Brand New Member with a ? about MCI-9 Tensioner

brett · August 15, 2011, 01:38:14 PM

I work at a non-profit that does bus parties in the Boulder, CO area. I was referred to this site by a friend.

We recently bought an MCI-9, a standard transmission. It keeps throwing the belt off the tensioner, and we are hoping for a little expert advice out of the members of this site. I'd love to gain some perspective on what might be causing this, and what the best approach to fixing it might be. Whether just taking it into somebody or any suggestions for how to fix this ourselves. We bought a new belt for it, and when the air pressure is built, the belt does not have any excessive play. From what I can tell, the fly wheel is at a little bit of an angle and the belt is riding off the back lip, as opposed to the front lip (closest to the back bumper...) anyway, we're into this bus for quite a bit as we've bought it twice. First time we bought it we gave it to an employee as a severance package, and then when he no longer had a use we bought it back. We got a decent deal the second time around, but it's still yet to transport a single passenger, as we've been trying to get all the issues with it worked out. We feel that this tensioner problem is the only thing separating the "Silver Streak" from being a genuine road warrior for us. Thanks in advance for any helpful information! This is my first post, but I'm looking forward to being involved with such an outstanding community.

bevans6 · August 15, 2011, 01:52:20 PM

I didn't think MC-9 had a tensioner pulley, I thought they just had two pulleys, one on the nose of the crank and one on the gearbox for the fan. Tension is applied via an air cylinder. The first thing that comes to mind is the engine isn't installed far enough back and the crank pulley is out of line with the pulley on the gearbox. The other idea is the belt is toast and you need a new belt. Sometimes once they start to throw or turn inside out, they are no good anymore. A slight angle shouldn't make much difference, the MC-5 has a far larger angle to the engine and it keeps belts on fine.

Brian

Boomer · August 15, 2011, 01:57:48 PM

One cheap improvement is to replace the air tensioner cylinder with a manual turnbuckle. Available from MCI or other common sources. Solves the air leak issue and holds the tension a lot better. Cheap fix.

Scott & Heather · August 15, 2011, 02:00:40 PM

Quote from: Boomer on August 15, 2011, 01:57:48 PM
One cheap improvement is to replace the air tensioner cylinder with a manual turnbuckle. Available from MCI or other common sources. Solves the air leak issue and holds the tension a lot better. Cheap fix.

Yeah, I'm wondering if his air cylinder switch is turned off. The little silver lever near the pulley at the top. If you turn it so it points down, it should fill with air once the coach is aired up and tighten the belt. If it's turned the other way, it won't ever tighten. Am I right on the direction of the lever?

brett · August 15, 2011, 02:10:02 PM

It is the pulley on the gearbox for the fan which the belt slides off of. Our first conclusion was the belt was bad so we bought a new belt for it, and then that belt broke, so we bought another brand new belt. I was thinking that there is an angle to the gear box pulley. We were calling the gearbox pulley the "tensioner" wheel. Not sure if that's the correct term, but it does depress and raise up with an air cylinder. We can release the air with a little switch which lowers the wheel (pulley?) down and lets us put the belt back on. Then when we flip the valve back, the pulley rises up another 2 inches. (approx)

I guess the engine may indeed not be installed far enough back. That's very likely. Hope we can make some use of that in what we plan to do from here. That sounds like a pretty complicated fix..

Thanks very much!

-------

Our first attempt to fix it had us looking at that air cylinder system (we do have the valve in the correct position to use the air pressure to raise the wheel and thus create appropriate tension with the belt.) we had a screw that was loose on the face of the cylinder, which pointed to the back of the bus, and when we tightened that we noticed a significant increase in the pressure, and we could no longer manually push the cylinder in to lower the belt when air pressure was built. So we thought at that point that we'd fixed it, that it had to do with air pressure, but I noticed it came off on the next drive which was only a mile or two.

so the pressure in the cylinder sustains, and the belt is nearly brand new... eliminating those two possible cheap fixes...

bevans6 · August 15, 2011, 02:32:28 PM

You may have put the pressure regulator for that cylinder out of adjustment - too much tension will do what you are describing, and breaking that belt would be a total trick, it can probably transfer 50 hp. The regulator should be set to 21 psi. Not a lot. The cylinder is a 2" dia cylinder, at 21 PSI it has 65 lbs of push, but if it's seeing full pressure at 120 lbs it will have 377 lbs of push.

It is a Willams WM-279-E1, it's used in many places including the emergency brake circuit, so having a spare and learning how to calibrate it is a great idea. It's also used for the air cylinder for the air conditioning belts.

Brian

brett · August 15, 2011, 02:54:05 PM

ok i am very interested in learning how to calibrate, so i'll be doing a cursory google search and trying to get a handle on it. thanks for that info.

bevans6 · August 15, 2011, 03:23:26 PM

You put air in the input side, a pressure gauge on the other side, and turn the screw until you get the pressure you want. Could not be simpler. I have an MC-5C, it actually has a schrader valve (tire valve) so you can read the pressure with a tire gauge on that particular regulator. There is also the switch valve that was mentioned, it is designed to dump the pressure so that you can change the belt in a minute or two - dump the pressure, pull down the upper works, belt is off like that.

