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 recently sold at the Autumn Stafford Sale. Quite a few peope have asked me why I was selling them. Well, I have enjoyed the challenge of building them, seeing (and hearing!) them burst into life for the first time, sorting them out, riding them, taking them to a few events and writing about them on my blog. But I needed to make space in the garage for the Velocettes that I am now building.

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 these bikes 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 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. There is an INDEX PAGE for this engine rebuild and work is progressing well. The crankshaft has been rebuilt using MOV flywheels and "K" mainshafts and I have just completed work on revising the lubrication system to mirror that of the Mk V KTT engine that is in my workshop.

 

Further 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.

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 1

The DOHC cambox was designed with 2 oil feeds at the extremities which direct oil directly onto the cams and a drain pipe which would have scavenged the oil by gravity back into either the oil tank or the crankcases, all circled in the picture below.

There are essentially 2 ways in which oil can be provided under pressure to the cambox. The easier way would be to tap into the lower bevel drive chamber (for example, via the tapped hole for the drain plug) and add a pipe with a bifurcated union to provide oil feeds to both sides. However, there is a problem with that, namely that by combining 2 essentially different lubrication systems – pressurized lower bevel/upper bevel chambers (the existing design on the Mk 1 engines) together with a directed and targeted approach to the cambox it would not be straightforward to control the different amounts of oil going to each part.

On the Mk V KTT engine that is in my workshop the lubrication system was completely revised to provide oil under pressure directly from the pump to a quill in the end of the crankshaft for the big-end (see picture below)

and a jet that is directed between the inlet and exhaust cams

plus another feed that provides oil to the upper bevel box and which then drains back to the lower bevel box by gravity. This approach avoids pressurisation of the bevel gear chamber.

The castings for the timing-side crankcase and inner timing case on the Mk V KTT engine were substantially revised compared to previous cammy Velo engines to support internal oil passages and there is an oil take-off in the timing side crankcase, indicated with an arrow below, to provide oil to the upper parts of the engine.

There is also a drain from the lower bevel chamber back to the crankcase. This picture is of the engine “as received”.

My preference is to replicate this approach on the DOHC 250 engine so that key parts of the system are targeted directly. This avoids pressurisation of the internal cavities of the engine and the oil flow rate to different parts of the engine can be controlled by choosing appropriate diameters for the various holes feeding them.

The disadvantage of choosing to modify an existing “K” engine to strategic lubrication is that it is not a simple 5-minute job. As I indicated in a previous blog, a number of modifications are required:

 1)  The small passage on the end-cap of the pump that connects the feed side of the pump to the lower chamber (indicated with an arrow on the picture below)

 needs blocking off. (I have made this modification previously for the Velo oil pumps on both the AJcette and the AJS V-Twin – see here) by building up with braze and machining.

2)  The drive-side crankcase needs modifying with a passage to take the oil directly from the pump outlet to a union to connect to the “outside world” - as in the picture of KTT 581 above

3)  A quill to provide oil into the end of the crankshaft for the big-end and a modification to the timing gear cover, K45/2, for an oil feed needs to be added

4)  The crankshaft must be modified at the end of the timing-side mainshaft to accept the inserted quill

5)  Oil feeds to the cambox (2) and to the upper bevel will be needed. A drain back to the oil tank will also need to be added.

6) A drain needs to be provided to scavenge the oil from the lower bevel chamber back into the crankcase

7) Some means of regulating the flow/pressure will be required.

The first step in making these changes was to modify the K-45/2 cover with a small (5mm) hole aligned with the end of the crankshaft. I have found on previous projects that the easiest and most accurate way to do this is to insert a centre into the end of a piece of solid bar, 22mm diameter in this case,

to pass through the bearings in the assembled crankcases and with the timing gear cover screwed into place, drill a 5mm hole in the cover.

The next step was to make a boss/oil channel to feed the hole (which will support the quill) out of a piece of aluminium. I didn’t have any material of quite the right size but I did have a few lengths of 40mm diameter 7075 (thank you Christer) and used one of these to carve out an appropriately shaped piece

and with a boss on the inside plus a 6mm LH threaded piece of steel

the collection of bits could be assembled

and then laser welded in place.

The piece of 6mm diameter steel is only to aid setup to unsure that the holes are aligned (and a cable tie was also put around the whole assembly to hold it together prior to welding); it will be replaced with the quill. A 6mm LH thread is used because if there is any interference between the crankshaft and quill then the quill would tend to tighten rather than unscrew. There is a 1/8” BSP thread on the end to feed oil to the assembly.

The quill was made with a 1.3mm diameter hole and fits perfectly into the hole in the crankshaft.

