Cota349 Shop Manual/articles needed

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OregonTYist
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Cota349 Shop Manual/articles needed

Postby OregonTYist » Sun Jan 28, 2018 4:04 am

Hi fellows.
My son and I have a Montesa 349 that we are resorting which has a seized engine. I managed to remove the cylinder and will need to split the case. All we have is the parts diagram. We could really use any technical documentation on rebuilding the engine. Also any pointers and advice.
Thanks in advance.



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Re: Cota349 Shop Manual/articles needed

Postby David Lahey » Sun Jan 28, 2018 8:46 pm

I don't have anything more than the parts book either but I have put a 348 motor together.
Some people are surprised to find that the conrod is held in the centre by the little end and when you are reassembling, that the left-right position of the crankshaft requires careful setup to avoid putting a bend in it. The crank is shimmed on both sides using shims between the seal retainers and the main bearings.
Something to watch for during disassembly is removal of the primary drive gear from the crankshaft (it's on a taper) which usually requires the manufacture of a custom puller, to avoid damaging the teeth on the gear. It can be very tight on the taper.
The gearbox output shaft sprocket is also on a taper. There is enough room to cut the sprocket down to next to the shaft using a 100mm angle grinder. It can be very tight to get off too. I got to about 1mm from the shaft with the disc when I did it and the loading of the taper was enough to split the sprocket at that point, avoiding damaging the shaft. If you decide to try a puller on it (using a puller didn't work for me), heat will help and if you are pulling the engine apart it doesn't matter if the shaft seal gets too hot.
I can't remember if the gearbox shafts have shims or not. It's an odd gearbox in that it has very long shift forks and the gearbox air space breathes through a hollow chamber at the rear that has a tiny hole to the outside world near the swingarm pivot.
The gearshift mechanism is fiddly to set up and 348s are known for being unreliable at selecting the lower gears properly.
I suggest you buy the highest quality crank seals you can get because the drive side is such a pain to change the seal.
The drive side flywheel is known to fall off (the crankshaft breaks) so maybe do crack testing while you have it apart.
If you are doing a rebore, do some research on the best way to do it because when there was development work on 348s and 349s, it was discovered that you could reduce the piston rattle by making the bore a bit tapered.


relax, nothing is under control

OregonTYist
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Re: Cota349 Shop Manual/articles needed

Postby OregonTYist » Mon Jan 29, 2018 4:43 am

Thank you David. That’s good info indeed. I had a hunch this one would be interesting. Odd that there is not more out there in terms of a manual. We have a Clymer book on Montesas with no mention of the 349.
Let me know if you think of anything else.
Patrick



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Re: Cota349 Shop Manual/articles needed

Postby OregonTYist » Mon Jan 29, 2018 9:34 am

One detail:
Is the safety wired flywheel nut reverse thread?
I think the clutch’s is standard threading?
Thanks.



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Re: Cota349 Shop Manual/articles needed

Postby David Lahey » Mon Jan 29, 2018 8:24 pm

OregonTYist wrote:One detail:
Is the safety wired flywheel nut reverse thread?
I think the clutch’s is standard threading?
Thanks.

Sorry, I don't remember that. Did you know there is a facebook page for Cota 348 enthusiasts? I'm sure you will get sensible answers on technical stuff from some of the participants, even if it is a 349 that you are asking about
https://www.facebook.com/groups/57549537568/


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OregonTYist
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Re: Cota349 Shop Manual/articles needed

Postby OregonTYist » Fri Feb 09, 2018 1:49 pm

Hi David.
I was able to pull the primary gear off with some effort.
Do you use a case splitter? If so what sort? Also,any pointers doing this operation ?
Also, can you elaborate a little more on the codrod centering on the little end?
Thank you
Patrick
Here are some pics of our progress.

https://www.instagram.com/motosgaragistes



David Lahey
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Re: Cota349 Shop Manual/articles needed

Postby David Lahey » Fri Feb 09, 2018 9:00 pm

Warming the casings so the bearings are a looser fit in the cases will reduce the risk of damaging the bearing seats.
There should be a spacer on each side of the conrod on the gudgeon pin that hold the conrod in the middle of the motor. If you use a different width conrod or different piston then you will have to make sure that the spacers provide a bit of side clearance. 0.5 mm should be enough.
When you fit the crankshaft into the cases, make sure that you centralise it so that the conrod has side clearance to the crank wheels, and ideally the conrod sides are equidistant from the crank wheels.
If you are reusing the piston and conrod and using the same width main bearings there really is nothing to do except to make sure you put the main bearing shims back where they were and use the same thickness gaskets for the centre gasket and the seal carriers.
If you are fitting a new conrod kit the crank wheels might end up a different distance apart so you would need to make sure that the crank seal carriers are re-shimmed properly to prevent squeezing in on the crankshaft. I've seen a 348 crank refitted with the seal carriers squeezing on the crankshaft and it caused the ends of the crankshaft to run out. The clue was that the primary drive gears were noisy (thumping) when the motor was running. It was recovered by straightening the crankshaft in-situ.


relax, nothing is under control

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Re: Cota349 Shop Manual/articles needed

Postby OregonTYist » Sat Feb 10, 2018 5:17 am

David.
Would such a tool make our lives easier upon reassembly of the crank into the cases?
Then it'll be a matter of figuring out the shims. Still a little fuzzy on this.
Can you see any reason this tool would not work on the 349?
Have a great weekend.
Patrick



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Re: Cota349 Shop Manual/articles needed

Postby OregonTYist » Sat Feb 10, 2018 6:09 am




David Lahey
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Re: Cota349 Shop Manual/articles needed

Postby David Lahey » Sat Feb 10, 2018 8:53 am

Yes, a tool like that makes installing the crank easier, but the case half you are pulling a bearing into should still be heated around the bearing hole, to reduce wear and tear of the aluminium bearing seat.
If you haven't changed anything dimensionally on the drive side of the crank, just use the same shims and gasket thickness as what came out and pull the crank in until the side of the drive side bearing touches the seal retainer.


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