Hello.
Has anyone ever tried to have gold star touring cams instead of an M20: cylinder head modification, power gain, speed gain? Thank you I wish testimonials on a personal experience.
Patrick
email (option): patricklena@netcourrier.com
Gold star bits !! You will need better brakes if you do that LOL , andrew
Yes I have indeed. Post war M.21 engine in a JM20 frame you need to pack out the rear section of the frame to get it to clear the oil pump bulge. Aircraft spec dural engine and gearbox plates, Post war medium close ratio gears in the WD gearbox shell, lucas racing mag, Amal Monoblock 376 Carb, idler wheel drilled and lightened as per DBD 34, inlet port opened out a little and polished - inlet valve guide cut down to line flush with inlet port, cylinder head partially filled with cast iron and polished to same profile as Norton SWD Big 4 gets the compression ratio up to about 6 : 1 (Ricardo Principles),top of barrel liner radiused towards inlet valve, DBD Gold Star timing cover and rev counter drive, Gold Star Daytona racing seat - 1930s BSA fuel tank - twin fillers possibly C.10 or earlier both sides used for fuel, 1938 M.Group oil tank, single spring clutch, AM4 brake linings, ribbed rear sprocket, alloy rims, alloy guards and stays, racing tyres, cut down DBD 34 exhaust pipe and megaphone should paint the picture.
Tried various cams but no real improvement so it runs on the original post war M.21 cams.
The bike however, goes extremely well.
There was a M.20 in Australia that ran with Gold Star cams and a 40mm carb set in the side of the barrel to reduce angles into the combustion chamber and I believe that achieved a speed of around 108mph. Pat Jeal ran a racing M.20 in the UK some years ago and you can find details of that via Google.
email (option): keithchandler@clistandchandler.co.uk
I run them in mine.
Put them in cause they were the best of a bad lot of cams.
Bike runs fairly well, a bit quicker than most M20's I come across but it also runs an concentric.
I used get a touch under 80mph out of it , eventually on fairly flattish roads with high gearing & the 930 carb
It also uses a lot more fuel and does not have the same bottom end torque as it did when I first got it and rarely idled when hot.
When we were coming back from the BSA National in Torquay a decade ago I was riding with friend on his A5F with the small 2 gallon tank & std Firebird gearing trying to stay awake on the Hume Freeway.
He was getting further on his 2 gallons than I was on my 3.5 gallons to put the fuel consumption into perspective .
So my safe riding range was 200 km which is a bigger problem down here than it would be in the UK.
It is now fitted with a 626 concentric and that has knocked about 10 mph off the top speed, reduced the rate it goes faster ( can't call it acceleration ) and returned a bit of the bottom end.
So what is cam & what is carb, don't know .
What I do know is I was working hard to get 40 mph out of it when I got it and could not keep up with my housemates bog standard 38 M20 ( Deluxe ).
By the time I was finished he could not keep up with me.
However no one in their right mind buys an M20 to go fast and on the quieter slower backroads the bike runs well & I just point blank refuse to ride on expressways any more.
If you are thinking about running WFO you really need to fit an alloy head.
After an hour on an expressway , even with the concentric you could not turn the bike off to refill unless you had a 1/2 hour to let it cool down.
email (option): bsansw1@tpg.com.au
I have a M21 crank & piston making it 600cc, along with Gold Star Touring Cams (Ex 65-2450 & In 65-2448) in my '41 M20 which makes it a different bike. Very rideable. I also have a 20T engine sprocket ready to fit when it is pulled down at some stage.
email (option): grcajol@bigpond.com
Trevor,
i can imagine the bike was running hot, especially in Australia...:sunny:
And I was wondering how much space is there for lift of higher cams, before the valves touch the cilinder head ?
Hello. Thank you for your answers. I really want to ride gold star touring cams. For this, it will dig the cylinder head at the valves.I stay tuned for other experiences.
email (option): patricklena@netcourrier.com
For approx. measurements, the Gold Star Exhaust Touring Cams open 5 degrees earlier than the M20 cams & close 20 degrees later than the M20 cams. The Gold Star Inlet Touring Cams open 18 degrees earlier than the M20 cams & close 8 degrees later than the M20 cams. The Gold Star Touring Cams lift approx. 2.17mm higher than the M20 cams & go straight in to the M20 motor.
email (option): grcajol@bigpond.com
Anything over that and you really notice the limitations of the iron head to dissipate & radiate heat.
City traffic is what it really hates, it is a contest between the head & the clutch to see which one can overheat first.
As for the difference in valve timing note what I said about fuel consumption.
It had the nice new 628 for the international last year but the nice new head gasket blew so I ended up running a borrowed 200 main to compensate for what was either getting sucked in or blown out of the gasket.
Having said that it did all but the first run without problems engine wise.
Could not say the same for the nice new stand or speedo drive both of which failed
But that is all part of the fun of riding anchient bikes.
Performance wise the text books say to go for a shorter duration inlet with a higher lift opening latter
And a longer exhaust duration with little to no overlap .
If I had more good cams I would try a std inlet ground for higher lift and the touring exhaust.
But right now I need to get some more bikes running so I can play with it.
Hard part down here is finding people to do things like grind cams who know about side valve engines.
Got a few spare heads & was thinking about putting some inlet & exhaust tracts in it but to date every one I have spoken to tells me different things.
What I am thinking of at present is a wide funnel shape into the exhaust valve and a narrower inlet coming in tangential to the barrel. Then shifting the combustion chamber a bit to the left more over the piston and the tracts will occupy a lot of the current combustion chamber.
We do that with SV Briggs engines for the mower racers and it seems to work reasonably well but they have a lot squarer stroke than the M20. All good fun provided it does not go bang and no one is physically hurt.
email (option): bsansw1@tpg.com.au