Rpm related vibration

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BB70
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Re: Rpm related vibration

Post by BB70 » Mon Feb 12, 2018 2:42 pm

Find a means to keep the rpms where engine misfires- buddy holding the throttle, small screwdriver between throttle lever and stop, ect. Lightly introduce some spray carb cleaner into the engine to see if rpms climb or engine smooths out. If nothing changes get a pair of insulated plug wire pliers and pull the plug wire off at the plug or at the cap and see which cylinder doesn't change the rpms. Be careful . Point is to find if it's fuel or ignition.

John

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Re: Rpm related vibration

Post by pjc360 » Mon Feb 12, 2018 9:07 pm

BB70 wrote:
Mon Feb 12, 2018 2:42 pm
Find a means to keep the rpms where engine misfires- buddy holding the throttle, small screwdriver between throttle lever and stop, ect. Lightly introduce some spray carb cleaner into the engine to see if rpms climb or engine smooths out. If nothing changes get a pair of insulated plug wire pliers and pull the plug wire off at the plug or at the cap and see which cylinder doesn't change the rpms. Be careful . Point is to find if it's fuel or ignition.

John

I’m thinking it’s mechanical inside the engine somewhere, maybe a valve spring or a valve.
Every single piece to this ignition is brand new and has been installed correctly.
Fuel part of this set up is on par as well.
Quick fuel super street series 680cfm vacuum secondary carburetor, Mopar Performance Dual Plane M1 aluminum 4bbl intake manifold.
I’m running an Aluminum 2 inch 4 hole carburetor spacer.
Main jets are 65’s secondary jets are 75s, idle feed restrictors are .031, idle air bleeds are .065’s, high speed air bleeds are .033’s.
Power valve is a 9.5hg, power valve Chanel restrictors are .049’s.
Idle mixture screws set to the highest vacuum reading which is about 3/4 of a turn out on all 4.
Float level is half way up the sight glasses.
I get 6 to 6.5 lbs of fuel pressure from my mechanical fuel pump.
I don’t see how this could be fuel related at all, I realize the main jet is a little lean but I’m also 3500 feet above sea level here in Montana.
The carb originally came with 68 main jets and 78 secondary jets.
I went down 3 sizes for the increased elevation.
My carburetor is brand new with less then 5k miles of run time on it, every piece to the ignition right down to the spark plugs and wires are brand new with less then 1k miles of run time.
I thought for sure the new Msd box would take care of this issue because I thought I had an issue with my crane hi-6 box but apparently that wasn’t the answer.
I’m just behind frustrated with this truck right now.
With all the parts I have on that thing it should be running flawlessly.
Drivetrain is all brand new, brand new 8 3/4 rear axle with brand new 4.56 gears and a sure grip, brand new axle shafts and wheel bearings, brand new 1350 series cv driveshaft on the rear with the spring perches being re-located to put the pinion directly inline with the shaft.
Brand new 4.56 gears in the Dana 44 front, brand new wheel bearings, new warn locking hubs.
Transmission was overhauled about 7k miles ago even though it was a few years ago, I hardly put any miles on this truck mainly cause I ended been trying to work this bug out of it and it ends up pissing me off and I park it for long periods of time and take a break from it.

Circlotron
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Re: Rpm related vibration

Post by Circlotron » Tue Feb 13, 2018 12:55 am

I know the feeling.
Just gotta day it again.
Needlessly hard engine mounts.

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Re: Rpm related vibration

Post by Belgian1979 » Tue Feb 13, 2018 3:03 am

Don't forget the half shaft's balance. Most shops don't balance these with the argument that they turn at too low a speed to induce vibration....
Also the angle between drive shaft input yoke and output yoke maybe something to check

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Re: Rpm related vibration

Post by Newold1 » Tue Feb 13, 2018 7:00 am

I am not sure if I am reading what you posted last about the driveline, but I believe you are saying your rear driveshaft is directly inline withe the pinion shaft on the rear axle. If you mean the angle of the pinion is directly on the same angle to the transmission or transfer case as the driveshaft, that is WRONG and the result can be a pretty bad vibration! There has to be an offset in those two angles for the driveline to work correctly with each other.

As for the possible miss or problem inside the engine if the engine is popping through the exhaust or surging badly in neutral it could be a few things. One, obviously tune, too tight of valve adjustment on one or more exhaust valves, intermittent spark to a cylinder or two , or three an exhaust gasket leak.
I seen bad distributor caps and rotors do this crazy miss too. Try a replacement cap and rotor and see what that does.

