Recently acquired a 72' RT2MX 360 that I couldn't pass up in spite of loads of rust and some engine issues. Guy had a 74' DT360 motor that he was intending on swapping. I told him that was a no go in terms of a bolt in swap. Cracked the right side cover and attached a pic of what I'm looking at. I'm curious what parts I need to fix it or if I could use the applicable parts from the spare motor. Problem is anything inside the right side cover is extremely foreign territory for me and I know this is a case split repair so I'm definitely going to need some guidance. Everyone I know is saying part out but I can't bring myself to do it to an early mx. Two days after this purchase I got a running MX360 so pretty sweet how the starts aligned on that one.

Considering its all new territory & if you're not 'Really' into it it might be best to offer it up as is for sale on here or ebay or both. At a minimum you'll need the gearbox output shaft that's broken. Has the sprocket on the other end. Then all the associated bit need a close look 'if you have them'. Looking for bent or broken teeth considering the forces that broke the shaft. Nothing useful out of the later motor will fit unfortunately. Ball's in your court & depends how deep you want to go to part it out. Think i've said--i'd love to have it but half a world away doesn't work. Cheers.

So the output shaft parts won't work from the other motor eh? I'd like to learn but maybe it would be best to pass the bike on and focus on my mx360. Let someone else bring it back to life. What's an estimate of what I should ask for the bike as is? Part of me wants to keep anything that could be used on my mx360, pipe, tank etc. but then there's not much left but the frame and motor. Not a huge fan of part outs though.

If you look on Partzilla you'll see the shaft you need was used on a lot of bikes. Chances are you can pick one up cheap.

I say tear it down and try to fix it. If nothing else, you'll gain valuable experience on an engine that if you screw something up, what did you lose? If you part it out, most people won't want a whole engine anyway...

As far as parting out? I'm not a huge fan either... but you also have to think about how parting out one bike might be able to save dozens of others from the scrap heap.

ok, just when i thought i knew everything "i know !@#k all". The part numbers look the same if 'partzilla' can be believed. I felt sure they wouldn't interchange because i know the "73 MX had a needle roller bearing where as yours had a normal bearing where yours is broken. I thought the sizes through that area were different. So--there is hope after all that so it's back to you & anyone who can help. Very interesting. Look at #18 on both links & can see the differences between the two bearing. But bearings aren't the problem as you'll be using your existing one, or a new one the same. Bearing might be a yamaha special as there was a change in outer shell thickness back in the earlier days by memory. Then again the middle of the part number is 6203 so ok could mean they've gone back to a standard easily bought bearing & a stronger case around it--i'm guessing.
www.partzilla.com/catalog/yamaha/motorcy...2/rt2mx/transmission
www.partzilla.com/catalog/yamaha/motorcy...3/mx360/transmission

I think stator and CDI tests may be in order first. I fear that kickback caused the initial breakage from bad CDI or pulsar issue and if those are an underlying problem I'm not sure I want to enter that rabbit hole for the 3rd time. I compared the broken shaft to the parts the 74 has and they measure the same in addition shift shafts are all over eBay. All good info from you guys to get the ball rolling though.

Whats up with the shift shaft. Are the splines stuffed on the lever end. I think the main problem with the broken shaft on those is lack of flywheel inertia. Only have a small internal rotor cdi & that's ok on a 250 but is hard on the gear in a 360. Those two stage pulser coils start on retard then go straight to advance, but they seem to still kick back if you don't kick it hard & kick it right. You could find tdc as best you can, then mark the rotor against something stationary close by or felt pen or white twink it at the trigger as easy to see, then strobe it while spinning the crank & see if its close--like retard--or a long way off. I think on those if the retard half fails then it won't start at all. But if the advance fails it'll start but not get above idle. Could be wrong but had similar with my DT360A with a faulty retard half on a similar trigger, albeit a full flywheel type, but operated the same principle & had no spark. So wired it on advance & just kicked it hard. Was my daily transport to work.

While I never like seeing bikes parted out, this one might be cost prohibitive to save unless many parts are on hand.

The obvious is the broken gearbox shaft. That will be easy. In order to repair that though, you must split the cases. Once inside, expect to be replacing a minimum of gaskets, but more likely all seals and some bearings. No telling what you find once the cylinder is removed.

Beyond that, the shocks and chassis looks rough.

Ultimately though, it simply depends on you goal and purpose for the RT2MX. If to build a simple rider, then maybe sinking $500 to get it ridable is a good value. If you plan to make it nice, you might check sales of recent same models to gage value and estimate how much to invest.

In the photo I see a lot of crud inside the cases. That is concerning in some ways. Myself, I would remove the engine sprocket cover and inspect the cases just aft of the countershaft sprocket. See if the case is intact, repaired, or has the common hole knocked through the left center case. Pretty typical damage when the chain came off.

All the best, whatever route you decide.

Personally I would dig in or sell it as is. I could not part one of those out.

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