cracked exhaust

[Delbert]

Morning all
350 LC with thick collar exhausts
Right hand pipe has cracked under foot rest almost in half ,, it did this last year further forward , is there a problem that causes this or does it just go with the grain so to speak , I have new damper washers on the engine mounts . Any thoughts ?

[steven]

Hi,
Is it a tie bar model or not?

Have you done the "mod" to the rear hangers? I beleive the "mod" was one of the official Yamaha mods at the time regarding all the exhaust cracking probs. I did mine, but cant remember the sizes. It said that you were to cut the "top hats" or whatever their called. The small metal tubes with a washer at one end, that goes through the middle of the exhaust mounting rubbers in the rear of the footrests.
I cant remember the sizes off the top of my head, but it said you were to cut the "top hats" in length from .....guessing now.....20mm to 12mm?, which has the effect of not holding your pipes as "ridgid" to the frame, allowing them to "move" along with the engine, and put less strain on your pipes, and hopefuly stop them cracking.

Please check the sizes before you reach for your hacksaw, as I honestly cant remember what it should be.


I havnt had an exhaust crack, but I have had one break a stud in the past.

What size are your exhaust studs? standard M8? or Iv seen a few that have been drilled out and fitted with M10,s or mabey even M12,s.

I will be interested to hear what you find, as I have a non tie bar engine, standard thick flange exhausts, standard m8 exhaust studs,old type barrels, but I have done the mod to the hangars, but i have not done a lot of miles on it yet.

steven.

[Delbert]

Thanks for your input Steven
Mine is also non tie bar model with later barrels , im still on m8 stainless studs
I did notice the last time the exhausts were off that the top hats had been cut , whether correctly l cant be sure but will check that , you would think that by cutting them you are making them tighter to the foot hanger !! . One thing I did think of was that I suffered bad vibrations just under the power band to the point of lifting my feet off the pegs slightly as it was that bad , having tried many things to cure this , it disappeared after a carb overhaul & set up .
This was only recent so may be that contributed to it early on ?

[steven]

Hi,

I had to think about the top hat thing too, in that, I also thought that a shorter "tube" would secure it tighter, but I think the shorter the "tube" the more the rubber comes into play and flexes more???
I did ponder it for a while at the time, and saw the method in their madness, I think.
My heads not up to too much pondering at present though, after doing a nightshift....yukkkk.

I also put stainless studs in mine during its recent overhaul, then, after more "pondering" I decided to take them back out.
I decided that if I had to try and drill out a broken stud, Id much rather it wasnt stainless steed due to it being a bit of a hoor to drill, but nice new drill bits usualy do the job.

I also pondered for a while about using brass exhaust studs, as I have seen plenty engines with brass exhaust fixings, but in the end, I went with M8 x 50 GRUB SCREWS, M8 s/s flange nuts and m8 s/s dome nuts.
As its a grub screw, you can use an allen key to screw the exhaust studs in and or out, and I think it looks quite good with the flange nuts then the dome nuts on top.

For no other reason than peice of mind, I think tie bars would be quite nice.

I have an LC frame that some "heathen" has, what looks like, BITTEN OR CHEWED the complete front engine mounting out of, and welded/electric glue gunned two wee plates onto the frame, to accept an RD aircooled bottom end.
It also had LC barrels and side casings etc, and looked exactly like an LC.....to the untrained eye...my eye was not very trained when I bought it !.

I bought a complete front engine mounting section cut from a tie bar frame last week from a forum member, so its destined to be peiced back into where it belongs, soonest !
I have a set of vapout blasted tie bar cases waiting also.

Im wondering what else I,ll be "concerning" my self about once I have tie bars?

steven.

[sunsetrider02]

The trick is not to overtighten the hanger bolt and as you have already suggested, this will allow the exhaust pipe to move slightly back and forth as the exhaust expands with the heat.

[copper99]

Oct 10, 2013 9:32:13 GMT 1 steven said:

Im wondering what else I,ll be "concerning" my self about once I have tie bars?

steven.

One thing is for sure Steven, there will be something else to keep the mind "concerned" or busy when you have an LC...