No compression

[JimF]

After driving the Mach 1 to work yesterday, at quitting time I could not get the bike to start and run. It fired up about three times but I had to hold the throttle open to keep it running and each time I tried to take off it died immediately under load.

I suspected a fouled plug and since I had a spare plug in the toolbox it would be quick to change that and either drive away or eliminate that from consideration.

I changed the plug and gave the bike a kick. The engine rolled over smoothly. I thought to myself "The next kick then will take me past compression and I'll see if I fixed it." Kicked it again and again and thought what the he..? I was not spinning the engine through any compression. I diverted my eyes to my hand to make sure I was not squeezing the clutch even though I knew I wasn't.

The new spark plug was in tight.

I had to abandon the bike at work, and I probably won't be able to get it home until Monday.

So begins a new (and unwanted) adventure...

[Bevel bob]

Lets hope its just a stuck valve , from your previous comments you had a good piston and barrel.

[DewCatTea-Bob]

" I was not spinning the engine through any compression.
The new spark plug was in tight. "

____ First thing to try is, remove the plug and lightly stick a finger into the hole and then note if there's any compression enough to push your finger back-out. _ If not, simply feel if any air at all is being expelled from the plug-hole, while the engine is kicked-over - (note I stated "engine", not 'bike').
__ If compression seems week (but still evident, as engine turns-over), next thing to check is exhaust-valve clearance.


Hopeful-Cheers,
-Bob

[JimF]

Mach 1 will be coming home on Monday 6/5/11. Diagnosis to come after it arrives.

[DewCatTea-Bob]

" Diagnosis to come after it arrives. "

____ Did you happen to ride it for very-long with the ex.pipe-ring loose ?
It could be that rather than a too-tight valve-clearance, your exhaust-valve may have become warped (with an edge kept from fully sealing against the v.seat).


Hopeful-Cheers,
-Bob

[JimF]

I did notice the exhaust pipe ring was loose last weekend. I tightened it up.

Too much heat on the exhaust valve?

[DewCatTea-Bob]

" I did notice the exhaust pipe ring was loose last weekend. "

____ There's then the possibility that if you had run under load at a constant high-RPM for a fairly lengthy time period, and then suddenly shut-down the throttle fully while leaving the motor gear, (perhaps for the purpose of full compression-type braking), especially when at any colder air locations,, it's then possible for outside (of exhaust-system) cold-air to get sucked-in over/past the ex.valve-head, and thus possibly cause the valve to rapidly cool-off & warp.


Dukaddy-DUKEs,
-Bob

[JimF]

____ First thing to try is, remove the plug and lightly stick a finger into the hole and then note if there's any compression enough to push your finger back-out. _ If not, simply feel if any air at all is being expelled from the plug-hole, while the engine is kicked-over - (note I stated "engine", not 'bike').
__ If compression seems week (but still evident, as engine turns-over), next thing to check is exhaust-valve clearance.

IMG_0621.JPG

Plug removed. Finger over the hole and a few kicks - some compression. Some air pushing on my finger and making a good wooshing noise as my finger moves aside. I can feel intake suction too.

But as tightly as I can keep my finger over the spark plug hole there is just not enough brute force to push my finger aside.

I removed the exhaust valve cover and saw nothing broken or suspicious. The valve opens and closes as I spin the engine. I have no timing wheel on the bike but nothing appears wrong; at some rotation of the engine I have what looks to be a reasonable valve clearance.

[Bevel bob]

A few more twirls of the spanners and the head will be off, It is possible that you have a slippy clutch and an ignition/carb problem, but having got this far i would want to check the valves and rings,also look for broken spring/retainer. Your bike looks very correct with all the parts mine is missing!!,I'm very envious.

[DewCatTea-Bob]

By: Jim...
" But as tightly as I can keep my finger over the spark plug hole there is just not enough brute force to push my finger aside."

____ I believe I recall it being pretty darn hard to keep a finger in the hole while kicking-over the near 10:1-cr.piston.
__ With finger or s.plug left tightly plugging the hole, can you then detect any air escaping elsewhere, (while slowly turning-over the engine) ?


" at some rotation of the engine I have what looks to be a reasonable valve clearance. "

____ If you're still sure that lack of compression is the cause of your running-issue, then either your exhaust-valve has warped or your intake-clearance is too tight, (or perhaps both comp.rings have broken-up).
__ At this point, I'd have someone apply constant light pressure against the compression-stroke (with s.plug fully tightened), while I listen-closely for air-leakage at the intake of the carb, and also again at the end of the exhaust as well, (in a very quit location of course).
Cuz such air-seepage ought not be detectable from either valve-port during the actual air-compression (during the compression-stroke), or else you then know that the related valve & seat are leaking.
If the compression-leakage test passes-over too quickly while you're reasonably sure that you heard no noticeable air-seepage (from either valve-port), then the p.rings are the next suspect.


Hopeful-Cheers,
-Bob