Hi Jim!
> This summer while returning from Carlisle Pa.
> The motor started to
> knock and loose power. We were towing a trailered Vette.
> ( about 4300 pounds).
Thats a big load!
> The motor had 14000 miles on it. It was a rebuilt Jasper
Hope someone's writing this down.
> When I tore the motor down I found #6 rod bearing
> welded to the cap. ( this is what froze the motor )
> The #5 bearing gone allowing the piston to hit the head.
Ouch
One other bearing was spun.
My questions are #1 am I trying to pull too much weight?
Yes. Plain and simple thats totally overloaded! Still doesnt account for the
engine failure however, just makes it s-l-o-w.....
( I have
installed the Caspro 3.66 drive, headers, 3 in.
exh.and a MDS Ign. box.)
#2 I am looking at the Mondello catalog and wondeing about the stroker
crank. Does any know the pros or cons of this."
Well, here's my outlook-
The damage you describe is typical of the type incurred from engine
overspeed, and or very shoddy engine overhaul. I would be interested in
knowing what brand of bearings you discover in the rest of the engine. The
Clevite 77 and its close relations (tri-metal type bearings with copper
underlay) are notorious for eating cranks. They're nearly universal however,
usually its all you can get. Drag racers love them, because they're very
tolerant of heavy pounding, but they are not suited to passenger car
engines. Best bearings I've ever seen thus far are Moraine '400' type, which
are aluminum faced, tin plated steel back. Almost every GM engine since 1962
has used an aluminum bearing from the factory, and they are extremely
reliable in service, and seldom at the root of a problem.
I have never examined a Jasper engine, and cannot comment upon the
particular quality of thier products, but I can state that if the connecting
rod big ends are not immaculately machined, and the crank surfaces are not
perfectly true, intense wear will occur very rapidly with this sort of
result. Using a tri metal bearing exacerbates any problems. They are
especially unforgiving of out of round cranks, particulates in oil, and
temperature variations. Much of this is due to their extreme lack of
'embedability' and low fatigue resistance.
A second possibility is operating an engine at such a high speed that the
connecting rod journals sling oil off faster than it can be pumped in the
mains. This is a special problem for long stroke engines in particular.
Chevy 454 and 400SB engines fail from this often, in particular.
The damage to the con rod bearings may have occured a long time ago, from
one incident at very high speed, say a long pull in second gear perhaps, and
opened up the clearances enough to allow accelerated wear and finally
failure. On older high mile engines, this often occurs in tandem with broken
top piston rings, one blast over 5000 rpm is enough to run the top ring into
the cylinder wear ridge. This occurs from connecting rods stretching, which
they can do up to perhaps 0.040" or so at very high speed.
You'll be able if you measure and inspect the remainder of the bearings and
journals to determine what happened. If the rod big ends are egg shaped, and
theres torque variances on the rod nuts, or the cranks is scored heavily
(scratched up) or the bearings exhibit bare copper colour patches or offset
wear patterns, its Jasper. If the rest of the bearings and rods look
perfect, but you find a broken ring or two on a 'good' journal, its more
likely overspeed.
The Mondello theory of restricting lifter oilflow is specious in my view.
Yes, great amounts of oil can be pumped thru the valvetrain, however this
doesnt run the con rod journals dry. The crank is not pressurized by the
pump per se, its the spinning of the crank that produces the pressure in the
journals, all the pump has to do is make oil availible for the crank to
'pump'. once an engine is running faster than idle, the pump is a very
minimal influence on whats happening there.
Anyhow, I would sure be interested in seeing what you find when you
dismantle the engine, and finding out what happened. I suspect Jasper is at
the bottom of this, actually, as the engine overspeed issue is far more
likely to occur on a very high mileage engine with considerably opened
clearances. Also, rebuilt engines are such a poor bargain that its pretty
common for them to blow before 20,000 if they're going to. I tour the
machine shops in my metro area regularily on business and have never seen
one yet I'd trust with my own engine.
Best of luck, and keep us posted!
Brent Covey
Vancouver BC
deville
