing: engine bearing caps, replacement bearings, engine bearing

Question
It's me again Dan. I seek your advise based on your vast experience on engine building. For my 4-cylinder 1275cc A-series British Leyland engine, I normally torque up the main cap at 60Ib/ft and big end cap at 33Ib/ft in accordance to the manufacturers recommendations. It just occur to me, when the job is done, is there any way I can check for any abnormal high spots at the bearing/crank pin journals or piston to bore clearance just by turning the crankshaft in the block with a torque wrench prior to fitting the head and the timing chain? What should the torque reading be if the reciprocating parts are all in good condition and the clearance are not interfered by any high spots? This would then give me double assurance that the re-build is truly OK.

Answer
Hello again, I apologize for the delay, I was out of the country (to Brazil)  for a few days, and just returned.

Modern replacement bearings are so trustworthy that it's hardly worth the effort.  But what most people do is use an inside micrometer or a dial bore gauge to check the size in several locations. With the bore gauge, you can rapidly check in numerous locations for any problems . But you won't find any unless the rods or main bearing lands  them selves are warped. Either of these situations is easily corrected by a machine shop and should have already been done.

Piston -to-wall clearance is another matter and should be checked more thoroughly.  Mic each piston in several locations around the skirt just below the wrist pin opening. Lock the mic, and set up the bore gauge on the piston measurement (set the dial to 'zero' when it's centered in the mic) .  Then measure each bore up and down, and side to side.  I like a clearance of .005" for small racing engines, a little less for street use and more longevity.

There is no standard torque reading for checking these things, each engine is different, and each type will reveal a different torque value.  Part of the reason for the recommended "break-in process" is to reduce high spots to non critical dimensions, and allow new rings to seat properly before heavy use.

Find a flat road, and run the car at 3000 to 5000 RPM alternating, Then while at the 5000 RPM speed, lift your foot from the throttle and let engine braking slow the car,  Accelerate at 1/2 throttle back to the 5000 RPM speed. Be ever watchful for policemen, they have no sense of humor whatever. The process is a continuous one of acceleration and deceleration for perhaps 100 miles or 2 hours running time. Then for the next 10 hours  it varies between the accel-decel routine to flat running at speeds of 3000 to 5000 RPM for 10 minutes at a time.  It is VERY tiresome and only valid for street use.  For pure racing engines, I run them at conservative speeds on the race track, staying out of the way of competitors, and run it like that for a 20 minute practice session. Then I head for qualifying and  from then on  it's go, or blow , or leave a hole in the fence !

Best of luck to you !

Dan Liddy