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B44 spring startup, lost compression #733955
05/03/18 3:53 pm
05/03/18 3:53 pm
Joined: Dec 2010
Posts: 251
NYC & Upstate NY
A
AML Offline OP
BritBike Forum member
AML  Offline OP
BritBike Forum member
A
Joined: Dec 2010
Posts: 251
NYC & Upstate NY
This morning I decided to try and start the bike for the first time since October.
I removed the bash plate and then the drain bolt in the sump plate, when I walked back a few minutes later there was about 2+cups in the pan.
Filled the gas tank, ticked the carb and kicked 3 or 4 times. It sputtered on the last kick and seemed about to catch.
I tried to find compression again but it was gone.

At TDC I still have 8 and 10 thou clearances, so presumably it's not a stuck open valve? I slackened the compression release in case that was holding the valve open.
I checked the sump after all this and got about another cup.
I rode the bike into the shed last fall and drained the gas tank and carb bowl and haven't touched the engine, until today.
What am I missing; anything ideas? Head gasket, rings?
Thanks,
Adam

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Re: B44 spring startup, lost compression [Re: AML] #733957
05/03/18 4:05 pm
05/03/18 4:05 pm
Joined: Dec 2004
Posts: 9,430
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,430
Scotland
I had that happen on the way into work on a C15, it just stopped and I found no compression, I kicked it over a few times and it got compression back suddenly and off I went, it must have been a small piece of carbon got stuck on a valve seat and it then got knocked off. Time for a leakdown test to see where the air is going instead of being compressed.

Re: B44 spring startup, lost compression [Re: AML] #733964
05/03/18 5:56 pm
05/03/18 5:56 pm
Joined: Dec 2010
Posts: 251
NYC & Upstate NY
A
AML Offline OP
BritBike Forum member
AML  Offline OP
BritBike Forum member
A
Joined: Dec 2010
Posts: 251
NYC & Upstate NY
Usually, my first thought when something goes wrong is to ask myself if I just did something stupid.
So kommando, thanks for sharing your experience.
I went back to the shed and after about 6 kicks compression started coming back and I had to readjust the compression cable in order to get it over tdc.
Bike started within a a few more kicks and I stopped and started it several times while topping off the oil tank.
Curious, but it seems to have resolved itself.
Thanks again Kommando

Re: B44 spring startup, lost compression [Re: AML] #733970
05/03/18 6:42 pm
05/03/18 6:42 pm
Joined: Sep 2004
Posts: 818
Farnham, Surrey, UK
gunner Offline
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gunner  Offline
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Joined: Sep 2004
Posts: 818
Farnham, Surrey, UK
Have occasionally had the same problem on my B44 but never managed to find out why the compression was lost.

My guess is that one of the valves has become partially stuck open after the bike has been standing for a while either because one of the guides is a bit tight or as Kommando suggests a bit of carbon got stuck on the valve set.

The problem only happens after standing for a few weeks and disappears after a few kicks.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: B44 spring startup, lost compression [Re: AML] #733978
05/03/18 7:39 pm
05/03/18 7:39 pm
Joined: Dec 2004
Posts: 9,430
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,430
Scotland
If you had a twin you would only notice the odd falter, the joy of singles wink

Re: B44 spring startup, lost compression [Re: AML] #734168
05/05/18 4:08 am
05/05/18 4:08 am
Joined: May 2004
Posts: 3,763
Sydney Australia
B
BSA_WM20 Offline
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BSA_WM20  Offline
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Joined: May 2004
Posts: 3,763
Sydney Australia
pour a little oil down the plug hole then kick the engine over a few times to distribute it.
Pop the plug back in and see if it will start.
If it does, go for a short ride then come back and do a compression test.
These singles have a habbit of grabbing a ring when they cool down and rings rusting into the ring grove when not used for a long while.

I have it happen to me on more than one occasion with both the B40 & the B50 although the latter did it a lot more often.
A run down a reasonable hill would usually get it up and running when this happened..

Have also had carbon stuck on the valve seat and to an extent . if you can start it, it will usually just burn off or blow off.

Last edited by BSA_WM20; 05/06/18 1:59 am.

Bike Beesa
Trevor
Re: B44 spring startup, lost compression [Re: AML] #734234
05/05/18 9:10 pm
05/05/18 9:10 pm
Joined: Dec 2010
Posts: 251
NYC & Upstate NY
A
AML Offline OP
BritBike Forum member
AML  Offline OP
BritBike Forum member
A
Joined: Dec 2010
Posts: 251
NYC & Upstate NY
When Kommando suggested a leakdown test, which requires is a tool I do not own, I put a couple of cc's down the plug hole to see if I could tell rings or valves.
I started kicking and compression started coming up slowly, and then was full on.
So I still don't know whether it was a stuck ring or something on the intake valve (when there was no compression there seemed to be more hissing than there normally is, but maybe it's always there but I can't hear it over my huffing while kicking), but I went on a short 17 mile test run and all seems mostly ok.
I have to check timing as there's a stutter pulling away in first at 1/8 throttle; if I back off and open the throttle very slowly it goes away. My first thought was pilot jet (premier Concentric) but the jet is clean and it idles very evenly and starts easily. The timing mark on the rotor doesn't line up with the pointer so I'm questioning my finding tdc with my dial gauge.
Adam

Re: B44 spring startup, lost compression [Re: AML] #734249
05/06/18 1:58 am
05/06/18 1:58 am
Joined: May 2004
Posts: 3,763
Sydney Australia
B
BSA_WM20 Offline
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BSA_WM20  Offline
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B
Joined: May 2004
Posts: 3,763
Sydney Australia
Adam,
It is fairly common for the pointer not to line up with the line on the rotor.
I usually use a piston stop & degree wheel to find TDC and then mark the rotor at TDC which makes future ignition work easier.
A lot of times the TDC mark is way off the raised pad in place of being just near the edge ( line is of course full advance ).


Bike Beesa
Trevor
Re: B44 spring startup, lost compression [Re: AML] #734270
05/06/18 7:16 am
05/06/18 7:16 am
Joined: Dec 2004
Posts: 9,430
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,430
Scotland
The stutter at 1/8th throttle is likely the cutaway on the slide, you can compensate by having a weak or rich pilot setting depending on whether the cutaway is lean or rich.


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