Engine Bad vibration 3500 RPM+

Vulpes5.0 · Sep 8, 2021

Hey all, I've been having an issue that I've been trying to troubleshoot for a bit with a high RPM vibration. At about 3500 RPM in any gear, my car has a vibration that can be felt strongly through the shifter to the point of the center console making noise. It only gets worse with higher RPM and can be felt in neutral too. Speed and load seems to amplify the vibration, and it feels like it's damaging things, so I can't realistically go above 70 with the 4.10's I currently have. The vibration itself feels "harmonic" in that it tends to be an oscillating hum.

So far I've replaced the driveshaft, tried running my car without rear wheels to see if it was a balance issue (This was before I knew it was RPM and not speed related) and I have since replaced the harmonic balancer which I was confident would fix the problem, but did nothing. The car has a resurfaced flywheel that came off the donor car, and a King Cobra clutch that was replaced within the year. I replaced the transmission bushing with a Prothane one, and have yet to install the Prothane motor mounts that accompany it. I'm running out of ideas as to what to replace. I tried removing the serpentine belt as well just to rev and I can't tell if it gets any better or worse because it's much more noticeable when cruising.
Does anyone have any ideas? Would an out of balance flywheel cause this or would it be noticeable at all RPMs? Maybe even my engine fan? It is cracked but this seems extreme. Could be unrelated but my exhaust header bolts keep backing themselves out too. Passenger side closest to firewall is the worst about it. Could a bad injector cause this kind of thing? slight misfire that's almost undetectable? I've been pondering this for so long it's driving me crazy and I just want to drive on the interstate comfortably. Too many forums without resolutions.
Thanks for your time

90sickfox · Sep 8, 2021

Try it with the serpentine but off. The fan can cause a bad vibration. The next thing I'd check is the balance on the flywheel. There are 2 one is 28 other is 50....well 3...there's one that is neutral balanced but very uncommon on a regular car.

Vulpes5.0 · Sep 8, 2021

90sickfox said:
Try it with the serpentine but off. The fan can cause a bad vibration. The next thing I'd check is the balance on the flywheel. There are 2 one is 28 other is 50....well 3...there's one that is neutral balanced but very uncommon on a regular car.

I gave it a shot with belt off earlier today but I didn't notice a ton of difference. If I rev the car in neutral, while at high speeds, it seems to vibrate much more than at idle, would higher speed cause higher fan speed? I've been thinking it could be a lower plenum vacuum leak, or injectors doing it since I have a misfire under load sometimes. Does that sound plausible? I'm working on a 3g alternator upgrade so I can move to an electric fan as of right now, parts on the way.
Also, any way to get eyes on the flywheel balance without removing the transmission? starter hole maybe?

General karthief · Sep 9, 2021

Don't add stuff that is non stock to an ill running vehicle, it can make finding the problem harder.

Vulpes5.0 · Sep 9, 2021

Yeah, you’re right on that one. It’ll be a while until all that arrives anyway. Just lost on this one, running out of ideas. Clutch pedal likes to pulse/shake when I’m in gear off throttle (engine braking, i guess?) if that might be part of the problem. My dumb ass cobbled a car together with parts from all over the place and it’s been a fight to fix what problems I can before more show up. Most wear item stuff is new but the long block and T5 swap i bought used.

General karthief said:
Don't add stuff that is non stock to an ill running vehicle, it can make finding the problem harder.

General karthief · Sep 9, 2021

What do you know about the flywheel you used?

7991LXnSHO · Sep 9, 2021

General karthief said:
What do you know about the flywheel you used?

And what year is the short block?
The key phrase may be “cobbled together”.

Vulpes5.0 · Sep 9, 2021

General karthief said:
What do you know about the flywheel you used?

I took it off a 90 mustang with an older block 302 that was previously used as a drag beater, got it resurfaced. It had some minor heat damage but nothing obviously jumped out as a problem. If it was a mismatched flywheel, wouldn’t my engine be shaking like crazy at any RPM? My engine shakes a bit but i always assumed it was from the cam. And above idle it’s smooth until 3500 RPM

Vulpes5.0 · Sep 9, 2021

7991LXnSHO said:
And what year is the short block?
The key phrase may be “cobbled together”.

