Hi all,
Here's an experience to share - along with a question.
The hydraulic motor on Foretravel's Detroit Diesel is belt-driven, and mounted low on the engine. I've replaced the belt twice in the past three years (20,000 miles) and it looked like it was happening again - a loud clacking revealed that the tensioner was bouncing on the belt. When I removed the belt, it turned out to be in fine shape. The races of the pulleys seemed fine as well, and the driven pulley turned normally. So I assumed that the tensioner would have to be replaced, and I began by cleaning it up so it could be removed. I was surprised how much road grime and oil had built up in the area, but hey - today's roads will to that, I guess. After I cleaned up both pulleys and the idler wheel, I replaced the belt, aligned it, and started the engine. To my surprise and delight, the problem was solved!
So I'll be watching carefully, but I don't fully understand what happened here. Even before I thoroughly cleaned the area, the pulley races and the belt seemed clean, and I wasn't able to see what was causing the bouncing. Could it be that it was caused by an intermittent but more serious problem, unrelated to the build up of dirt, grime, tar, and oil?
So I share this. If you have a similar issue, you can save a lot of money if the problem can be solved by a good clean-up instead of replacing an expensive part. But that's a big "if." And I'll welcome your insights, caveats, and advice. Thank you.
That tensioner does get tired after more than 20 years. Cabin Diesel replaced ours two years ago when we had our big breakdown.
Larry,
Your 1994 should have the horizontal radiator with two fans. If so, you should have the 8 rib belt installed, NOT the 6 rib. Foretravel missed the update when they changed pumps/fans/etc. Your problem is in the vertical angle of the tensioner. Mine was off 3 degrees causing the belt to jump and wear on the edge, causing a failure. With a slight misalignment, the belt moves sideways a little, then jumps back, repeating this several times a second. This is what causes the noise, movement, etc. I placed a washer under one edge of the tensioner to bring the crank pulley, hyd motor pulley and the tensioner pulley all in the same plane. I did check for a dry bearing and broken spring but just oiled it and at 100,000 miles, it's still working fine.
Go online and buy the Gates Green Stripe Fleet belt. It's the best and will only cost a buck or so more if you get it at a discount web site. NO one is going to have the 8 rib at a truck stop so order a couple. The belt should ride fairly close to the middle of the tensioner pulley and NOT hang over the edge.
Engine failure scenario is as follows. The tensioner is not in alignment, the belt rubs against the crank pulley shoulder, it frays and is finally destroyed. The engine quickly overheats. The DDEC II goes into shutdown more but the coach is not in the best location on the road/tunnel/bridge/etc so the operator uses the OVERRIDE dash switch to move it. The engine really overheats, ruins the liner O rings and has to be overhauled and costs $20K to $30K to repair. All because the belt tensioner was not set up correctly in the first place. This is EASY to fix.
Here is my old post: belt tensioner (http://www.foreforums.com/index.php?topic=29839.msg254825#msg254825)
PM for photos and part number.
Pierce
Here are photos and belt part number. This was taken right after we purchased it and drove it across the U.S. (losing one belt). The previous owner had several failures while they owned it and told stories about waiting for the tow truck and the new belt. The coach had been sitting for three years hence the rust on the parts. Running a straight edge across from the crank pulley to the pump pulley, you must allow for the thicker lip on the crank pulley. The large mount bolts to the block with four bolts. It can be moved fore and aft but may need the holes elongated. This is so the belt will be centered on the roller. The motor pulley will then be off the amount the mount was moved but after loosening the four bolts on the face, the pulley can be moved on the shaft.
Note: the coach can be at any angle when taking the angle measurements.
Pierce
Thank you to all - especially Pierce! When I started ol' Deedee up, the idler was bouncing again. My 1994 has a vertically-mounted side radiator, but the pulleys and tensioner look exactly like your photograph. I had just ordered a couple of belts - same part number as your photo, but the bigger issue that might remain is that of alignment. That's what I'll check next.
Again, thank you for taking the time - and having the expertise - to help. I often wonder how I can pay forward such kindness!
