OVERHEATING AND WATER CONTENT

[Roger Hulett]

I have a major overheating problem. The engine starts easily, and runs smoothly. Tick over is very good. After approx 10 mins on tickover the water in the radiator erupts like Vesuvius. I assumed that I had either a leaky head or a faulty head gasket. No, head and gasket appear OK. There is no water in the sump and no misfiring.
When the engine is relatively cold ,with the rad cap off the thermo cycle appears to be ok.
I have come to the conclusion that the radiator is faulty. It has been flushed many times and does not leak.
Question……What should be the capacity of the engine and radiator ? I drained my engine and measured in exactly 3 pints to full. Is this correct ???
Regards Roger

[BRIAN MARSHALL]

The coolant volume is very variable, depending on the model, type of radiator, (Full-width core or a slot up the middle, honeycomb or film core, size, etc..) I think that most Scotts will come to the boil after 10 minutes or so not moving ! The old honeycomb cores are very efficient, and if you come to the boil in traffic, they will come off the boil after you have only gone a few yards. I’ve said this before, but when filling your radiator you should always ‘burp’ the trapped air out of the top shoulder on the opposite side to the filler. Fill up to the level of the breather pipe, then lean the bike well over to the side opposite to the cap, and you will hear a glug-glug-glug sound as the trapped air goes over to the filler side and then escapes. Then top up again. If you think about a bit of schoolboy physics, gases expand a lot on heating, while water expands very little in comparison. So, any trapped air expands a lot as the coolant heats up, and immediately increases the level of the coolant, which promptly escapes down the overflow pipe, leaving you with a low coolant level and far more prone to overheating. Please also check that your overflow pipe isn’t blocked.
Brian

[gammakeith]

I’m struggling with the same thing though mine only erupts when I open it up to approx 60 mph and above. In my case it seems a smaller than normal non-honeycomb radiator is responsible as rad and engine have been well flushed and the engine is no longer running lean. It takes a lot of energy to boil water so the engine is still being cooled but obviously only while the water level remains at reasonable levels 😯

If your bike doesn’t boil when given some “beans” then your radiator must be working fine.

Keith

[BRIAN MARSHALL]

On the shelf I have a Dirt-Track Model radiator that was fitted to my 1929 bitsa sprint bike, and it is TINY. It was OK for a quarter-mile sprint, marginal for a kilometre event, and a prolonged wait at the startline for other riders, with the engine running, was out of the question as it would rapidly come to the boil.
I don’t know what fuel they ran in Speedway/Dirt-Track back in the late 1920’s, but IF it was Methanol, letting the engine run much cooler, it would have been no problem.
Brian

[Roger Moss]

Richard Moss runs a dirt track rad in his (My old) racer. I did have overheating problems years ago and even tried slight pressurisation to cope with it.
It worked, but the real problem was carb weakness. I cannot remember at this distance in time whether it was insufficient fuel flow of incorrect jetting.
Richard must be getting about 40 bhp now but runs on dope. By the by, as regards smoothness and good take off, it is standard practice for me to put a weight ring in the flywheel to increase the weight. It also reduces chain snatch and sprocket wear. Roger

[midge]

Hello to all readers. this is my first post so forgive me if I stuff it up a bit ! I bought a 49 f sq. 600 in the u.k. and imported it to Australia ” very costly”! Imediately had overheating problems after trying many many solutions which didn’t work ,I finally found a way ! I mounted a freezer block , square flat plastic thing ,1Ltr cap ,onto theengine guard made the cap of the ” bottle” removeable ,drilled 1/4″ hole in said cap then fitted areasonably stiff plastic pipe from the overflow of the radiator into the bottle ensuring the pipe went to the bottom where 1″ of water waited . I made sure the rad cap was airtite & took the bike for a spin in 32 degree heat . It worked great the rad breathed fluid in and out of the bottle and none was lost airtite

[Roger Moss]

Well done Midge. There are quite a number of Scotts In Australia and if you have not met any yet contact Steve Enticott who should have contact details
senticott@optusnet.com.au As regards the Radiator, then I respectfully disagree with the design of the radiator for the normal 3 Speeder.
The point I have reservations about is the practice of positioning the bottom fixing hole immediately above the bottom hose outlet. This leads to clogging with calcium if the bike has been used in hard water areas. In fact I much prefer not to use a bottom fixing and let the rad hang on the top two fixings only. The bottom is controlled by the short pipe from the head / water jacket and this causes much less stress. I use a less wide two speeder radiator, as it is less likely to get damaged if I crash the bike during a track event. I asked Graham Moag to remove the bottom fixing to give better flow and I can use all 42 bhp for long periods with no overheating. Welcome to the Clan. Kind Regards Roger

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