!?$!?$?! Vibration!

[Kaegi]

how are the plugs? I had a similar issues when it got warm would start shaking and barely lost a bit of power. it was the Chumpion plugs I had in there. 1 and 6 couldn't handle the slight lean condition at highway speeds and they were failing. eventually they centers melted out of them. Went right back to autolites of course. no more Chumpons for me. except chumpion does make good really high end plugs. their cheapos are the worst tho.

[RMS]

im still thinking this vibration in a the given rpm range is due to timing. it may not be related to base timing but to mechanical advance. I have not used a dial type timing light to see where the advance starts and when its all in, but I do know that there is a ruff zone ( on the 251s ) between 37mph and 45mph. this ruff zone is more pronounced with more advance. this ruff zone on a 230 could be at higher rpms due to the decreased dwell @ tdc because of the rod ratio of 1.68 to 1 vs the 1.75 to 1 on the 251 (is the timing curve the same between the dizzys ?).

it would be interesting to see if changing the tension of the secondary spring in the dizzy would alter the rpm range were the vibration is felt. if the vibration changes maybe a re curve of the distributor is in order ?

[ashyers]

Travis,
The mounts are new.

Kaegi,
The plugs crossed my mind. They look OK, but who knows. I pulled them after playing on the dyno and none had any signs of issues. I will say that last set of "Autolites" I purchased were reboxed Champions. I think Autolite stopped making the plugs and just sells reboxed plugs. It would be interesting to see what others have found. I purchased from O'rielly's. They carry the plugs in the industrial section.

RMS,
If memory serves I'm running 22 deg all in. This works out to 4 deg initial. The manual suggests 18-22deg at 2250 RPM. I have not seen what the intended curve is, but I suspect it's in one of the manuals dedicated to the military dizzy's, unfortunately I don't have one . I do have a Sun machine so recurving the dizzy is not an issue, in fact I'm building a spare now.

What I can do is monkey with the initial, run up to the troubled RPM (2500-2700) and see if it cures the vibration, then record the timing and recurve from there. I should be working on the truck again soon, been busy getting the autocross car back on the road after a 2 year hibernation...

Thanks All,
Happy New Year!!!!

[Kaegi]

as far as I know autolite and chumpion are still different companies. the champions are plated and the autolites are not plated but have a copper core that doesn't melt like a chumpion. I would be shocked to find champions in an autolite box. just bought a set recently and they were autolites in the box

[RMS]

any luck sorting out the vibration ?

it was suggested to me from a few old timers that vibration at higher rpm on the Chrysler flat head is due to the absents of oil groves on the bearings....something to do with the oil holes lining up at certain rpms creating sonic resonance as the oil presser flutters ???? I was told that cutting an oil grove in the center of the bearing will create an even flow and reduce the flutter and vibration.

sound good in theory but in the real world ? any validity to this ?

[ashyers]

RMS,
Some work, but no real progress. Since last post here's what we've done:
* verified the resonance is engine driven and buzzes the steering wheel most effectively at 2500 RPM
* swapped the belt due to a bit of delamination (1.5 year old Dayton B52, make in China )
* run w/o the belt, quiet and nice, but no real change
* run w/ the motor mounts loose, no change
* run with the steering column bkt. loose, no change
* checked torque of all steering mtg. hdw., no change
* checked torque of all body mtg. hdw., no change
* ran engine on dyno to verify power/torque, it's the same as it was 1.5 years ago, 50 HP @ 3000 RPM BABY!!!
* checked timing 23 deg @ 3000, 22 deg @ 2250 per spec.

If I get some time today I may reduce the timing to the low end of the spec which is 4 deg retarded from where it is, but I don't expect a change.

At this point I'm about out of ideas. The engine's performance is consistent and shows no signs of decaying over the last 5000 miles. I'm not sure what's driving the buzz in the steering column!

I have my doubts that full grooved main bearings would cure this... I guess it's possible, but if the crank is flexing around so much that a full grooved bearing helps to smooth it out I suspect that sucker would snap pretty darn fast from fatigue, plus there's little chance of it supporting an oil wedge if it's that flexible. Who knows?

We're going to pull the transmission soon, so we'll root around a bit and see what we can find.

Andy

[Elwood]

Andy, you may have already posted the answer to this question and I missed it, but what is the history of this engine? Have you had it apart at some point? Do you know if the internals have ever been balanced?

Chrysler flatheads are not known for being especially well balanced from the factory, so perhaps you have some sort of internal combination of pistons, rods, and crank that is causing an harmonic in certain RPM ranges?

