Design and Prototype-Brian Mackenzie

Design and Prototype-Brian Mackenzie Velocette engine work and machining

01/06/2026

With the sleeve pressed and bonded in I parted off the excess and turned the ring entry on the bottom. I was pleased it went back in the fixture true (4 more Rizlas used).
Next I sharpened up the HSS tool, although it hardly needed it , and started rough boring out to near final size.
So far so good.

22/05/2026

Out for an evening run in the glorious Northumbrian countryside to test the effect of carb adjustments and the addition of a screen. The bike is our Vybrid Velocette Twin spark Squish Head, pulling a 19 tooth sprocket.

Crunch day for the ‘39 MAC. (and my shop-made kit). The only bought in item was the Rizlas 😃)I had to take out 70 thou j...
21/05/2026

Crunch day for the ‘39 MAC. (and my shop-made kit). The only bought in item was the Rizlas 😃)
I had to take out 70 thou just to get the bore round, and square to the barrel. I have worked a boring machine in a past life and we normally worked from the base fl**ge and centred on the unworn top.
In this case both the bottom and top fl**ges were well off square and the final rebore was 38 thou out of parallel.
I resolved that by mounting the outside of the spigot in a 3 jaw chuck and a pipe centre located the top. I squared off both fl**ges which then allowed it to run true in the fixture, without shims. Having got the barrel straight I then bored it parallel.
The Hall Green Gods were smiling and it cleaned up with 17thou to spare. Not a lot for a sleeve which is 3mm larger than the original bore.
I bored it for a 2 ½ thou interference and pressed in the sleeve, pausing halfway to give the barrel a good coat of green Loctite. I will also peg it, as Tokyo is a long way to go to correct any problems.
That will have time to go off properly as I am waiting for a new hone to be delivered in a few days, before final boring to size.

Cylinder boring bar out of 35mm stock. Built in 3 deg negative rake for cast iron. I’ll either make a HSS tool to suit (...
20/05/2026

Cylinder boring bar out of 35mm stock. Built in 3 deg negative rake for cast iron. I’ll either make a HSS tool to suit (no top rake required) or put a round tip on a tool blank. I reckon it will do the job. Time will tell.

The Velo gets the last laugh. Having trued the faceplate, made a precise adapter plate and substantial clamp I assemble...
15/05/2026

The Velo gets the last laugh. Having trued the faceplate, made a precise adapter plate and substantial clamp I assembled it all only to find :

The barrel top face is not square to the barrel

It has been bored +60 30thou off centre

The bore is way off round.

Consequently my 100mm pipe centre is of no use in aligning the barrel and I had to shim the top to get it running true. Much use was made of the dti and copper hammer.
The top location fixture was bored 1.5 thou oversize and snugged up with Rizla papers for a zero clearance fit.
I did a test bore in the end and it just cleaned up at 70.3mm. The sleeve is 71mm. If it doesn’t clean up over the full length I’ll have to go to the next sleeve size up, which thins the spigot.
Now to make a long boring bar.

Not as much progress as I’d hoped today. Started on the fixtures to position the barrel in the faceplate and squared off...
13/05/2026

Not as much progress as I’d hoped today. Started on the fixtures to position the barrel in the faceplate and squared off the base fl**ge. It then transpired I need to make an adapter plate to mount the barrel in the face plate. Left that until tomorrow.

Truing up a faceplate, to Colchester standard, before embarking on some cylinder boring tomorrow. (1939 MAC).
12/05/2026

Truing up a faceplate, to Colchester standard, before embarking on some cylinder boring tomorrow. (1939 MAC).

Completed milling jacks. Very close fitting threads and 26tpi is fine for this application. I use these projects as trai...
09/05/2026

Completed milling jacks. Very close fitting threads and 26tpi is fine for this application. I use these projects as training exercises for precision work, so they are deliberately made more accurate than they need to be. I’ve got some tricky work on a 1939 engine barrel next week so need to have my eye in. Well pleased.

Finally got around to making some jacks for the mill. Since it’s for vintage motorcycle work I made the thread ¾” Britis...
08/05/2026

Finally got around to making some jacks for the mill. Since it’s for vintage motorcycle work I made the thread ¾” British Cycle thread (26tpi).

25/02/2026

First proper road test of the D & P, Stage 1, Twin Spark /Squish Head/Revised Cam upgrade, of a Viper head on on a Venom barrel.
This is a different approach, based on improved combustion efficiency, achieved by better gas flow, induced turbulence and optimised flame path, rather than big valves and high compression. The valve timing is more moderate than a Viper/Venom cam resulting in improved tractability and flexibility and an MSS piston optimises the combustion chamber shape. We use standard Viper valves, induction and exhaust and 100% Velocette parts
I hope you can see the benefits, which include reliable tickover, strong, steady torque from under 1500 rpm, and ample power capable of 3 figure speeds, pulling a 19 tooth gearbox sprocket, on a Venom final drive.
The object is a powerful, flexible power unit which is easy to ride yet retains the unique Velocette character.

https://youtu.be/nty_RJkw1pg?feature=shared

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