Trials Australia Forums

Quick metal/ JB weld / Devcon FasMetal are all epoxy based products and as such can't take the heat required to get a sleeve to drop in. It would have to be applied after the sleeve is in. Up that transfer passage would be a bit tricky once the sleeve is in, to match the inlet port would be do-able but I'm not a big fan of the stuff for anything inside an engine. Welding is permanent and epoxy fillers are not in my opinion but then I have a TIG welder so I'm biased.

You need to show the broken Monty shaft if you want an opinion on the potential to re-make it. That needle bearing could be replaced with a thinner walled bush to increase the shaft size to strengthen it up. Don't think anything else would be easily adaptable.

Why don't you put all 3 Monty motors into a concrete mixer, let it mix for a hour or so and see what combination comes out!!!

Good point George. I just checked JB Weld Industrial:- not recommended above 600F/320C. Its a long time since I used Devcon but I seem to recall it was only rated to about 100C. (It was used on a low temp application of oxidised magnesium cases (SWM) which have since successfully survived over 15yrs regular VMX racing). I've heard some say JB Weld is much better than Devcon, others say its much the same.

One problem with applying it after the liner is inserted is preventing it bonding to the liner. Otherwise I'd think it'd cause considerable problems if the liner ever had to be removed again.


Yeh Greg, the problems with the 242 kickstarter are well known. I was assuming it had broken/missing k'start gears but I don't know if you have any of the kickstarter mechanism/shaft/gears/lever. I'm lead to believe much of the cause of the problem of broken gears is that when not carefully assembled/aligned (even from the factory) the gears which are already narrow only partially engage/overlap and therefore break the teeth, but I'm sure Chippy would know more about that.

If that issue can be addressed with careful (re)alignment/assembly, & if you have the rest of the mechanism in working order, the gears are currently available from inmotiontrials in the UK:

https://www.inmotiontrials.com/product- ... s-montesa/

My thinking was that if you combined that with fitting a compression release ALWAYS to be used while starting, it might be a whole lot less work compared to your current option when you consider what that will entail: raise tranfer ducts & inlet tract, fill/reshape inlet tract and boost port duct, bore cylinder to take liner, machine top & bottom of cylinder, fit liner, fabricate new engine mounts, modify connection to air-box/cleaner to suit, modify double down-tubes to suit side-port exhaust, build suitable exhaust system, switch rear wheel to RH drive & modify brake accordingly. That's a heck of a lot of work & if you have to pay for some of it to be done, does that make it uneconomical?

Come to think of it, compared to all that, perhaps your original option of adapting the 242 cylinder onto the 247 bottom end is worth considering again! Are there less problems to surmount there ???

Or another option with considerably less work might be to find a 348 Cota engine (as they have centre port exhaust) for an engine transplant ??? That might turn out more economical in the end. 348s were fairly common and stone reliable, and if you prefer 240cc to 306cc, it can easily be converted with a 248 Cota cylinder which are often on ebay.

Anyway, just tossing ideas forward Greg, not trying to convince you one way or the other. I'ts very interesting thinking thro the options & potential problems on projects like this. I've no doubt in your skills to make whatever option you decide on to work.

Not too hard to stop it sticking to liner, the advantage of using it is how it's liquid so you can use tape etc to form dams where you need it to be.
Biggest real problem is that you'd have to do it with the cylinder lying on it's side & only do 1 side of the port at a time
I've been a bit sceptical about using it in ports but quite a few engine builders swear by it in intakes as they're the cooler side of the motor.
A few years ago I had to machine a Honda car oil pump housing that was filled with jb weld on 1 side to allow it to be machined to let the pump work with the motor rotating the same direction as most others. It was going to be used in a rear wheel drive race car. Everything about machining it was the same as if it was aluminum

Tony27 wrote:Not too hard to stop it sticking to liner, the advantage of using it is how it's liquid so you can use tape etc to form dams where you need it to be.
Biggest real problem is that you'd have to do it with the cylinder lying on it's side & only do 1 side of the port at a time

I'd have tho't getting tape on the liner with sufficient precision in the appropriate places down the inlet tract (& boost port) with the liner in-situ would be fraught with difficulty to say the least. Easier said than done.

Perhaps a film of oil or greece on the liner in the appropriate places when its in-situ may prevent it bonding to the liner, but that's problematic too - can you guarantee that the oil/greece wouldn't be displaced, or there would be absolutely no bonding to the liner, or that the oil/greece wouldn't chemically react with the Devcon/JBweld? A bit risky for me.

TriCub wrote:Why don't you put all 3 Monty motors into a concrete mixer, let it mix for a hour or so and see what combination comes out!!!

George, my cement mixer is only big enough for 1 Montesa motor and some random parts so I think I need to choose carefully plus I like the idea of crinkly fins not crackly Fins!

Tony27 wrote:Not too hard to stop it sticking to liner, the advantage of using it is how it's liquid so you can use tape etc to form dams where you need it to be.

