Hey guys do you have to split the case to change crank seals?

[runutz698]

Hey
 I just got my montesa running, it ran for a minute then I gave it a small amount of gas and away she went 10,000+Rpm with no spark plug lead attached had to drain the bowl on the carby.....So I am guessing I have an air leak.....
do you have to split the case to replace the crank seals??

I have put new base gasket and  laped the head in so the top end should be spot on..

Cheers
Tom

[mx250]

Mind you I haven't done it but I can't see why not. The seals are in holders that are bolted in from the out side. Take off the mag and primary drive and you should be able to get to the holders.

[runutz698]

Thanks looks easy enough will have to have a look!!

[cappra]

And while you have the magneto off, please lap the flywheel
to the shaft.  You will thank me later!

[mike1948]

Hear hear!  When I got my VB bottom end, the previous owner had not lapped the Mag flywheel, and it fell off in my hand, complete with sheared key.  It's now lapped, torqued to specs, then for a bit of ensurance a socket & steel bar is given a few good taps as well ( if I had a rattle gun, I would have used that also - suggested by friend Radar, who is very handy with a spanner or two, though he seems to prefer EVO Maicos, don't know why).  Also, after about 10 minutes running, tighten the nut again.  It is that important!

[cappra]

Also might want to heat up the flywheel a bit.
I heat mine up on the stove, hot enough to have to wear
a glove, mount and then torque down within a couple of
minutes.  I think the lapping in is more important though.

[lms6201]

when u remove the seal holders , check the gasket or o ring that seals the holder to the crankcase , sometimes the gasket can become brittle , and may be causing a leak , if it has o rings , check the fit , i goop mine ,just in case the holder is warped or whatever , bultaco but monty,s are similar  

[Hoony]

why do you have to continually do this? as 390 ross mentions he has lapped it so much that it needs a washer to pull it up? please enlighten me, i would have thought once was enough, are the flywheels very heavy?

[David Lahey]

Hey
 I just got my montesa running, it ran for a minute then I gave it a small amount of gas and away she went 10,000+Rpm with no spark plug lead attached had to drain the bowl on the carby.....So I am guessing I have an air leak.....
do you have to split the case to replace the crank seals??

I have put new base gasket and  laped the head in so the top end should be spot on..

Cheers
Tom

If your Monty is like my Cota 348, you will need to make or buy a special puller to get the primary drive gear off it's taper to change the seal on that side.

[cappra]

The post 1977 mx models (250/360/414) all have splined
primary drive gears, and countershafts.

[runutz698]

WOW Alot of information about laping in the fly wheel, we are going to test if it is the bottom seal by filling the gear box up over half way with fluid and replacing the mag. side seal and redoing the retaining gasket!! That way if is the gearbox seal it will suck oil and we will see the smoke nicely, or if not it will be fixed, I am just praying I don't have to split the case..... The base gasket is new and the head has just been laped in so I am 100% it is the bottom end. But either way I am going to do both seals.

Jared how much are the seals I may need 2??

I tell you what 10,000rpm+ this baby went to for like a minute and the top of the pist still looks good. so atleast I know it is strong. I had to change my pant after the event it was a minute of oh F*^% what do we do now with my mate rib holding the spark plug lead in a pair of pliers.....The only way we could kill it is to drain the fuel bowl as I was not going to try stalling this beast(it had no chain on either). So all I can say is you learn something new every day.... and wow. It still has heaps of comp, I mean heaps it feel like an IT490 to kick over.

Cheers for your input guys I must say that this is the most helpful group on the fourm and most active....

Tom

[GMC]

And while you have the magneto off, please lap the flywheel
to the shaft.  You will thank me later!

Why didn't you tell me this 18 years ago when I had a Cota 304. I got sick of the flywheel falling off all the time no matter how hard I did the nut up. I sold it after a year, biggest lemon I ever bought.

[lms6201]

oil in the magy , what a mess !!   do a pressure test , cap the intake and exhaust , and see how long 10 (ten )psi lasts , only use a bike pump , for spigot type exhaust manifold i,ve used a short piece of bike tube (frount ) with valve stem , a yellow reo bar cap or a pvc pipe stop end with two hose clamps , intake , spigot type carb , can use a pvc stop end or a welsh plug ,shaped piece of wood ,  flange mount is easy , big leaks can be heard , a squirt of soapy water on the seals , u,ll see bubbles , piss easy , and a lot more acurate , can leak from a few spots , if not top end or seals or holders , can be crankcase half joins , harder to detect if leaking at the inner wall, but u might be able to pick it where it comes out ,that means a split ,   loss of one psi per minute is considered bad   

[mx250]

[runutz698]

So Jared I thinking about this lapping in of the flywheel, do you mean to lap in the back of the flywheel where it joins the crank so that when the bolt is done up it is mated flat togeather??

I am a bit unsure on this as I have never done a flywheel like that before!!!

Tom