KTT 581

I wasn’t planning to build any more early cammy Velos but a few weeks ago a buddy of mine drew my attention to a very interesting lot in an upcoming auction. The auctioneers, H G Pugh, are a long way from where I live and as it was difficult to judge the condition of the engine from the online pictures my buddy, who has a house close to the auction house, inspected the engine on my behalf to make sure that there was no structural damage that could not be seen in the partially dismantled state that is visible in the pictures. Anyway, he bid on my behalf – I was on holiday in Morrocco at the time, and won.

Picture courtesy of H J Pugh and Co website

And so, I am now the proud owner of a Mk V KTT engine. It wasn’t cheap and it needs some work, but then how often does one of these come up for sale? I’m already rebuilding 3 early cammy Velocettes and which are progressing well, I have 2 flat-tankers in the pipeline (and for which much work, that I haven’t yet reported, has been done) so why not add another and very interesting project. The engine is now in my workshop and I’m pleased to report that, apart from the fact that the piston was stuck in the barrel, the engine is complete and in remarkably good condition.

I have already done quite a bit of work on this engine. This has not detracted from rebuilding KTT 305s engine, which is progressing well and on which I will update my blog very soon.

KTT 581s engine is pretty well complete as can be seen in the 2 pictures below.

The first step was to extract the piston from the barrel – which was well and truly stuck with the top ring half in and half out. It’s much easier to work with this on the bench and so after removing the gudgeon pin, soaking in KROIL for a few days and applying some heat it was clear that the piston had taken up permanent residence in the barrel.

and the only way to extract the piston was to put it in the press. With a large piece of round aluminium (with a large hole in the centre to avoid applying single point pressure on the top of the piston) under the hydraulic ram and a large and very solid cylinder to support the base of the barrel

the piston popped out.

I wouldn’t say that the rings came off easily

(I ground down a piece of key steel to prise them out of their grooves) and there is a bit of historical damage to the top ring groove adjacent to the exhaust valve cutout.

Judging by the colour of the metal where the small piece broke away this happened many years ago. After vapour blasting and a trip to EMP tooling there is a bead of laser weld that now needs fettling to restore the integrity of the piston.

I was amazed that I can still buy piston rings “off the shelf” for a pretty obscure 90 year-old engine. I called Cox and Turner, told them that I needed a set of rings for a standard bore (74mm), 1935 Velocette KTT and the following day these arrived in the post.

The cylinder bore is in perfect condition; the picture below shows the surface after blasting.

The bronze head has been vapour blasted,

the valve springs and retainers put in the tumbler for a few hours

and there is a new 3/8” diameter exhaust valve in the above picture after a visit to G&S valves who are a 40 minute drive from my house.

The BTH TT magneto has been rebuilt (rewound armature, remagnetised etc.) by Paul at APL Magnetos

I have not yet stripped the bottom-end of the engine but the crankcases contain plenty of dirty old oil (it might be a pain in the butt to clean out but it really is the restorer’s friend) and the crankshaft rotates freely.

I will get back to working on this the engine in due course but I will complete the build of KTT 305s engine first.

The original petrol tank from KTT 581 was also sold at the auction.

Picture courtesy of H J Pugh and Co website

I didn’t buy this at the time but the buyer, Sam Jones, the proprietor of Yeomans Motorcycles, has graciously agreed to sell it to me. Thank You Sam. Just FYI, Yeomans will be hosting an autojumble at the National Motorcycle Museum on 5th May.

And so, another project starts to take shape. I have no idea if the rest of the bike, ie the rolling chassis – frame, forks, wheels, gearbox etc. is out there somewhere - it would be great to be able to reunite all the bits that came out of Hall Green 90 years into the original bike and if anyone knows of its existence then I’d be very pleased to hear from them – my contact email is vintage.ajs.uk@gmail.com. If not, then I will be keeping my eyes open for a Mk 2 KSS or KTS “project” which has the same loop frame. Searching the auction sites, it seems there are plenty around. In fact, I restored one of these back in 2006.

(yes, that’s a Series D Vinnie in the background – I had more space in my workshop in those days)

 

Rebuilding the engine of KTT 305 – Part 1

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.