"Roger M" <rnddmauck@[EMAIL PROTECTED]
> wrote in message
news:46145298.35CF5876@[EMAIL PROTECTED]
>
>
> 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
I had a low oil pressure problem with my 390 which turned out to be worn
camshaft bearings!!
KenG
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