Well, I’ve after tripping over the engine in the workshop for the past year and it’s finally on the bench.
It does not take long to strip one of these engines – checking various things along the way such as wear, bevel gear engagement etc to get a first impression of what will need attention.
The main findings (and remedies) so far are as follows:
The bore had been increased to 80mm (the original would have been 74mm), giving a capacity of 407cc.
The diameter of the inlet valve has been increased from 1.723” to 1.797” and the exhaust valve reduced to 1.582”. The inlet tract has been opened out to 1 5/32” and a correspondingly larger Amal TT carburettor fitted (you may recall from an earlier blog that this bike was raced in vintage club events in the 1970s/80s). The 2 pictures below show both valves and the cylinder head (after cleanup).
The valve springs were about 3/16” shorter compared to a new Terrys VS 147
and the springs were replaced on reassembly.
The cambox was in pretty good condition - threads, lugs and none of the usual damage to the top of the cam chamber where the rockers enter but clearly someone in the past had a serious argument with the rocker spindle end caps
However, I was very pleased to find that all the castings and assemblies such as the oil pump, shock absorber etc were in good condition and apart from needing to replace the timing-side main bearing, the magneto chain and a few smaller bits and pieces, engine reassembly should be straightforward.
The cambox and cylinder head have already been rebuilt.
New end-caps for the rocker spindles were made on the lathe and milling machine
to replace the chewed-up originals. The rockers/spindles showed little wear and the skids were in good condition,
The cam appears to have a K-17/5 profile (the picture below compares the new K-17/5 that I’ve recently made on the right to the one that I’ve just removed from KTT 305 on the left).
However, the surface of the cam has seen better days
and is now with Newman Cams for regrinding the profiles.
By luck, a new K-17/5 cam in very good condition turned up for sale and which I bought.
and this, together with a new camshaft bearing and a couple of (annealed) copper washers
have been reassembled into the cambox.
Something that I should have perhaps mentioned in a previous blog, and it may be obvious, is that the easiest way to tighten the nut on the end of the camshaft is to hold the bevel gear in the lathe chuck and use a socket on the other end.
Bevel gear engagement was checked and adjusted in the same way as described in my previous blog for KTT 55, the cylinder head and barrel mating surfaces have been ground together and work on the cylinder head and cambox is now essentially complete.
The damaged cambox scavenge oil pump and poorly home-made Oldham coupling were discarded and replaced. Both this engine (KTT 305) and the earlier engine (KTT 55) have been fitted with new oil pumps that I made last year. These are driven via small Oldham couplings (different from those that drive the bevel gear) and were made from O1 tool steel
and heat treated.
As the location of the slot in the end of the camshaft to drive the pump depends upon the axial positioning of the camshaft and which, in turn, has been set up to give the correct bevel gear meshing, the dimensions of these Oldham couplings are very slightly different and have been tailored to each engine.
All the work on the cylinder heads, camboxes and upper bevel drives for the 3 engines is now essentially complete
and I am just waiting for a batch of 3/16” BSW screws to arrive in the post to replace some of the old ones with chewed-up heads.
KTT 305s small-end had a bit of wear (!!!)
The small-end bush was pressed out of the con-rod
and a new bush made and fitted
and reamed to fit a new 0.75” diameter gudgeon pin from a spare and unused Hepolite New Imperial piston that I happened to have.
Incidentally, the pin that I removed from the engine had 0.004” of wear in the centre.
It’s now time to start on the cylinder/piston assembly and the bottom-end.
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