348 Exhaust

[bigshineybike]

My 348 runs well now particularly since retarding the ignition to somewhere around 4mm BTDC I had been setting it to 14 based on an old manual which it must be said didnt specifically cover the 1978 348.

I have been told that running too far advanced is the cause for the burned fibreglass on the tank seat unit.

Also that I have proabbly burned out the inside of the exhaust centre section.

So my next task is to cut open the centre box to have a look.

have any of you done this job?

[feetupfun]

Are you saying 14mm BTDC on the rim of the flywheel or 14mm BTDC of piston travel?

Running too far advanced will not cause your exhaust to burn out inside and any heat damage to the fibreglass next to the centre box is quite normal for bikes that have lost the insulation layer from the inside of the fibreglass.

[dabber]

Used to do this regularly - slice it open, pull out all the old packing and gunk, repack tightly and weld. makes a huge difference to the smoothness of the bike.

Not sure about timing though.

[02-apr]

If my old brain cells are working correctly I recall the timing figure being 1.8mm BTDC measured with a dial gauge down the plug hole. I can't imagine it would run at 14mm. Worth checking very frequently.

I did both silencers and the difference in smoothness, from memory, enabled the use of one gear higher on the right section.

[bigshineybike]

and again:

Thanks for the above, I cut open the front exhust box this afternoon. There is a perforated tube inside the box, this was loose it has about a half inch of float within the box. There is no rust in there and no packing material at all.

I have spoken to one person who knows a lot about Montesas says I should repack it with Steel wool. I am considering riveting a cover so repacking in future is easier.

Might this be worthwhile or is it simply that my bike is 30 years old and will be another 30 before it needs to be redone?

And

I have been told the 348 exhaust can be taken off without removing the engine, what do you all think?

[feetupfun]

Yes the exhaust comes off without having to move the motor but it is a bit of a trick

Yes a removable hatch is a good idea if you are going to ride the bike for a few years.

Please ask your friend what benefit come from using steel wool compared with mineral fibre. I'm just about to repack my 348 exhaust too and might give it a go.

Edited March 20, 2010 by feetupfun

[bigshineybike]

OK I did the resuffing of the front box.

What a difference!

the bike sounds so much better, I have the engine ticking over so slowly.

Its so much easier to ride, power up slopes is smooth, low speed trickling through sections it has made riding so much more enjoyable.

I have put a removable 2mm thick alluminium plate over the hole so it will be easy to have a look at how the fibreglass mat I used is standing up.

I know its not the best stuff but I have masses of it in the workshop.

For the first time since I owned the bike I got it into top gear with some proper trottle on what fun.

I was ready to abandon this project but not now.