OzVMX Forum

Clubroom => Tech Talk => Topic started by: Ji Gantor on March 27, 2009, 09:45:55 am

Title: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:45:55 am

This Bultaco head had a fin broken off that needed to be replaced.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:47:18 am

It was decided to build up the weld instead of welding in a new piece as this should give the best result.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:48:45 am

The building up process is not just a single pass.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:50:58 am

After there is enough weld to fill in all the gaps the weld is ground to see if there is any imperfections.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:52:26 am

Next some fine grinding is applied to shape the fin.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:54:15 am

The last process is to bead blast the head so that all the fins look the same.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 27, 2009, 09:55:39 am

Looking good.
Job well done.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: mainline on March 28, 2009, 08:17:19 am

very nice Ji, impossible to see the the repair. Tig welded I assume?

I saw an old Matchless the other day that had been used as a speedway bike back in the 50's /60's. Every fin had been knocked off with a hammer (to save weight?) might be a bit too far gone for your method ;D

Title: Re: Replacing Alloy Fin On A Head
Post by: Ji Gantor on March 28, 2009, 08:37:19 am

Hi mainline,
Thanks for the kind words.
It is TIG welding.
You can fix anything as long as you have the patients, tools and time.
It just depends if it is worth it.
Some times it is easier to buy another half decent one if one is available.

Ji

Title: Re: Replacing Alloy Fin On A Head
Post by: pmc57 on March 28, 2009, 07:51:40 pm

Hi Ji,
I like the way you apply your knowledge on tech items and your preparidness to share some of the finer points of the metal trades. If you don't mind me asking, what's your background? You seem to have access to a wide aray of remanufacturing resources. It appears you're an avid DIY'er and enjoy playing with all things mechanical... like most of us VMX'ers. Spill your secrets.
Peter

Title: Re: Replacing Alloy Fin On A Head
Post by: LWC82PE on March 28, 2009, 07:57:36 pm

Quote

I saw an old Matchless the other day that had been used as a speedway bike back in the 50's /60's. Every fin had been knocked off with a hammer (to save weight?) might be a bit too far gone for your method

now is that all the fins or just the ones on one side of the barrel? if its just one one side its to do with using a AJS barrel on a Matchy or a Matchy barrel on a AJS. (i think of the exact way, been  while since i was familiar with them). one has the magneto at the front and one at the rear and when you mixing and matching AJS and Matchy top and bottom ends, to get it to work you have to chop off the fins. Besides doing them for normal motorbikes i have also rebuilt several AJS/Matchy engines for an old TQ speedway car and i cant remember if it was originally built for a AJS or a Matchy but some one had changed motors or just barrels at one stage which ment the barrel fins had to be chopped off to get the magneto to fit on. instead of neatly cutting them off, they just broke them away by hand which was rough as.