Good Day from Malaysia and owner of BSA M21 1957.
Although the posting dated back to 2015, just recently manage to get the SV Temperature data after running-in the beast and clock out the mileage @ 1200 miles (occasional ride).
The restoration completed in 2015 and the set-up as below :
Model : BSA M21
CC : 600cc.
Piston : Standard
Piston clearance : @max-6 thou
Cylinder Head : Alloy
Cylinder Barrel : Iron
Ignition : Magneto @ full advanced
Spark Plug : NGK BP7HS
Temperature measurement set-up :
Temperature Read Out :
Blue DC12V Digital Thermocouple Thermometer Temperature Meter 9~999°C
Temperature Probe ( Sensor ) :
K Type Thermocouple Temperature Sensors with 14mm id Washer for Cylinder Head
Extra DC Voltage Read Out :
Mini DC 0-30V LED 3-Digital Display Volt Voltage Voltmeter Panel Accurate Meter
Temperature : @right - Blue LED
Voltage : @left - Red LED
K Type Thermocouple Temperature Sensors with 14mm id Washer fastened to NGK Spark Plug and cylinder head.
Temperature Data :
Operating temperature ( riding@ 40 - 45mph ) : 98°C - 120°C
Idle for 5 - 10 minute after riding : 125°C - 140°C
140° above and rising showed a leakage at combustion system such as carburettor, carb manifold, exhaust valve, inlet valve or both valve.
Seizure Temp : 250°C and above.
Regards.
Roslan Subri
email (option): roslansubri@gmail.com
Hi Roslan...Interesting figures which I've made a note of..
Any comparison figures from contributors in a temperate climate available yet?....Ian
email (option): ian@wright52.plus.com
In both M21 spec and now with ith Ian's 720 kit installed albeit with about 60 thou piston/ head clearance, I regularly see 450F and higher (525F...note the melting thermocouple wire insulation) The bike is being run quite hard with long distances at full throttle. Another friend with a New Imperial 350 saw 625F before his thermo wiring lead parted.
email (option): teladelujo@msn.com
I doubt that there is any difference in the quantity of heat energy being created with either head configuration, iron or aluminium (assuming compression ratio and ignition timing are the same), but I think it's safe to say that the properties of the aluminium head allow it to shed combustion heat faster than the iron variant, no doubt why the factory installed them on the M21 sidecar "slogger".
The thermocouple ring is copper, so I did remove the spark plug crush washer to install; sealing has not been an issue.
A spark plug of a given heat range is designed to transfer enough heat away from the plug's tip to prevent it from becoming an incandescent "glow plug" during hard running, but at the same time keep it hot enough to prevent the plug from fouling,
By design, combustion heat is to be transferred through the body of the plug into the head to be dissipated. (One of the reasons a plug is to be properly torqued during installation) The wrong plug in an OHV engine can lead to major engine failures due to combustion chamber hot spotting and "holing a piston". Our SV engines are much more forgiving in that regard.
Just casting about here, but it makes me wonder if the plug body in the head is not one of the hottest points on the engine, right along with the exhaust valve.... (?)
Also, if you check for head temp operating ranges set for reciprocal aircraft engines, 450F is commonly considered a safe max head temp. If you consider that aircraft engine operating parameters are extremely conservative, there could be considerable latitude for safely pushing the limits on a motorcycle engine.
email (option): teladeluji@msn.com
Visions of crumbling aluminium cylinder heads....
email (option): teladelujo@msn.com