Seemingly compression comes and goes.

[DewCatTea-Bob]

Jim I was going to say to check your clutch because of the way you described the kickstart "spinning the engine freely"
Like Bob said you should be able to tell the difference between the feel and sound of the clutch spinning and of a valve stuck open. Imagine holding in a compression release and kicking a bike over. Go to your other Duc and hold the clutch in and kick it over. Then try to decide what your Mach1 is actually doing.
Good luck

____ Thanks for your welcome input Aaron !
(And although I sort-of once-again felt tempted, I've come to know better than to try any joking-around with your chosen-wording indicative of "kicking a bike over" !)

____ I-myself am rather pretty-confident that Jim has more than sufficient perception to sense & realize that an 'ENGINE' is 'spinning' "freely", rather than anything other with less mechanical-workings resistance,, since I happen to already know that Jim has fully realized that just because the kick-lever is worked-through, that doesn't necessarily always mean that the engine is also rotating (extra freely or not) ! _ As Jim has already before gone-through such similar circumstance and dealt with it quite competently ! - (As can be noted within an old thread-post of his, which can be found with this link... viewtopic.php?f=3&t=1193&p=8121#p8121 .) _ And a slipping kick-start mechanism isn't too awfully much more freely-spinning than with a fully disengaged clutch.


Dukaddy-DUKEs,
-Bob

[amartina75]

Jim seemed unsure of what was actually happening. That's how I read it anyway, if he is questioning his problem being related to a valve problem, then a clutch problem. Like you pointed out those two things should sound and feel different.
So the first step as I see it would be to define what is happening.

By the way Bob, ALL of my BIKES run and drive just fine and I KICK them over all the time.

[DewCatTea-Bob]

[quote= JimF ...
" Well it's been a couple years... "

____ A "couple years" ? _ That statement leads me to assume that you've still missed the link I posted to your 2011 related thread, from back in June of that year.
So I'm left to assume that you've still failed to notice that my very-first hastily posted initial-response posting had since been fully updated/completed to my rather finished edited-version. (?)
And that's possibly the reason why you still haven't yet answered as to whether your Mach-I has been able to start & run or not, (since you've once-again found it to have compression, this-year).
__ Anyhow,, under normal conditions, I don't think a valve could ever get stuck-open stiffly enough to keep normally operative valve-springs from completely doing their job. _ So I'm wondering if you think it may be possible that somebody may have chosen to screw-around with you and possibly repeatedly inserted some small objects into the carb.inlet, which could then cause a valve to not fully seat and-thus leak-out the otherwise expected compression. (?)
If you've had a muffler (with baffle) installed,, then perhaps you could remove it and check for any foreign-objects still caught within, which may've been responsible for your previous episodes of lost compression.
__ Just an unusual-suspect thought, for your very-UNUSUAL mechanical circumstance.
But perhaps not TOO unusual, as 'kids' are quite well-known to insert sticks into all sorts of orifices ! - (I know one kid -[myself], who used to take-off the caps of car-batteries, and insert all kinds of little pieces of stuff to see what would happen,, [and my mother always used to wonder what kind of bugs kept eating those tiny-little holes through my cloths] !)



" I can't think of any scenario regarding the clutch that could create a disengaged condition without the cable being pulled. "

____ Well I can... As the clutch-spring screws could possibly come-loose & fall-out. _ But I've not before mentioned that (unlikelihood),, cuz that's another impossible scenario, which can't possibly self-repair !



" I am still playing with engine rotation so as to check 'valve cap' clearances and I have been using the kick start lever but I may need to use the rear wheel with the bike in gear to get a finer resolution. "

____ Rather, you possibly could instead remove the bevel-cover and use a socket-cap with breaker-bar to slowly turn-over the camshaft-nut and-thus more finely control engine-rotation,, (with spark-plug removed, for reduced resistance).



" So far though I see nothing odd. "

____ Well then I'd next take a look inside the exhaust (and combustion-chamber) for anything 'odd'. ...
Perhaps some rather thick built-up carbon-deposits have worked-loose from the combustion-chamber and happened to get temporarily caught between valve & seat, then later fell-out ?



Hopeful-Cheers,
DCT-Bob

[JimF]

I am unclear because as Bob has uncovered, it has actually been three years and not two since I last experienced the symptom(s).

I expected to find the bike in the inoperable state I left it in was surprised to find that it's back to 'normal.'

As I recall, it had done the 'compression loss' once before and self rectified ahead of the repeated failure three years ago.

Just to bring you up-to-date, I got a new job three months ago and have NO vacation time. I work side jobs at night and just got a new side job to start on, which will cut deeply into my wrenching time.

Also, the side jobs spawned a third side job; making LED taillights for old Porsches, and I just got an order today for one so again a cut into my wrenching time. And I have to repay a friend by rewiring the pigtails connectors in his Sears Allstate alternator.