The second part of this project was to cut out another chunk of metal in a similar way and attach that to the crankcase

where the boss would be needed for the oil feed to the upper part of the engine and to then carefully drill

a hole through in exactly the right place to meet the exit of the oil pump

and to tap 1/8” BSP for a union.

It’s always a good moment to see the drill emerge in the right place - THIS was another instance, because a “fix” would not be straightforward.

There was insufficient material in the crankcase casting to allow an uninterrupted hole

and so, a 6mm OD/4mm ID aluminium tube was added to transport the oil from the pump to the boss. It’s held in place with JB Weld.

This completed the work on the aluminium components.

The external pipework to supply the oil to the upper parts of the engine – the bevel drive and the cambox and also means of controlling the flow rate - will come later.

The return paths for the oil must also be considered. The cambox oil will go into the oil tank under gravity but the oil that is provided to the upper bevel and which will then flow down to the lower bevel needs to be scavenged from the lower bevel chamber.

On KTT 581 there is a passage that is cast into the timing-side crankcase which connects the lower bevel chamber to the bottom of the crankcase. Here, rather than drill more holes in the structure, I have simply modified the K-163 Drain Plug with a 3/16” OD copper pipe silver soldered inside that will take oil from inside the chamber (at the same height as the scavenge hole on KTT 581) and which then connects with a modified B-38 crankcase drain plug to return the oil to the crankcase.

The last part, for now, was to modify the pump. I indicated earlier the opening that needs to be blocked and this was done by adding braze to the gap

and then carefully machining back to a cylinder.

to prevent the oil discharging into the lower bevel chamber.

 

…..And Finally….. While I was machining one of the pieces of aluminium on the milling machine there was muffled “pop” that appeared to come from the motor. Everything seemed fine and so I kept working until a few minutes later the machine lost power and I was forced to stop. The electric motor was so hot that I couldn’t touch it and, clearly, something was seriously wrong.

The next day, when the motor had cooled down, I found that the electrical junction box on the side of the motor looked like this inside.

It seems that the capacitor had exploded. I am not an “electrics” person but Google tells me that a capacitor can explode for any number of reasons – I have no idea which applies here.

Anyway, I ordered a new motor; this turned up the next day and was easily fitted.

As you can see, it’s made by Polestar – a Chinese manufacturer of electric vehicles. I fitted the last motor (the one that blew up) about 12 years ago so we’ll see how long this one lasts.

KTT 581: An Update

In an earlier post – here – I mentioned that the owner of the original chassis had contacted me. He also lives on the South Coast in the UK and subsequently visited me and was able to provide quite a bit of further information about the history of the bike.

Firstly, and for me extremely useful, he has a picture of Doug Pirie astride the bike after coming 4^th in the Junior TT.

The bike now sports the number 4 rather than his racing number of 19 to indicate that he came 4^th. I don’t know how to interpret his expression - he does not look happy! It may be that having raced very hard and come 4^th he was disappointed. Alternatively, having just raced over 7 laps of the Mountain Circuit (yes, it was 7 laps in 1935!) – 264 miles at an average speed of over 77 mph on roads that are not the lovely smooth tarmacadam surface that we have today that he was simply exhausted.

Anyway, the picture is extremely useful to me – details such as the form of the mudguards, mudguard stays, whether wheel rims were chrome plated or painted etc will help me in recreating the bike.

The other information that is of interest is the history of the bike immediately after Doug Pirie’s death in the lightweight race. It seems that his brother, John Pirie, then took charge of the bike and had it road registered. A copy of the old-style buff log book

shows that he became the registered owner in June 1936 (the first owner is “Stevens”, the London Velocette dealer to whom the bike was originally delivered).

It is believed that John Pirie did not ride the bike but simply kept it as a memorial to his brother. The minimal wear inside the engine would support this,

The bike was then sold to Geoff Monty, a very successful racer of 250cc bikes in the 1950s and who subsequently teamed up with Allen Dudley-Ward to develop a business producing racing motorcycles (see here). Although there is no date in the log book it is believed to be around 1950 when Geoff Monty acquired the bike and it was at this time that the engine and other parts were removed, to be replaced by a 250.

Thankyou Mick for providing all of the above information.

Earlier this year I put an advert in the “Wanted” section of Fishtail seeking an “oily rag” Mk 2 KSS or KTS that I could use as a basis for the rebuild – the chassis of these bikes are the same as the Mk V KTT – the plan being to use a donor bike and replace the engine, exhaust pipe and petrol tank from the original KTT 581. After quite a few months I have heard nothing.

