I have a vibration in my 94 5.0 v8 in my 72 comet. It can be felt at rpm's of about 2,000. It is there during acceleration up to about 45 mph and then it isn't so noticeable. Installed new 50 oz. flex plate, new torque converter, new 50 0z. harmonic damper, then unbolted torque converter to eliminate the transmission. Still vibrates. Could it be related to the motor mounts in some way? Pulling my hair out here.
I have several questions. I'm assuming you replaced the parts you listed in an effort to eliminate the vibration? You also indicate the vibration is there at 2,000 RPM and the car is not moving and the torque convertor is disconnected, is that correct? Is this vibration something that just started at some point or did you install this 5.0L engine only to find it had a vibration? Is this vibration something you hear, feel or both? Give us more detail as to when the vibration started and the history of the engine. Is it a remanufactured unit, a salvage yard refugee, a Craig's-List purchase with no history?
This is a machine shop complete rebuild. I asked for it to be balanced and they finished the engine and then ordered the balancer and flexplate. They installed a small bell c4 28oz flexplate and a 50 oz balancer so obviously then we got it running we had a hell of a vibration. We got a 157 tooth 50 oz flexplate installed and aabout 90 % of the vibration is gone. I can feel the vib when in park and bringing the rpm up to around 2,000 and above. When driving you can feel the vib slightly throughout the car, steering wheel, seat etc. We replaced the torque converter and still have the vib. Installed a new harm balancer and same thing. Disconnected the torque converter to see if it might be in the tranny but still have the vib. It has new motor mounts since the restoration. The crank assy evidently was never spun up and balanced. Could the crank have some odd imbalance in it? There is about 1000 miles on the engine and entire car since finishing up.
I'd think they'd have at least ordered correct balancer and flexplate, sounds like someone didn't have a clue... If they've ground on the crank counterweights or installed heavy metal in it, the rotating assembly may be so screwed up it won't balance with either 28 or 50 oz components... I believe piston weight is different in 28 & 50 oz engines, I know cranks are different... As far as motor and transmission mounts, if they are metal to metal or something from drivetrain or exhaust touching chassis, that can cause a vibration...
Sadly I have first hand experience, the 306 in my Comet suffers from this exact condition... Current plan is to pull it down and install everything on a good Exploder 5.0 I have... BUT that could change at a moment's notice, besides the 331 I've never installed in T-Bird, there's also a fresh 415Hp, 349 here(.040 vs .030 over 347)... I have other plans for 349 so I don't really want to use it in Comet... Those other plans also have a 408 lurking in the background, till worked out I'm settin' tight...
I agree but before I pull the engine I am going to replace the motor mounts again. The engine sits too high in the front and I have heard that some suppliers have shorter mounts than others. Maybe something is hitting with these that I don't see. Any idea where I could buy a shorter set of mounts?
Thanks for your comments Hotrock. Before pulling the engine I am going to replace the motor mounts again. When I first put the new set in I noticed that I had lots of trouble getting the bolt thru the frame mt and the motor mt. Foung it for some time and then drilled out the front hole some to get the bolt to feed thru. Today I put a level on the top of the engine (on top of a valve cover front to back) and boy is the engine way up in the nose. Friend of mine said he had a collection of new mounts some time ago and some were shorter than others. I would love to get ahold of a set of the short ones and drop the motor down a little and eliminate the possibility that I may have some metal to metal there somewhere. Any idea where I might order a short set?
If engine is too high you likely also have a mismatch in driveline angle... Rough on U joints and can can cause vibration, but not setting still...
Personally I have never heard of long and short sets of engine mounts for our vehicles. I have an after market set of mounts on my Comet. They are nothing special. They are not modified and I do race, therefore they get a workout. More than likely I got them at my local Auto Zone store. If I were you, I'd get a set of mounts from my local auto parts store and compare them to the mounts in the car. You can then decide if installing them might eliminate your engine tilt and perhaps the vibration as well. Sourced locally they would be easy to return. I've attached a link to a set of mounts that Auto Zone carries. They are not an in-stock part and would have to be ordered. I get most of my AZ parts the next day delivered to the store. That way they are an easy return. https://www.autozone.com/external-engine/motor-mount/duralast-motor-mount/155689_0_12553
Sounds to me like they did not balance the engine at all. I doubt that new motor mounts will help with your problem but when you get some drill a hole through the center of them and install a 1/4" bolt and nut to keep rubber from separating from metal especially on drivers side mount. Like Hotrock I have never seen or heard of a shorter mount. Perhaps you have the wrong frame mounts as well a picture would help to identify this. Are you 100% sure you have good fire to ignition (good wires, plugs, distributor). Good luck with your problem solving as vibrations are usually hard to find the root cause especially when drive train has been eliminated
I had a balanced 347 that had a vibration. the builder suggested pulling it down and checking the balance. we did and he said all was good. we put it back together and installed it in the car...no more vibration...
