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Jubilee Big Bang engine


Hi All,

Before I start, yes I accept buyer beware and that I have been well and truly conned. However, has anyone heard of any enterprising engineer trying to make a Big Bang Jubilee engine? When I bought my little Norton the V5 stated that it was a 500cc, hmmm I thought, a slight error by somebody. Today I have taken the heads off and was surprised to find that the pistons come up the bore together, now I’m an electrician but should they not alternate? Has someone tried to make a Big Bang engine? Please see the attached photo.



Brit twins are nearly all 360 degree engines, the pistons go up and down together but as the 4 stoke cycle takes 720 degrees of crank rotation the camshaft and ignition are set so one piston is on the firing stroke and the other is on the exhaust stoke ie 360 degrees apart. So to get it to act as a single you need a new camshaft.


Even if both pots fired at one - it would still only be a 250cc engine - as each cylinder is 125cc.

You have been conned! - Was it a dealer, or private.

If a dealer - go straight back for a refund.

If private, Caveat Emptor - buyer beware, as you say.

Can we see a picture of the wee beastie?

It would appear that I am just being a doughnut, like I said I’m an electrician says it all really. Didn’t believe it was a 500 anyway just think someone Balls’d  up the registration document, it also has the year of manufacture as 1983 ish. So someone has re-registered it at some point, would like to get an age related plate but I don’t think the bike is complete enough for that and I have no intention of returning it to standard.I either will build a cafe racer or a desert sled , sort of an Atlas scrambler copy. 


Thats not a heaglamp - its a lantern!

She looks good - nice little project. The pistons have seen better days, though!

To get an Age Related plate, you start the process once she is ready for the road, by contacting our 'Twins' Dating Officer. He will provide with dating info. Meanwhile, if you know your engine & frame numbers, I would be interested to add your baby to my Register. You can email me at the address on the back of Roadholder.. (or if you binned it already its:

Have you found your frame number yet? Picture attached where you might look for it.



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