***THINKING ABOUT EXTENDING a 121"? READ THIS FIRST!**

[thegrizzly1]

 

[Jigger]

When I installed a MPI extension on my Mountain sled, it came with instructions to notch a portion of the cast piece of aluminum if installing a rear heat exchanger. I haven't had any problems with trimming this piece of metal. I understand I didn't extend my sled like you did but if you chose to trim the metal I think it would be fine.

 

[thegrizzly1]

First it looks like you are starting with a mountain sled to begin with. I know if had I had a stock 136" or 144" (which they don't make till the 09's) it wouldn't have been an issue. I am fairly certain Yamaha actually has different tunnels for their longer machines vs. add on pieces similar to aftermarket extensions. Perhaps is should have included 121" in the subject line. I'll see if I can figure out how to edit it.

Second, having the mountain sled to begin with, I am guessing your suspension is mounted slightly lower in the tunnel to begin with. I.E. more clearance between the track and exhaust. Others can pipe in about this, but I think the ZX-2 is actually mounted higher in the tunnel than the stock suspension in the location of the rear arm. This is reducing clearance between the track and exhaust from stock.

You are correct, I could trim out some of the aluminum, however that is the only thing protecting my crossover tube. Unless I redo some plumbing, I want to do anything I can to prevent the track from touching the crossover tube.

 

[LazyBastard]

It doesn't make a difference if you start with a long or a short tunnel, the exhaust support bracket is the same. In fact, the tunnel up to the exhaust support bracket is the same, the mtn differs only in the extension. In fact, this problem occurs with the STOCK mtn, I think 06, and required a number of people to install a ramp over that piece in order to save their tracks and tunnels in the time before Yamaha issued a solution. The track will still rub it, but it won't CATCH.

I myself, with ExpertX-144 (full 144" rails, so it wouldn't qualify so much as "custom"), noticed this clearance problem as well, but I noticed it BEFORE running it. I run a rear heat exchanger, which I modified to sit flush against the tunnel, and I cut down the part of the exhaust bracket that you mention is being caught. In order to prevent rubbing, it also required that the rear mount bolt on the ExpertX be lowered by about 1/2".

 

[rxrider]

I do not understand what ADB means that 136 is for a 136 sled??? The Warrior and the Attak shares the same frame as the shorties and all other RS, RX-1 and Apex type sleds. The problem will be the same on the stock 136 sleds, or even worse as the tunnel extension does not tilt upwards like most of the aftermarket extension does.

This is what happened to mine.

I cut off 3/4" off the rear cast aluminum bulk head frame, track and studs are not hitting the frame anymore. I don't think the structural integrity of the rear frame has been weakened much if any.

If you have a crack you better drill a hole at the end of the crack to stop it from cracking any further.

I had to refabricate the rear cooler to make it fit inside the tunnel extension flush with the top of the extension. The exchanger sits much higher up in the tunnel compared to an Attak or a Warrior. I have added tunnel protectors that goes all the way back. I also had to add slider material to the protectors to keep studs from hitting the charge tube, exhaust, rear cooler and rear bulk head.

IMO it's the 8" rear wheels that causes the problem, as the sled bottoms out the track goes 1" higher up into the tunnel in the rear. With my MPI extended 136" proaction skid I did not have studs hitting the rear bulk head, NONE. The PA skid had 7" wheels and close to no transfer.

 

[thegrizzly1]

Excellent point about the 8" rear idlers! I never thought about that. I am going to create a term I'll call the departure angle. Think of it as the counterpart to the approach angle. Having larger rear idlers will decrease this departure angle effectively flattening it out. Stretching from a 121" to a 144" is all done in the rearward direction drastically flattening out the departure angel. This combination really encroaches upon the rear cast bulkhead you mentioned. One option is to drop the rear mounting holes, however as you can see from the picture, the bolt is tight above the running board. I would have to lower it 2 1/2 inches or more to clear the running board heat exchangers. Since the sled already sits considerably higher than stock, I don’t see this as a viable option.

 

[Jigger]

In the mnt version the skid is mounted lower than the tunnel. It's close to the orginal distance below the tunnel only further forward. The skid does sit alot higher with the extra travel of this skid. I'm not sure if this is a viable option in the shorter sleds.

 

[rxrider]

As you said I don't think is a viable option either for extending a 121" or 136" to 136" or 144", the mountain sleds however will benefit from the added hight specially for deep snowriding.

ZX-2 Install guide for 136" and 144" skids should have had a section about trimming the rear bulk head frame 1" and adding 1" tunnel protectors all the way back.

 

[Dano]

 

[mattsapex]

why dosen't adb have you guys trim that piece out so there is clearance for track to go by. i did a conversion from 121 to 144 on an arctic cat zr 900 and the kit came from tracks usa and in the instructions for the tunnel extension it said to trim the folded down flap on the back of the tunnel and the extension piece gets riveted over the modified tunnel. there was an optional hose protector if you were running studs. if you guys are worried about the exhaust mount make a thinner version that can attach to the top of the tunnel under the seat that way the track has the most room it could have. just my 0.02 cents

 

[rxrider]

 

[tkuss]

Anybody have any more info on this or updates, I am thinking about extending my 121" apex with the mono to a 144 ZX2. And am trying to figure out what problems I might run across and obviously this seems like a problem.

 

[rxrider]

If you're not going to run studs remove the tunnel protectors and trim off an 1/2" or 12 millimeter from the rear of the cast aluminum bulkhead and you're good to go. There will be no clearance problem with the tunnel protectors removed and trimmed rear bulk head.

 

[tkuss]

Thanks for the response, I was planning a 144" zx2 with 1.5" lug track so I would'nt be running studs. Thanks for the reply.

 

[yamadoo]

Silly Question maybe.

As I look at the pictures, I wonder if that piece of aluminum that closes the tunnel could be bent toward the front and not only loose the height, not catch the track with a sharp edge but act as a guard for the cross over tube as well.


Would this work?

Yamadoo