Sherpa T Exhaust

[ryanroz]

Has anyone used the Sammy Miller Bultaco Sherpa T Main Box Exhaust? I seen that it was aluminum and repackable. If you have used it, what kind of performance increase did you see if any? Any other knowledge of this product would be appreciated as well.

here is the link for it: http://products.sammymiller.co.uk/store/st...?stock_index=16

Thanks

Edited January 20, 2008 by ryanroz

[bultaco49]

Hi ryanroz

I have just finished a rebuild of a Miller framed model 49 and used the Miller exhaust system. The system as a whole has some manufacture problems. The front pipe is made of a thicker guage pipe and this makes it much heavier than original. The bends are made over bobins so the pipe is narrower at the radius of the bends (original item is parrallel even on bends). All of the pipes are made slightly different so expect to have to adjust the bends. This has to be done by heating cherry red rings and gently easing the pipe into shape. This, of course, is the end of the chrome but to be honest, the chroming is not the best anyway. The middle box has the same bends issues as the frontpipe though much tougher to sort out as pipes are so short. Only the box of the mid section is aluminium. Pipes and caps are steel. it is very easy to dissasemble and re-pack as it is riveted together with end caps. I use an early end spark arrestor (simmilar in shape to that fitted to model 125). It was a bu**ger to get the whole thing to line up and not foul frame, tyre, shock absorber etc. I would also suggest brazing on a loop to mid section and spark arrestor and using a spring to locate and join the two. However, having said all that it was worth the effort. Just having a properly packed exhaust makes the greatest difference to the performance. I also have a model 85 Alpina with standard exhaust contemporary to the Miller 49 and in comparison I would say that I prefer the characteristics of Miller exhaust. The power delivery seems much softer and exhaust note crisper. The Miller system also complements the Miller frame a treat.

To get a good performance from any Sherpa the mid box must be packed properly. Those I have ridden with packing degredation have poor, jerky low rev reponse in my experience.

Much as I admire Sammy Miller the trials rider my experience of the after market parts his shop sold is that they are generally better than original in concept but manufacture and quality is a bit dissapointing. This Sammy Miller brand is now. of course, under new ownership and I have found the new owners very helpful. Having said that my experience of the Spanish produced aftermarket parts is similar only add things 'in stock' are invarably not.

Tim

[swooshdave]

I'm looking at the same problem.

Here's a link to how I think I'll tackle it:

Blog Entry

(just have it stuck at the back for fun, will be mount in the center when I'm done (hopefully).

Basically taking a modern rear silerncer (easily re-packable) that's approximately the correct size and getting it to work. Probably will end up spending way more for the used muffler and modifications than to just to buy the Miller part. But that wouldn't be the first time I've made that mistake.

[greeves]

It is the first time I hear about this Bultaco exhaust.

To open and repare a Bultaco exhausts is not easy, and it is one of the main problems of the engine not working properly (with the ignition), so I can understand many paople buying this item. In the other hand, Bultaco exhausts are very good when you know what to do inside, and how to modify them to improve it. But aniway not easy at all.

[dabdab]

hey Senor Greeves, do you have some different tips on re-packing the two mufflers on a Sherpa T. Whats the hot set-up in Spain- any trick modifications you might care to share with us

[greeves]

Hi DabDab, at the moment I have no photos of the inside of a Bultaco exhaust improved. As soon an we open one I will post them. (I say "we" as I have someone who does it for me, I give the "orders" and he cuts, weld etc..... it is imposible for me to do that properly).

Wll try to explain it a little, but my English is not so good.

Basically you have to open and completely empty them. Then fill it with a drilled pipe that must be welded inside (the diameter varies if it is a 250, 325 or 340) and a good special fiber glass or any other sound absorver. In the big box of some of the final silencers in the last Bultaco

[shercosteve]

Hello, I have a 199A Sherpa, I am looking to modify my exhaust as discussed above, does anyone have photos of these mods ?.

Thanks, Steve

Edited February 26, 2016 by shercosteve

[pschrauber]

May be for those that haven't seen the inside interesting, here an opened rear silencer,

with the hole tube in the first section and the chambers and tubes inside the rear section.

The first section works as an standard absorber, the rear section after the Helmholtz principles:

 

Her one of many possibilities, in comparison (top original, below modified):

 

From the rear:

 

The Helmholtz section works nice each chamber or hollow is different so when the fumes go through parts of the noise spectrum will be filtered away or weaken, any way due to the small openings the system provides a constant back pressure.

 

Which limits the "free breathing" of the motor, it would a likewise effect to close partial the openings to the air box. BUT as the standard 2stroke engine has flushing losses (beside the exhaust fumes also fresh gases exit), most 2strokes need and have a return flow function, provides through a pipe that has a cone tube that opens slowly and then is closing in diameter again. The original shaped mid section of the Bultaco doesn't have any cone form beside the end of it were a small hollow is, see picture:

 

So with none additional "back pressure" you might get a worse performance, the solution in the picture above show a bigger hole oval shaped hole tube that has a slightly s-shaped curve inside which is in own experience a good compromise between a straight tube with no back pressure and the original one, too isn't visible at once narrower then the original and quite lighter. (a suggestion of many possible ...).

 

 

 

 

 

 

 

 

 

[noel063]

Hi pschrauber You used to have more photos of the exhaust you modified on one of the photo sharing sites. I have been searching for them but cannot find them. can you point me in the right direction.

many thanks Noel

[pschrauber]

Hi Joel,

I' ve sent you the link to my picture stack where you can take a look, with a smart phone my performing depending the www are sadly very limited, you might lol there.

[jonjeans]

Excellent information, thank you all. 

I have yet to clean up my Model 191 exhaust. And am a tad nervous about the process, so it is most useful to see what is inside.

jj

[JeJeBul198]

hello, is it possible to have pictures? thank you