As I understand it, the engine was totally rebuilt at about 82K....it now has
about 150K on the car.
Of course, by process of elimination on the other items, we can hope
vibration will disappear before he has to dig any deeper.
Not surprised at crack remarks: Autocrossed my TR4A in the 70s....had the
engine on the shelf several years later and was going to use crank out of it
in early 90s. It was cracked and I figured it was likely that way for several
thousand miles before retiring it.
Thanks for the additional insight.
Joe Alexander
<< As the vibration is described as being RPM related, it seem to me that it
is
probably something out of balance that turns at engine speed. If the
engine has never been apart, the most likely culprit would be a clutch,
probably a "rebuilt" unit that was not rebalanced after being "rebuilt." We
have found that any imbalance in the engine rotating masses first
manifestes itself as a vibration between 2700 and 3200 RPM.
On race engines that I have built that were in very good balance and that
were perfectly smooth when first assembled, a vibration around the 3000 RPM
engine speed always meant that the crankshaft had cracked!
This crack always began as a very small crack in the rear radius of the #4
rod journal. This would occure after 7,000 miles of hard street driving,
drag racing and autocrossing and happened 4 times in a row until we started
nitriding the cranks. If the vibration that was an indication of a crack
was neglected, the engine would go about another 5,000 miles until the crank
would actually break in two pieces between the #4 rod journal and the front
of the rear main. As the crack got worse, the vibration got worse and the
2'nd order of the vibration which first occured at around 6,000 RPM would
move lower in the rev range. The crank broke in two just after that 2'nd
order vibration had moved down to 4,000 RPM.
I would check into the clutch being out of balance.
Regards,
Greg Solow
>>
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