Engine: Replacing Hydraulic Pump Tensioner

I put together with photos of our tensioner replacement project.

Motorhomes may or may not have the same tensioner part number for both alternator & hydraulic pump.

Foretravel Group member Mike OLeary encouraged me to seek out Gates tensioners as they have an improved design.

Found them only at NAPA, a major Gates vendor.

Installation was quite simple. Used a 3/8” breaker bar to swing back original tensioners to remove belts.

Then remove the single bolt holding tensioner on to its mount.

Tensioner base is held is kept from rotating with a single round key that fits into a hole in the mount.

New Gates tensioner uses a ½” breaker bar to rotate the idler against the built-in spring.

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Good idea to install new belts at the same time. I prefer Gates belts.

Original hydraulic pump tensioner had a 1/8″ space between the backside of the tensioner and the engine mounting plate. I almost missed seeing the spacer as it was stuck to the tensioner and looked part of the tensioner. Without spacer, belt would not ride in the center of the idler.

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Hydraulic tensioner spacer is 1/8″ thick and still allows enough of the alignment round key to fit into engine mounting.

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New Gates 38504 tensioner. Note closed case to help prevent dirt entry. We think Gates has an improved design and may have advantages over other brands, Dayco being the most common.

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On our coach, both alternator & hydraulic pump use the same tensioner part number.

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New Gates 38504 tensioners installed for alternator & hydraulic pump. The original spacer was installed between hydraulic tensioner & mount. New belts were also installed.

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New hydraulic tensioner showing the position of 1/8″ spacer

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Original alternator tensioner

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Original hydraulic pump tensioner

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Cummins etches their part number on the tensioner

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Engine with both tensioners removed

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Here is an excellent video by Gates to help identify good/bad automatic belt tensioners

And, to adjust the tension on an automatic belt tensioner, merely change the location of the detent hole.  Many of us have DE-tensioned the hydraulic belt tensioner.

To Install the belt on the Belt Tensioner on a Caterpillar 3116 is a challenge with that short belt and only two pulleys

Loosen the tensioner center bolt just enough that you can get the detent out of the hole.  Install the belt.  I then use a large pair of water pump pliers to rotate the tensioner enough to engage the detent.  You could also use a pipe wrench. Brett Wolfe

I Replaced the tensioners on my Cummins ISC 8.3 350hp Electronic engine and wanted to share some detail. They were squeaking very badly and I would have most likely been in a great deal of trouble with a failure on the road.

There were several Numbers on the tensioners, I guess they may have been original equipment.

The Alternator Belt tensioner was as follows:

It is a grooved pully and the Gates replacement required a bit of manipulation to install

Cummins /Bluebird /Ford 3945527
Etched Number 174934
Goodyear 49521
Dayco 89406
Gates 38516

The Air Pump Tensioner had a smooth pully and the one from Gates installed easily, here are the details

Cummins /Bluebird /Ford 3934818
Etched Number 189932
Goodyear 49501
Dayco 89409
Gates 38504

The R&R too right at 35 minutes. So it isn’t bad at all. A large channel Lock Plier allowed me to twist the Alt tensioner to line up the tab, as it hit the bracket. Chuck & Brenda 2000 U295