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.
Don’t forget to checkout the Sunbeamland shop where there are a variety of items in stock including a limited number of these vintage tax disc or license disc holders. They are replicas of an original late 1920’s Pennant item that was loaned to me some time ago and would make a great addition to any quality vintage motorcycle i.e your Brough Superior, Sunbeam, Velocette or cammy Norton.
There are also various other vintage motorcycle spares that are left over from various projects that might be useful. For example, we have quite a number of different controls and levers including items from Amal, Amac and Bowden. Decompressors, valve lifters, magneto advance/retard control.. that sort of thing. Have a look round and let me know if there is anything you might be interested in.
There’s not much left in the seat department, so grab a bargain whilst there is anything left in stock. I’ll accept sensible offers on most items just to clear the space.
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!
The latest project coming to fruition is a limited edition run of 50 Pennant replica tax disk or tax disc holders. They are UK made from solid brass using a beautiful original Pennant as a pattern and feature the Pennant logo on the rear of the holder. Be warned, they are a seriously weighty item!
As we’re all worried about global warming and the resulting floods, the holder is bang up-to-date with the tax disk sealed from the elements in its own rubber pouch. Available in nickel, chrome or un-plated brass they will come complete with a bracket and stainless fasteners.
Please contact us for prices or visit the shop more information.
What a lash up!!! Just in case anyone was wondering how the carburation was developing on the 1930 M90 I thought I’d post this picture of the steps taken to check and correct the float height on the Amac 10MDY currently fitted to the bike. It’s the wrong carb for the year and I’d like a later Amal 29/001 if anyone can help but “we are where we are” on this one…
The Amal twin floats are most likely 15 degree items that have been machined to operate on the level so to speak. But they were clearly never designed to operate with the Amac. After making up a new, elongated float chamber holding bolt complete with a spigot for some clear plastic pipe it was easy to see that the float level was some 6mm too high. Adding the aluminium spacer drops the level back downwards and this setup should help with fine tuning once back on the bike. I’ll make up a proper brass spacer and new banjo bolt once the correct dimensions are established as the existing one is too short to work with the spacer.
All this is yet another example of how much time can be spent trying to get groups of disparate components from different eras to work together with some degree of harmony.
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.
I’m pleased to say that we now have the recently manufactured high-quality, lightweight forged 7.5:1 pistons available on the Sunbeamland Shop in +0.020″ and +0.040″ oversizes. Modern materials and CNC machining mean that all-up weight is within a few grammes of the original Marston’s item and I’m enjoying the experience of running one in on my own 1930 Model 90. They should fit any of the late 20’s early 30’s 500cc OHV bikes and we hope to be following up with production of a small batch of 6.5:1 pistons aimed more at the Model 9.
Forged piston for Sunbeam Model 9 and Model 90 7.5:1 compression ratio
This little beauty arrived today and I couldn’t wait to put a post up on the blog here at Sunbeamland. It is the first from the box of a batch of forged Sunbeam Model 90 pistons. It is modelled on an original Sunbeam 7.5 : 1 piston and, unlike some alternatives that are available, weight has been controlled so that the combined weight of piston, pin and rings closely matches the original.
Next job is to bore a spare cylinder to suit either of the +0.020 or +0.040 sizes we have produced and get some testing done before winter sets in.
A new development here at Sunbeamland is that we now have a vintage motorcycles for sale section added to the shop. To get the ball rolling we have this rather interesting 1929 BSA sloper. Being 1929 vintage, it is of course eligible for VMCC events such as the Banbury Run. If you’d like to know more, drop us a line and we’ll put you in touch.