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Topic: Belt Tensioner  (Read 442 times) previous topic - next topic

Belt Tensioner

Is it possible to change the bearings on a belt tensioner? Or do you just have to buy a brand new assembly?
2008 Nimbus 342
Build# 6464
ISM 500
Allison 4000 w/retarder
2021 Jeep Grand Cherokee

Re: Belt Tensioner

Reply #1 –
Most have two side by side bearings and can be pressed out and replaced. Bearings are metric and available most parts stores.

What symptoms are you having? Dry whirring sound or do they catch as you spin them?

When I did our belt alignment, I pulled the tensioner, put in on it's side and lubed the bearings. They were a little dry but that cured the dry feeling and the OEM tensioner is fine going on 120K

The jumping tensioner Gates video is designed to sell tensioners when the problem is alignment.

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

Re: Belt Tensioner

Reply #2 –
I haven't had any symptoms that I'm aware of. But I was going to update my charging system. So I thought I would change the bearings while installing a new alternator since the coach is almost 14 years old. Easier done now than out on the road. I didn't know you could lube them. I'll lube the old ones and keep for spares. What did you use for lube?
Thanks,
Robert
2008 Nimbus 342
Build# 6464
ISM 500
Allison 4000 w/retarder
2021 Jeep Grand Cherokee

Re: Belt Tensioner

Reply #3 –
The alignment depends on what engine you have,the 8.3 the pulleys are all aligned and no adjustment,agree with Pierce but if
your tensioner is jumpning badly and a new one cures it you had a worn tensioner.To above comment,lubing will not do any good for the worn coil spring.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Belt Tensioner

Reply #4 –
To evaluate your tensioner, there are THREE things that are important:

Bearings-- yes easy to replace.

Tension-- need proper tension, spring not serviceable.

Dampening (keeping belt from bouncing=  loading/unloading)-- not serviceable.

Two very good tutorials by Gates Corp:

http://www.youtube.com/watch?v=Hza9Ulhe4DQ


http://www.youtube.com/watch?v=h8pQT3YZAwo



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: Belt Tensioner

Reply #5 –
Quote from: John44 –
The alignment depends on what engine you have,the 8.3 the pulleys are all aligned and no adjustment,agree with Pierce but if
your tensioner is jumpning badly and a new one cures it you had a worn tensioner.To above comment,lubing will not do any good for the worn coil spring.
The U300 Detroit has a longer belt path and the tensioner/pump combination and is never aligned properly when originally installed leading to early belt failures, etc. Our tensioner jumped exactly like the failed tensioner in the Gates video Brett posted. But, aligning the angles and moving the tensioner in so the belt was 100% on the tensioner roller completely cured the problem. The PO had several belt failures in the previous 60K miles before we purchased it. We also had a belt failure on our trip home after purchasing it. After doing the alignment, we still have the original tensioner and the  belt we installed has been on for another 60K without showing any wear. When I used the breaker bar to move the tensioner arm to remove the belt, it was obvious the spring was not worn. The jumping has completely disappeared. As I've posted in the past, the jumping is caused by the belt being out of alignment and moving to the side a tiny fraction of an inch many times per second. When it moves to the side, it's path is shortened and when it jumps back to the proper position and LENGTH, it makes the tensioner jump. This is most apparent at idle. Some have tried to rationalize it's OK to run a 4 or 6 groove belt instead of a 8 groove but this is not OK. The eight groove is installed for a reason. I even called Detroit about this. If the belt touches the side of the crank pulley, it will fray and eventually fail. Follow the instructions for aligning the angles and pulleys, install an 8 groove Gates Green Stripe Fleet belt and you won't have any trouble with the tensioner or belt. Buy belt online or you will pay more.

Note: This is for a U300 Detroit with two radiator fans on the side radiator.

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

Re: Belt Tensioner

Reply #6 –
If this seems hard to visualize, the tensioner roller has a flat surface and the back side of the belt (which is also flat) rides on the tensioner roller. So, both surfaces are flat. Our tensioner angle was 3 degrees different from the crankshaft pulley so as the belt moved over the roller, it tried to move sideways and when it did, the total path of the belt was made a little shorter for a tiny fraction of a second until it jumped back into place on the roller and so the roller/tensioner jumped.

The belt surface should be entirely on the roller and not hang over the edge a little. If it does, the entire large steel mount will have to be moved as the tensioner cannot be adjusted in or out. Only the angle can be changed with a shim. The hydraulic pump pulley has four bolts that allow it to be move in and out on the shaft to keep it in alignment with the crankshaft pulley. A straight edge can show any discrepancy.

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

Re: Belt Tensioner

Reply #7 –
Quote from: Pierce & Gaylie Stewart –
If this seems hard to visualize, the tensioner roller has a flat surface and the back side of the belt (which is also flat) rides on the tensioner roller. So, both surfaces are flat. Our tensioner angle was 3 degrees different from the crankshaft pulley so as the belt moved over the roller, it tried to move sideways and when it did, the total path of the belt was made a little shorter for a tiny fraction of a second until it jumped back into place on the roller and so the roller/tensioner jumped.

The belt surface should be entirely on the roller and not hang over the edge a little. If it does, the entire large steel mount will have to be moved as the tensioner cannot be adjusted in or out. Only the angle can be changed with a shim. The hydraulic pump pulley has four bolts that allow it to be move in and out on the shaft to keep it in alignment with the crankshaft pulley. A straight edge can show any discrepancy.
Pierce

On my 1997 I had it jumping and the belt was not running true to the tensioner, wanted to run partway off.  I guess I never thought about it being out of alignment.  I was told to get a new tensioner, I did and it solved the problem.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Belt Tensioner

Reply #8 –
On some of the older coaches with the hydraulic motor mounded on a separate bracket, there were some failed welds that allowed the motor to shift by about 7 degrees-- enough to create all kinds of issues.

SO, if this is how your hydraulic motor is mounted, a quick and easy check:  Pull up HARD on the belt next to the hydraulic motor (yes, with the engine OFF).  If the motor deflects, FIX THE BRACKET.  Been there, done that on the 1993 U240.
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: Belt Tensioner

Reply #9 –
Quote from: turbojack –
On my 1997 I had it jumping and the belt was not running true to the tensioner, wanted to run partway off.  I guess I never thought about it being out of alignment.  I was told to get a new tensioner, I did and it solved the problem.
A lot of time, a new tensioner just changes the frequency of motion and may only postpone the problem.

I agree that checking the mount security but ours was dead on. It was the tensioner that was off 3 degrees, not the mount.


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