Bought another non-running 802a, begins to start, then falls off (Now an excessive vibration fix up thread) (SOLVED)

[Digger556]

After starting reassembling and starting this unit up, I through a load on it. The unit was very shaky for a 802a, even after I tighten some loose isolator bolts. The unit could pull 6000 watts and seemed to be running fine, but anything over 3000 watts and the overload fault would trip after a minute or so. On the suggestion of a few members, I bought some Deoxit and hosed the S6 and S8 and exercised them thoroughly. I haven't retested it yet because the vibration issue really needs to be addressed. I fired up my other 802a for comparison and this one is much worse, so something is going on.

Since this unit had major oil pressure issues due to a stuck relief valve, I pulled the valve covers and inspected the push rods for bending per the TM. All looked good, so I reassembled the unit per the book procedure, waiting 90 minutes before hand turning the engine and restarting it. I also pulled the back cover of the genhead and look for a loose bearing. All looked good there. I also made sure the IPs were rotated to the same position, fully counterclockwise. It's worth mentioning that it seems to run good, pulls a full load, and the exhaust manifold is nice and dry with minimum soot buildup.

The front of the engine / genhead combo moves considerably more on its isolators then the rear. I've been thinking about what Guyfang has mentioned in several threads about the isolators, especially since the forward ones were missing hardware like someone had been messing with them. I'll look for part numbers tomorrow when the light is better, but here is some slow motion video of both. It doesn't look good.

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What do you all think?

 

[Guyfang]

Way too much motion.

 

[Digger556]

Way too much motion.

That's an understatement. It makes my other 802a look like an 803a.

I will try swapping isolatators from another 802 to start with and hope that is the issue, otherwise it is likely the genhead and engine need to be separated.

 

[Guyfang]

There is one other possability. When you have the isolatators out, see if they have a part number on them. Check that against the -24P. If someone put MEP-803 isolatators in the set, that could be the problem. The 802A has a much stiffer isolatater.

 

[Digger556]

There is one other possability. When you have the isolatators out, see if they have a part number on them. Check that against the -24P. If someone put MEP-803 isolatators in the set, that could be the problem. The 802A has a much stiffer isolatater.

Well, no luck here.

The paint shaker shows 88-21070-1 isolators, which crossreference correctly with-24P part number (88-21070-3)


My 803a uses 88-21070-2 isolators. The -24P calls out 88-21070-4, which I can't cross-reference, but the convention follows similar to the 802 isolators.

 

[Digger556]

Looking at the wear pattern in the skid base and broken weld in the left battery area, this unit has been shaking hard for a long time.

 

[Digger556]

At this point, it seems like I need to separate the engine and genhead to verify proper assembly and/rotate their relative positions.

For those that have done this, is it possible to separate the two in the enclosure just enough to unbolt the genhead from the flywheel and re-index them to each other? (Rotate the rotor 90° relative to the crankshaft? Or am I stuck disassembling the majority of the enclosure?

 

[Digger556]

At this point, it seems like I need to separate the engine and genhead to verify proper assembly and/rotate their relative positions.

For those that have done this, is it possible to separate the two in the enclosure just enough to unbolt the genhead from the flywheel and re-index them to each other? (Rotate the rotor 90° relative to the crankshaft? Or am I stuck disassembling the majority of the enclosure?

Went ahead and disassembled the genhead in place by removing the rear sheetmetal and sliding the housing and stator out the back after supporting the engine.


The rotor looked visibly off center when observing the gaps between rotor poles and the stator laminations.




I placed a dial indicator on the rear bearing and measured .021" of total indicated runout (TIR)

 

[Digger556]

I pulled the rotor out and set it up on the lathe between centers to measure runout. Axial runout on the adapter plate was .006", measure mid-radius.


Since the adapter is sheet metal and not necessarily true, I removed it and the support bearing and remeasured axial runout on the rotor's mounting flange and came up with .002" TIR. To help eliminate any contribution to the problem, I made a skim cut to square the pilot bore and mounting flange. You can see the runout on the partially machined face.

 

[Digger556]

With the rotor out, I measured axial runout on flywheel face and didn't see anything out of the ordinary.

Reassembling the rotor onto the flywheel, I remeasured runout at the end of the shaft and was still getting at least .020".

I called it a night, but tomorrow I plan to remove tbe rotor and measure radial and axial runout of the adapter when installed on the flywheel to determine what demon I'm fighting here.

 

[Digger556]

The mystery deepens...


I measured flywheel runout again from a more consistent point on the engine block. Found a low spot measuring .010". Pulled the flywheel and found out its about 1/8th inch too big to fit in the lathe. The crank bolts were not fully tight and the mating face of the crank has a few rough spots, so this could be a contributing factor.


I setup my rotary table and measured baseline radial and axial runout. (0.000" axial, 0.0005" radial)


Leveling the flywheel, I found a high spot about .004" in a different location from before. Radial runout was basically zero, so that's some good news.



Tomorrow I'll clean up the crank face, measure runout there and then look at the adapter plate again.

 

[Digger556]

Reviving this thread:



I pulled this thing apart last year and measured considerable runout at the end of the rotor shaft. Some was flexing of the [35] plate, but I fully disassembled the whole rotor, adapter plate and flywheel, measuring excessive runout on each interface. I've designed and machined crank adapters in the past for custom engine applications and typically aim for less than .0005" runout, so seeing .009" TIR on the end of rotor was shocking.

I spun up all the parts in the mill or lathe and squared all the interfaces, then bolted the adapter plate to the flywheel and squared them as a matched unit, then installed a new bearing and torqued all the bolts to spec per the TM. Crank to flywheel runout was <.0005" and the end of rotor was now .001".
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After reassembly, vibration was noticeably reduced, but still was shaking a bit more than normal. Taking some high speed video of the engine, the isolator displacement looked normal, so it's still a bit of a mystery. I did confirm I have the right isolators by P/N, checking the TM and other 802s.

