WELCOME to my blog about restoring vintage overhead camshaft AJS and Velocette motorcycles

 

Apologies to anyone that has come to this page expecting to see exclusively vintage AJS motorcycles .....scroll down the page a bit and you will find plenty of them.

However, I recently sent all of my cammy AJSs to Bonhams and they were sold at the Autumn Stafford Sale. 

The URL of "vintageajs" for this blog is now somewhat misleading but it's too late to change it and there is still plenty to read about the AJAY projects. If you happen to be the new owner of one of the bikes that I recently sold then there is plenty here to read about its build. I still have 2 early Big Ports waiting in the wings ....but they will have to wait until I've completed the Velos. 

In 2023 I started the restoration of 2 early Velocette KTTs plus another Mk 1 OHC cammy special - a few details about each of these bikes can be found here and here. 

A lot of work has been done on these bikes over the past  2 ½ years and the INDEX PAGE provides links in chronological order of the project so far.

Earlier this year I acquired a DOHC 250 Velo Engine and now have a Resurrection Plan. The crankshaft has been rebuilt using MOV flywheels and "K" mainshafts, I have revised the lubrication system to mirror that of the Mk V KTT engine that is in my workshop, made eccentric studs to be able to fit the upper parts of the engine and, more recently, machined all of the cylinder head and cambox retaining studs and bolts. The cambox has been stripped, checked and reassembled. 

Links to all of the work done so far can be found on the DOHC 250 INDEX PAGE.

Over the Christmas period I completed the lubrication system. Details here.

During the last 5 years I have posted quite a lot of information and to aid navigation the "Labels" section on the right side of this page lists the various projects.

The labels marked "INDEX" give a link to a page that provides a complete list and links to all of the separate sub-projects related to that main project.

Alternatively, scroll down this page and see what's here.

When I started this blog I owned a 500cc AJS R10

that I've been riding for many years and wanted an early 350cc bike. I bought one at a Bonhams auction; this is what I brought home....

....a bit of work was needed to bring it back to life 

Full details of the restoration can be found here.

During the restoration of the K7 I figured that I could put an early overhead camshaft Velocette cylinder, cylinder head and cambox onto the crankcases of an AJS 350cc engine from 1931, convert it to chain-driven OHC and make an engine that looks like a K7 but has a Velocette top-end. I had a 1928 350cc AJS sidevalve that I had bought on eBay and used that to create the AJcette ....giving credit to both manufacturers.

It looks pretty similar to the K7 and to demonstrate that there really are 2 bikes, here they are both together.

Details of the AJcette project can be found here.

I have quite a lot of early Mk1 OHC Velocette parts and after completing the AJcette I decided to use some of these to make a replica of a one-off bike that AJS built in 1929/1930 for an attempt on the world speed record. The original is a huge V-Twin beast that started out with a naturally-aspirated engine but, having failed to gain the record, was supercharged ...and again failed. The bike ended up in Tasmania for many years and, after being repatriated to the UK and restored, it is now in the National Motorcycle Museum.

This is what the original looked like:

and this is my recreation.

 

 

Like the AJcette, the V-Twin uses Mk 1 OHC Velocette cylinder components. The full story of how this bike was built can be found in the links here.

There is also a 14 minute edited Youtube summary of how these bikes came about here and a longer unedited version here. 

This bike is now in the Sammy Miller Museum.

 

In January 2022 I started the restoration of a 1933 AJS Trophy Model

and this was completed in March 2023.

 

The Index Page for this project can be found here.

I also reported briefly on a couple of my other projects ....vintage OHV Nortons

 and putting a Marshall supercharger onto my 1934 MG PA

 

I hope you find something of interest.

The DOHC 250 Velo Engine: The Lubrication System – Part 2

Having decided to change the lubrication system to take oil directly from the pump and direct it to important parts of the engine (see here) it was now time to fill in the details. A few decisions needed to be made to be able to proceed:    

     1)    I decided not to introduce any kind of overall flow control or pressure regulation – the entire unrestricted output of the pump would be used.

 2)    4 parts of the engine would be targeted directly: (1) the crankshaft (and therefore everything accessible in the inside of the crankcases – main bearings, piston/cylinder); (2) the upper bevel and (3) & (4) both cams. Oil from the feed to the upper bevel chamber would flow down to the lower bevel chamber and then, via a drain, to the crankcase. Oil from the cambox would be scavenged via an internal tube the height of which has been set at the bottom of the gears and returned to the oil tank by gravity.

 3)    The relative flow rates to each part of the engine would be controlled by the diameter of quills. Now, a quill is essentially a small diameter pipe rather than an orifice but, in both cases, the flow rate is related to the square root of the pressure drop. The upstream pressure is the same for all of the quills – it will be whatever the pump delivers, but the greatest unknown is the downstream pressure which will be different for each and, for the crankshaft and upper bevel feeds, an oscillating pressure resulting from the crankcase pumping. The effective area of the crankshaft oil drilling/big-end bearing assembly downstream of the quill in the mainshaft (which is where the oil ends up before it gets thrown out into the crankcase) provides an additional flow restriction and is also unknown.

     4)    Bearing these considerations and uncertainties in mind it is difficult to do anything else but to assume the downstream pressure for all of the quills to be similar and to base the flow rates solely on the area of each quill.

The sizes that I have chosen for each quill and the relative flow rates using these assumptions are given in the table below.

Targeted Engine Part	Quill diameter (mm)	Flow Area (mm2)	Relative Flow Rate (%)
Crankshaft	3.25	8.30	47
Upper Bevel	2	3.14	18
Inlet Cam	2	3.14	18
Exhaust Cam	2	3.14	18

 (Yes, I know they add up to 101%!)

If all of the flow areas are added together and, hypothetically, the oil exited from a single quill then the diameter of that quill would be 4.75mm (3/16”).

Lubrication of the K-12 phosphor bronze bush and shaft supporting the K-18 bevel gear is also a bit uncertain. These will have to rely on oil finding its way behind the bevel gear and being transported by pressure pulsations from the crankcase and any pressurisation that the upper bevel quill feed provides. In practice, I don’t think there will be a problem here.

It took a couple of days of machining to make all the brass bits and pieces for connecting the ¼” OD copper pipes and making the quills etc. The T pieces are bought-in items. I would also normally buy the fittings that are commercially available but as the post is usually a bit slow over the Christmas period and it can get quite expensive with the sheer number of fittings required it was more expeditious to make them. 

I showed a picture of the crankshaft quill arrangement in a previous blog (which has a LH thread to prevent it unscrewing) and is made of aluminium

but the bevel gear quill

and cambox quills

are made of brass and are silver soldered into the screw caps.

After bending a few copper pipes, the arrangement looks like this

 ….and is starting to take on the appearance of a model steam engine.

When I made the fittings, I didn’t appreciate how far those for the cambox quills would protrude and end up interfering with the frame down tube at the front and the carburettor at the rear. I therefore decided to remake these for a more compact assembly using 90⁰ brass elbows.

The oil feed to the engine and the scavenge back to the oil tank will be plumbed in when the engine is in the chassis. The oil tank that I have will also need another entry to accept the oil return from the cambox.

And so, the completed network of external piping looks like this.

The RN carb has been loosely fitted to check that the pipework avoids contact.

There are a few small jobs to complete the engine build but is nearly time to start putting engine and chassis together.