Sunday 9 August 2020

The Dry Build

 As with any dry build, this is a process of adding more and more “bits” to the bike until it is complete. It is then stripped, painted and plated and rebuilt into the finished bike.

The following sequence of pictures shows various stages during the dry build.

Measuring up for engine plates.......
 Now a rolling chassis with mudguards fitted....

Plus tank and seat. New petrol tank has been made by a guy that specialises in making only petrol tanks although he needs all the brass fittings to be provided for fixings, petrol taps, tank rubbers, gear change and filler caps.

All the all plumbing for the oil pipes is now done and an original AJS oil tank has been fitted. The oil tank was an ebay find but was intended for a total-loss lubrication system, probably for a big port. It is identical to the correct K7 oil tank except that it has no provision for oil return. An oil return pipe was therfore plumbed into the top of what was previously an adjuster for a drip feed to the chain.

A tap has been inserted into the oil supply to the pump to avoid wet sumping as the Velocette gear-type oil pump will allow oil to pass when standing for long periods.

The lubrication system on vintage OHC AJSs is quite sophisticated and a giant leap from the total loss lubrication used on the previous OHV engines. It is a full recirculating system with oil feeds to the big ends via a drilling in the crankshaft, to the piston/cylinder via radial drillings at the bottom of the cylinder and to the cams and bearings in the cambox via a pipe that feeds into the bottom of the cambox.

The picture below shows the oil feed into the engine for the bottom-end and the oil drain pipes back into the engine from the cambox. The oil feed into the cambox is on the other side.  The smaller pipe that is seen entering the crankcase around the main bearing feeds oil to a distribution annulus and then via a crankshaft drilling to the big end. Oil that leaks around the sides of the distributor annulus lubricates the drive-side main bearings.

The Velocette gear pump has a much higer flow rate and higher pressure than the somewhat lazy AJS reciprocating pump fitted to all OHC AJS engines of the period and the tap is effectively a manual pressure relief valve that dumps excess oil directly into the crankcase. It was setup using a simple flow rig at the final build and has never been touched since.

The exhaust pipe was made by Pipecraft on the Lancing Business Park. I don't have a pipe bender for this diameter..... They made a good job.

Cables and controls and the dry build is now complete

The dry build of the AJcette was carried out at the same time as the K7 so there are now 2 bikes to be stripped, painted and plated.

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