Stock long block 5.0 from 1994. Was running on the highway and all the sudden, bad vibration appears. Towed car home and balancer bolt broke and balancer too. No visual damage to crankshaft itself. Bought another balancer from ATP and ran since. Few hundred miles later, medium vibration appears so I've replaced again balancer for a Powerbond. Vibrations seems cut in half but still present. Now started some tests.
Transmission removed and engine supported with a frame that used transmission mount on stock crossmember.
With Powerbond balancer (50oz) and Fidanza flywheel (50oz) and no clutch, vibration at approx 1200 and between 2200 to 2800 RPM. I can feel it seated. Bought another stock replacement flywheel (50oz) and issue remains. Verified all spark plugs, wires, no arcing and engine mount seem perfect. With or without engine strap and still present, no change. Found nothing in the oil too. It is possible main bearing have something that cause vibration? When I use force to move up/down the balancer, I can feel a very small bit of moving. Thanks
The next thing to investigate IMO is the rods. Run a compression test and see if one hole is way down on compression. If the rod is bent that will be the hole. I have seen stock 5.0s bend rods but it has usually been from nitrous.
There is a possibility of a "compression imbalance" but I would really think the crank snout got bent when the first balancer blew.
First off, it seems like you would be able to see that at the balancer when checking timing, but if not, perhaps use 6" stud (with nut) to mount the balancer so that most of the stud extends out past the balancer and you would get a much more visual "read" on whether the snout is straight when the motor is spinning. If it is, the stud would spin perfectly with no wobble, if it off at all I would think it would be really obvious with the stud sticking out. I know it's a crazy idea, I'm just trying to help!
This seems like a lot if this is the crankshaft snout where the balancer mounts... I would think it would be .001 or less... Maybe someone else will chime in..
Thats 8 and a half ten thousandths, correct? .00085. Thats nothing, thats remarkably good. What does the crank snout measure? Bearings are reminiscent of a 25 year old bearing. Little more than 3/4 wipe pattern, crap run through the oil in the last few decades. Nothing shocking. Unless the main bearing clearance is very wide, over .004, main bearings just sit there and go along for the ride.
With the car in Park rev the motor slowly up to 4000K and see if there is a vibration. If not the motor is probably fine and I wouldn't spend any more time on it.
From here drive the car on the street until you feel a vibration. When you do, put the car in Neutral and let off the gas and just coast at that speed. Is the vibration still there? If so then the vibration is somewhere in the chassis, tires, wheels, driveshaft, rotors, etc, either in the front or rear...
I haven't re-read this thread but motor mounts are cheap and would eliminate them as being an issue.
Yes, the crank snout is perfectly fine. That is not where the vibration is coming from.
Here's some far-out reaches that could be easy to check that I would do if it was my car:
Replace all injectors or send them all out to have them flow checked. Don't assume they are good. Have someone flow them.
Replace all the plugs. I know you said you checked them in the first post but if you haven't, just replace them.
Insert a scope through the spark plug hole and check the top of the pistons. It's possible some detonation has caused some piston damage and that's causing the sudden vibration.
Jim, If you read this thread, your knowledge is welcome. I started to dissassemble the engine today and except what said previously, I havent found nothing else that will alarm me the cause of the vibration. When I remove the timing cover, I could put the dial gauge further the first main cap and get 0,0020 at max.
thanks
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Ford Mustang Forums
9.8M posts
200.7K members
Since 2001
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, production numbers, VIN decoders, modifications, troubleshooting, power adders, DIY tutorials, and more!