Short block is from another 1987 mustang, guy took it out running to go to a 347 motor.

7991LXnSHO · Sep 9, 2021

If your HB is right, but the flywheel isn’t, it sounds like the right symptoms to me. But I am sure we want to rule out other causes before you tear it apart.

Vulpes5.0 · Sep 9, 2021

7991LXnSHO said:
If your HB is right, but the flywheel isn’t, it sounds like the right symptoms to me. But I am sure we want to rule out other causes before you tear it apart.

I'm going to try and look at the harmonic balancer on the older 302 motor that's still lying around my garage somewhere. It's been rebuilt and has .040 over pistons so it's definitely possible that it has 28 or neutral imbalance, especially being that it was an older motor. 70's truck, if I recall, but I'll have to head over to my pop's house where it's stored so I'll update that whenever I get a chance.
Any tips on HB identification? I have the 50 oz. off my car for reference because it was falling to pieces and replaced it with a Summit one. (Don't recommend it btw, it's a one size fits all deal, was a pain to assemble with the spacer...)

7991LXnSHO · Sep 9, 2021

I cannot find good pictures, but Ford part numbers will help by telling the year.

I have swiped this info below from another forum, but it confirms my experiences. The local mechanics in little town I took a job in did not listen to my parts list of things that needed changed when I had them replace the 79 302/5.0 with an 87 up E7te long block. (I had already been talking with them as a Marshall (Blueprint) engine dealer when it probably spun a bearing not far out of town. The people at work eventually told me the guys often took a liquid lunch at the bar and grille, and were not surprised with my warranty trouble. :-( )
It idled fine, but shook like hell after the rpm’s were up a ways in N or any gear. There was no mistaking it for a misfire. Swapping the flywheel and balancer (and starter?) for 87 up take off parts fixed the vibration, but did not fix how much oil the Marshall rebuild sucked oil past the valve stems.

“1968-80 302 engines were built with a 28-ounce imbalance factor.
1981-2001 302 engines were built with a 50-ounce imbalance factor.
1969-97 351W engines were built with a 28-ounce imbalance factor.
1970-74 351C engines were built with a 28-ounce imbalance factor.

Note: Severe engine damage will result if you use the wrong flywheel or damper on your engine.

It began with the introduction of the 255CI and worked it's way through the 302/5.0L.”

And, I remember there being 3 bolt v belt pulley and balances vs 4 bolt serpentine pulleys and balancers. If you were able to bolt up to the Summit balancer, that’s not a concern.

Vulpes5.0 · Sep 9, 2021

7991LXnSHO said:
I cannot find good pictures, but Ford part numbers will help by telling the year.

I have swiped this info below from another forum, but it confirms my experiences. The local mechanics in little town I took a job in did not listen to my parts list of things that needed changed when I had them replace the 79 302/5.0 with an 87 up E7te long block. (I had already been talking with them as a Marshall (Blueprint) engine dealer when it probably spun a bearing not far out of town. The people at work eventually told me the guys often took a liquid lunch at the bar and grille, and were not surprised with my warranty trouble. :-( )
It idled fine, but shook like hell after the rpm’s were up a ways in N or any gear. There was no mistaking it for a misfire. Swapping the flywheel and balancer (and starter?) for 87 up take off parts fixed the vibration, but did not fix how much oil the Marshall rebuild sucked oil past the valve stems.

“1968-80 302 engines were built with a 28-ounce imbalance factor.
1981-2001 302 engines were built with a 50-ounce imbalance factor.
1969-97 351W engines were built with a 28-ounce imbalance factor.
1970-74 351C engines were built with a 28-ounce imbalance factor.

Note: Severe engine damage will result if you use the wrong flywheel or damper on your engine.

It began with the introduction of the 255CI and worked it's way through the 302/5.0L.”

And, I remember there being 3 bolt v belt pulley and balances vs 4 bolt serpentine pulleys and balancers. If you were able to bolt up to the Summit balancer, that’s not a concern.

Alright, I went and did a little looking around and comparing!
The older one is the one that looks like it’s falling apart

Original HB (50 oz.)
Casting mark: E4TE-A3A
Left: A/F 8
Middle: 112216
Right: 261
Notes: Less holes (more oz?)