However, it seems that every time I go on holiday something turns up. I was in Marrakech when I bought the engine and my wife and I were in Cornwall a couple of weeks ago for a short break when a 1936 KSS turned up on eBay. After a brief negotiation I have now acquired this.

By coincidence, it was also first registered in June 1936 and it will now form the donor bike to build the replica of the original TT bike.

There will be quite a few bits coming up for sale from this bike, notably the engine, petrol tank and exhaust system but also other extraneous parts such as the entire electrics, primary chaincases (screw type), mudguards, toolbox etc. The engine runs just fine.

I know that some people will be horrified that I am effectively breaking an original bike, however, I consider it more important to see and hear the original KTT engine running again as it did 90 years ago at the TT. And if the parts from this bike help to get someone back on the road, then so much the better. So, if you are interested in any of the parts that I won’t be needing then please contact me via email.

The DOHC 250 Velo Engine: Rebuilding the Crankshaft

The objective here is to build a crankshaft that has a 68mm stroke and with mainshafts that are appropriate for the Mk 1 cammy engine to accept the bevel drive on the timing side and a taper on the drive side for the crankshaft shock absorber assembly – standard “K” practice.

Although I have a spare "K" crankshaft, this is of no use as it has a 74mm stroke and the starting point is an MOV crankshaft (an eBay find) that I have stripped and cleaned and which has the required 68mm stroke.

A few words about disassembling one of these crankshafts:

The first step is to remove the big-end nuts and press out the big-end pin – quite straightforward.

Removing the mainshafts, however, has to be done with care. When they were assembled a ¼” BSF threaded section was positioned midway between the shaft/flywheel interface into which a truncated screw was inserted and was put there to prevent the shaft rotating in the flywheel (in addition to the interference fit). It can be clearly seen in the picture below.

This needs to be removed and I do this by drilling to a depth of ½” with a 7/32” diameter drill

so that after pressing out the mainshaft (from the outside in) only the remnants of the screw remain and there is no damage to the flywheel.

After degreasing and with the smaller parts in the tumbler overnight (except the mainshafts, which will be scrapped), the collection of bits looks like this.

The separate tasks to rebuild the crankshaft are:

-       Replace the big-end bearing, which is worn

-       Remove material from the flywheels to give the correct width to fit the available space between the bearings in the crankcase

-       Replace the mainshafts with those suitable for the “K” engine and with a central hole on the timing side to accept a quill

-       Assemble and check

Before disassembling the crankshaft, I made quite a few measurements. One of the most important of these is the internal distance between the flywheels, “B” in the picture below.

The second measurement that is of importance is the available distance between the bearings when assembled. This was done by making 2 new solid “bearings” in mild steel that are exactly the dimensions of the actual bearings (22mm x 50mm x 17mm),

dropping these into place in the heated crankcases

and measuring the distance between them when assembled using a telescopic gauge that can be easily inserted through the main hole for the cylinder barrel.

The MOV flywheels are wider than the "K" flywheels and both were reduced in width to fit the "K" crankcases.

I have retained an overhang (0.040”) on the outer rim width of the flywheels.

I was very lucky to find new mainshafts. I was talking to Nick Payton on the phone a few weeks ago (I have known Nick for many years – since my early days of Velo-ing) and he mentioned that he had a couple of KTT mainshafts. He sent me these in the next post

which are exactly what I needed. The section that fits into the flywheels is the same diameter and they have the correct dimensions to accept the bevel drive on the timing side and a taper for the shock absorber assembly on the drive side.

A bit of work is required to set them up. On the timing side, there is a drilling along the axis of the shaft that supplies oil to the big end and for which a radial 1/8” hole needs to be machined to line up with the corresponding hole in the flywheel. However, the axial drilling in the mainshaft would have needed to be extended and, in my opinion, would have come too close (or, worst scenario, broken through) into the hole that was originally used to grind the shaft between centres.

I therefore drilled the radial connecting hole at the end of the existing drilling and made a short slot (0.1” deep) to connect it to the hole in the flywheel.

The other end of the timing-side mainshaft was bored 5mm diameter to a depth of 0.75” in readiness for accepting a quill. 

Both shafts have a moon-shaped segment removed to allow the big-end cage to fit (see the 1^st and 3^rd pictures down from the top of this page). The diameter of the recess in the flywheel is 2” and to remove material of the correct size in the end of the mainshaft I used a 50mm diameter x 4mm thick slitting saw mounted on a mandrel.

This slitting saw is made of HSS and needs to be run slowly using small cuts and plenty of lubricant as the material is tough and the shaft is case hardened (Grinding would be better – or machined before heat treatment but I don’t have these as options. There are also alternative ways to machine this using either the milling machine with a smaller carbide cutter or the lathe but the way I used has a far simpler setup although HSS is not the best material for cutting through case hardening!). The machining operations on both shafts turned out OK.

