Running hot

Mine's been all right this weekend. Side-valves do run hot but Nortons with their stub-mounted carbs are generally less susceptible than bikes with flange mountings such as M20s.

If it's running too hot, I'd suspect retarded timing, perhaps a lean mix, or maybe an air lock in the fuel feed, depending on the set-up.

A worn inlet valve guide will cause a lean mix on a '37 pattern 16H.

What fuel are you using, a which sparking-plug ?

I would check your fuel mixture first (look at the colour of the plug... sooty too rich) and then check the valve clearances are right. If all that fails you may be due a decoke as she aint breathing correctly.

Previously antony_ryan wrote:

Hi, my 16H is running very hot, so hot that the fuel is vaporising and causing her to cut out for short periods until it has cooled enough to re fire, usually before I come to a halt she fires once more! I have carefully checked the timing, do you think it is carburation ? The carb is getting very hot. Cheers Tony.

Hi Tony...

Took mine for a run today also - having had annoying misfire problems and blaming the carb - and delighted to say the problem has gone away - the mag sprocket had slipped on its taper and it was too retarded. Are your pipes as blue as mine? They look like a modern Bonnie.

I've now timed mine at 1/2 inch BTDC on full advance and that seems to be fine - and slightly better than the book value of 7/16 inch. Everything was rather hot today - especially me - but no odd vapourisation. Carb needle is middle setting.

After riding a Dommie with Concentric carbs I love the accessibility although I hate trying to remove the magneto cover.

I'm now using NGK AB-8 but tried several typeswith little difference between any of them. I can understand how an engine can make a plug too hot but I've no idea how a plug can heat up an engine.

If I remember it this evening I'll drag out my Maplin infrared thermometer and see howhot the enginegets. 'Very' seems a good description. 'Don't do more than 30mph for first 500 miles on a new engine' is what it says in the handbook of course. Could take a long time...

Previously antony_ryan wrote:

Hi, She's just had an overhaul new bearings,valve guides etc, and I set the timing slightly advanced so I think I'll have a look at carburation next.the plug in there is a Bosch -M5AC, I also have a NGK AB- 8 to try, the gap is 17thou, any ideas. Actually if it runs hot do you need a hotter or colder plug? Or doesn't it work like that, also how do you find out which is hotter or colder anyway? Questions, questions!

Alright David,

with ref. to the recommended max 30mph for first 500 miles, if you've had the barrel rebored, honed and then plateau honed by a competent machine shop who have kept up with surface finishing technology then the piston rings to bore should have bedded in with in a few seconds of starting the engine,

Simon.

That's fine, Simon - but why is Tony's machine running so hot?

Admittedly Sunday wasn't the coolest day on record. And I feelvery much more aware of engine heat on a 16H than on a Dommie - I suppose partly because seat height is lower and my legs seem to be closer to the engine. And side valves have the exhaust pipes so much closer to the barrel (part of the barrel) that they are bound to run hotter.

I don't know why Tony's machine is running hot, I was only pointing out the difference that advances in technology have made to the recommended running in period you made referrence to. Hope he gets it sorted,

Simon.

Hi Tony,

Just came across your post of Sept. 1st 2012 where you have similar problems with the bike and mention the bike was getting very hot and partially seizing. Is the heat a result of friction between the bore and piston? I think it maybe worthwhile to check the clearances etc. Bore ovality should be no more than 0.0002" after honing.Clearance would depend on the piston manufacturers recommendations plus allowing for the apparent extra heat side valves retain,

all the best, Simon.

A plug check will tell you if the carburation is ok. The usual white, too weak sooty black, too rich, grey/tan colour is good. Best to check on slight incline at 3/4 to wide open throttle. Hopefully you haven't now got too much piston to bore clearance,

cheers, Simon.

A big main jet should make it run rich and hence cooler. For the curious, a richer mixtureburns faster than a weak one and has the effect of advancing theignition timinga degree or two.

Running with retarded ignition will make the bike run hot. It might be worth re-checking the ignition timing.

Rule of thumb - a hot engine needs a 'cold' plug. A cold plug has more insulation on the electrode to stop it being melted at extreme temperatures. It is more prome to oiling up as it does not burn off deposits as well as a 'hot' plug.

Hi Antony

I will put my two bobs worth in, I doubt changing the main jet will make much differnce at 30 mph as I would imagine it would be lucky to be off the pilot circuit or maybe just into the needle jet at that stage? Have a look at an Amal tuning guide for best reference. I have seen many chaps having trouble with running hot, opening up bore clearances etc only to keep on seizing. Some of these issues have been incorrect valve timing usually exhaust resulting in losing the fuel air charge out the pipe and running lean, seen altered exhaust systems resulting in the same.

If timimg is correct (Valves and ignition), go for carby tune and do it by the book. Must admit I haven't had much side valve experience.

Good luck

Best Regards

Mark

Shorter insulator allows heat to esacape quicker therefore colder plug. Longer insulator hotter plug. AB-8 is shorter than a couple of plugs I tried.

If the cab is original, just maybe it's too lean owing to wear allowing air round the slide? But the old carbs were much more robust (much bigger wear surfaces) than the Concentric so I doubt if that's it and i won't affect 'cruising' much.

You are certain the mag is timed on full tight wire at about 7/16 or 1/2 inch? Maybe it was when you set it up but they can slip and retard themselves. Is it misfiring? You mentioned overheating and fuel evaporation - maybe your fuel tap is partly blocked? Or even blocked fuel cap vent hole? It isn't easy to tell what 'too hot' means on an air cooled side valve with no water temperature gauge. Mine misfired and ran hot when the timing slipped.

I'm going for a short run now after work. I'll try and find my infrared thermometer.

Best regards

David

I use a Champion D9 plug in my 16h and goes well on it.

Try running on BP Ultimate if you are not in the South West. There is no ethanol inthat for now. Just about all 95 RON is now contaminated with ethanol. One of the many problems with ethanol is that it makes engines run hotter. Hope this helps.

This may sound silly, but, have you checked that you still have some valve clearance when the engine is hot? With an old bike, the "book" clearance may no longer be correct. I had this problem with my Dominator, I set the clearance as per handbook. The engine nearly always started at the first kick, and, performance was perfect for 15-20 miles. After this, the bike slowed and would not restart until it cooled down. A previous owner had fitted alloy pushrods (instead of the correct steel ones), these expanded with heat until the exhaust valves did not fully close. A little extra vave clearance solved the problem, and the engine now runs perfectly. Regarding running-in at 30 m.p.h. Speed (within reason) is not important, what matters is to keep the engine running smoothly on a light load. 30 m.p.h., in top gear, on an incline, will cause more wear than 50 m.p.h. downhill.