 

[Digger556]

VIBRATION PROBLEM SOLVED!

I had made myself a list of things to try from pop-testing the injectors, to swapping the isolators, to changing the engine out with a spare.

While pulling the engine isolators, I noticed it was harder to lift the left side of the engine enough to free the isolator, and in doing so, noticed the isolators were not evenly loaded. I did a bunch of measuring, shimming, and more measuring to make sure they were loaded evenly. Re-running the genset, it now has a normal level of vibration, problem solved. So if you can't seem to figure out why your set shakes too much, verify the engine mounts are level to each other and loaded evenly. In this case, the difference was only .060" between mount heights.

I made a video to help explain what I saw. Hopefully this can help someone else out in the future.

 

[2Pbfeet]

VIBRATION PROBLEM SOLVED!

I had made myself a list of things to try from pop-testing the injectors, to swapping the isolators, to changing the engine out with a spare.

While pulling the engine isolators, I noticed it was harder to lift the left side of the engine enough to free the isolator, and in doing so, noticed the isolators were not evenly loaded. I did a bunch of measuring, shimming, and more measuring to make sure they were loaded evenly. Re-running the genset, it now has a normal level of vibration, problem solved. So if you can't seem to figure out why your set shakes too much, verify the engine mounts are level to each other and loaded evenly. In this case, the difference was only .060" between mount heights.

I made a video to help explain what I saw. Hopefully this can help someone else out in the future.

I really liked your video and the analysis of your vibration issue. I found it very informative. I do not know that I would have thought of a height difference in the mounts being an underlying cause of a vibration issue, but now that you have pointed it out, "Duh!", I can see how a lack of equal compression due to a lack of coplanarity would make vibration worse as only one diagonal would be effectively damping vibration. Fascinating!

Thanks for sharing and making the video. I enjoyed seeing your machining efforts and the improved results.

All the best,

2Pbfeet

 

[Digger556]

I really liked your video and the analysis of your vibration issue. I found it very informative. I do not know that I would have thought of a height difference in the mounts being an underlying cause of a vibration issue, but now that you have pointed it out, "Duh!", I can see how a lack of equal compression due to a lack of coplanarity would make vibration worse as only one diagonal would be effectively damping vibration. Fascinating!

Thanks for sharing and making the video. I enjoyed seeing your machining efforts and the improved results.

All the best,

2Pbfeet

It seems like a flaw in the design to mount the engine/generator assembly on 4 points. Most automotive applications mount on three points to avoid torquing the drivetrain. Generators get away with 4 because the isolators are typically soft enough that small differences in height do not have a significant effect. However, an 802a series engine isolator is relatively stiff, and the genhead isolators are really stiff, so they are no help evening out manufacturing variances in the skid base.

 

[2Pbfeet]

It seems like a flaw in the design to mount the engine/generator assembly on 4 points. Most automotive applications mount on three points to avoid torquing the drivetrain. Generators get away with 4 because the isolators are typically soft enough that small differences in height do not have a significant effect. However, an 802a series engine isolator is relatively stiff, and the genhead isolators are really stiff, so they are no help evening out manufacturing variances in the skid base.

I agree 100%. It does seem like an unusual design / specification choice, but one made repeatedly. So I'm probably missing some important design consideration. Three points alone define a plane; four takes alignment. Losing one of four mounts leaves the load well out of vibrational balance due to the location of the center of mass.

All the best,

2Pbfeet

 

[Guyfang]

It seems like a flaw in the design to mount the engine/generator assembly on 4 points. Most automotive applications mount on three points to avoid torquing the drivetrain. Generators get away with 4 because the isolators are typically soft enough that small differences in height do not have a significant effect. However, an 802a series engine isolator is relatively stiff, and the genhead isolators are really stiff, so they are no help evening out manufacturing variances in the skid base.

There are two different isolators. The original isolators were a problem, and later on, the Army bought different isolators. I dont remember when this happened. My moth eaten brain is saying 2008? But I sure would not bet any money on that. I will see what I can dig up.

 

[Digger556]

It seems like a flaw in the design to mount the engine/generator assembly on 4 points. Most automotive applications mount on three points to avoid torquing the drivetrain. Generators get away with 4 because the isolators are typically soft enough that small differences in height do not have a significant effect. However, an 802a series engine isolator is relatively stiff, and the genhead isolators are really stiff, so they are no help evening out manufacturing variances in the skid base.

There are two different isolators. The original isolators were a problem, and later on, the Army bought different isolators. I dont remember when this happened. My moth eaten brain is saying 2008? But I sure would not bet any money on that. I will see what I can dig up.

That would be great information to have. I did some napkin math and believe the isolators should be softer to reduce transmission of vibration to the skid, but that would likely come with increased vertical motion of the engine, impacting wires and hoses.

 

[2Pbfeet]

That would be great information to have. I did some napkin math and believe the isolators should be softer to reduce transmission of vibration to the skid, but that would likely come with increased vertical motion of the engine, impacting wires and hoses.

I agree a softer isolator set with increased sway is going to be hard on a number of things. That is not to say that the current set is the right stiffness. I've been down that path with a number of pieces of custom equipment, and I think that it is often like the old story of pulling on a thread and the fabric unraveling. I'm not sure that there is a pony in that pile. With a two cylinder diesel, I think that absent a counter rotating shaft, there isn't a lot to be done after checking that the injectors are matched, though of course an engine rebuilder might have fun balancing the crank and pistons. For an 802...?

All the best,

2Pbfeet