Rebuilding My Bultaco 159 Engine

[johnjsy]

Hi everybody,I am following this with interest. I did see somewhere that Kevin Breedon Racing has a large range of Pistons,may be worth a look. A request. Does anybody have a used but not very good std: 85 mm piston ? To explain,I have a relatively rare 1974 only M 173 motor,basically a MK 9 Pursang,but it is a 346 cc made for grass track racing. I managed to get a barrel from Spain,but it is 85 mm bore & will need a new liner at 83.2 to get down to 346 cc as original. I would like to run it a bit to see all is well & set up the clutch before getting the new lined job done.When finished I will sell it on as I have no competition chassis of any kind to put it in. Recently I have built a hybrid Alpina -- Sherpa M92--M99. 326cc now in my road bike.Goodness me,talk about torque ! I have used a Pursang gear set,lovely to use on the road. I too had the little end float problem so made my own alloy spacers from dural. I fit them with a close 2 to 3 thou clearance. One other thing, I put the crankshaft in the cases these days,no bearings,bolt together with a gasket,then measure the cases to crankshaft gap. Calculate half that then make up shims to that size. When the first case is heated to the drop in the crankshaft it then sits on the shim. This way I can get it to be as central as possible. On the timing side I use a roller bearing,so easy to assemble. I hope this is of help,regards,John.

[johnjsy]

This is the little end spacers I made.[

attachment=17257:image.jpg]

[bondy]

I have a 85.25 i took out my 199b i replace it with a new piston the old 1 is ok

[pschrauber]

I still have the 85mm piston of my Sherpa 199b model left,

the piston is ... well ... pretty used and the rings worn

(as you can see by the blow by) so the cylinder got an

overbore and 1st overbore piston.

 

But watch out the piston too has the both holes drilled

and the piston pin shaft is too a little bit out of the center.

 

See here:

 

 

 

 

[guys]

Quote:

 

"But watch out the piston too has the both holes drilled

and the piston pin shaft is too a little bit out of the center."

 

 

No need to worry about that, it's done for a reason:

 

https://books.google.be/books?id=Yn9F0RhJ0EkC&pg=PA244&lpg=PA244&dq=piston+pin+out+of+centerline&source=bl&ots=SaF7EHQBw4&sig=iSSXHxYKUXyoe5YuebcrJeQpjsg&hl=nl&sa=X&ved=0ahUKEwi8x9-H5NXJAhWBPxQKHR3uAqQQ6AEIHjAA#v=onepage&q=piston%20pin%20out%20of%20centerline&f=false

[johnjsy]

Thanks Guys,yes,most Pistons have the pin offset a little to quieten the motor on the down stroke. In the 1960's I spent a lot of time at our Kart track,learning about engines. We had a lot of Villiers engines for the 200 cc class,& I used to fit the Pistons backwards so as to get a few more revs. We did crazy things to those motors that if the original designers knew of they would of had a fit ! A good time to look back on. Patrik, I would be happy to purchase your old piston from you. Is it in order to put my email address on here & make the arrangements to buy? Please advise,somebody. Thanks,John,Island of Jersey.

[guys]

. Is it in order to put my email address on here

 

I think it's better to send it in a personal message, just click on his name, and on the right you'l find the "send me a message" button

[bult360]

Hi everybody,I am following this with interest. I did see somewhere that Kevin Breedon Racing has a large range of Pistons,may be worth a look. A request. Does anybody have a used but not very good std: 85 mm piston ? To explain,I have a relatively rare 1974 only M 173 motor,basically a MK 9 Pursang,but it is a 346 cc made for grass track racing. I managed to get a barrel from Spain,but it is 85 mm bore and will need a new liner at 83.2 to get down to 346 cc as original. I would like to run it a bit to see all is well and set up the clutch before getting the new lined job done.When finished I will sell it on as I have no competition chassis of any kind to put it in. Recently I have built a hybrid Alpina -- Sherpa M92--M99. 326cc now in my road bike.Goodness me,talk about torque ! I have used a Pursang gear set,lovely to use on the road. I too had the little end float problem so made my own alloy spacers from dural. I fit them with a close 2 to 3 thou clearance. One other thing, I put the crankshaft in the cases these days,no bearings,bolt together with a gasket,then measure the cases to crankshaft gap. Calculate half that then make up shims to that size. When the first case is heated to the drop in the crankshaft it then sits on the shim. This way I can get it to be as central as possible. On the timing side I use a roller bearing,so easy to assemble. I hope this is of help,regards,John.

Hi, why not run it as a 363cc with the 85 mm piston ? like you say its basically a mk9 but they were 1976 ish . I don't think it would put prospective buyers off if its a full 363 , a Spanish collector would be far more interested in the 173 prefix as like you say are relatively rare  .One year at the mavern off road show there was a guy selling 2 of these 173 motors serial nos 1 and 3 , at the time I baulked on the price,i will check if I have a std 85mm piston  

[guys]

Wössner do make custom pistons to your requirements.

They made the piston for my TR34 for a fair price.

 

Apparently France Trial Classic had a Mahle piston in the size that I need, which is very nice.

[bondy]

They have had that for some time as it's a standard size 85.25

Edited December 13, 2015 by bondy

[guys]

Apparently France Trial Classic had a Mahle piston in the size that I need, which is very nice.

 

 

They have had that for some time as it's a standard size 85.25

 

I was talking about a 84.45 mm piston for the rebuild of my Sherpa 159

 

Maybe Johnjsy better starts his own topic, because it seems to be getting confusing

Edited December 13, 2015 by guys

[guys]

Apparently France Trial Classic had a Mahle piston in the size that I need, which is very nice.

 

And I just got the message that Club Bultaco in France also still have some Mahle pistons in stock.

So if anyone is searching for one, contact: http://trial-classic-bultaco.fr/

 

[johnjsy]

Hullo Guys,apologies for being a nuisance,but have a look at Kevin Breedon Racing. All the following in stock,all at £143.86. Pencil ready ? 83.4---83.6---84.00---84.50---85.00---85.25---85.50---86.00 . O.K. Mate ? That should help you along a bit. The factory only made 500 of the 159, so relatively rare. I have a bottom end in very good shape,but no barrel or head. The parts can sit there for now,more important is a Metralla to be completely re-built. Regards,John.

[guys]

Hullo Guys,apologies for being a nuisance,but have a look at Kevin Breedon Racing. All the following in stock,all at £143.86. Pencil ready ? 83.4---83.6---84.00---84.50---85.00---85.25---85.50---86.00 . O.K. Mate ? That should help you along a bit. The factory only made 500 of the 159, so relatively rare. I have a bottom end in very good shape,but no barrel or head. The parts can sit there for now,more important is a Metralla to be completely re-built. Regards,John.

 

Hi John, thanks for the tip, but I already ordered a Mahle piston in France.

 

Good luck with your Metralla build.

 

Guy

[guys]

The engine cases are split and all in all it doesn't look to bad for a 40 year old bike

One crank and one gearbox bearing is damaged/worn.

 

Santa came early this year 

 

 

Home made case splitter

(had to insert a V-coil because one of the case threads was damaged)

Used a paint stripper hot air gun to heat up the case, which worked very well.

 

 

Some damage by the kick start mechanism

 

 

The middle gear on the left axle seems to have to much play.

 

 

And this is how bad bearings sound like

 

Edited December 19, 2015 by guys