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How To: FMF Turbine Core 2 modification for a Montesa 315r

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I wanted to write up a quick How To for anyone interested in doing this mod for their 315 because there was very little information out there when I was looking to do it.

The first step was to order a Turbine Core 2 for a 1996 CR250. Here it is next to the stock silencer:


You can see it needs to be shortened and to have the bracket moved.

The first step is to grind off the lower bracket, be careful not to gouge the outer tube.


Bracket removed:


Here is the tube all cleaned up with a file:


Next step is cutting down the outer tube. I trimmed 68mm off the end. Protip: Sharpie then scribe line makes it stick out more.


After the bandsaw! Note I left some space to so I could sand it to length on the belt sander:


Sanded to the correct length:


Next is to cut off the second bracket. I latter flattened the area I cut with the milling machine but I forgot to take a picture.


The bracket is then flattened on the bottom. I did this in the milling machine but you could do it with a hacksaw if you're careful. I just eyeballed the height, but it turned out to almost exactly 40mm so you could trim it to that. The top edge was squared to the bottom, tangent to the outer radius.


Next it's time to cut off the end of the pipe (Stinger?):


And fabricate the adapter tube. I had a piece of 316SS tube in the shop, I'm pretty sure it was 1.5" OD seamless with .065 wall. I bored the inside to 35.5mm, 30 mm deep and parted it off:



The adapter tube is then welded onto the endcap. I still suck at TIG welding, but I managed to get it done!


It is also important to note that there should be a pretty large chamfer on the inside edge of the adapter piece so it doesn't bite the orings on installation. I didn't get any pictures of this.

The next step is to trim the perforated tube. Here are some measurements I took:


120 mm will be trimmed off the length, this is the 68 off of the tube, plus the 52 below for the desired overlap.


Now it's time to drill the holes in the outside of the main tube. An easy way to locate the holes it to use a bent piece of aluminum like in the pictures below. Once the endcap is in the tube, simply slide the tool with the hole on the outside and the "L" foot on the inside and line it up with the pen marks!



I drilled the pilot holes with a 1/8" drill and finished them with an "E" (0.257"). The holes turned out to be 57mm from the edge, like it was meant to be!


The last step for the fabrication is to weld on the bracket. I'll admit, I've never done TIG welding on aluminum and I wanted it to look good so I had my dad do it. But I did the heavy lifting knowing he has a bad back. Me: "would it be easier if it was on the bench?" Dad: "yeah, but..." Me *picks up bike and puts on bench* Dad: "well, that works too...". Gotta love these little bikes!


Thanks dad!


The final step is to disassemble, put in the packing, and re-install. It turns out that the perfect way to cut the packing string ad insulation is in half! That leaves extra packing for next time!

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And here it is all installed on the bike:


As for how it works, it may be because the old packing was completely caked with hard buildup, but the new silencer sounds so much better! It's hard to tell but it might be slightly louder, but it is also deeper. Almost like a thumper, but with the same old put put sound. I really love how it sounds now! I didn't get a chance to ride test it because it was already dark when I finished, gotta love the north in the winter!

I hope this helps anyone looking to do the same for their old Cota!

Next step is a total tear down and cleaning of the bike. I'll be going through it top to bottom!

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Cool. Like that a lot.

I wonder if there'll be any performance differences?

Never heard of this being done over here.

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Yes, I like the way it looks much better than the stock one, especially without the bolt on spark arrestor!

I'm not sure about the performance. Everything around here is covered in ice so I decided to start the full tear down toady. It'll be a little bit before I can try it out...

Apparently Lewisport used to do the mod and sell them but when I called they said they no longer sold them.

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Great report there with picts to boot!keep us updated on the performance of the new pipe? Looks good I like it!

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Thanks guys! I've learned so much here, so I try to give some back when I can.

So far the tear down is going well. I've got the engine all torn apart and it looks really good. I'll be ordering all the parts I need hopefully today or tomorrow, and then I start cleaning everything while I wait.

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Sorry I know this is an old post but I ordered the turbine core for my 315r and the silencer box doesn't  fit the centre box very well at all, it is a different profile (to wide and not quite tall enough).

I don't mind doing the fabrication on the rest of the silencer but I looked around for a box of the same profile (to no avail) and thought this was the answer.

I will still use it but just thought I would let everyone know that it is a fair bit wider and you will have a fair gap between the centre box flange and the side of the silencer. 

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