creaking noise with new damper plate

[P69]

All right ya'll, here is a puzzle that is baffling me.

I've hit a roadblock in my brain with my engine.

It's a Universal 5444 (4cyl diesel) that it's about 32 years  old with reportedly 1900 hours (1982, 367 hull #42). I just got done rebuilding the engine  (I stripped it down to block and head, sent that to machine shop to deal with pistons, honing, valves, etc..). I then reassembled it and it runs (surprised the hell out of me, but it runs).  It runs smooth, shuts off quick and starts within a second. I am really impressed with its behavior. I thought there was nothing wrong with the old engine, but I sure was wrong. I guess if you don't know something is wrong, you don't know it's wrong.

The only problem is a creaking noise emanating from somewhere in the bell housing area of the engine.  The noise also has a corresponding vibration that can be felt in many parts of the engine: crankshaft, transmission, exhaust riser, raw water hoses, and many other areas, except the larger metal chunks like the block and head. It kinda sounds like the creaking a rubber impeller makes when it's dry.

While reassembling the engine, I turned it by hand and never heard the noise, which did not appear until after first run of the engine (last Saturday). Noise and vibration cannot be heard or felt when engine is running because of all the other noise/vibration sources. That doesn't mean it is not present, just that I can't perceive it over the other racket that the engine makes.  As engine shuts off, vibration can be felt momentarily.

Noise is very apparent when hand cranking the crankshaft. It does no matter if transmission is in fwd, rev. or neutral.
It does not matter if the decompression lever is on or off

I removed the bell housing (to which the transmission is bolted) and the noise was not apparent.

I put the bell housing back on (with transmission) and loosely fitted it (about 1/4" gap between bell housing and block mating surfaces): no noise

I tightened the bell housing bolts and as the bolts closed the gap to about skinny a 1/4 to 1/8", the noise became  apparent.

The noise is related to how close the bell housing is to the block. When the bell housing is completely mated to the block, the noise is readily apparent.

The damper plate is new (old one exists, but rattles a bunch). 

I put the old damper plate on and there was no noise, even with bell housing firmly bolted to the block.

Another important note is that with the new damper plate, I could put the bell housing on up until about a skinny 1/4" gap, then I had to use the bolts to close the gap.

With the old damper plate, I could close the gap without any bolts, just as if there were no damper plate. It just slaps up right against the block

The damper plates have the same part number, they should be identical.
The new damper plate is much quieter than the old one (except for the creaking noise)

1. What is the relationship between the nose and the new damper plate?
2. Is there a break-in period for damper plates, during which they will make this creaking noise?
3. WTF?

Thanks for helping me out on this one.

I cross-posted to cruisersforum
http://www.cruisersforum.com/forums/f54/creaking-noise-with-new-damper-plate-169035.html

Link to page that has pictures and a video of me cranking the shaft and hearing the noise:
http://www.bodylens.com/engine

Edit:  One possibly important observation is that when I turn one direction (clockwise) the noise is present, then when I turn counter-clockwise, the noise is absent for about a 1/4 turn, then resumes.

[S/V Deo Volente]

Well it seems you have proven there is a clearance problem with the new damper. I suggest taking some measurements with a caliper. I wonder if the input shaft of the transmission is bottoming out in the damper plate.

[P69]

 I found the problem. 

I removed the housing and compared the distance that the damper plates travel along the gearbox input shaft and the new one bottoms out about a thick 1/16" before the  old one.

In other words, the new one travels down the spline ~0.48" and the old one travels down ~0.53". That's a approximate difference, errors exist in cheap calipers and the fact that I gently slid each plate down the shaft until I felt slight resistance. If I pushed to hard, the metal would bind and make it very difficult to remove.

I then compared the part of the damper plate that bottoms out on the gearbox end and saw that the old one appears to have been modified slightly. The face of the damper plate spline ( the collar that has the grooves in it that mate with the gearbox input shaft) is flat on the new plate, but the old one is concave. Looks like someone took a large counter sink and machined out a slightly concave shape (inward bevel), allowing that old plate to travel farther down the gearbox input shaft.

Not sure if this concave shape is part of that design of that old plate or a modification. Either way, I'm going to have a machine shop countersink the new one a bit so it will travel all the way down as far as the old one.

[P69]

In all my excitement about figuring this out, I forgot to tell ya'll what was actually causing the creaking noise: rear thrust bearing. Because the damper plate did not travel all the way to the gear box, when I bolted the whole bellhousing/gear box assembly onto the engine, it pushed inwards (forwards) on the flywheel, which then put fwd pressure on the rear thrust bearing inside the crank case, causing the thrust bearing to make the noise. I checked the oil pan today and found no metal, so I think it's not too bad off. I only ran it for about 45 to 60 minutes total (few minutes, here, few minutes there, etc...).

Interestingly, a guy over at orangetractortalks.com nailed it a few days ago when he watched that short video of my turning the crankshaft by hand. Neither one of us was sure why the thrust bearing would make such a noise until I removed the bell housing and slowly bolted it back onto the engine, testing after each couple of millimeters until I heard the noise. I feel really fortunate that it's a kubota-based engine and that the folks at orangetractortalks.com are really smart and nice.

Machine shop that did the internal rebuild thought it was a loose nut or bolt and I had no idea. I'm just glad it's solved and that there are no metal fragments or dust in the pan.

Now I can put it back together, stick it back in the boat and put a load on it to seat the rings.

[S/V Deo Volente]

That's great, I wonder if Universal modified those originally, or it could be a manufacturing issue with the new one.
Maybe they missed that recess when determining compatibility.

[P69]

Well, looks like I was wrong in my assessment of the cause of the resistance. I wish I were smarter. I feel so defeated.  A weeks worth of anguish and a few gallons of sweat trying to figure out what I did wrong.

Turns out it was much simpler: the damper plate is warped!
I discovered this when I put the damper plate on the gearbox input spline (instead of bolted to the flywheel), then set the whole gearbox/bell housing in place. It fit  perfectly against the engine with no gaps or resistance, just like the old one.

Next, I loosely bolted the damper plate to the flywheel. Again, easy fit of the bell housing. Snug tightening of the damper plate bolts resulted in skewed center axis of the damper plate, causing the gearbox input spline to not slide all the way in. Hardly noticeable, but it made a big difference!

Removed it all and put a straight edge across the back plane of the damper plate to discover that it's warped by nearly 2 mm!

Now, I have to wait for RMA/replacement-by-mail cycle and hope the replacement is not warped.

Oh well.  Thanks for ya'lls help.