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6.5L Vibrations, any ideas what it can be?

The harmonic balancer, the flex plate (or flywheel if manual trans) the crankshaft:
All mass produced with the attempt to all be made the same so the unbalance of the crankshaft is counter acted by the flex plate and harmonic balancer.
You remove one flex plate and install another - you don’t remove or add weights.

Now, because of mass production inconsistencies and the tolerances allowed for that issue- you can get a really bad engine or a really good one by simply luck of the draw.
The more balanced it is, the more efficiently the engine will run and the smoother it runs.
This is why when someone is building an engine and trying to make good improvements on mass production errors or tolerances- they have the lower rotating assembly balanced. The rpm it is balanced at can even be tuned- like say your engine will run at 2400 rpm while you cruise the hiway- you can specify that to the machinist and he will make sure that rpm is the best point for lowest vibration. This is ancillary to this issue the original poster brought up, and should not be the issue.
Something could have been assembled wrong inside the engine- or he has a serious flexplate/balancer/pulley issue.

@Scott_2255 have you done anything, learned anything yet?
 
That wobble in the flex plate from his video he posted is really pointing at a bad flex plate as the cause of his vibration issues. It's been a while since @Scott_2255 last posted, hopefully he's had a chance to do the work he said he would and get the tranny dropped to pull the flex plate and examine it and we can get some sort of update from him shortly.
 
I wonder if @Scott_2255 could manually straighten his flexplate with a prybar while rotating and correcting it to see what happens. Just curious as to why you would get warpage on a flexplate in the first place? Of course, if it is cracked, nothing would help. I would be inclined to rotate and hold a straight edge to it and "try" bring it back into shape with a bar. If it was never "warped" but hurt instead during installation, it may be correctable and diagnosable. If you start after straightening, you know that isn't the problem if the vibration is still occuring. In all his videos including the higher speed you can see the in and out movement. If wobble remains, flexplate wobble is random and it must be changing positions during rotation of the part. Obviously tying the converter to it should elimate the wobble (horizontal component). Strictly speaking unless mass moment is changing with each rotation, there must be loose metal walking around the circumference. One would think that should not occur when rigidly attached to the converter. I assume due to dowelling, the flexplate only can attach with counterweight facing torque converter?
 
MrMarty51 said:
Maybe flex plate installed backside forwards 🤷‍
Dont know if it could happen on these engines.
If so, that could cause some out of conformity 🤷‍♂️
Click to expand...
That is what I was thinking too. that also would throw the balance off some. the weight would still be in the general area, maybe about 15-20 deg off. might be enough to cause a vibration that would alarm a fella but so so much to cause an auto self destruct on first start up.
 
But how does installed "wrong side out" (if at all possible) account for the very noticeable wobble in the edge of the flexplate we saw in his video, let alone how that would affect the starter pinion gear to ring gear engagement enmeshment depth when he engaged the starter or how it would affect disengagement of the pinion when it started and he let off the key?

I'm still leaning toward a bent/warped flexplate or a crack in the center/arm of the flexplate accounting for the vibration.

Of course, we won't know anything until @Scott_2255 gets back on here with what he found after dropping the transmission to see why the flexplate has that wobble.
 
I wish I hadn't tossed my old flex plate when I replaced it. I have that 6.2 on the stand I could have a looksee if it would even be possible to install backwards. other than that, it would be ether bent or cracked. it could have taken the damage before Scott received it and possible even be missing the added weight from the damage which would also explain the vibration too.
 
Husker6.5 said:
But how does installed "wrong side out" (if at all possible) account for the very noticeable wobble in the edge of the flexplate we saw in his video, let alone how that would affect the starter pinion gear to ring gear engagement enmeshment depth when he engaged the starter or how it would affect disengagement of the pinion when it started and he let off the key?

I'm still leaning toward a bent/warped flexplate or a crack in the center/arm of the flexplate accounting for the vibration.

Of course, we won't know anything until @Scott_2255 gets back on here with what he found after dropping the transmission to see why the flexplate has that wobble.
Click to expand...
If the flexplate has that ever so slight of a ridge around the center cranking shaft hole like some FPs I have seen, then tightening down the bolts would cause the FP to sort of tweak off and not run true.
But still be close enough to centerline for the starter to take a holt.
Many years ago, a friend stopped over, had a vibration after installing the used transmission in his car. FP was wobbling. I didnt get involved but asked him if he installed it bassakwards. He pulled trans, and, Yup.
I dont remember what brand a vehicle it was.
 
Studebakers with automatic transmissions were like that @MrMarty51. When I was helping dad to reassemble a car during restoration, he told me to always remember flat to flat when putting a flexplate on the crank flange and everything will run true. There was a slight bead around the center hole of the flexplate - I don't know if it was there to relieve stress, to strengthen the center hub, or was just the result of being stampped out on a press - but as long as that bead was staring at me, I knew it was on right.
 
Allfritz123 said:
I looked at my flexplate. It looks like it is impossible to mount incorrectly. The counterweight actually faces the engine block and the dowell insures that it only fits one way. Forgot to mention this is a 6.2 but assume 6.5 is no different!
View attachment 80117
Click to expand...
That FP in the pic; is the engine out and the FP removed ?
If it is, if You have the means to mount it up and spin it and see whats up with it.
 
Allfritz123 said:
I am not sure what that would do for me! It is @Scott_2255 that has the problems. I could lay this FP on a flat surface and I don't see any issues with mine.
Click to expand...
I think he thought you were the op. Btw, people often install the flexplate backwards. It will bolt up but depending how bad the curl is from stamping the center hole they will go on part way to all the way. Sometimes go on slightly crooked, rubbing issue can occur, starter alignment issues can occur. Often this breaks the flex plate if operated this way.

I have also seen one that a guy put in backwards and put 40,000 miles on. He never noticed anything because he bought it a basket case and everything sounded loud and rattling to him so he thought it normal. That was kind of a fun one because he came in for it smoking- had 180, 000 miles on it and i put in a new set of injectors- I taught the guys at the shop how to balance them with his set so it smoothed the engine nicely- and fixing his flexplate rub- then his outside balancer ring was spun- so replaced balancer and pulley. The truck noise cut more than in half and ran very smooth. The guy was beside himself- swore we swapped in a new engine. Haha.
 
Does that mean the 6.5 crank end is different than the 6.2 that I took a picture of? I could hardly see how you could ever misalign the dowel! While the FP might bolt on an angle, I think the bolts would be too short to catch and it should be obvious that you are not installing it in correct position - especially if you took it apart! Are you suggesting the dowel pin gets ejected back with incorrect position as FP metal knocks it back and so was missed for location? I guess you could hammer the pin in and or take a cutting wheel and cut it off. I wouldn't think anyone would do that as you would be a pretty crude engine rebuilder! I could hardly fathom someone would use this as a solution without realizing they have a problem.

I will look at a 6.5 that I have on a pallet and see if it has a dowel. I thought 6.5 and 6.2 were the same cranks others than the rear seal makeup.
 
do all 6.2/6.5's have the dowel pin on the crank? Honestly, I don't remember if mine had one or not when I replaced the FP. I can look at the 6.2 that's on the stand ether tonight or tomorrow (working late today)

@SnowDrift might be able to answer this question as he has been working on replacing his and iirc was talking about a forged crank for his build
 
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