[Kaegi]

I would pull trans and start it and check, if still vibrates pull pressure plate and disk and check again. maybe a spring broke in thepressure plate and threw assembly out of balance? or maybe a welded weight flew off p plate? disk centers fail on rebuilt disk sometimes causing issues. usually just cause noise tho not vibration

[ashyers]

Elwood,
We don't know the history on the engine. The pan was pulled when we started working on the truck and it actually looked great inside, which was a nice surprise after the differentials! We did not pull the bearings because the oil pressure is OK. The vibration is a recent development.

Kaegi,
We need to pull the trans because it bleeds a bit too much and I'd like to give the guts a look over. While we're at it we'll check the clutch assembly and pressure plate. I may see if I can have the balance checked.

This is kind of like a splinter...

Andy

[ashyers]

Since we pulled the transmission off the other day I checked for the vibe with no pressure plate/clutch. There was no change.

I also measured the end play of the crankshaft. It measured .014" which is beyond the wear limit of .010" and well beyond the new spec of .003"-.007" recommended in the TM.

This concerns me, but lacking much experience in these motors, I'm not sure if it's time to yank things apart. Oil pressure is fine and performance is normal.

Thoughts?

Andy

[w30bob]

Hi Andy,

I just read this thread..........very interesting (and frustrating). Do you guys have a Tri-Axial vibe pickup you can mount to the engine or steering column? It would be good to know if the vibe is happening at once per rev or every other. Understanding the vibe profile might help point you in the right direction.

regards,
bob

[ashyers]

Bob,
No vibe pick up, but if you could recommend a tool I might pick one up. I've heard the electronic ears may be useful for this too.

I'm thinking this may be originating in the bottom end and it just happens to be on a frequency the steering shaft sings at.

At the moment the excess end play in the crank has me concerned. I don't know if it's related to the vibration, but I'm contemplating pulling the pan and inspecting the bearings. I'm not committed to rebuilding the spare engine due to $ right now so I want to make sure I don't hurt the one in the truck.

Andy

[Elwood]

The excessive endplay is reason enough to drop the pan and take a closer look. Combined with the vibration, that engine is telling you that something is not right.

[w30bob]

Hi Andy,

I'm with Elwood on this one. Regardless of the vibration, you need to pull the pan and see why you have excess endplay. Normally excess endplay would manifest itself as a single noise every time you let the clutch out (and drove the crank into the thrust surface of the bearing). For it to cause a vibration the crank would have to move enough to let something else start making contact with another part of the engine. I don't see how this would be RPM dependent......but my vision sucks. The bad news is that excessive endplay ends up putting extra stress on the rods, timing chain, etc....so even if the endplay isn't causing the vibration you might want to consider putting in some new bearings (if the old thrust surface is worn. If the crank was just machined wrong I'm not sure how they correct that.

Pulling the pan and rotating the engine (with and without thrust applied to the crank) will at the least give you some piece of mind. I don't know which main bearing takes thrust in the flathead 6, but that would be the surface to get a good look at. When cranks are machined many folks don't think twice about the surface finish on the thrust face of the journal......but that surface has to be smooth as a baby's ass, with no grinder marks showing, to keep the thrust bearing alive. Any grinder marks will act like a windshield wiper (I wanted to say sqwee-gee....but I don't know how to spell skwee-gee) and remove the oil from the thrust face.

Oh.....I forgot to respond regarding the tri-ax. If I can get over to our test cells today I'll find out the name/model etc of the ones we use. I think now-a-days they're affordable, but I'll check.

PS.......can someone please tell me how to spell "skweegie"?

regards,
bob

[Elwood]

<snip> I don't know which main bearing takes thrust in the flathead 6, but that would be the surface to get a good look at. When cranks are machined many folks don't think twice about the surface finish on the thrust face of the journal......but that surface has to be smooth as a baby's ass, with no grinder marks showing, to keep the thrust bearing alive. Any grinder marks will act like a windshield wiper (I wanted to say sqwee-gee....but I don't know how to spell skwee-gee) and remove the oil from the thrust face.

Bob, the rear main bearing also controls crankshaft endplay. Not only must the thrust faces be machined correctly, but the radius from the thrust faces to the bearing face must be correct.

Perhaps an excessive amount of endplay could allow some sort of harmonic in the crankshaft. I'm not familiar enough with small block Dodge/Plymouth flathead sixes to know how flexible the crankshafts are.

RMS' description of the oil groove thing might have some merit if the excess endplay is allowing the crank to move enough to affect oil flow through the crank bearings?

PS.......can someone please tell me how to spell "skweegie"?

"Squeegee"