| Author | Message | ||
| Tom Dessert (Mci5er)
Rating: N/A |
I'm curious about a modification made to my 6V92TA. There is a belt tensioner that I was told, came from some older model car, installed to maintain some level of tension on the squirrel cage fan drive belt. I don't recall ever seeing a tensioner in any of the pictures I've seen of other DD configurations. Is it needed? Just a good idea? or what? Thanks | ||
| David Hartley (Drdave)
Rating: N/A |
Is this on an MCI? If it is, That is a factory item and all MCI's with the squirrel cage fans above have them. There should also be an air pressure regulator and two-way dump valve to release the tension so that you can change the belt. My MCI MC9 also had one of the a/c compressor to tension the belt for that. | ||
| Tom Dessert (Mci5er)
Rating: N/A |
David, This is on a repowered MCI5A 1965 vintage. The configurations is a single long belt around the crank then straight up to the squirrel cage pulley. The tensioner is located somewhat closer to the crank than center of the belt. I don't see any air lines or anything that would let you adjust the belt tension. The cage pulley assembly has a small sightglass and is rubber mounted. If this helps. Thanks | ||
| David Hartley (Drdave)
Rating: N/A |
The MC9 has the blower gearbox mounted on a small rubber mounted platform that hinges on one end with the end closest to the pulley either shoved up to tighten the belt or retracted to loosen the belt. The cylinder is up in the top of the engine compartment and has a L- shaped lever that attaches to the tray that the gearbox rides on. A side mounted tensioner like you are describing may be a spring loaded cylinder that either pushes or pulls on the idler pulley to keep the belt tight? aka Belt Tensioner in form like what is used on cars and trucks. They are spring loaded and takes a breaker bar in a socket to provide leverage to release the tension enough to change the belt. The RTS buses used one with the serpentine fan belts where they had a belt driven fan hub. It was about 3 inches in diameter and had a smooth idler pulley that road on the back of the belt. It was mounted about where you are describing. I am trying to think if I have a picture of one and will have to search through about a thousand pictures to see if I have it. I will get back to you on that.... Dave... | ||
| John MC9 Rating: N/A |
The MC9 tensioner looks like this  | ||
| David Hartley (Drdave)
Rating: N/A |
John, When did you sneak out and take that picture of my tensioner????  They may look goofy but they do work.... | ||
| John MC9 Rating: N/A |
Dave - Can you check to see if my lens cap is in your driveway? These late night photos get the best of me! | ||
| Tom Dessert (Mci5er)
Rating: N/A |
John, Thanks for the picture. What I see here makes sense, with what David has said. I went out (flashlight in hand) and looked closely at the mounting of the blower gearbox. In may cause it has four large bolts that go through the blower gearbox base and into the mounting platform. I had mistakely thought the base was rubber, however it is definately metal. Just in front of the base is a series of metal shims about 1"wide x 5" long. This shim pack has a bolt that goes through on each shim and into the mounting platform. The buttom rounded section of the blower gearbox just behind the pulley is resting on this shim pack. I appears they have "hard mounted" the blower gearbox. The tensioner which also applies pressure to the backside of the belt, is the only moving part I can see. The drive belt has alot of slack in it (2" backside of belt center and 1+" just above tensioner). What should it be? Like a car 1/2 deflection? Thanks | ||
| John MC9 Rating: N/A |
Tom - An MC5 guy would answer your question best. I would imagine that 1/2" deflection should suffice. I'd look at the belt movement, and insure that it isn't going to slip under power. The air tensioner allows the engine to warm up faster, but you can toss off a belt, if you gun the engine before the air pressure's built up. I personally would prefer the mechanical tensioner over the air type. | ||
| Tom Dessert (Mci5er)
Rating: N/A |
John, My 5A Challenger Maintenance book doesn't mention this belt other than to replace if worn kinda thing. Since the original engine was a 8v71, I wonder how it was done on them, cause I don't see any extra holes or brachets in or near the gearbox plateform. If you got a 5a-c I'd appreciate a comment or two. Thanks Guys for the insight ... | ||
| rodney (Invaders)
Rating: N/A |
John MC9 can you take another pic of that motor i would like to see how your cable on the governer is connected and to look at the motor | ||
| Bill K Rating: N/A |
John I removed my air cylinder and installed a turn buckle. The air cylinder was leaking, and I spoke to the local charter co. and they said they did away with all there cylinders and used turn buckles, less trouble. | ||
| Bob Wies (Ncbob)
Rating: N/A |
I'm reading all of the above with great interest because My 5A is in the shop now and one of the items which need attention is the blower drive belt tensioner which is strictly manual. However the "B" manual speaks to a system incorporating an air cylinder and the adjustment procedure. Being that mine is such a 'fistfight' to adjust I might shop around to see if I might find a "B" system and retrofit it to my 'A". NCbob | ||
| Stan Rating: N/A |
MCI introduced the air operated belt tensioner on the MC-8. Prior to that tension was maintained by a spring loaded pulley on the fan gear box. Problems with that pulley caused many owners to bolt it solid and attach some sort of idler pulley on the belt. All were a homebuilt (shopbuilt) design and vary from bus to bus. One word of caution if you are replacing the belt. There are two different lengths, determined by the rear axle ratio. | ||
| John MC9 Rating: N/A |
Rodney - I'll grab a few pix this afternoon for youse. I've washed the engine since that last pic.. It was back when I first bought the thing. (6v92 / MC9) Bill K - Yup, the local bus company mechanic claimed they did the same thing to the older units. He said the drivers would race the engine to build air up (the fast idle won't work until air's up), and the belts would get tossed off... the turnbuckle cured that. I carry a spare fan belt. It doesn't hurt the pocket as much as losing a belt in East Overshoe, and not having one to replace it with. | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Ncbob - What type of manual adjuster do you have on your 5A? Since mine is a "ole timer" retrofit you got any ideas as to what the tension should be and where it should be checked at? Thanks | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Stan - Can you give me some insight as to how the rear axle ratio is related to belt length. My reason for asking is that I can't find any numbers on my belt. My rear axle ratio was changed during the DD6V92 re-power (now 3:70 to 1) by previous owners. This belt seems too long to me. Which is why I'm concerned about the adjuster and adjustment. | ||
| Stan Rating: N/A |
Tom: If you read my post carefully, you will see that I did not give you any specific advice, just generic facts on the MC-5. When a bus has been changed (different engine, different axle) no one can possibly know what was done by the person doing the modification. The MC-5 originally came with a 3.36 for highway use or a 4.10 for shuttle service. With a 4.10, the engine is turning faster, so a larger pulley is on the gear box, taking a longer belt. Again, I have no idea what you have on a modified bus. If you have the original split sheave (spring loaded or bolted solid) you can make some adjustment by setting the width of the sheave. To obtain a different length of belt, you have to go to a place that are experts in belts. There are a lot of factors to be considered besides the length. Since I am officially off this board you can email me if you have more questions to sdmcwatshaw.ca. Just change the at |