Welcome to the hypothetical Tony, everyone's opinion is valued. Not having used any of these quick type metals, if we tape the liner to prevent it bonding, then how do we remove the tape as it would be sandwiched between the liner and Cylinder? Secondly are these quickmetals like loctite in so much as heat releases the Bond? What I am trying to say is if the liner is bonded to the cylinder and we have to remove the liner again, would the heat required to remove the sleeve be sufficient to release the Bond?

JC1 wrote:Come to think of it, compared to all that, perhaps your original option of adapting the 242 cylinder onto the 247 bottom end is worth considering again! Are there less problems to surmount there ???

John, your thoughts are inspiring and elaborate. The Montesa 242 cylinder is 84 mm at the skirt that goes into the cases whereas the 247 cases are 80 mm so need to be bored. The hole centre's are 70 mm apart on the front and back of both 242 and 247 cylinders but the 242 hole centre's are 80 mm front to back and 70 mm on 247. So half a hole out on all 4 stud holes.

This whole concept has had me scratching my head for days as I am having trouble getting my head around it or in this case head into it. Main problem is I am comparing the inside of crinkly fin cylinder to the outside of 247 liner so I have come up with his idea:


The 80 mm aluminum tube slides into the 44M cylinder so I have clamped it in situ and scribed the inside of the ducts/ports onto the tube, then colored in the duct/port area with texta. This allows me to compare apples with apples, now I am back to wondering if it will be a problem to have the sleeve holes smaller than Casting? In commercial air conditioning terms, the registers/outlets are always smaller than the the duct work, yes there are more outlets than ducts but even the end/last one in the system is smaller than the Duct!
Now I have not forgotten your other suggestions John, my original thoughts were: what can I make with what I have ended up with?
Let me talk about KERMIT and the starting procedure: Depress the decompressor before doing anything hot or cold Every time! OK so let's assume for arguments sake that the smaller missing Montesa 242 kickstart shaft is as strong as the bigger TY 80 one. KERMIT is 157.8 cc or let's say twice as much capacity as TY 80 so it is like starting 2 x TY 80 motors at once.
Here is another mudmap including one of my formulas:

When I removed all external signs of my Ty's oil pump on the sidecover I just used the tape on the inside of the cover & folded up around the gasket surface to form the barrier, the JB weld made contact with the glue side where it was exposed. Came off fairly easily

I think the fear of using the JB weld in a position where it is in contact with both the cylinder casting and the cylinder sleeve, is that if you want to take the sleeve back out again, the JB weld will hold the two parts together

Only suggestion I can make is to build the port up using tape inside the casting before fitting the sleeve then blend things afterward

I think we've already established that JB Weld probably wouldn't stand the temp required to refit the sleeve. According to my Clymer manual for Montesas, that requires oven temp of 600C then place cylinder in it "for 3 or 4 minutes". JB Weld says max temp 320C.

So unless you're going to narrow the boost port duct with weld, Greg, it seems fitting the 247 sleeve into the 44m cylinder is fraught with grief in that area & looks to me like a lost cause.

Seems to me your best cylinder option is the 242 - more modern porting, less readjustment of frame etc. Is it too difficult to weld up the stud holes in the 247 cases then re-space them to suit 242 cylinder, & either bore the 247 cases (if they can take it) to suit the 242 cylinder skirt or turn the skirt down to suit the 247 cases ??


Another option you could consider is to fit the 44M sleeve back in its cylinder & use the whole 44M engine. According to the info/specs I have the 44M piston has a 4mm longer skirt than the equivalent Cappra 73M engine (and it does have a 44 part # as opposed to a 73 # for the cappras) That would give it port durations of 179deg Ex, 126deg Trans & 140deg Inlet, or thereabouts. Which is not too far removed from the 349 Cota. Compare it with other trials spec engines (including the 349) by clicking on the following:

1st gear ratio on the 44M is the same as a 247 Cota (2.60), as is the primary drive reduction (2.65), but 2nd is not close to 1st as on the Cota. The 247 ignition/flywheel should fit and if my memory serves me correctly they already have an extra flywheel behind the primary gear (like the 242) so overall flywheel weight may also be in the right ballpark. You should also be able to use the super slim Cappra/Enduro clutch cover if you wished, and knowing how you like such trick-looking clutch covers.....

It would still require frame mods of course, but here are some Sprites which had (narrow spaced) double downtube frame with side-port exhaust:




But I think if it were me in your shoes, I'd sell all the spare Monty stuff then procure & fit a 348 engine to the 242 roller. Then you'd have something like a 330 Cota which I'm lead to believe were just about the pinnacle of twinshock design. They sure look it:



Perhaps create your own unique 342 Cota model!

600C is definitely higher than the only sleeve I've had in & out before required.
My CZ only requires about 200C to get out, throw it in the oven cold sitting on the sleeve & turn on to 200, come back an hour later & the cylinder has slid down the sleeve
Can't suggest anything else