Help! 1988 I-Mark engine knock

External Since: Jun 03, 2004 Posts: 5

Son bought an 88 Isuzu I-Mark (1.5l, non-turbo, carbureted). Prev.
owner provided lots of repair bills. Her son had taken the engine out
by not monitoring oil level, even with a known rear seal leak. Given
the age of the car, they got a replacement engine from an auto wrecker.
Rear seal leaked on that, as well, so they had that replaced.

Motor is clean; didn't make any noise during a warm look-over, or during
the test drive the next day. But since then, it has developed a real
knock. From above, it doesn't even sound like its definitively engine
knock, but we had it on the hoist at my father-in-law's, and from
underneath, it sounds like the world is ending....

Engine has to warm up to get noisy. Knock is quite quiet at idle, but
gets worse with RPM. Seems to be worse at steady load (as opposed to
higher load from acceleration, or no-load when coasting down).
Had the pan off; rod bearings have a little scoring (187 000 km engine),
but NO visible color change or such to indicate wear. (sorry, didn't
have Plastigauge that day to check)
Mechanic's stethoscope run around on the engine doesn't point me to
anything. Noise seems to be worse from outside.
Doesn't seem to be timing belt slap, or anything like that. Engine does
not appear to have a harmonic balancer, either.

The only thing I can think of is possibly a wrist pin. Anybody have any
other thoughts?

Thanks in advance.
DanR

External Since: Sep 21, 2005 Posts: 54

"Dan Richards" <danrichards.DeleteThis@shaw.ca> wrote in message
news:WEqlf.52445$ki.4192@pd7tw2no...
> Son bought an 88 Isuzu I-Mark (1.5l, non-turbo, carbureted). Prev. owner
> provided lots of repair bills. Her son had taken the engine out by not
> monitoring oil level, even with a known rear seal leak. Given the age of
> the car, they got a replacement engine from an auto wrecker. Rear seal
> leaked on that, as well, so they had that replaced.
>
> Motor is clean; didn't make any noise during a warm look-over, or during
> the test drive the next day. But since then, it has developed a real
> knock. From above, it doesn't even sound like its definitively engine
> knock, but we had it on the hoist at my father-in-law's, and from
> underneath, it sounds like the world is ending....
>
> Engine has to warm up to get noisy. Knock is quite quiet at idle, but
> gets worse with RPM. Seems to be worse at steady load (as opposed to
> higher load from acceleration, or no-load when coasting down).
> Had the pan off; rod bearings have a little scoring (187 000 km engine),
> but NO visible color change or such to indicate wear. (sorry, didn't have
> Plastigauge that day to check)
> Mechanic's stethoscope run around on the engine doesn't point me to
> anything. Noise seems to be worse from outside.
> Doesn't seem to be timing belt slap, or anything like that. Engine does
> not appear to have a harmonic balancer, either.
>
> The only thing I can think of is possibly a wrist pin. Anybody have any
> other thoughts?
>
> Thanks in advance.
> DanR
>
Dan, you have nothing to lose, so try this... put the car outside, exhaust
end away from the house or anything you value and don't want to have to
clean. Take off the air cleaner so you can get to the carb inlet throat. Get
some Motor Mystery Oil (red can, available at any good parts house) and put
it in a squirt oil can (not a dripper). Start the car, and with your hand on
the throttle, open the thtottle, and as you're revving it up, squirt the MMO
into the throat of the carb. You will make LOTS and LOTS of smoke, and
probably the engine will shake, rattle and roll... (well, not roll, but it
sounds good) - but if it is carbon on top of a piston, which is what I think
it is, you'll be doing your best to dislodge it and blow it free. Other
people have used water to do the same thing - I prefer MMO. I'd run about a
cup to 2 cups of MMO through it, and take it for a drive. Assuming you don't
have a broken piston, a wrist pin that's come loose, or a spun rod bearing,
you've probably got carbon buildup on a piston.
Of course, you can't hold me liable for blowing up your engine if you
actually do have one of those other things, but I doubt that's it, and
that's what I'd do if I were you. I hope this helps.
r/
Steve