dcnisbet@[EMAIL PROTECTED]
wrote:
> Hopefully somebody here knows where to look or possibly know of a
> newgroup like this that deals with Ford engines. I've got a 74 Ford
> F-100 with a 360 converted to 390 apx 10 years or 40,00 miles ago. I
> did an in vehicle overhaul, having the heads rebuilt at a machine
> shop. I replaced rings, rod bearings and did not balance the rods. I
> replaced the 360 crankshaft with a re-ground 390 crank kit with
> bearings. It still has decent compression with pump regular knocking
> at acceleration. Usually a 50/50 gasoline blend eliminates the
> knocking.
>
> After apx 10,000 miles on the overhaul the engine started vibrating
> about 30-35 mph or 18-2000 RPM. I get the vibration whether it is in
> neutral or in gear. Having the older style rebuilt 3-finger pressure
> plate and way to many miles on the clutch I suspect and out of balance
> pressure plate might be where the vibration is coming from but don't
> know for certain. The vibration is getting progressively worse. I
> replaced the vibration damper apx 5 years ago and the vibration did
> not improve. The conventional ignition was changed over years ago
> prior to the vibration problem and I recently had it scoped and there
> were no problems. Advancing and retarding the timing beyond the books
> does not help with the vibration.
>
> Any suggestions on where to look next?? I'm trying to avoid the
> clutch. Being a 4X4 with a minor nuisance oil leak in transfer case to
> deal with, changing the clutch is not an option until it wears out.
> Dealing with the greasy transfer case and extremely heavy cast iron
> drive train is no picnic and apx 5-700 $'s worth of labor if I don't
> do it myself.
>
> The biggest problem is oil pressure. Normal in town driving the
> pressure is fine even at idle. After a short trip on the freeway or
> high RPM's, the pressure drops the zero when it returns to idle or low
> RPM's. After returning to idle after driving just a few miles on the
> freeway I have to pick the RPM's up or I will get a lifter ticking
> from oil starvation if I sit at a stoplight for a few minutes. I can
> drive around town all day and the oil pressure will remain normal even
> at idle speed. If I take the truck on a long haul like an out of town
> hunting trip I have to add a can of STP or Motor Honey to maintain
> decent oil pressure. I've pressure tested the oil pump via the oil
> sender outlet both hot and cold and it is doing it's job.
>
> I don't know if the vibration and oil pressure problem are related but
> both problems are getting progressively worse. I've talked with a few
> mechanics and naturally they try to sell an overhaul or short block.
> None has been able to say where the problem is. At a shop that uses
> wet back labor speaking through a translator one mechanic that
> exclusively rebuilds engines all day said main bearings most likely
> fix the oil pressure problem but he had no idea on where the vibration
> was coming from. His suggestion was to use 50 weight oil until the
> engine goes and live with the vibration.
>
> Any suggestions on where to look for the problem or a newsgroup where
> I might look for answers are appreciated. With all the big-block Ford
> engines I've owned since the 60's the easy fix to engine problems was
> finding a wrecked Mercury, T-Bird, LTD or station wagon and using the
> engine until it wore out. Good used 390's used to be a dime a dozen
> but now finding a low milage wreck with an engine that is an easy in
> and out to fit a 1974 drive train is near impossible to find.
You lose oil pressure because the bottom end has a bunch of wear. Likely
the source of your vibration also. When driving on the highway the oil
gets hot and thins out causing the oil pressure loss. In town driving
should net the same result but may require a lot of in town driving. Your
vibration is probably coming from a bunch of mismatched parts wobbling
around in a bunch of loose bearings caused by poor assembly techniques. IE
poor quality parts (crank kit), no balancing, dirty assembly environment,
etc.
I would stop driving it, remove the engine, disassemble it, measure
everything, replace parts as necessary then carefully and cleanly
reassemble it. I would also spring for a professional balancing job,
professional crankshaft servicing and anything else that was absolutely
needed to make it last. You got ten years so you did ok time wise but
mileage wise you didn't get much for your rebuild money.
Roger
|
