Multifuel Rythmic Shudder

[MarcS]

Got a multifuel LDT 465 1D in a M35A2C that has had a rythmic shudder ever since I bought the truck about 20k miles ago. Almost like a pulse every second or half second. Any rpm but really noticable between 1500-2200. Feel it parked or driving so it's not driveline. Excellent oil pressure, no knock hot or cold, runs awesome. In the last year I've rebuilt the heads, injection pump, had the injectors checked out, and today replaced vibration damper. My old damper was bad, the outer ring was seperated from the inner. I had the style with the pulleys and inner one piece. Replaced with the other style where you can change the pulleys. I thought since my old damper was bad that was surely the problem but it still has the same shudder. Maybe try another damper? Timing is spot on as well.

I'm at a loss as to where to go next. The clutch was rebuilt a few years ago and the engine shaked before and after. I did use the same pressure plate, but nothing seemed out of order and nothing was broken so I'm kind of ruling that out.

Maybe I should pull the pan and check out bearings although wouldn't we hear a knock or have bad/erratic oil pressure? Perhaps engine mounts? They don't look bad but maybe it's hard to tell.

Like I said, it's been doing this for a long time but I never worried about it before I run a couple other deuces and they were smooth running.

I hope you guys have some ideas since I've got a 3000 mile trip coming up again and I really don't want to start shedding engine pieces 1000 miles from home.

Marc

 

[StrykerPez]

Air compressor? Could that cause enough vibration if something was wrong with it to feel?

 

[randyscycle]

Possibly a motor mount transmitting some harmonic vibration into the frame?

Bad body mount making it seem like there is more vibration than there really is?

Exhaust contacing the body and/or frame?

 

[ctmustang]

I would also go with the flywheel balance or the engine mount possibly collapsing. Ben working on engines professionally for 24 yrs and can say that it happens once in a while to have a crank-rod or piston slightly out of balance just enough to cause a shudder. GM had a problem some yrs. ago with the 2.8 liter v6. after rebuild and balancing smooooooooth. If its not jarring your eyeteeth i'd drive on!

 

[MarcS]

Ok, if it is the flywheel I can static balance it on a surface grinder wheel balancer (our surface grinders run 20" wheels) But, is that how they balance these engines, one component at a time? Or do they balance as an assembled rotating assembly? Still not understanding why it's a cyclical shudder rather than a constant vibration if it's balance though.

 

[jimmcld]

My guess would be a roller bearing. When the worn bearings get to a worn place on the race, you get the shutter. It could take a second for the rollers to come around to the worn place on the race, maybe?

 

[JasonS]

Could two slightly different vibration frequencies occasionally mix to produce a low frequency shudder? I've experienced it on farm equipment with LOTS of rotating components.

 

[G-Force]

Is it a physical shudder with no change in engine rpm or is it a roll with slight drop in rpm. If it is a roll with slight rpm drop then I would suspect the governor. In other words the governor is hunting for the rpm but cannot stabilize the speed.

 

[Stein12501]

I have a 1971 AmGen and it does the same thing. I've done nothing to the engine but I kinda fell like G-Force I think it is something in the Gov. Under a load it pulls fine, under no-load or running down a grade it shutters and fells like the governor is hunting. Parked with the engine running no-load @ 1000 rpm it shutters. Love to know what it is.

 

[MarcS]

Ok, you might think I'm nuts but I think I've narrowed it down. Tonight I pulled the radiator again (for easy access). Then started it, same shudder/pulse. Took the fan off, same shudder/pulse. Then took the alt. belts off, still shuddering. Took the compressor belt off it smoothed right out, no shudder at all. Put the alt belts and fan on without compressor belt on and still smooth. Put the compressor belt back on and the shudder came back.

So I narrowed it down to the compressor I'm thinking even though it works fine, no endplay, oil leaks, funny noises, etc. But I put a different compressor on anyway and same rythmic shudder (now I'm getting mad). Changed out two piece pulley with no change. Took the belt off again and it smoothed out again.

So I figure maybe I got the wrong belt on so I came on here in the cross reference chart and I've got the exact belt listed, a Napa 25-9510. The belt does whip around a lot when running, do your deuces compressor belts whip too? However, I took a wooden dowel and used it for a tensioner and the shudder was still there.

What the hell is going on? I'm not crazy, I've had two diesel mechanics feel the rythmic shudder and it's there for sure. If there was something going on with the crank how could that single belt make it show up but the two alt belts wouldn't?

You guys are probably writing me off as nuts but if someone could go out and observe how their belt is running I'd be grateful.

 

[MarcS]

One more thing, I'm running the single cylinder compressor, both the old one and the new one.

 

[scooter01922]

You are certainly not nuts, well not any more than the rest of us. Keep up the good work, i'm interested to see what the results are, i too have a bit of a shudder.

 

[G-Force]

Whats your air pressure like?
Disconnect the air line from the compressor and run it.
Maybe the relief valve is stuck.

 

[Stein12501]

As soon as you mention the air compressor belt. Mine seems extremely loose. Replacing the hoses and tightening the compressor belt was first on the list. I will try that on mine and see what happens. Let you know what happens on my end.

 

[williamh]

not just the belt, but if the bolts have wear it will let the compressor jump around.

 

[Mudstone]

we had this exact problem with my M109 when i was stationed in germany. Motorpool NEVER figured it out and we drove the thing a lot... Changed Belts compressors then they replaced something in the lower end of the motor... nothing ever fixed it... is it just perhaps a personality trait of the truck?

 

[bassetdeuce]

Single cylinder compressor, good belt tension, newish dayco, and lots o whip. Shudder? I don't know. My pressure holds steady around 100psi.

 

[MarcS]

Thanks for all the replies. They helped a lot. I haven't figured it out yet and decided I probably won't. It's got new oil in it so I'm using that as an excuse not to pull the pan. I'm afraid I might find something in there I don't want to see anyway... For now I'm just going to run it, probably be fine anyway.

 

[Wildchild467]

I know this is an old thread, but i have the same vibration you guys are talking about and i have a single cylinder compresser also. im wondering if it has to do with the single cylinder compressor spinning a little faster or slower than the engine crankshaft. say the ratio would be like 1:10001 just to throw a random number out there. so when it viberates in and out, its because the harmonics of the engine and the compresser jive differently. my vibration seems to go away after it warms up though.

 

[rchalmers3]

Wildchild you may be right. It may be harmonics going in and out of phase. I believe your situation is that when your engine achieves operating temperature it settles down at a RPM and smoothness that prevents or is outside the window of allowing the harmonics to occur.

Question: What are the diameters of the drive and driven pulleys?

Rick