I have spent the last 4 months rebuilding the clutches, gearboxes and positive stops for the 3 immediate cammy Velo projects plus the 2 flat-tankers for the follow-on project. I’m sure there will be a few details yet to sort out but, in the meantime, it’s time to start building/rebuilding the engines.
So, what is the starting point? ….and the plan?
The starting point for KTT 305 is simple – it’s the engine that I removed from the frame a year and a half ago and have been tripping over in the workshop ever since.
The only bit that is obviously missing is the cambox oil pump, which I removed some months ago to reverse-engineer to make some new ones.
So, all 3 engines will get a nice new cambox oil pump.
The bottom-ends of KTT 55 and the Model K engine that will form the basis of the cammy special were rebuilt many years ago by Alpha Bearings
Both of these engines have complete new crankshafts/con-rods/bearings that the late Max Nightingale masterminded.
and which have been balanced to new pistons and rings manufactured in the US by JE Pistons and Total Seal respectively.
A batch of 4 of these was made based on an original KTT piston but redesigned using modern technology. I have used one of these previously in the AJcette project (see here); I took this bike to the Manx GP back in 2019 and found it went like stink for a little 350 and so I’m optimistic that this performance will be repeated here. I have 3 of these pistons left and, because the ring pack is designed to run in a Nikasil plated bore, I have 4 cylinders (I only need 2 for the immediate projects) that have been Nikasil plated. KTT 55 and the cammy special will use these.
I have also been working on rebuilding cylinder heads in the background. All of these have new valves, guides, springs etc. and some of the heads have valve-seat inserts where it was necessary. 3 of these heads were used on the V-Twin and AJcette projects and I have just completed 4 more for the current projects (I managed to sneak into the workshop for a few hours over the Christmas period).
The mating surfaces of the head and barrel have been ground together with fine/medium grinding paste in the time-honoured fashion ….and before the valves were fitted. Incidentally, I always measure the depth of the recess in the head
and the protrusion of the spigot on the barrel
before grinding – they need to be pretty well the same value, because there is no point in trying to make good contact surfaces if there is a large disparity. The worst case is if the protrusion on the head spigot is significantly greater than the depth of the recess because this will result in bending loads around the periphery of the head joint when it is bolted down.
These are the other heads, barrels and one cambox which have been completed.
Most of these have 5/16” diameter inlet valves although I used a 3/8” valve (part number k2/12) for the most recent one. I also found that the K4/5 top collars do not fit the Terrys VS 147 valve springs – they are designed to fit an inner spring with a larger ID. So, if you plan to use NOS VS 147 springs, as I did, make sure you look after your original K4s!
I have 3 period carburettors – 2x AMAC 15 TTs and a slightly
earlier AMAC T15 HXDM, all of nominal 1” choke size. All of these were rebuilt by Martin Bratby some years ago.
The diameter of the stub fittings on the carbs is slightly larger than the stubs currently fitted to the cylinder heads but it won’t be too much work to make and silver solder a sleeve onto the stubs where necessary.
One of the heads has a cambox that I refurbished some time ago but I need to complete the rebuild of at least one more cambox.
I have plenty of crankshaft shock absorbers that are in good condition – some new ones that Dave Smith in the US made for me some years ago (one of these is fitted to the AJcette).
These have a different spline to the original and the parts are not interchangeable with original parts. I also have a number or original shock absorbers that are in good condition and which I have cleaned up and chemically blacked, which is why they are hanging up to drain off the excess oil.
I’m not expecting that much work will be needed on these.
There are a lot of ancillary parts – bevels, oil pumps, sprockets, casings etc that I won’t go through in detail here
and a new pair of bottom bevels if needed.
thanks to the Velo Owners Club spares scheme.
Most of these parts are in good condition, considering their age.
Square ML magnetos with anticlockwise rotation were generally fitted and I have a number of these
all of which have been rebuilt (armature rewinds, remagnetised etc.) by Paul at APL.
So, this is the starting point – a pile of bits! Lots of them. As with previous projects, the plan (loosely) is to rebuild large “chunks” – cylinder heads (already done), cam boxes, complete bottom-ends, complete bevel drives etc and then to ensure that everything fits together properly. I also need to strip KTT 305 to see what lies inside.
This should keep me busy for a while.
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