Following on from the successful production of pistons for OHV 500cc Sunbeam models Chris Odling and I thought it would be useful to produce some high-quality forged pistons suitable for the Model 6 side valve long-stroke. The Model 6 was produced from 1922 until 1939 becoming known as the Lion after takeover by ICI. With its 77mm x 105.5mm bore and stroke this was the last side valve powered motorcycle to win a Senior TT.
There were of course changes along the way and the piston produced is nominally compatible with models produced from 1925 until 1929. Before 1925 a 5/8″ gudgeon pin was used rather than the later 7/8″ type and the change to a scavenge pump from total loss oiling in 1930 means a different piston ring configuration is required. It is possible that these pistons could be adapted to suit.
I have limited availability of pistons in 77.0mm +0.000″ and +0.040″ sizes. An all-up weight of 434g has been achieved for the 77.0mm which is within 2g of the target weight that we set out to achieve.
Once we have given the new items a good look-over I’ll be contacting those who have reserved pistons already and adding them to the Sunbeamland shop.
I’m pleased to report that a rather pretty box containing a small batch of low-compression Sunbeam pistons arrived this morning. Like the 7.5 :1 CR Model 90 versions produced earlier, these are a lightweight forged item but will give around 6.5 : 1 CR depending on the head and barrel combination in use. Targeted at the Model 9 it is suitable for late 20’s early 30’s 500cc OHV bikes and we have limited availability of both +0.020″ and +0.040″ over-sizes.
Our research showed that the weight of Model 9 pistons varies surprisingly depending on both year and manufacture. After collecting and checking pistons from Marston, Heplex and Specialloid a target weight of 400g was achieved for the new item – including rings, pin and clips.
Once we have given the new arrivals a good look-over we’ll be making contact with those who have already reserved their pistons. So be quick if you don’t want to miss out!
Having recently re-acquired my little Emco Compact 5 CNC lathe I found time over the Xmas holiday period to experiment with a little project that I’ve had in mind for a short while. I had noticed that the ’30 M90 was running rich at running-in speeds and sooting up the plug. Not a major problem, but closer investigation revealed a home-made needle jet in the Amac 10MDY carb.
Although, conveniently, this needle jet was made to accept the later small Amal main jets it was badly worn and the likely cause of rich running low-down. I asked around but was unable to locate any replacement needle jets or needles for that matter. So, following a chat with the ever helpful (and patient) Martin Bratby I decided to look into producing an adapter that would allow 29 series needle jets and needles to be used with the earlier Amac carb.
After a few false starts I came up with a design that could be produce on the little Emco. It was tight as there isn’t much wall-thickness to play with if everything is going to line up correctly but I was pleased with the result. The photo above shows the Amac jet-block with an original needle/main jet assembly next to a 29 needle/main jet screwed into one of the new adapters.
The next job is of course to try one on the bike to see how well it works. The plan is to start off with a 106 needle jet and the middle-clip of a 29 needle. I’ll probably adjust the position of the needle jet up/down in the adapter to fine-tune rather than move the needle clip itself as the “correct” relationship between slide-needle-needle jet is of course difficult to establish when mixing and matching the 29 and 10MDY elements.
To help with this, I have use of a decidedly un-1930s Innovate LM-2 AFR data logger that uses a Bosch car-type Lambda sensor rammed up the exhaust pipe to monitor the exhaust gases. Once lashed up on the bike, it is relatively easy to record the air-fuel-ratio at different throttle openings, engine speed and load. This makes fine-tuning of carburation using the modern fuels a lot less hit-and-miss for someone with my lack of sensitivity in such matters.
I was short of a set of handlebar clamps for the ’28 bull nose Model 90 that we are working on and so had a few sets cast and machined-up using an original Marston clamp from the ’30 bike as a pattern. They came out quite nicely in high-tensile brass and will be serving in place of decorations over the Christmas period.
Handlebar clamps for Sunbeam motorcycles with Druid rather than the later Webb-type forks.
I had a few extra sets produced and will put them on the shop in due course in case anyone out there is also in need of a set.
Browsing the web one evening I came across an advert for, as it were, “replica” Rudge TT replica chainstays. Wondering whether these items could replace those on my own 1930 Ulster I duly contacted Wayne at Classic Components. The stays on my bike are actually from a later model and being necessarily fitted upside down have caused certain problems with chain adjustment and wheel alignment. I have been looking for a replacement set for quite some time with no success and was delighted when Wayne said he could produce some for me. The originals should look something like items 6007 and 6010 in this picture from the Rudge spares book…
Frame group 1930
With the help of Alistair from the Rudge club, a set of drawings for the correct stays was obtained and Wayne manufactured a set in record time. Fitting the new stays will be a job for the winter as it means re-engineering the rear wheel spacers and adjusters but the end result should mean a much improved rear-end on the bike. Have a look at the photo below to see the high quality of the work.
After being picked up at auction a few years back, this pretty 1930 Rudge Ulster has probably been neglected for too long now in favour of other projects. A brief outing yesterday confirms that it does go as well as it looks being fast, light, comfortable and with excellent handling. It’s easy to see how these bikes could be purchased from the factory with a 100mph guarantee.
Over the winter, oil leaks have been fixed with a new timing cover and the slipping clutch relined by Saftek. But more work is needed.
The chainstays are from a later model which don’t really work well and the front brake drum is oval. Although a common problem the braking does make riding the bike a problem and will need to be addressed before the bike can be used regularly. The most practical fix is to shrink a strengthening “muff” onto the drum before rebuilding the wheel and skimming to suit. And, if anyone has a pair of the correct chainstays for sale, I would be extremely grateful if they would get in touch.
I had thought about selling the bike to someone with more time as, with the Sunbeam 90, this makes for two 1930 saddle tank sports bikes. But yesterday’s ride showed what a lovely bike this could be with some work. So, after a clean and polish for now it is under cover at the back of the garage until the time comes for its place in the sun once more.
A variety of items are for sale on the new Sunbeamland shop. I will be adding new items over coming months as I get around to photographing them should the shop prove effective. Other bits and pieces will go via the eBay route. The parts are a mixture of vintage Sunbeam spares and assorted vintage motorcycle spares for bikes from other manufacturers.
The first items up for grabs are not actually vintage spares but were, until the arrival of sparkly new ones, my spare pair of Honda RS250 NX5 cylinders.
Back on track with vintage parts we are also, selling on behalf of a good friend, a rather lovely Amal T10TT. Not sure what this would be from, maybe Norton or Velocette? Any information would be appreciated.
We are always interested in acquiring vintage spare parts, particularly for Sunbeam and Rudge motorcycles.