Hi, any ideas to why the cylinder engine mount on my sons 2011 st125 has fractured. Bike has had only little light use. Would this be weldable ?

 

I don't think it would weld too well but certainly worth having a go. There are a number of reasons why this might have happened. The other engine mount bolts, including the s/arm bolt and bash plate bolts may have been loose plus one of my dislikes about some of the trials bikes, is that, generally the engine bolts tend to go in from new with the apparent use of a hammer as the mounting brackets are not quite where they should be, this puts the motor mounting lugs in a stressed condition and eventually something has to give, especially when the bike is being bounced over rocks. I haven't worked on a Sherco so cannot comment about these. Bye, Peter B.

 My son`s 2012 frame was like butter. Luckily we just lost that bolt every 10 hours. Sure glad it was not the tab!

Are the frame front down-tubes still ok?  The fork triple trees hit the frame down tubes on these and can collapse the tube/s, weakening the frame and perhaps eventually causing movement and stresses at other places.

 

Best thing to do first is slacken all the engine mounts and the swing arm pivot, thats slacken not totally undo. Now pull and push the engine to see if that crack can be closed up. Do not try to weld before doing this as it will probably snap again. If the gap can be closed up then a good TIG welder might, I emphasise, might be able to weld it up. Being based in Sheffield you should be able to find a competent person. You will need to remove the engine so that the welder can get best access to all of the crack in front and behind for both cleaning and weld preparation. Has the bike been dropped on its side? Has it been yanked down too tight when transported? 

You may consider some form of extra support brace from the cylinder head bolts.

Maybe after all this years, plating isn't that good on this cylinder. Worth looking for new one if it is the case.

Welder has to be very carefully to not ovalize the bore with heat.

Check frame for cracks.

Edited November 4, 20196 yr by cascao

We have had more than one of these bikes crack the frames on the lower mounts under the engine; the frames are - as stated above - like butter, but also like glass. If the lower mount let go, the engine drops, which is what it looks like in your picture.

 

S