I set this site up mainly to provide a platform to share some of my experiences and endeavours in developing the engine of my racing 1932 Scott Flying Squirrel.
The simple reason that I’ve not been updating is that I’ve not been working on my bike much or racing it either.
I did have a rather memorable meeting at Cadwell park in June, but not for the right reasons.
I have not given up on petrol or AVGAS (as I have have most recently been using) but my experiences with seizures in 2015 made me realise that I had more development work to do before I could confidently go to a racetrack again using that fuel. I have my suspicions that the diameter of either the ‘stinger’ or the muffler outlet pipe on the exhaust is inadequately sized and that excess pressure build up is creating heat at sustained higher revs. I’m not convinced that the exhaust is actually the optimum design anyway (Supposed to be a direct copy of Roger’s, but Gibsons didn’t make it with quite the same dimensions), but it certainly goes well with it on methanol and I simply didn’t have the time (or the TIG) to make test modifications at that (or this) point. However, as I’m sure I reflected on at the time, the problem may be something else entirely or indeed a combination of factors. Certainly, the seizures were not something I managed to replicate on a dyno during short output-measuring runs, although I since discovered that the dyno can indeed be set up to provide a constant load condition to replicate the conditions experienced when flat out for a period of time. It’s not really about measuring power but simply observing what is happening. To make the most of a morning on the dyno doing this, I would need to get some datalogging going to be able to really study the effect. I have thermocouple ports in the headers but I could also do with the temperature in the water jacket being monitored as well. I can switch exhausts to a standard straight-through pipe to make comparisons.The radiator is only small on my bike and may be a significant factor as well. It would likely be a couple of hundred quid for a morning on the dyno so I would have to make it count.
So, with the petrol incarnation of my engine needing time to work through the options, I thought I would return to good old methanol to give me some limited riding in 2016.
I was still hoping to try to squeeze more power out of my engine, and had the combustion chambers to my cylinder head welded up to enable a new profile to be tried. I didn’t have much time for the work on this and Roger kindly did some machining on it for me. He checked the head for flatness, which he thought was fine and I built it up.
The premise is simple. The Scott engine is limited to fairly low revs by several design constraints; you simply have to make the most out of the available range, which is effectively up to ~5000rpm (with peak torque somewhere between 3000 and 4000 rpm). I had done some development work with the cylinder head previously and seen on the dyno the effects of lowering the compression whilst improving the combustion chamber shape; I lost low rev torque whilst the engine revved to higher RPMs. If the engine was capable of breathing at higher revs, then an increase in power may have been the effect but as (according to my calculations and observations) the ports restrict the gas flow required for anything above about 3750rpm, then there’s just no point holding on.
When you also take into account the three speed box the task as I see it is to maximise low rev torque and discount the pursuit of revs entirely.
Now I would like to say at this point that a good strong engine can be made to run very reliably on petrol (of course!) and I raced it without mechanical problems for years like this (with a far less radical pipe, prior to fitting the expansion chamber I received as a wedding present from Roger!) but it is at this point where you are trying to experiment where you have to accept that you might hit trouble. I have built many engines for other people and I wouldn’t build an engine for anyone else with anything but tried and tested clearances and configurations, as we know that these work and work well but I have always wanted to keep experimenting with my own Scott engines and in doing so you commit to the highs and lows associated with that development process.
The Cadwell park meeting in June was a big event. An anniversary meeting for the British Historic Racing Club and also the Scott Owners Club, which had a stand in attendance.
The Friday had given people the opportunity to ride around the circuit on their road bikes, with a full weekends racing ahead.
I had returned to methanol for the meeting, thinking that was the safest option as I had never had problems running on methanol before. I was also quite excited at the prospect of the improvement I may find with the new cylinder head design. That excitement was short lived however as the head gasket was obviously not sealing and the water was being blown out the radiator expansion pipe.
I will not make a long story out of this weekend as it simply consisted of various attempts to seal the head (with associated peaks of hope and troughs of disappointment) aided by several kind and enthusiastic helpers. Kev Bayliss and Alan Noakes deserve a special mention.. many thanks.
Unfortunately, It was not to be. In that moment, having hired a caravan and being accompanied by my wonderful wife and two small children and being surrounded by so many Scott owners who, I’m sure, would have loved to have seen Roger and I trying our best in the vintage races, I was left with the feeling that I simply had to re-assess my approach to racing given the available time and finances available.
I never wanted to simply ride around, and when you feel like you could get more from your engine, it’s hard not to succumb to the urge to tinker. You must have the time to see it through though.
My main plan for 2017 is to finish the rebuild of my lathe and build a workshop to house my other machines; a Thiel 158 universal mill and most recently acquired, my Jones and Shipman 1014 grinder, which is a true universal toolroom machine with surface grinding, cylindrical internal and external as well as tool and cutter grinding capabilities. These are currently in storage and I need to stop playing with bikes for a while and make them a home. This has to be a priority above racing and bike development. I will rebuild the engine but I may do it as a good road engine to run with a normal pipe and finally register it for the road. I’m not certain about it, but I could possibly do some local events, hill climbs, sprints etc and enjoy it in a different way whilst building up the workshop. We’ll see but I quite like the idea. Racing is very expensive and there’s a lot of tooling I can get for the price of a two day meeting.
I have also been rebuilding a couple of engines for other people and it’s obvious that I need to have better facilities in place if I am to continue doing this within any reasonable time-frame as I’ve had to rely too heavily on Roger fitting my work into his already packed work schedule. It’s been a lesson which has contributed to my resolve that this year must be the year of the workshop.
So it may be that in 2017 my posts are less racing oriented. I’m still working on Scott engines anyway so I’ll post about that as well as my machines and any related progress.
We’ll see what happens…
Happy New Year to all who visit and good Scotting!