converting 125/150 blocks to 200

[camel]

with the recent price hikes of 200 blocks its got me thinking about converting a 150 to 200,what is involved?i know people used to do this back in the 80,s when 200 blocks were like hens teeth to find....is it really necessary to weld up the old stud holes,cant you pug them with an ally thread locktighted in place and re-drill using a packer or base gasket as a template?does a 150 block need to be jig bored to a 200 spec spigot size?surely this must be commercially viable to do and offer now?

[Doom Patrol]

You've got to have the right casing to start with. You can't do it on any old casing you know.

[Knowledge]

I’m thinking about converting a 150 to 200 …...is it really necessary to weld up the old stud holes? Can’t you plug them with an ally thread locktited in place and re-drill using a packer or base gasket as a template?

I have also been thing about this. Some 150 casings are significantly better for conversion than others. Some Spanish and some Indian 150 casings are ideal, but not all of them take the weld particularly easily (if at all). These casings are 200cc blocks with 150 stud spacings and a 150-width spigot hole.

You could plug the holes with some threaded ali rod, but the new hole would be drilled only slightly off-centre from the 150 hole. The risk here is that the plug will move as you drill, tap or screw-in the new stud. I wouldn’t trust locktite for such a purpose.

I do wonder if it would be possible to use threaded ali rod, but leave it a few millimeters below the gasket face, and then ali weld it into place at the gasket face. Once dressed and re-drilled, the insert would not move as it is ali welded in place. Does anyone have any thoughts on this solution?

…… and re-drill using a packer or base gasket as a template?

Personally, I would never trust a gasket, or even a space plate. These holes need to be very accurate in location and perpendicular-ness to the gasket face. I have a 200cc barrel from which the top has been hacksawed off. Once the mouth of the 150 casing has been opened out, the scrap, cut-down barrel can be slotted into place and used as a guide for drilling the new stud holes. Long drills are available, but are they long enough?????

Does a 150 block need to be jig bored to a 200 spec spigot size? Surely this must be commercially viable to do and offer now?

I think this is the only safe way. There are a number of dealers who have jigs (Rayspeed, JB, Jahspeed, Harry Barlow etc) and I would think that if there was a better way to do it, someone would be making their fortune and shouting about it.

Commercially viable? Well, there are only so many suitable casings around, and converting a “true” small block casing to 200cc sounds like a lot of extra welding with a risk of distortion.

[camel]

im not so sure you would have to weld the holes up,locktite produce all sorts of wonderfull "glues" for different applications,ie different strength of threadlocks and bearing fit etc,and if you used an ally thread the drill wouldnt be "pushed" as you drill it taking the easiest route say if you plugged it with a steel thread,i realise its not the sort of stuff youd want to be doing in the garden shed and i take your point about accuracy.but i think if someone had access to say a machine shop or toolroom!!!!that this wouldnt be rocket science....hmmmmm

[Knowledge]

.....but i think if someone had access to say a machine shop or toolroom!!!!that this wouldnt be rocket science....hmmmmm

I have access to a machine shop, but I wouldn't do it without a jig. I don't have a jig, so I will entrust this work to someone who has.

[camel]

wouldnt it just be a case of "clocking"up to the origional spigot bore and boring out to the new size?...or am i barking up the wrong tree

[vince]

I havent really looked into this , but why not get a new crank case spigot made with studs holes in place machine the old one of then fit and weld the replacement. a bit like the DAK idea but on a much smaller scale.

[sean brady scooters]

sorry to interupt folks ...but it seems that you must have missed this topic....


http://scooterotica.org/forum/viewtopic.php?f=7&t=3204

[DJB]

I havent really looked into this , but why not get a new crank case spigot made with studs holes in place machine the old one of then fit and weld the replacement. a bit like the DAK idea but on a much smaller scale.

I think for the price it would cost, i would look for a 200 case.

[camel]

sorry to interupt folks ...but it seems that you must have missed this topic....


http://scooterotica.org/forum/viewtopic.php?f=7&t=3204

indeed i did miss it....apologies