Cota 348 cracked engine case

[DavidSweden]

Hello,

Newbie warning: I bought a cota 348 a couple of weeks ago and noticed an oil leak from the timing flywheel cover, pulled off the cover and saw that the case has cracked bý the kick start shaft . 

Questions:

Is it wort welding the case and can I disassemble just the right hand side of the motor?

I removed the sprocket gaurd but the bolts seem to rotate what is it on the inside of the case that the bolts screw into?

 

 

 

 

 

[feetupfun]

Those nuts are on the ends of bolts that hold the two centre casings together. The other ends (inside the clutch compartment) may need to be held to retighten them.

As for the crack, there is a common mode of failure with 348s caused by the kickstart shaft being rotated too far during a kickstart stroke. This usually punches a hole into the magneto compartment and is not a big deal. The marks on your inner casing and the position of the crack does not look typical for the damage to be caused that way.

I'll take a guess that someone has attempted to kickstart the bike without the magneto cover in place. Because the kickstart shaft loses it's outer support when that cover is removed, kicking it with no cover in place could cause a crack like that.

The crack is fixable by welding and to do it properly, requires disassembly of the motor (removal of the cylinder and separating the left and right inner casings).

Rather than welding, you may be able to source a second-hand RH inner casing.

Whether it is worth fixing or not depends on many things that you haven't mentioned.

[larry s. k.]

 Hi just my opinion ,, older montesa , takes time to rebuild and requires ,$$$,,, mechanic exp , berings gears , small pain ,,  there are quite a few , montesa engines complete 348  on line in the states  under 1000. USD ,, I purchased one few years ago complete cheep ,,,, In good shape , I just got lucky , I have 4 montesas,,,  old models ,,, I have a montesa Rickman vr 250 ,, , I rebuilding ,the trans was blown , when I purchased bike ,,,upon,,,, splitting case , gears , needle berings  , we’re not in place ,was a mess , WAS BLOWN ,,, , so,, I found a vr short block in Oregon state  , from a montesa parts dealer on ebay ,    I would sell this shelf 348 ,, I on the other side of the world wash state ,, maby you could advertise wanted 348 short block  you might get lucky.  ,,,,  Well good luck ,,, 

[Tr1AL]

@DavidSwedenIts a very quick job , it should only take you a minute or two. https://youtu.be/BqccnNejZbY?feature=shared

[dr nosh]

Very common problem.

That lug on the kickstart shaft always causes this damage if rotated too far round.

Seen it lots of time, and search posts on here for other pictures etc.

Will need proper welding - preparation is key. If the case is oily welding will be difficult. Casting will need thorough degreasing.

So, engine out, head and barrel off, split crankcases etc, etc.

Otherwise the timing case will fill with water, mud, oil etc and spoil the Electrex electronic ignition that somebody (you?) have fitted.

[DavidSweden]

Thank to everyone for the advice.

I removed the engine from the bike and removed the outer casings. It looks like the crack has been welded before but the weld has failed.

How do I remove the right hand case half, do I need to remove the clutch etc....and what about the gearbox?

 

[feetupfun]

It sounds like you haven't pulled a motorbike engine apart before. The Cota 348 is far from being an easy one.

To get that casing separated on many other bikes is straightforward. The primary drive components are removed, the shifting components are removed, the gearbox output sprocket is removed, the ignition flywheel is removed, the shift drum indexing plunger is removed. All the fasteners holding the halves together are then removed and the crankcase halves are separated.

Cota 348s have a few unusual things that can prove to be more challenging than on most other bikes.

The drive gear on the crankshaft is on a taper that can be very difficult to release.

The sprocket is on a taper that can be very difficult to release.

The gearbox components are positioned precisely left/right with shimming that can fall off the shafts during disassembly.

The crankshaft seal holders, gasket thicknesses and shimming are what positions the crankshaft in the right spot left/right and provides correct end float.

[DavidSweden]

I have started to dismantle the engine in order to split the case, the case does not seem to want to come apart, is there something more that I need to loosen or do I need to hit it harder?

 

[Tr1AL]

4 hours ago, DavidSweden said:

I have started to dismantle the engine in order to split the case, the case does not seem to want to come apart, is there something more that I need to loosen or do I need to hit it harder?

 

Localised heat to inner bearing race of main bearing , oxy acetalene welding torch  or use of a case splitter tool home made or ready made ?

[DavidSweden]

Thanks for the advice I heated up the case and it came apart.

It looks like the crack in the case was not the cause of the oil leak, The oil was coming from the seal on the kick start, also the main bearing was rough so I think I will replace both main bearings and all the seals,

This means I will have to remove the gearbox, I am unsure how to do this, is there some way to remove the whole assembly in one piece so it can be replaced as a unit when its time to put the case halves together?

Thanks in advance

[Tr1AL]

Make drawings and take photographs /video when you strip the gearbox to remove it and place  it in its  order using rubber bands to keep everything held together in their specific order on the different shafts to help you when you put it back btogether again.  

[larry s. k.]

 Great  , ,,,,,did not fall apart ,, LOOK at gears , top front looks worn ,, ,  cheers 

[DavidSweden]

I think the gears are ok its just a bad lighting on the picture

 I have removed all rhe bearings except for 1 which is in the case and its blind bearing, the bearing race is stuck in the case see picture. Can anyone tell me how to remove the race from the case?

[Tr1AL]

16 hours ago, DavidSweden said:

I think the gears are ok its just a bad lighting on the picture

 I have removed all rhe bearings except for 1 which is in the case and its blind bearing, the bearing race is stuck in the case see picture. Can anyone tell me how to remove the race from the case?

Hello again @DavidSweden you will need a blind hole bearing puller or home made expanding type tool to grip the inner surface of the bush bearing then apply heat to casing  around the part to help extract it

Edited December 12, 2023 by Tr1AL

[DavidSweden]

I cannot get the bearing racer out of the case even with a puller, the race is conical so the puller just wont grip, if anyone has some advice I wil be glad to hear it.

I was looking at the through bolts that hold the case halves together, some of the nuts look like they are in bad shape, but they are not standard M8, does anyone know what size the thread is?

Also what is the torque for the through bolts?

 

Thanks in advance

Edited December 17, 2023 by DavidSweden