Bus Conversion Magazine Bulletin Board

Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: TEAKNE on July 15, 2010, 03:33:23 PM

Title: Engine Vibration
Post by: TEAKNE on July 15, 2010, 03:33:23 PM
I have been working on my bus (PD4106 w/8V71 and 4 speed spicer) for several years now and recently I have been getting engine vibration at low to mid RPM but not noticeable at high RPM.  I have also noticed a “flat spot” when I press the accelerator petal. It will build RPM for the first half inch of petal travel then nothing for another half inch. After that the bus builds RPM normally. I have not noticed any loss of power or oil usage.  It is really noticeable when warmed up and attempting a dead throttle start.  Then the whole bus will shake.  It is also noticeable when shifting up through the gears.  I first thought I had a clutch issue, but I still have the vibration with the clutch pushed all the way in. Could I have clogged injectors and how do I find out which ones are plugged or do I have bigger problems?

Title: Re: Engine Vibration
Post by: Lin on July 15, 2010, 03:40:42 PM
Could be several things I would guess.  Does is happen in reverse also? 

Title: Re: Engine Vibration
Post by: TEAKNE on July 15, 2010, 03:52:52 PM
 It will also do it in rev.
 Just a note..No strange sounds are noted and have not noticed any oil smoke or black smoke (unless I'm pushing it a little on a grade).

Title: Re: Engine Vibration
Post by: Dreamscape on July 15, 2010, 05:32:27 PM
We have an 8v17 in our Eagle. Have you checked your engine cradle? This is just a wild guess.
Vibration is not normal.

Maybe Clifford or Geoff will chime in.

Our foot feed is giving us a similar result, but I've dealt with it so far. It doesn't respond for about 1" of travel, then all is normal. The linkage is 42 years old and joints are worn. I'm assuming you have linkage.


Title: Re: Engine Vibration
Post by: Bill B /bus on July 15, 2010, 05:39:39 PM
Replace the engine mounts on the cradle. The leaking DD engines soak the mounts in oil and they slowly deteriorate. Changed the engine mounts on a Buffalo and cured the vibration problem that was evident on take off and low to mid RPM. Another thing to check is the driveshaft and u joints. Bolts tight the rear end and joints tight and properly greased.


Title: Re: Engine Vibration
Post by: luvrbus on July 15, 2010, 08:56:35 PM
Could be the pilot bearing in the flywheel has gone bad also over time the flywheels will warp and the clutch will break springs causing the vibration doesn't sound like a engine problem too me

good luck

Title: Re: Engine Vibration
Post by: OneLapper on July 16, 2010, 08:19:16 PM

My 4106 had an engine vibration when i got it.  It eventually just got worse and worse.  I knew I had a "wet" cylinder, either from a cracked oil ring or a low compression. I never determined exactly what it was.  Injectors can easily give a vibration and are the one of the "cheaper" items to replace.

People are right in saying that a healthy 8V71 is very smooth at all rpms.  I have run my new engine on the garage floor several times to test things, and it was smooth with the original injectors in it, but even smoother with the new N65's I installed (I also advanced the timing, that might have affected things, but advancing usually makes engines run a bit rougher).

Good luck!  Let us know what you find.