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Topic: Alternator Idler shimmy (Read 550 times) previous topic - next topic

Alternator Idler shimmy

Will replacing the idler on the alternator belt on an 8.3C reduce or eliminate the shimmy? Its a bit noisy to, the bearing rolls easy with no play but it bounces a lot at idle. Alignment looks good.

I saw the Gates video posted (by Brett I believe) and it shows replacing fixed the problem, but others have posted they experienced no change in idler shimmy (or  bounce) after installing a new one.

Is it normal to install an idler on the "driven" side of a belt like on the 8.3C in the U280 rather than the back or "slack" side?
 I'm thinking this could be the reason it doesn't run smoothly.
Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Alternator Idler shimmy

Reply #1 –
Will a new belt tensioner "fix" an out of line accessory-- NO.  Nor will it "fix" bad bearings or bad mount on an accessory.

But, just as the Gates video shows belt tensioners have TWO jobs-- to tension and to dampen.  And often it is the dampening function that fails first. This puts a lot of unnecessary strain on bearings as the belt loads and unloads.

Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Alternator Idler shimmy

Reply #2 –
Quote from: wolfe10 –
Will a new belt tensioner "fix" an out of line accessory-- NO.  Nor will it "fix" bad bearings or bad mount on an accessory.

But, just as the Gates video shows belt tensioners have TWO jobs-- to tension and to dampen.  And often it is the dampening function that fails first. This puts a lot of unnecessary strain on bearings as the belt loads and unloads.



I wouldn't expect it to "fix' those things, but if the other parts of the system appear OK?
The alignment seems fine, (just checking with a straight edge tho') alt and idler bearings are tight, no play or roughness, brackets are tight. Guess it won't hurt to start with a new tensioner if it still bounces at least I will have a spare.

I do question why the idler is between the water pump pulley and the alternator rather than the crank pulley and the alt. (where the fixed idler is located) The load of the alternator pulls against the idler.
Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Alternator Idler shimmy

Reply #3 –
Does the 8.3L have the same belt lay out as the 5.9L 'B Series?

If so, it isn't that hard to string the belt incorrectly. 
I've seen it done too many times to say that it's not out of the ordinary.
Not correct, but it will work in spite of the error.  pc
S/W Houston 95" U320C SE/40' 
Build #4778  Cummins M11
Repairs & Covered RV Parking (BAO)
PPL is close..

Re: Alternator Idler shimmy

Reply #4 –
Replaced the water pump/alternator serpentine belt today and its belt tensioner. The belt runs much quieter and smoother now, no more shimmy or bounce. Also replaced the hyd fan pump serpentine belt while it was off as it had to be removed to access the water pump belt. The belts actually looked good but I plan on keeping the old ones as spares. It would be easy to replace them on the side of the road if necessary. The whole job only took about 30 minutes and is easy to do on the C8.3

I should have taken before and after videos, but the results were the same as the Gates video show:
not sure this link still works....

http://www.gates.com/tensioner/tensioner_video.html

water pump/alternator tensioner (NAPA# 3854)
water pump/alternator belt (NAPA# 25-080605)
Hyd fan pump belt (NAPA# 25-060445)



Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Alternator Idler shimmy

Reply #5 –
Here is the current Gates Corp Tensioner Video:
http://www.youtube.com/watch?v=uTLV5IU_IMM
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Alternator Idler shimmy

Reply #6 –
Quote from: FourTravelers –
The whole job only took about 30 minutes and is easy to do on the C8.3

It is a whole lot easier if you have a 3/8" breaker bar in your tool kit.


From the videos, it is obvious that the old tensioner needed to be replaced. Is there some criteria that describes how much shimmy is too much?

Thanks,

Trent

Trent and Jean Eyler
2000  U295  4003  WTFE  ISC  350
Build#5603 MC#17385

Re: Alternator Idler shimmy

Reply #7 –
Quote from: TulsaTrent –
It is a whole lot easier if you have a 3/8" breaker bar in your tool kit.


From the videos, it is obvious that the old tensioner needed to be replaced. Is there some criteria that describes how much shimmy is too much?

Thanks,

Trent


Yes..... it would have been a real PITA without a 3/8" and 1/2" drive ratchet or breaker bar.
The new tensioner from NAPA required a 1/2"

Not sure on how much vibration or shimmy is acceptable :-\  as in the video, mine was obvious.
Maybe Brett can comment on how much, if any, is acceptable.


Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Alternator Idler shimmy

Reply #8 –
I am not aware of a hard and fast "this much is OK, this much is bad" rule.

If there is any movement of the tensioner, I try to find the source by:

With engine off using a straight edge to verify that all the accessories and crank pulley are aligned.  Also pull hard on each accessory to verify that the mounting is tight.  If it is a belt driving the hydraulic pump on many Foretravels, the bracket mounting it to the engine is subject to failure at the weld. Easy to find by pushing on the belt and watching the whole pump and bracket move.

On some, the crankshaft pulley has some adjustment (mounting holes large enough to allow some side to side movement). Determine by starting engine and slowly AND CAREFULLY bringing a straight edge up toward the pulley with engine at idle speed. Check for run-out.

If all the above OK and you have shimmy, replace the tensioner.  It IS a wearing part and is designed to perform both tensioning and dampening duties.

Loading and unloading bearings is really hard on them, and often leads to bearing failure.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020