Just some thoughts to look at. Don't want you jumping off the top of anything tall for resolution! You'll find the gremlins, don't get to frustrated just breath in and out real slow! :)

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Re: Rpm related vibration

Post by Belgian1979 » Tue Feb 13, 2018 9:48 am

Newold1 wrote:
Tue Feb 13, 2018 7:00 am
I am not sure if I am reading what you posted last about the driveline, but I believe you are saying your rear driveshaft is directly inline withe the pinion shaft on the rear axle. If you mean the angle of the pinion is directly on the same angle to the transmission or transfer case as the driveshaft, that is WRONG and the result can be a pretty bad vibration! There has to be an offset in those two angles for the driveline to work correctly with each other.

As for the possible miss or problem inside the engine if the engine is popping through the exhaust or surging badly in neutral it could be a few things. One, obviously tune, too tight of valve adjustment on one or more exhaust valves, intermittent spark to a cylinder or two , or three an exhaust gasket leak.
I seen bad distributor caps and rotors do this crazy miss too. Try a replacement cap and rotor and see what that does.

Just some thoughts to look at. Don't want you jumping off the top of anything tall for resolution! You'll find the gremlins, don't get to frustrated just breath in and out real slow! :)
I didn't say in line, I said the angles need to be checked.

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Re: Rpm related vibration

Post by Newold1 » Tue Feb 13, 2018 7:16 pm

Belgian1979 , I was not commenting on your post but the OP's last post where he describes his pinon shaft alignment with the drive shaft.

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Re: Rpm related vibration

Post by Circlotron » Tue Feb 13, 2018 9:23 pm

pjc360 wrote:
Sat Feb 10, 2018 4:03 pm
The transmission shop that did my transmission made a couple stupid mistakes that cause them to have to pull and install the transmission a couple of times before everything was straightened out and it was good to go.
pjc360 wrote:
Sun Feb 11, 2018 6:17 pm
This engine was at one point in a different truck, and it never had vibration issues in that truck.
Seeing that transmission shop has already made several stupid mistakes, I'd check and see if they put the correct length bolts back in the rear transmission mount. A friend had this issue once where he put long bolts in and touched all the way through to the other side of the mount and effectively provided a solid metal path across the rubber block to the cross member. Very difficult to track down and much face-palming when it was all over.

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Re: Rpm related vibration

Post by pjc360 » Wed Feb 14, 2018 8:55 pm

Thanks for the idea’s and suggestions guys.
First of all I am running a Constant velocity rear shaft.
It doesnt operate the same way a conventional 2 joint driveshaft operates.
With a cv shaft you want the pinion directly inline with the shaft at cruising speed for the cv head assembly to function correctly.
But I know this isn’t drivetrain related because this vibration has nothing to do with speed, it’s an rpm dependent vibration.
For example I’m running 4.56 gears and 33.12.50/15 tires in the truck, when I’m going down the highway in 3rd gear at 55 mph I’m turning roughly 2400 rpm, and it will be vibrating to beat hell the second I shift into overdrive (4th) gear the vibration goes away even though I am still maintaining the same speed of 55mph.
The reason it goes away is cause the rpm drops and I am no longer spinning the engine at 2500 rpm, more like 1800-2000 rpm in overdrive at 55mph.
It’s easy to think ignition right away but I just don’t see how it could be ignition when every single piece of the ignition is brand new with less then 1000 miles of run time on it, new distributor, new distributor cap and rotor, new plugs, new plug wires, new coil, new ignition box.
Trigger wires and coil wires separated from each other on opposite ends of the truck.
Timing has been verified multiple times with multiple lights that are all within 1/2 of a degree of each other.
Timing mark on balancer has been verified with a piston stop, the mark in the balancer is accurate.
I’m beginning to think this is an iternal issue, my guess at the moment is a bad/broken valve spring or a bad rocker rocker arm or push rod or maybe even a valve.
But what’s throwing me off is when I do a compression test with the engine fully warmed up I get 155psi on every cylinder.
If it was a valve I would think the compression test would reveal it, but I have heard a bad or broken valve spring can sometimes hide from a compression test because sometimes the issue isn’t until a certain rpm or vacuum.
So my next move is to find someone that has an engine analyzer or a sun machine that can monitor the ignition and the firing events at 2500 rpm where I’m having the issue and have them do a power balance test on it to see if there is a problem cylinder and if there is to find out which one.
Cause I’m tired of trying to guess what this is, I want to know exactly what it is so I can finally fix it.
I’ve been chasing this for a very long time and I’m just over it.
For the longest time I thought it was drivetrain, and because of that my entire drivetrain consists of brand new systems right down to the axleshafts and wheel bearings and driveshafts and brand new gears.
It wasn’t till a few months back I realized it had nothing to do with speed and everything to do with rpm.
At least if everything checks out on an engine analyzer then I can stop wondering if it’s ifnition or engine related and dive right into the converter and flex plate which I have t been able to completely rule out yet but I don’t think it is an imbalance issue cause at idle and below 2500 rpm it’s smooth as glass.
If it was an imbalance issue you’d think I’d be feeling it all over not just at certain rpm’s.

