I realize this discussion is tractor-engine related but the engine design is
basically the same as the Spit engine, typical long-stroke 3-main, big
difference being the weight. I normally run my (stock crank) small-crank 1300
to 8200
rpm. Teardown is @ 6-8 hours, done mainly in order to crack check the crank, &
they usually give good service. I ran the last 2 events last season very
hard, up to indicated 8800 several times. The end of the second weekend put my
time on the short end of TBO @ 6 hours so I tore it down. Inspection revealed 3
cracks, 2 on the rear & 1 in front, 2 of which can be seen w/o magnaflux. That
one was close to a pile of stanpart shrapnel.
Copy & paste this url (hope it works) for your viewing pleasure. This is
Moldex big TR that failed on us recently. It was buzzed & chucked a flywheel
several seasons ago. Crack check following that incident did NOT show crack
(liquid
mag) but I do feel that that gross over-rev initiated the crack at that time,
& subsequent normal (?) over-revs worsened it until it reached its limit &
failed a number of race weekends later. Note the enlarged area of tiny axial
cracks & the really clear beach marks.
http://www.members.aol.com/fubog1/moldex3.jpg
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