Forum

[Martin]

Had queried a few blogs down about mix-matched
camshafts installion on earlier Twins. Mark kindly
reminded me that Super Meteors and the US Twins had
used two 32705 exhaust camshafts for sportier pep,
but with a 36140 duplex camschaft sprocket on the
inlet side. This sprocket presumably has a changed
timing mark or woodruf key position to deal with the
more radical cam profile. Is anyone able to compare
on their bench how many teeth or degrees the latter
timing mark has shifted to between the early 34359
sprocket, and the later 36140 one? Have several of
the former sprockets already, so would take thirty
seconds to modify one of them anyway. Mark & Dennis
had answered a similiar query from another a few
years back. Thanxs

[Mark M]

Gordon, if I recall, the difference is half a tooth. You may be able to achieve this by adjusting the timing chain on a standard sprocket. I have never seen a sprocket marked "A" so can't help with measurements. You could try emailing Allan, he is a mine of info on this kind of stuff!
REgards, Mark

[Martin]

Mark, grateful for your comments. Initially felt
the half a tooth cam sprocket adjustment would be
to miniscule until I re-read Phil Irving's chapter
on cam profiles. Apparently the Velocette singles
with their fine 46 tooth helixal timing gear are
the only geared 'bike motor where fine cam tuning
is possible by installing the gear either way.We're
talking geared timing not chain as per our Enfield
Twins of course. Anyway the subject is intriguing!
Will mail Allan when I checked the timing yet again
and can pinpoint the actual problem. Thanxs, Mark!

[Mark M]

Gordon, good luck and let us know when the old girl is finally running! REgards, Mark

[Norm]

Hi Gordon,
is this to get it running or are you looking for a performance improvement

[Martin]

Hey Norm, always good to hear. Actually had been down Miami
etc. and only dusted off the motor last week and attempted
another saga with it after lapping in the oil pump again with
that non oil return issue you and Colin had helped me with.
You may recall the distributor that a Lucas friend modified
after we discovered it had come from a Truimph TRW, Anyway,
still runs with poor fast idle and a surge of higher revs
before expiring a couple of minutes later.The stock 276 Amal
is back on with correct slide and middle needle nitch and
correct float position. As you may have read,got the obeessive
idea I may have installed the camschafts arse-about, but disk-
dialled and set up a dial indicator and the valves open and
close as per specs roughly although will recheck them. Today
checked the timing marks for the tenth time and they are spot
on. My friend has since acquirred the correct distributor shaft
and we will attempt that too when he is back in town. Should the
camschafts be incorrect chosen from several Tomahawk and early
Rwins will have to strip motor..hence all the interest in the
more peppier use of two exhaust camschafts. Will be sure to up-
date you and Mark as to how we made out.

[Norm]

Hi Gordon, I doubt the cams would be an issue in getting it running, the fact it will rev up indicates to me they are somewhere in the right paddock at least for it to just continue running. The fact it does run and then stops does indicate to be a fueling problem for some reason.

[Mark M]

Could it be fuel related, it sounds like it? As Norm says, it runs, so can't be a camshaft problem. The revving then dying sounds like fuel starvation to me, check that the fuel pipe is not introducing an air lock and that the tank cap has an air bleed hole in it. REgards, Mark

[Martin]

The motor is perched on a separate pod out of the
frame with a jam tin w/ gas tap hovering a few
inches above, hence the air vacuum issues was
nipped on day one. The poor running pattern has
been consistent all along despite replacing the
slighly larger 389 Monobloc with the original
refurbished Amal 276 with choke and aircleaner
to contain the sporadic backfire from igniting the
expidient gas tin. However the stubby exhaust pipes
sans mufflers may gladden the the heart of the next'
door Harley chopper owner, but offer little back
preesure for the presumaable touring camscafts profiles.
Sometimes wonder how I was called upon to resuscitate
such an orphan motor, and can only confide my anquish
to fellow aficionados here!

[Norm]

Hi Gordon,
exhaust back pressure is not the problem. I often start these motors without any exhausts when I am working on them, bit noisy but no problems getting the motor running