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strange cutting out incident

Posted: Wed May 29, 2019 10:30 pm
by admin
KH500
Been on the road around 4 years but I doubt I have done much over a thousand miles since ..

Going down the dual carriageway at a strady 60/65mph. Oil pressure around 30 psi. Done about 20 miles like this
Suddenly slows and then cuts out - in with the clutch and coasted to a halt.
Hard to tell if it just cut out though ... I had the clutch in pretty fast ..

Engine free and readily restarts and then does another 30 trouble free miles.
Could have been a siezure but could also be electrical ?

Anything to check easily ?
(and yes, as per the previous post - the timing cover seal had failed and there was oil everywhere .. )

Re: strange cutting out incident

Posted: Wed May 29, 2019 10:36 pm
by Bob.Murphy
Air vent in the petrol filler cap ??

Next time ( :roll: ) check for a spark as soon as it stops.

Bob.

Re: strange cutting out incident

Posted: Wed May 29, 2019 11:42 pm
by Simon.Gardiner
If it's seized and you drop the sump plate you'll find some ally particles??

SG

Re: strange cutting out incident

Posted: Thu May 30, 2019 2:18 am
by nevhunter
Don't count on it. I had a full throttle seizure at over 80 mph on the VCH once and it had a seizure mark on the piston skirt but no ally on the bore or anywhere else. THAT piston is still in the bike but they sometimes collapse a bit when they are trapped in the bore like that. Consequently it now has a minor rattle until it warms up.
There could be a low fuel flow rate John, restriction in the tap/ fuel line/ filter/ cap vent Some of the Caps don't have the hole drilled in the knurled bolt in the centre. Nev

Re: strange cutting out incident

Posted: Thu May 30, 2019 3:05 pm
by admin
It didn't feel like a fuel starvation thing .. I've been a victim of the blocked fuel cap vent (on this bike actually), fuel tap vibrating closed etc and they feel more gradual.

hey ho .. I'll change the oil and look in the sump plate (it has an oil filter as well) and also check the mag cut out ...

It ran fine afterwards ...

Re: strange cutting out incident

Posted: Fri May 31, 2019 2:45 am
by john.whiting
if the engine turns over straight away ,i cant see a piston seizure.....usually thats a 10 minute wait for the bits to cool before its free enough to kick over........but a tight piston can cause a lot of drag without actually seizing....another thing to look at is valve clearance disappearing,and exhaust valves held open,possibly by rapid seat wear

Re: strange cutting out incident

Posted: Fri May 31, 2019 2:49 am
by nevhunter
IF the motor is tending to nip up, at the first sign of a slight slowing, pull in the clutch with the throttle at idle. It will stop instantly if it's nipping and also be ready to start by the time you pull up as it will have cooled just enough to do that. IF you are really cracking along the rings may get trapped in the grooves and not contact the bore well and your compression will be BAD.
On the electricals, If the maggy is a bit old it will often get a weak spark after an hour or so when the armature gets hot and cut out when idling and won't want to restart for a while. Might also shed "shellac" from the winding and jamb it when it cools. Have you had that yet? Nev

Re: strange cutting out incident

Posted: Fri May 31, 2019 9:32 am
by admin
nevhunter wrote:IF the motor is tending to nip up, at the first sign of a slight slowing, pull in the clutch with the throttle at idle. It will stop instantly if it's nipping and also be ready to start by the time you pull up as it will have cooled just enough to do that. IF you are really cracking along the rings may get trapped in the grooves and not contact the bore well and your compression will be BAD.
On the electricals, If the maggy is a bit old it will often get a weak spark after an hour or so when the armature gets hot and cut out when idling and won't want to restart for a while. Might also shed "shellac" from the winding and jamb it when it cools. Have you had that yet? Nev


It's the first time Nev, after several hundred miles. Hence my feeling it perhaps wasn't a seizure.
The mag on this bike was redone when it went back on the road.

I changed the oil and it looked ok. The breather is also fine.
My money is now on electrical or fuel, and I looked at the obvious stuff there and all good. I guess I wait for it to happen again (if it ever does ..)

I have had the shellac melting thing.
The bike was hard to start but got me home - the next morning the armature was jammed solid to the extent that the mag sprocket came off the taper after repeated kickstarts !!

Re: strange cutting out incident

Posted: Fri May 31, 2019 10:02 am
by nevhunter
OK Remove your points assembly from the maggy and carefully inspect it and put some test power through it There can sometimes be an unwanted intermittent earth. Is the kill button on the end of the maggy? check it's action Check the flat spring for right shape (tension) and the backing spring correct way up. Check end float and points gap. sometimes it disappears on a rebuilt maggy Nev