an idea

sometimes in the quiet moments when there is no one around (to tell you perhaps you need to up the medication) you have an idea. this one was inspired by a thread about distributors on the samba. it talked about how the stock distributor car is a limiting factor to the voltage you can run to your plugs. from my VERY limited understanding of electricity a higher voltage = a larger gap the spark will jump. also a fatter spark across the same sized gap (err i think). all usefull if you wantto run high compression etc.

whan i read this i thought to myself, "what about a big cap distributor?" aka an early 40hp distrubitor.thes then lead to the question "could you fit the guts out of a VJ4 BR25 into the big cap body?" giving you a distributor that had the bigger electrode spacing than a stock mech advance unit that is built from early bosch components that are said to be very good quality. this is about as far as the idea got for maybe a year. (to be honest i can't remember when i had the idea but i think saying that it was only a year ago is year generous).

of late the idea had been floating around in the back of my hear with regard to the 36hp challange. the rules in several classes state something along the lines of "must use a bosch distributor and coil". maybe this idea may have a home...

one of the things i got in sydney was a cast iron big cap 40hp distributor, it kind of pushed this idea a little closer to the front of my concious. i've been in a rut of late, unable to get out into the shed and do anything... tonight i forced myself to go out there, i feel better within myself when i spend some time doing "shed" stuff.

so out i went with no fixed idea of what i would do, i sat in my "think'n" chair and there in front of my was the big cap. i had toyed with the idea of seeing if my theory was possible, but thought that it wasn't for tonight, but there it was in my center vision. it was a push to break the rut but i picked it up and pulled the "fakie" assistant over so i could grab some tools. i was off. note i didn't pull the VJ4 BR25 (010 for those that like the later bosch part numbering system) apart, instead i grabbed the spindle out of an oval dist VJU4 BR8) that was already loose in a draw, they are close/the same in a lot of diamensions.

observations:

a big cap must have been a pain to change condensers amongst other things when in a car.

the internals of the bigcap are very different to the VJ4 series. the big cap has a large hump in the middle of the body that sticks up 10-15mm, this carries the top spindle bush etc.

the bigcap shaft is slightly smaller diameter than the VJ4 range. usefull, the orig bigcap bushes could be reamed out larger in situ and reused.

the bigcap shaft is somewhat shorter than the VJ4 and the bigcap is one piece vs 2 peice. the difference in legnth is 2 fold, the shaft in the body is longer on the bigcap ( compared to the bottom half of the vj4), the points cam and partly in the top bit that the rotor sits on of the VJ4 is much longer than  (the top half of the VJ4). on the vj4 br25 shaft the top part rotates on the bottom half, the amount of rotation is controled by the weights + stops this is the total advance, the points plate doesn't move (on the VJU4 oval dist's it does but that is a different animal). 

when i tried the big cap rotor on the VJ4 shaft, it was too big... needs an adaptor bushing (or does it...)

to fit the advance weights into the bigcap the top bush will need to be pulled out, the hump cut almost to the floor of the body and the bush seat recut etc, some other clearancing may also be needed for the weights etc.

shortening the top section of the VJ4 to fit under the bigcap cap would be a several stage modification. i thought on this for a while then put the big cap back together. when i was wondering inside it hit me... cut the top off the big cap shaft and fit the weingt pin plate from VJ4 onto the bottom... much less work.

a custom points plate will need to be made or the stock VJ4 BR25 one modified to fit into a much larger body, but all in all i think that it is acheivable.

now i hit the two biggest stumbling blocks. i can't do the machine work and don't have a pet machinest either. plus i'm not chopping up my 1 big cap or my 1 VJ4 BR25.

i don't know if this idea really has any merit for the 36hp challange as i don't know if there is a bosch coil with enough bang to need a bigger electrode spacing (or can you run 2 coils firing in sync feeding into the 1 dist)(is it even legal to run 2 coils?)

if it is of benefit, i see it as being in the spitir of the 36hp challange as all the bits used in the dist are pre 64 or there abouts and none of the techniques needed in the conversion are post 64 either.

not to get some parts i can chop up and someone to turn the knobs for me.

if anyone reads this and can add comments of use or tell me if my rough ideas on electricals are sort of close to the mark or WAY off, please do so.

if i remember to take some pictures i'll add them so this make some more sense to people that don't have the distributors in question in peices in front of them.

henry.