Larry
Larry,
Some members have used the 6 rib as they could not get the 8 rib to ride in the grooves without rubbing on the pulley edge. They were able to get by with the 6 rib as it just jumped one groove. When I installed an 8 groove without the pulley vertical alignment, it also rubbed on the edge, frayed and broke.
I called Gates and was told that if the crank pulley and pump pulley both had 8 grooves, the belt needed the same number. I know it's a bit of work to shim the tensioner so the angles are the same and a lot more work to move the big tensioner/pump mount if the belt is not all the way on the tensioner roller but it's needed. I was lucky as a lock washer fit under the top of the tensioner and brought all three angles together.
To do most of the work to check the alignment, you only need either a 3/8" or 1/2" breaker bar plus the angle indicator. Our OEM tensioner had a 3/8" square recess. After practicing with it quite a bit, I was able to go from no belt to mounting the belt and ready to start the engine in 7 seconds. Naturally, having the spare belt and breaker bar handy is a good thing.
After changing belts, it's good to check the edges of the belt after a few miles and then with the morning oil level check to make sure it's not rubbing. A properly aligned belt should last well over 100,000 miles. Our RAV4 has a 7 groove belt that I replaced at 150K miles. The rule here is one visible crack per inch for each belt groove. So, an 8 groove belt could have 8 cracks per inch and then would be at the limit. With so much riding on the hydraulic belt, it's probably best to replace it well before the limit is reached.
Some have commented that installing a new tensioner did the trick for a while. Many have a rubber/vinyl face on the roller. It's coefficient of friction on the roller face will change over time as the belt moves sideways. Our big mounting plate was at the correct angle but I have no idea how the tensioner managed to be 3 degrees off in relation to the mounting plate.
Your hydraulic pump should have 8 grooves on the 1993/1994 U300 with the twin radiator fans but you might want to do a visual on it before ordering the belts.
Your are most welcome! Thanks,
Pierce
I followed the same procedure on Pierce's write-up when I was noticed the hydraulic fan belt tensioner on my rig was bouncing and there was only a 6 rib belt. I bought a couple of the 8 rib belt belts and tried one at first and quickly saw how it would jump to the edge of the pulley because of misalignment. I bought a $5.00 dial angle finder from Harbor Freight and used a washer about the thickness of 1 belt rib to bring it all back into alignment.
With that alignment correction the tensioner hardly bounces and the belt stays in place. It's a brilliant simple fix to a potential disaster if a belt breaks and you don't get off the road before overheating. The 6 rib belt is not the right one for that pulley and with the tensioner being out of alignment will make an 8 rib belt wear out faster with it riding on the edge. The system was designed for an 8 rib belt for maximum performance. Even with a new tensioner, if still out of alignment you haven't fixed the problem. I have about 5000 miles since the change and have had no problems with premature belt wear or bouncing tensioner. No guarantee against breaking a belt, but carrying a spare and periodic checking the alignment with the angle finder and will give confidence going down the road.
Thanks Pierce!
Jerry
Here is a good, short video on belt tensioners by Gates Corp: http://www.youtube.com/watch?v=uTLV5IU_IMM
They can fail in THREE WAYS:
Bearings can fail.
Tensioner spring can fail.
Dampening component can fail. This is harder than the others to detect (see the video to diagnose) but contributes to the destruction of anything driven by that belt, at is loads/unloads/loads........... all the accessory bearings on that belt several time a SECOND.
The dampener failure motion is much like an alignment problem as the two look virtually the same. Ours moved exactly like the one in the video but was cured when it was aligned properly. Since it only takes about 5 minutes to check alignment and costs nothing, it should be done first with tensioner replacement only done if the alignment does not cure the problem.
Replacing the tensioner is not a good remedy for a poorly aligned component in the initial installation. Check first, spend money second.
Pierce
We found that most tensioners have an open spot where the inner spring hooks on. Many of us have switched to Gates brand tensioners that are sealed, with no open spot for dirt to get in. This applies to Cummins engines also.