1941 16h running very hot ,advice please on where i should be looking
thanks in advance

Is this a gradual or sudden thing or has it always been like it in your ownership ?

Is it accompanied by loss of power ?

My first thought would be retarded ignition timing.

Exhaust valve problems.

Spark plug grade is unlikely as Nortons run such a hot plug anyway.

Possibly valve timing.

It's unlikely to be carb or fuel flow if it's all through the range, but a restriction in fuel could cause it at wider throttle openings.

Air-cooled side valves do run pretty hot. What makes you think that it's 'too' hot ?

Modern fuel burns hotter so standard plug setting may be too hot, may need a colder plug, mine did. Any sidevalve runs hot. My first M21 used to glow in the dark. Most likely to be retarded and/or not enough oil in tank. It's open the lever to advance the timing, opposite of M21s

many thanks guys for your answers ,i think regarding the timing being to retarded could possibly be the solution .
ive asked on another post re-removing mag sprocket , a guide to set the ignition timing
any help would be be gratefully received
thanks john

Hi John,

What exactly do you mean by running hot? Doesn't the engine run properly anymore?
Sidevalves become legburning hot you must know.

Regards, Sven

hi sven
wished i knew how to post a pic ,but better off telling the full story ,the bike is a mongrel i have built the bike to enter in to this years dirtquake race so its a dirt racer

engine 1941 16h WD,ive paired it to a later Norton dommie laydown 4 speed box modified 16h engine and gearbox plates running a bsa clutch ive put this in a 1958 ariel capr twin shock hunter frame ,bsa A10 totally modified swing arm to take 18" MX rear wheel running 55 tooth sprocket ,jap forks one off yolks and 21" front wheel ,no electrics no dynamo just mag powered

been building one off's for thirty years but never have i touched a side valve so have zero experience of running of them ....sorry to say with no offence meant, im a BSA man so the only Norton ive messed with apart from this engine was a crock of crap navigator that disappointed me that much i sold it after a week

always loved the 16h ,couple of years ago brought a vast amount of brit bike parts ,went to collect and amongst them was this engine ,been tripping over it ever since up until i decided to use it for this project .
the bike is now complete all up and running ,starts first kick idles great and runs up and down the box sweet as a sweet thing however with my very limited experience on these it seemed to be running hot,i put the points in it, but the mag was on already ,i felt it needed to advance more to be honest ,when i asked the heat problem question and the answers were pointing me to it being retarded it made sense that the timing needs to be set correctly ,so asked for a idiot guide to set the timing once the mag sprocket is removed ,going to sort it tomorrow and the manual ive got is about as clear as mud

i know engines and have read about how hot side valves run, but this is excessively hot and dont want to seize it
thanks for your patience.....john

all sorted ,thanks to the guys who confirmed it was a retard problem