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Engine vibration

Question I have significant vibration thru the coach when engine is idling in gear and in neutral. Engine RPM is 500 to 600.
Normal or not?
Rick and Julie
Grand Villa
Build #4689
1995 4000 U280SE WTBI
8.3L 300HP Cummins

Re: Engine vibration

Reply #1 –
If you bring the rpm up slightly in neutral, does it go away? Say 800-900 rpm. Go to the rear and listen to the exhaust. Is it even? Do that and post. How about driveability? Any loss of power? Start OK? If it does not go away, check in engine compartment for any diesel leaks around the injectors. If engine remains rough, first thing to look at would be restricted fuel supply-filters.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Engine vibration

Reply #2 –
That vibration should fade at about 750 or 800 but it's tough to get the idle speed to exactly that.  Also it shouldn't vibrate near as much when warm. 
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Engine vibration

Reply #3 –
RPM at idle has to be kept within factory specs or you get stop light creep and it's hard on the trans shifting into gear from neutral.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Engine vibration

Reply #4 –
What are factory specs. 
 I thought 750 was ok.    Mine is lower than that but I gave up trying to adjust it and it smooths out warm anyway. 
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Engine vibration

Reply #5 –
Quote
What are factory specs. 

My 8.3 book indicates the idle speed should be 750 rpm. I'm betting your shaky coach will be a lot smoother with the idle adjusted properly.

Here's a photo of the throttle linkage. The arrow points to the adjustment nuts.
jor
93 225
95 300
97 270
99 320

Re: Engine vibration

Reply #6 –
The idle adjustment in the rounded bolt head on the throttle shaft. If you are over 800 RPM it won't go into gear. If it is running
rough when cold and smooths out when warm maybe an iffy injector or two. On my M11 625 RPM it's a bit rough and 675
is smooth. It was at 775 when I bought it and was rough going into gear and a few times it didn't go into gear. 
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Engine vibration

Reply #7 –
Didn't those years have retarder out of balance/failing issues? Would only take a minute to check retarder for loosening
Scott
Transmission damper failure

Re: Engine vibration

Reply #9 –
With mechanical engines with the inline Bosch pump, the Bosch factory only gives the pump a limited amount of time to balance all the cylinders so each one gets the same amount of fuel at right time and at all speeds. If the valves are all adjusted and the injectors putting out a fairly good pattern, having the injection pump calibrated can make a world of difference between a rough idle and a smooth one. You can disassemble the injectors, lap in the seats, check the pressure yourself and it's not that much work or expense. Inline 6 cylinder engines are about the smoothest engine ever made and should not vibrate the coach.

Naturally, computer controlled engines regulate the amount of fuel and the timing leaving only a dirty injector as a potential problem. Hard starting and a rough cold idle are all signs of a dirty injector. As the engine comes up to operating temperature, the heat will explode the diesel even with a torn pattern and the idle may not suffer but the emission will.

Figure about $200 to re-calibrate a pump if you remove it and it does not need any parts. You do have to time the pump when replacing it so a little research needs to be done. But, it's not rocket science.

How to calibrate the mechanical diesel fuel injectors – Welcome to Marbed...

Old school way of calibrating a pump. This was the way it was done in my day. The new testers work quickly but cost lots more so may be more expensive getting the same result. InLine Diesel Injection Pump Calibration


Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Engine vibration

Reply #10 –
Thanks to all for the expert advice.
The idle adjustment solved the problem.
No more vibration!
Rick and Julie
Grand Villa
Build #4689
1995 4000 U280SE WTBI
8.3L 300HP Cummins

Re: Engine vibration

Reply #11 –
Forgot to mention,,  generally when cold your most likely building air pressure also.  That will also make a "small "difference in idle speed and vibration when cold.  Or so it seems. 

  Now I'm going to have to attack my idle speed cause it might be a touch low. 

    750 when warm ??
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Engine vibration

Reply #12 –
Would still check the balancer with the pry bar,caught mine early and saved on repair.
96 U270 BUILD 4810
85 380SL
Drummonds TN.