What does an unbalanced motor sound/feel like?

[Lawbreaker5.0]

so i've been working on my 92 vert for awhile now and i finally got her up and going and it vibrates and roars loud when i get to 75-80mph.

Backround: i bought the TF top end kit and installed a reman crank, new main and rod bearings, and new rings. I have all the supporting mods including 24lb inj, 70maf, 75 tb, adj fuel pressure regulator, new trans mount, full bearing uppers (which i hate), MM lowers, Moser axles. pretty much you name it i got it. The clutch is a new mongoose and i replaced the TO and pilot bearing

symptoms. When i accelerate doing 75mph it roars like an 18 wheeler and vibrates bad under the acceleration. As soon as i let off the gas its quite and smooth for about 1 sec than the vibrations come back but not the roar until i get back to 75-80 mph again. it vibrates pretty bad anywhere from 30-65 in the seat and mainly the car, NOT the steering wheel. The rims and tires are new so i know its not them and i know the guys that mounted them and watched them balance out.

The only thing i didn't do was get the crank and pistons balanced becuase my machine guy said i would be fine since it was a ford crank coming out and a ford crank going in. He said they are all balanced from the factory.

The motor was bored .040 over though i guess right before i bought it years ago.

Thanks in advance.

 

[Tanus]

my stock crank required balancing, Im surprized you machinst said otherwise.

do you have solid motor mounts? that could be it

 

[project67]

so it sounds like you cannot duplicate the problem just by revving the engine? you have to accelerating at fwy speeds? if so i would suspect a u joint or prop shaft. if you can duplicate it by just revving the motor, this is all wrong so post back to clarify.

 

[85_SS_302_Coupe]

If you have the wrong balance flywheel, it will feel like it's going to fly apart at about 40mph. The faster you go the worse it gets.

 

[95Vert383AOD]

Solid motor mounts wouldn't do that.

Does it vibrate like that when you rev it to say 3000RPM in park??? If not i would say to check your drive shaft....Check u joints for play.

I had a Mark vii that i was hotrodding and when i removed the drive shaft and shook it it felt like there was something loose inside the tube....like ford put a weight or something in there.

If it wasn't balanced right i think it would vibrate all the time. Kinda like a misfire does.

Chris

 

[Tanus]

oh yeah, check driveshaft bolts

 

[Lawbreaker5.0]

Ok, so i don't have solid motor mounts and it does NOT do it at 3000rpm sitting still. Well it def doesn't do it bad at all. i will know more tomorrow when i drive it to school.

It really sounds like a 18 wheeler is driving next to me. Its so bad that I forget sometimes and look over to see if one is passing me. lol.

The last time i had the trans out do re do a rear main seal which was a couple months back i checked the U joints for play and rotated them to feel if they bind and they didn't.

Maybe a weight fell off the DS. Corret me if i'm wrong but when the wheels are off the ground your speedometer is off by half, right? So if it says 30 you're roughly doing 60. i might try to jack it up and see if i can see anything moving.

Thanks again guys

 

[project67]

if you had the trans out recently, check the driveshaft bolts at the yoke to make sure they arent loose.

is the vibration/sound constant or does it oscillate?

 

[project67]

i just rear you put in control arms. are they adjustable? if so, you may not have the right pinion angle. try to adjust them slightly and see if it changes at all.

 

[boosted mustang]

my car did the same thing it ended up being the pinion bearing and it wouldnt do it on jack stands or couldnt shake the pinion by hand. It was enough to make the hole car viberate at like 50 mph but smooth out after 80 or so. Just a idea something to look at.

 

[Lawbreaker5.0]

This vib and noise happened before i took the trans out and has being doing it since i first did the hci. A bolt striped going on to the pressure plate/flywheel. So i thought it was off balance. Thats when i decided to tear into her again and change the clutch this time.

Its pretty consistent with rpms. I don't know if that helps.



edit: i do have a couple 8.8's around.

 

[Lawbreaker5.0]

Ok so I drove the stang today and it vibrates when sitting still at 3 or 4k. But not like previously stated. It does make the loud roar at 4-5k when I am accelerating in any gear. Anyone have suggestions?

 

[95Vert383AOD]

Ok so I drove the stang today and it vibrates when sitting still at 3 or 4k. But not like previously stated. It does make the loud roar at 4-5k when I am accelerating in any gear. Anyone have suggestions?

Heres something....pull the plugs...inspect. Check the clips on the wires. (seen plug wires with defective clips out the box)

 

[Tanus]

Heres something....pull the plugs...inspect. Check the clips on the wires. (seen plug wires with defective clips out the box)

I worked at a parts store for a while, and yeah the regular plug wires are garbage.

 

[BlownFiveLiter]

It might not be a bad idea to try pulling codes and also running a cylinder balance test. It does sound like there's more of an engine related issue with a misfire/weak cylinder than it does a balance issue. How do your plugs look? All a uniform color? Compression good and within 10% on each cylinder? With no load on the engine, it'll probably rev smoothly all day, but if there's a cylinder that isn't quite up to snuff, it's going to be the most pronounced at WOT under a load. If you find a weak cylinder, I would personally probably re-lash the rockers for peace of mind and maybe swap the plug wire and see if it solves the problem.

BTW, you might want to consider resizing that signature image. I'm not a mod anymore, but if one of the current ones sees it, they're going to ask you to.

 

[Lawbreaker5.0]

How do you run a cyl balance test again? i'll check compression later this week. school is killing me this first week