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Re: Rpm related vibration

Post by ozyfordman » Wed Feb 14, 2018 9:22 pm

I had a bad convertor on a Powerglide a couple of years ago. It only vibrated at 1900RPM. Everywhere else it was smooth. I undid the bolts holding the convertor to the flexplate and tied the covertor back with wire. I then ran the motor at 1900 and the vibration was gone. I clocked the convertor to all three positions, reattached it and did the same test, each time the vibration was there. I ordered a new convertor and the problem went away. Try disconnecting and tieing back the convertor and see if the vibration goes away. This won`t cost anything to try but a little time and sweat. Good luck.

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Re: Rpm related vibration

Post by MadBill » Wed Feb 14, 2018 9:31 pm

pjc360 wrote:
Wed Feb 14, 2018 8:55 pm
...With a cv shaft you want the pinion directly inline with the shaft at cruising speed for the cv head assembly to function correctly....
Sorry for the hi-jack, but is this a factory set up? Reason I ask is that although you would need zero angle in the front U-joint in order to play well with a CV rear, zero angle in a needle bearing U-joint usually means early joint death due to brinelling (technically, false brinelling). 40 years ago I was almost brained by a ski boat driveshaft after a joint failed due to being set up with no angle whatsoever, resulting in breakage after only a few hours running..
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Rpm related vibration

Post by BB70 » Wed Feb 14, 2018 9:34 pm

In my post above I advised to hold the rpms at 2500 and remove one plug wire at a time. When the plug wire is removed , note the rpm drop for each cylinder. They should all drop aproxx the same rpm. The one that barely drops is a cylinder that needs looked at. That test is called a power balance test. You said it pops in the exh at that rpm, if it stops popping when a plug wire is removed that is your problem cylinder. Just because you have new parts on doesn't mean anything. Good luck and be careful .

John

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Re: Rpm related vibration

Post by 4sfed » Wed Feb 14, 2018 11:43 pm

pjc360 wrote:
Wed Feb 14, 2018 8:55 pm
Thanks for the idea’s and suggestions guys.
First of all I am running a Constant velocity rear shaft.
It doesnt operate the same way a conventional 2 joint driveshaft operates.
With a cv shaft you want the pinion directly inline with the shaft at cruising speed for the cv head assembly to function correctly.
This is not correct. Unless there is some movement in the joint to move the grease around, the balls will not be lubricated and the bearing surfaces will be damaged. Two to three degrees is enough.
I know this isn’t drivetrain related because this vibration has nothing to do with speed, it’s an rpm dependent vibration.
Agreed.

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Re: Rpm related vibration

Post by modok » Wed Feb 14, 2018 11:57 pm

Exhaust?
Does it have some kind if.... straight pipes and glaspacks?
Timing chain?
Sloppy distributor gear?

Lot of things....one part on the engine can resonate, and UPSET some other part.
Glen Urban

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Re: Rpm related vibration

Post by pjc360 » Thu Feb 15, 2018 8:22 pm

4sfed wrote:
Wed Feb 14, 2018 11:43 pm
pjc360 wrote:
Wed Feb 14, 2018 8:55 pm
Thanks for the idea’s and suggestions guys.
First of all I am running a Constant velocity rear shaft.
It doesnt operate the same way a conventional 2 joint driveshaft operates.
With a cv shaft you want the pinion directly inline with the shaft at cruising speed for the cv head assembly to function correctly.
This is not correct. Unless there is some movement in the joint to move the grease around, the balls will not be lubricated and the bearing surfaces will be damaged. Two to three degrees is enough.
I know this isn’t drivetrain related because this vibration has nothing to do with speed, it’s an rpm dependent vibration.
Agreed.
Read this, this explains setting up the pinion angle with s cv shaft, you have to take in account a little bit of axle wrap while driving.
So the needles will have move inside the u-joint cap.
http://www.pirate4x4.com/tech/billavist ... ndex2.html

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