Camshafts and camshaft tunnel

[pqbell]

Hi everyone, I´m the owner of a 1956 g11,apparrently in original condition,one owner before me and in one lump when I bought it but not running.I have had this bike several years and never had it running properly....the mag ahs been rebuilt,no misfires but wont pull or drive over 60,like its hitting a wall,bike has the higher compression pistons(wire wound) its on std bores,which amazes me cos no air filter and 60,000 on the clock..has been rebuilt because there is evidence of break-up in the head,little dents etc..I stipped it down to clean the sludge traps and everything was fine so I put it back together but problem still there..I have now stripped it again and in doing so i have a doubt that I might be missing something..in the exhaust cam tunnel drive side is an alloy cylinder that angages with the end of the camshaft. on the outside of the drive side crankcase is a big chromed threaded bolt that with a thick fibre washer that "seals" the tunnel,the alloy cylinder is an oil distributor Yes? how does that work?...but what worries me more is I can`t find anything equivalent in the inlet camshaft tunnel that similarly engages with that camshaft am I missing a bit!? and if so what part number..would this cause the bike to run badly?

[saltbox alf]

Hi fellow francophone, are the dents you mention on the piston crowns or the combustion chamber or both?
I think you are taliking about the oil distribution tunnel which is only on front of the engine and not repeated on the inlet cam side. The other housing in front of the oil distribution tube is for the wire mesh/felt oil filter. (think I am right on this as not had to pull my 650 apart) Hope fully some one more knowledgeable than me on twins will give you a complet answer

However the dings and dents could be a sign of a very weak mixture or over advanced ignition timing, causing local hot spots and melt down of the piston crowns and cylinder head chambers. You say you have hi comp pistons, so with the merde fuel we have this a likely possibility.

[robcurrie]

There isn't anything on the inlet camshaft. The oil distributor bush gives a pulse of oil to the top end of the engine instead of flooding the top with too much oil.

Rob C

[SPRIDDLER]

wont pull or drive over 60,like its hitting a wall,........... everything was fine so I put it back together but problem still there..

Welcome, Paul.


Which problem?

If it's the 'pulling' and top speed problem the ignition timing may be retarded or the main jet's too small.

there is evidence of break-up in the head,little dents etc..

If the carb's under-jetted (or jetted for an air filter and one isn't fitted) the mixture will be weak on all throttle openings greater than half. A weak mixture will also result in holing of or damage to the piston which could be why you have historical debris marks in the combustion chamber.

[zwarts]

On the very early Twins, the inlet camshaft drove a timed breather. This is why the inlet camshaft has a slot in the n/s end. Your 1956 engine is well past the date when this was discontinued and replaced by the breather valve in the end of the crank.

[pqbell]

Hi everyone and thanks for the replies, sorry about being so long in replying(problemwith passwords)..so I understand that the empty inlet camshaft tunnel is normal on my bike,good thats out of the way!...as regards the damage to the head(one only) its old damage andmust have been repaired by the previous owner..is it possible that the higher comp pistons would affect the running and that I should be timing the motor differently?It does seem to feel like the timing is retarded and she warms up very quickly....when I had the mag rebuilt I specified it was for a 56 g11 ..is the ring that is moved by the advance/retard lever the same on all twins or does it have to be matched to the cams(inlet/exhaust) on the bike..sorry if this all sounds stupid but I am new to a bike of this age...for instance am I right in assuming that when setting the timing that the lever is in the closed position..i.e with the cable slack? If not then that would be the problem! Salut a Saltbox et merci pour l`aide, je pense que la becane na jamais eu de filtre a aire.

[Malleon]

Bon jour, Paul, et bienvenu au 'Forum',
The AMC twins of the '50s were fitted with Lucas K2F magnetos, and when setting the ignition timing the control lever should be pulled towards the rider so advancing the sparking point; the ring mentioned in your enquiry can be seen to move clockwise as far as the small pin engaging in a slot at the back of the ring will allow with the control cable under tension. Running the engine with the ignition retarded can cause problems due to overheating!
More advice can be found in 'Technical Tips' or if you 'search' using the magnifying glass logo in this site's heading.
Bon chance, a bientot.

[robcurrie]

....and when setting the ignition timing the control lever should be pulled towards the rider so advancing the sparking point....

Usually, pulling the lever towards you - tight cable - would be retarding the timing (if the cable entry on the K2F magneto is on the left hand side looking at the points).

The timing should be set with the lever at full advance.

Rob C

[ajscomboman]

Tut Tut! Malcolm having a twin you should know better. Pulling the lever back towards the rider retards the timing. As Rob says, the timing should be set to full advance 3/8" or 39 degrees before TDC, lever set as far forward as it will go.

[Malleon]

Oh dear! That is an acute attack of foot-in-mouth disease, possibly due to latent transient global amnesia, and for which I 'umbly apologise.