In a message dated 8/16/02 3:18:50 PM Eastern Daylight Time, vafred@erols.com
writes:
Good stuff cut from above.
<< I thought this was very interesting especially the short bursts of speed
and
in-town driving, he says oil pressure and normal temp are a must for good
engine break-in and the total life of the engine. "FT"
>>
Yep, all true. Running a autocross and limiting RPM would be good as well.
During normal operation, the piston rings are forced outwards ( and some are
designed to twist) under load. Running a engine at constant speed and /or
light load will not push the rings outward so the cylinder walls will glaze
from excess oil baking onto the bores.
Running the engine under a short moderate load pushes the rings out to scrape
off high spots, then while coasting, engine vacuum draws fresh oil up the
walls to wash off small metal particles. All good practice.
When building my Formula Ford engines ( 1.6 L Kent for Brit content ) the
rings are installed _dry_ with just a light coating of oil on the skirts.
This is the recommendation from Total Seal rings.
A crankshaft needs zero breakin if the clearances are set right( loose is
better than tight). Rubbing items such as push rods, rocker arms, valves,
timing chains and cam shafts do need a longer term breakin period. Running
too fast creates more localized heat while these parts run in.
The cam breakin for most designs( cam in block) need 1500 RPM. The only
reason to run a engine at a elevated speed for cam breakin is to assure ample
supply of oil ( thrown from the rotating crank shaft, mostly rods) to the
lobes and lifter faces. Many overhead cam engines have oil jets spraying
directly at the lobes, elevated RPM might not be needed in this case.
Some valves are ground with a interference fit on the faces, The seat at 45*
and the valve at 44* for example This allows the valve and seat to hammer
each other into each other creating a thin hardened layer that is more
durable than the base metal. This also assures a perfect seal between the two
but it takes a bit of run time to do so. It will cause the valve lash to
tighten up and the engine runs in though. I doubt a performance valve grind
would use mixed angles and the valves would most likely be lapped in anyway.
Mixed angles are more of a production line engine issue.
Harold
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