Other engine HB (?? Oz)
Casting mark: E4TE-A3A
Left: A/F 4
Middle: 112216
Right: 159

Notes: 134-2 on snout
More holes (less oz?)

Older engine casting # :E0AF D50 20

1980 truck engine?

7991LXnSHO · Sep 9, 2021

So, any idea on the flywheel?
i don’t think that block is a roller block. What I strongly suspect but do not know, is if that came with the earlier balance. If they used that casting long enough, it might have the newer crank in it. I doubt it.

The HB’s should be the same. I think the holes are just to get the right balance from the casting.

Vulpes5.0 · Sep 9, 2021

7991LXnSHO said:
So, any idea on the flywheel?
i don’t think that block is a roller block. What I strongly suspect but do not know, is if that came with the earlier balance. If they used that casting long enough, it might have the newer crank in it. I doubt it.

The HB’s should be the same. I think the holes are just to get the right balance from the casting.

Yeah, I’m pretty positive It’s not a roller block but i didn’t pull the lifters to check while i was over there. It’s been rebuilt and has .040 over pistons, no idea beyond that. It had a lot of older style pulleys when I pulled the motor. Maybe this guy was running the wrong flywheel too, and I just adopted his problem. When I took a look at the donor car’s driveshaft it had vibrated all but 2 bolts loose, so I dont trust it very well. This is sounding to me like it’s the flywheel but I’ll have to get a look. Can I see the weights through the starter hole by chance? The HB was so worn out I would think it was original but both castings are from 1984 right?

P.S… I’ve been driving it with this vibration for a few months now. I’m sure it’s terrible for the engine but as of right now it’s my only way to go lol. I just try and keep my car under 3500 as best i can, but my foot can only stay light for so long and it hasn’t blown yet lol

General karthief · Sep 9, 2021

I would find another mode of transportation till you get this worked out, you're (likely) only causing more trouble.

Vulpes5.0 · Sep 10, 2021

I know it’s a bad idea, but it’s all I’ve got right now. The only time I really fear damage is when I go on the interstate and have to hold high RPM, so I’ll just borrow a car when I have to do that. I went ahead and ordered the SVE billet steel flywheel, I’m pretty confident in the fact that it is just the flywheel, or maybe the clutch causing this. Rear header bolts backing out, front/rear seals leaking a little from the vibration, clutch pedal feeling chattery, it just seems like the solution. If not, it’s just yet another “upgrade” lol.
I’ll keep this post updated, so many threads I see the poster just disappears after a couple suggestions with no solution to be found. I appreciate everyone’s input and help!

Vulpes5.0 · Sep 13, 2021

Little update… I got the old flywheel out, and nothing looks out of place anywhere. The flywheel is cast iron and 50 oz, undeniably old, but shows no signs of bad wear or warping. I’m currently installing the new flywheel, which I bought as an SVE flywheel but came in a Mcleod box and everything, so that’s good, i hear they make pretty good stuff! Old flywheel has “engineered in USA” and PHT50-7 etched into the block side, and looks to have a large weight on it. I’ll update once i reinstall as to whether it helped anything. I have high hopes though. Even my starter bolts seemed loose from these vibrations.

7991LXnSHO · Sep 13, 2021

I am hoping I am wrong, but I bet it is a 28 Oz rotating assembly.

chrlsful · Sep 13, 2021

unhook DS & run 2 C if its uJoints or shaft (even angle)?
motor mounts? transmish?
Talk w/OP (if old noise).

Engine Bad vibration 3500 RPM+

Vulpes5.0

90sickfox

Wasn't a pretty sight...and I've got big hands

Vulpes5.0

General karthief

wonder how much it would cost to ship you a pair

Vulpes5.0

General karthief

wonder how much it would cost to ship you a pair

7991LXnSHO

wanna catch the space herp

Vulpes5.0

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wanna catch the space herp

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wanna catch the space herp

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wonder how much it would cost to ship you a pair

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Engine Bad vibration 3500 RPM+

Wasn't a pretty sight...and I've got big hands

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wanna catch the space herp

wanna catch the space herp

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wanna catch the space herp

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