I agree with "Btp44" that SAE30 is little heavy for the initial start-up
of a newly rebuilt engine. The dozen or so rebuilds that I have done
(including two TR6s) have all roared back to life with a light oil for the
first start up on the theory that getting lubrication everywhere quickly is
very important, and that clearances will never be as tight as they are on
that initial run. I always preoil the engine before the first start and
using 10w-30 or 10w-40 makes this easier and quicker.
Running the engine at a constant speed such as 2,000 rpm when breaking
it in usually is not recommended, as new pistons rings will not seat in
properly under constant speed and load. On my newly overhauled engines, I
employ a break-in technique that my father says was developed years ago by
Buick's experimental engine department and was recommended later by Tom
McCahill, the old automotive guru of Mechanix Illustrated magazine.
Basically the technique is as follows:
1) Pre-oil the engine until oil pressure is showing on the gauge. Then
start it up and double check ignition timing and make sure that the idle
speed is fast enough. The new tight engine may want to idle too slowly
until it loosens up.
2) Drive the car gently to a sparsely traveled road. Accelerate through
the gears normally until the engine is turning about 2,000 rpm in high gear
(not overdrive). Accelerate at full throttle until you reach 3,000 rpm and
then take your foot completely off of the accelerator. Let the car coast
until the engine slows back down to 2,000 rpm and then repeat the full
throttle acceleration back to 3,000 rpm. Repeat this cycle about ten times
and the new rings should be properly seated (assuming they were correctly
gapped and the proper cross-hatch pattern was honed on the cylinder walls).
The theory behind this unusual technique is that the full throttle
bursts create maximum pressure in the combustion chambers to properly seat
the rings and valves, and that the in-between coasting periods create high
vacuum to suck oil up the cylinder walls to lubricate everything and prevent
excessive wear or hot spots on the cylinders. In fact, if someone is
following behind the car being broken in, they may see little puffs of blue
smoke come out the tailpipes between each cycle of the
deceleration/acceleration routine. This is normal and good, as it shows
that the cylinders are actually getting an extra dose of oil with each
cycle. The smoking will stop as the rings seat.
My experience with this technique has been excellent. The only car
which I didn't employ the technique was my Healey 3000 Mk3 which was fitted
with 5-ring A&E pistons and chrome moly rings. I followed the instructions
which came with the pistons which only suggested gentle driving at changing
speeds. The car always burned a little oil the rest of the years that I
owned it! I think that those chrome moly rings really needed that
on/off/on/off treatment to correctly seat, and that the gentle driving I did
never loaded them enough.
Regards,
Rex Townsend
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