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Engine Vibrations/balance - help!

stevo

New Member
Joined
Jun 17, 2009
Messages
35
Need some help here guys:

Story so far - My sons '76 with 302 and 3 speed standard. Skirt on a piston broke then it let go of connecting rod which knocked a hole in cylinder #7 before it got shutdown.

Pulled motor and replaced with a 5.0 out of a '96 explorer. Swapped over intake, carb, new dizzy with steel gear, exhaust manifolds - kept the serpentine setup. Bought a cheap diaphram clutch kit off rockauto and a 11" flywheel for a late model f150 - sachs NFW1128 - shows to be the correct 50 oz. Swapped everthing over, new flywheel bolts, torqued and blue loctite, used the correct shouldered pressure plate bolts. Compared new flywheel to old one to make sure it was same diameter/tooth count.


I might have flipped it over and compared the weights between the old 28 oz and new 50 oz - but I can't remember.


Put it all back together - back in truck - fires up, fix a couple vacuum leaks, timed at 8 BTDC, runs good, pulls hard good idle - ~ 20 in vacuum at idle with some needle bounce < 0.5 inch. Super smooth at idle

Now here is the SOB about it - revs fine to (I'm estimating RPM) to around 3500-4000 rpm and then the engine vibration starts to come on - gets worse with increasing RPM - very consistent vibration - its not missing. Doesn't matter if its clutch in/out - rolling/still - on the gas or coasting.

Feels like a washing maching when it spinning at full speed and just slightly out of balance. Its not severe, but its significant - something is out of balance in motor. If I drive and shift normal I never notice it.


Removed serpentine belt - no change.

Pulled harmonic balancer as that was pretty easy and replaced with a new one - no change.



Now I'm thinking 3 options:

1. Clutch pressure plate was poorly balance/not balanced.


2. Flywheel is poorly balanced or possibly a 28 oz (rockauto hasn't been great at getting me the right part) - could have not been drilled correctly and pressure plate is not centered.

3. Crank is bent?


So my question - has anyone accidentally put a 28 oz on a 5.0 and was the vibration severe or "moderate". I'd like to rule out wrong flywheel. I'm thinking we will pull transfer case/tranny and remove pressure plate - then reinstall bellhousing so I can start engine and rule out clutch.
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,790
my vote is as you put it "cheap clutch kit" made in China? they don't balance anything as proven by an explorer balancer from there that had zero balance done to it as verified by my machinist.
 

barronj

Bronco Guru
Joined
Jun 6, 2009
Messages
1,859
(EDITED: It was the flywheel that I'm talking about in the first paragraph, not the pressure plate)

One time, when putting the flywheel back on the 5.0 (mustang), from under the car, I somehow managed to get it ever slightly off balance, as in not flush to the back of the crank... I think there was a knick somewhere that was screwing me up, but at a minimum, I was laying on my side to install it in the driveway, so I was comprimised there too. Vibrated just like you describe.

Regarding the clutch, I'd once replaced the 1/2 shafts in my VW Passat (2002 model? they were notorious for bad boots) & I used chinese 1/2 shafts I'd bought from A-zone. They vibrated over 2500 RPM. Couldn't figure it out, but the mechanic I trusted swore that if I put VW 1/2 shafts back in, even used ones pulled from their yard, it would go away. He was right. Chinese QC is totally hit or miss in the auto-reman world.

Also, I've put an early model flywheel on a late model 5.0 and it vibrated at idle. Didn't take long to pull that out.
 
Last edited:

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
My vote is for the transmission not being properly torqued to the engine block. Easy to miss... easy to check.

Eric
 

pcf_mark

Bronco Guru
Joined
Jun 11, 2010
Messages
3,566
As someone noted if you had the 28 v. 50 imbalance it would be noticable at idle and only get worse. I drove mine sporadically with that and you knew something was funky all the time.
 

Lunar-tic

Sr. Member
Joined
Sep 28, 2009
Messages
629
Loc.
Brentsville
I had the 28/50oz balance issue and it wasn't very noticeable at idle but definitely got worse the higher the RPMs went.
 
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