The positioning of the cut is important to ensure that the oil feed hole (slot in this case) in the shaft aligns with the hole in the flywheel feeding the big end bearing on the timing side and, on the drive side, the cut is positioned in the correct place with respect to the exit hole for the timed breather.

On both mainshafts I found that the diameter of the portion that enters the flywheel was 0.002” larger than the mainshafts that I had removed from the MOV crankshaft. This would have given an interference fit of 0.004 and would end up in either broaching or distorting the flywheels when pressed in. The surface of the mainshafts is too hard to machine by any means other than grinding. As these mainshafts are new (with good centres) and would originally have been finished by grinding between centres it was possible to remove this small amount on a cylindrical grinder. I don’t have cylindrical grinding in my workshop (only a tool post grinder – which is not sufficient here) and Peter at Jayess Tools did a great job in finishing these accurately to size to give a 0.002” fit.

The hydraulic press registered around 5 tons for pressing in the mainshafts and using Loctite 638 as a lubricant.

As I mentioned earlier, the mainshafts in the MOV crankshaft had the additional “belt and braces” fixing of a ¼” BSF threaded section positioned between the flywheel and the shaft. I had taken care not to encroach on the threaded portion when I drilled them out before removal as the plan was to replace them. As there is only “half a hole” after the new mainshaft had been pressed into place I couldn’t use a regular twist drill to reform the hole – it would wander off-centre, so I used a slot drill to reform the clearance hole

to be able to re-tap the thread back to the original size

before inserting a Loctited high-tensile grub screw.

The big-end had quite a bit of up-down movement before I had dismantled the crankshaft and would need attention. There was some visible wear on the ends of the pin on both sides where the bearing cage had been rubbing.

This phenomenon has long been recognized as an issue in caged roller big-end bearings (see, for example, Phil Irvings book Tuning for Speed, 3^rd edition, page 84). There are a number of mechanisms of how a soft material can erode a harder one (aluminium vs hard steel in this case) and I have no idea which of those mechanisms applies here – anyway, it happens. The damage it not all the way around the pin – it occurs either side of TDC and the loading on the assembly at this time of the engine cycle is quite complex – inertia loads resulting from the deceleration/acceleration of the piston, change in the direction of rotation of the connecting rod relative to the pin and cylinder pressure acting on the piston crown.

When I measured the central portion of the pin where the rollers are in contact, I found it was completely unworn and measured exactly 1.250”. Similarly, the bearing outer which is pressed into the connecting rod, is also unworn and measured 1.625”. Incidentally, when I measure these using a micrometer, I use a set of slip gauges

to check the calibration of the micrometer as absolute accuracy is needed here.

The really good news is that the rollers, which have nominal dimensions of 3/16” x 9/16”, were found to be 0.0015” undersize – which would have resulted in an additional 0.003” clearance in the bearing.

A new set up rollers

and the big-end is “as new” in terms of bearing fit. I can live with the wear that has occurred to the outer part of the pin and which is not too important for the functioning of the bearing; future wear on the pin extremities will, in any case, probably be reduced with new rollers fitted. Total cost of the rollers (including delivery) was 17 GBP compared to the cost of a new big-end assembly at 400 GBP so I’m more than happy with this outcome.

The final stage was standard crankshaft assembly: the crankpin was inserted into the timing side, ensuring that the oil holes were aligned, and the nut on the outside of the flywheel tightened. I put a small black mark with a felt tip pen on the pin to indicate its position - just in case it rotates when tightening the nut and putting the oil hole out of alignment. The bearing and connecting rod were then put on and the pin inserted into the other flywheel, pushed “home” and the nut screwed on. Adjustments were made (with a soft-headed mallet) before final tightening with plenty of checking for alignment on the crankshaft alignment jig.

I ended up with runout of 0.001” on the timing side and 0.0015” on the drive side which is not too bad for a crankshaft that is probably around 90 years old.

Although the crankshaft has been rebuilt and basic checks such as central positioning of the connecting rod etc. have been made there is still work to be done to complete the fitting of the crankshaft. The balance factor needs to be checked and the distance between the flywheels is around 1/8” less with the MOV big-end/connecting rod assembly compared to the “K” crankshaft which means the mainshafts are 1/16” further inboard which creates complications in fitting the shock-absorber on the drive-side. The location of the crankpin (closer to the centre resulting from the shorter stroke) also caused a problem by interfering with the main bearings which needed sorting out  ….more next time.