Engine Bad vibration 3500 RPM+

90sickfox

Wasn't a pretty sight...and I've got big hands
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Mar 2, 2015
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Just FYI - stroker engines take 28oz or 0. My 331 is 28oz. I've also seen 331 engines with ported e7 heads. This is one of those times when engine history could be really important. I hope you've solved it with the new flywheel though.
 
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1970machwon

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Nov 17, 2018
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unhook DS & run 2 C if its uJoints or shaft (even angle)?
motor mounts? transmish?
Talk w/OP (if old noise).
It's definitely not a drivetrain vibration, as much as I wish it were that simple. It's something from the transmission forward. I do need to replace the motor mounts but they aren't in terrible condition. It could potentially be a transmission problem but I truly doubt it. It happens with clutch in or out at high RPM.
 

1970machwon

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Nov 17, 2018
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Just FYI - stroker engines take 28oz or 0. My 331 is 28oz. I've also seen 331 engines with ported e7 heads. This is one of those times when engine history could be really important. I hope you've solved it with the new flywheel though.
As far as I know, this was a $300 engine that came out of another 1987 GT so that the guy could put a stroker into his car. It was taken out running with nothing that would lead me to believe it wouldn't be a 50 oz. imbalance. It was a roller engine that had original bottom end and all that mess.
I hope this fixes it too, I have to go over to my dad's place and finish up my work because by the time I got done parts places were closed and I needed to get some fluid that I lost... I'll update later today!
 
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1970machwon

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Update: I got it installed, took it on the interstate, and the vibration is still present. It seems to be reduced at least a little bit, before it was rattling my center console and now it seems to just be lessened a little bit. The vibration is a lot worse when I’m off throttle for whatever reason. I’m going to start looking at a fuel delivery problem or a pulley vibration. My car seems to do an odd push/pull like you were adding and taking off an engine load when im at about that speed which makes me think it could have something to do with, i dont know… timing or fuel. Most of my ignition system is completely new, but my fuel injectors are from the original engine that was practically falling apart, and my car backfires a lot which makes me think it could be dumping fuel out much of the time
 

General karthief

wonder how much it would cost to ship you a pair
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I don't remember you saying anything about surging or running bad when this began, I was not convinced it was a drive line issue from the description, it still may be part of the problem, so let's get the engine straight first. I would go through the surging idle checklist.
Replace the motor mounts, you did say they were suspect.
Everything starts with the engine, literally, if it ain't right, nothing is right.
DISCLAIMER: this is an opinion based on what I read, and my reading is suspect at best, not based on any real mechanical experience.
 
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1970machwon

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I don't remember you saying anything about surging or running bad when this began, I was not convinced it was a drive line issue from the description, it still may be part of the problem, so let's get the engine straight first. I would go through the surging idle checklist.
Replace the motor mounts, you did say they were suspect.
Everything starts with the engine, literally, if it ain't right, nothing is right.
DISCLAIMER: this is an opinion based on what I read, and my reading is suspect at best, not based on any real mechanical experience.
Yeah, I should've mentioned that early on, apologies for that... I did much of the stuff on the surging idle checklist, but I'm fighting a couple of them right now. I have a code 67, something up with my neutral ground switch. I replaced the switch so now I have to try and hunt down whatever funky wiring issue it could be, I've got another thread going on that one. I think I may have a vacuum leak but it's nothing on the top end of the engine, if it's anywhere it's at the intake gasket because I've even done a smoke test to no avail.
But yes, I do have an idle surge, and my car likes to bog down and stall when I put the clutch in at high speed, gets worse whenever I have added load like AC or power steering. I'll get hot on it lol. I'm tired of engine problems. It's been a crapshoot for as long as I can remember because I never started with a running vehicle, put it all together myself. My dad has a lot of experience but exclusively with carbureted older stangs so it's been on me to figure it out anything with EFI
 

1970machwon

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Haven't had a lot of time to mess with my car lately, but I was looking under the hood and just poking about at things, and found the my belt tensioner pulley moves back and forth ever so slightly. As in I can push the wheel itself forward and backward about 1/10 of an inch, just enough to click it back and forth, and this is with the belt on. Could this be a plausible source of vibration? Does anyone else's tensioner have play in it like this?