I really dread trying to find a failure that intermittent and currently not failing, but then I have to remind myself that I am lucky enough to own the fine motorcycles and this is the price that has to be paid.

Lastly, and probably best left for a new and different (or old and continuing) thread, the kick start lever once in while slips. It has the bridge style spring mechanism. As I recall, Bob hinted that this is indicative of a bad problem.

Jim

[graeme]

Valve sticking in a guide?

[JimF]

Help for a newbie...

If I take the head off to inspect it, what if anything should I do in advance to insure I don't break anything in the bevel tower?

What can I do to make sure that I don't screw up the timing of the bevel gears while the head is separated from the engine?

[DewCatTea-Bob]

[quote= JimF ...
" If I take the head off to inspect it, "

____ Have you yet first simply looked-through the spark-plug hole with a bright light shown inside there (to see if there's any chucks of carbon gone from the piston-crown, or anything else that's odd seen inside there) ?
__ I guess I'm left to assume that you didn't have a baffled muffler to check the input-side of, for any possibly captured foreign-debris (which had to've worked-through the combustion-chamber). (?)



" what if anything should I do in advance to insure I don't break anything in the bevel tower? "

____ Before pulling-off the cyl.head, you should first check that all-4 head-bolts have still been left torqued-down to at-least 20-ft/lbs, - (it may take well over the recommended 28-ft/lbs to break-loose those 10mm-bolts, so-therefore take your torque-readings right-after the bolts have broken-loose),, that-way, you'll then have had a chance to realize whether or not your compression-issue might've possibly been due-to air-leakage between cylinder & head.
__ There shouldn't be any way you could "break" anything,, however you still should-not do the same procedure as common newbie-wrenchers are most apt to do,, and rather-instead, leave the head and tower-shaft & housing-tube all together and left entirely connected as a complete-cyl.head-unit, (just exactly as it always exists when installed) ! _ Cuz that whole entire cyl.head & bevel-tower assembly comes-off the cylinder-jug & motor-case all-together in one-piece !
So there's no such screwing-around concerns to-be worried about ! _ (Although you might care to let the motor rest towards a rightward-tilt for some time beforehand,, so as to get the head drained of oil, ahead of time.)



" What can I do to make sure that I don't screw up the timing of the bevel gears while the head is separated from the engine? "

____ This worthy concern has been covered a few times before, so you now ought-to more thoroughly realize the gear-timing prep situation after this following head-removal preparation refresher-review ! ...
__ With the bevel-cover removed from the cyl.head, turn-over the engine until the timing-dots (near the teeth) on the ('upper-pair') of bevel-gears become aligned. - (With spark-plug removed,, it's more convenient to rotate the engine by gently wrenching-on the camshaft-nut, rather than attempting to use the kick-start lever.)
This logical preparation will conveniently leave all the timing-gears preferably positioned 'in-time', for rather quick reassembly of top & bottom ends (without any need to check/reset the gear-timing within the bottom-end) !
However afterwards (with head still removed), if the still timed crankshaft-position later happens-to become disturbed, [even greatly !],, it's really not an actual concern as most-all newbies believe it to be ! _ As there's a relatively simple fix-procedure* to get the timing of the top & bottom ends properly reset back-together (without having to screw-around with any-other timing-dot alignment checking !). _ So if perhaps you'd like to kick-over the bottom-end workings a few times (while the cyl.jug is securely held-down), so as to take a look-see at the piston as it reciprocates within the cylinder (and-also witness the rate of oil-flow from the oil-passage/nozzle),, then go-ahead & do so, as we can rather simply straighten-out the then lost gear-timing, later.
(* viewtopic.php?f=3&t=1606&p=12198&#p12198 )
__ Then once the four head-bolts are removed, (you then probably better place a piece of rubber-sheet or something soft atop the head [to protect that nice red-paint your M1.frame has]), then-next lift-upward (possibly along-with a slight back-&-forth shaking-motion) on the cyl.head-assembly until the bottom of it's tower-housing/tube lifts-out & slightly clears above it's tube-base/female-flange -(still-left attached to the motor-case), and-then slowly/carefully horizontally-twist* it clockwise (* around the tower-shaft center) as you continue slowly lifting (lifting more-so, after fully clearing the frame-tube), whilst proceeding to remove the entire head-assembly away from place, towards the right-side of the motor (& away from the bike).
__ While it's possible to remove a complete cyl.head-assembly from a n-c.250-motor & frame with carb & ex.head-pipe still left fully attached,, with a SSI-carb however, it's better for a 'newbie' to remove the carb.body off-from it's manifold-flange first, (before the head-bolt removal step).



____ Now next,
please ask any other newbie-type questions
which ya may now have.


Hopeful-Cheers,
DCT-Bob