Brian

Busted Knuckle · August 15, 2011, 03:44:17 PM

Last time I was asked this very question was by another new member on the board who had an MC9 as well he was driving down the road when it happened. (drove from Canada to Mexico, and was headed back to Mexico when it happened.)

What we found was his problem and sounds like yours too Brett, since you say. "From what I can tell, the fly wheel is at a little bit of an angle and the belt is riding off the back lip, as opposed to the front lip (closest to the back bumper...)"

His engine / transmission cradle had slipped back about an 2 inches from the proper location against the stops at the "front" of the engine rails.

Not a huge problem but it does take a little bit of work to get back where it belongs.

First you have to find the stops and determine if it has done this. (there will be a gap on the rail between the "cradle" and the stop if it has.)

If so you'll need to LOOSEN (of course they must be slightly loose already for it to have slipped) all the U-bolts and retaining bolts to where they are sloppy loose.

Then you have to find a way to "push" the engine forward until it bottoms out in the engine compartment against the stops.
A fork lift works great for this. (not everyone has one available.) A tow truck wheel lift works good too! As does good portapower unit if you have a good anchor to push off from with it.

But it is best to have someone experienced with it, that is set up for that type of stuff do it or at least help with it! A skid loader would work good too, but be careful WHERE On the engine/cradel you push or you'll have WORSE problems than being out of alignment!

BK

demodriver · August 15, 2011, 07:17:34 PM

^^ sounds as if one may be able to do it with a few good come alongs as well. And way cheaper

Busted Knuckle · August 15, 2011, 07:45:51 PM

Quote from: demodriver on August 15, 2011, 07:17:34 PM
^^ sounds as if one may be able to do it with a few good come alongs as well. And way cheaper

Eric you are exactly correct. BUT AGAIN it is best to have someone familiar with the process of removing and re-installing an engine/trans do it so they can hook to it in the right places and not cause more damage turning it into a 45' flower pot!

In order to come a long you'd have to get under it and find a solid anchor point or go ALL the way out the front to a stationary anchor.

Now comes the tricky part of where to hook onto the engine/trans combo in order to get an even pull with out destroying something.

I know I use the hydraulic wheel lift on my tow truck or the fork lift to push rather than pull, but not everyone has these toys in their back yard.

BK

brett · August 15, 2011, 08:10:01 PM

unfortunately our executive director wants me to get it fixed with a tight budget of $300 by wednesday.. he did say i could keep what i don't use of the three hundred, but it's kinda a bit of pressure since my first introduction to an MCI was about a month ago. but it's not as if i'm not up to the challenge. we actually drove it about three miles today without the belt coming off. but we drove with the back hatch sorta propped up so I could drive behind it and observe what was happening. I noticed that the belt was only coming close to jumping off the wheel at one place. Everytime that place came around... it looked as if it was going to pop off. The way I described this to our director who was driving was that it's like a bike wheel that has one dent in the rim, and every time that rim comes to the ground you get a "thud." so the belt only seemed ready to pop off at that one point on the wheel. And it was just like clockwork. Each time it went around, the belt looked ready to ride off. I wished I coulda taken some video of it. Does that seem to indicate it's still the engine being too far forward? Also, that rail that I'm looking for it to be up against, that's gonna be on the side of the engine that is closest to the front of the bus, yes? So if I get underneath and check out whether it is up against something, I should be able to determine whether it needs the recommended action to be moved closer to the front of the bus, am I correct on that? This info is a big help. I think I understand the problem more clearly now. Thank you!

Scott & Heather · August 17, 2011, 05:03:33 AM

It would be kinda interesting to see some video of it popping off if that's possible.
Anyway, I'm in a photo-taking mood today and the weather is great...do these photos help any of you to explain the engine cradle shifting issue? If I can take a better/more descriptive photo, give me some instructions and I'll go back the engine bay and do them over. Sorry for the cruddy looking motor. I haven't gotten around to cleaning it yet...for large high resolution versions of these images, click here: http://livinginacoach.blogspot.com/p/1984-mci-9-technical-photos.html

brett · August 17, 2011, 03:28:16 PM

alright, I am going to attempt to take some video to post.

bevans6 · August 17, 2011, 03:41:27 PM

The cradle is in the right place based on the fixed swing-up hold down bolt shown in the upper left hand photo. That bolt is on a hinge, it swings up and bolts down the sliding cradle, and the fact that it has engaged means the cradle is in the right spot. I bet the pulley on the mitre box is bent, or the tension is too high.

which pulley seems to want to make the belt jump? The lower pulley is a huge cast piece, it won't bend it will break.

Brian