Commando decompressor

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concours said:
"Some electric ignitions do not fire on the first trigger -"

Please explain.

WHICH ignitions?
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Not sure but you hear it here a lot. The one that comes to mind is Pazon but I don't use them so I can't say for sure. I only use/sell/recommend Tri-Spark.
 
robs ss said:
There is one potential downside.
The rocker cover studs were never designed for loading like that.
...another place to helicoil the head!
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Actually, there's another and much scarier downside. The lever holds the valve open by the top collar (I'm fairly sure). Pushing down on the top collar can free the retainers. I'm sure it only pushes down a little, but if used wrong it could be a problem. Engines are not supposed to be started with the decompressor on, it's there to get just past compression and then supposed to be closed before kicking.
 
Mart UK said:
I could kick start an Enfield 500 I used to have. I've not yet managed to kick my 850 mk3 into life. Hot or cold, it's incredibly resistant to spinning. The kick-start will happily hold my weight! May be technique, but I've tried everything that I've read on the forum. Not sure how a decompressor would help.
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Looking at the photo on your icon the kick lever needs to be rotated back a notch or two. If the kick start paul in gauges at or just above the 9:00 o'clock position it will be much easier to kick. Maybe all that's needed.
 
I have moved it anticlockwise a little since that photo. Thanks for the 9 o'clock test, I'll check that out. It may need some more.
 
marshg246 said:
Actually, there's another and much scarier downside. The lever holds the valve open by the top collar (I'm fairly sure). Pushing down on the top collar can free the retainers. I'm sure it only pushes down a little, but if used wrong it could be a problem. Engines are not supposed to be started with the decompressor on, it's there to get just past compression and then supposed to be closed before kicking.
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I don't doubt that but on my 441 Victor just barely cracking the compression release while kicking it made it MUCH easier to start when you got it just right and had no ill effects so far as I could tell. FWIW the valve cover had 9 studs securing it so no problem there...
 
bluto said:
I don't doubt that but on my 441 Victor just barely cracking the compression release while kicking it made it MUCH easier to start when you got it just right and had no ill effects so far as I could tell. FWIW the valve cover had 9 studs securing it so no problem there...
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The weakness with the Victor valve lifter was the short length of the bush in the rocker box this made it very prone to wear
Especially if for example used as an engine cut out
 
marshg246 said:
Actually, there's another and much scarier downside. The lever holds the valve open by the top collar (I'm fairly sure). Pushing down on the top collar can free the retainers. I'm sure it only pushes down a little, but if used wrong it could be a problem. Engines are not supposed to be started with the decompressor on, it's there to get just past compression and then supposed to be closed before kicking.
Click to expand...
My little GN400 is kick started with the exhaust valve slightly open at the start of the kick.

Commando decompressor
 
slimslowslider said:
My little GN400 is kick started with the exhaust valve slightly open at the start of the kick.

Commando decompressor
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I have similar on my KLF300, for pull starts you operate the decompression lever, on pulling the start cord you get to go past one TDC with no compression but then the lever shuts and so for the next TDC you have full compression but the crank is now up to speed and the inertia takes it over TDC.
 
Just got a (former) derelict Suzuki DR 650 out of my garage. Learned about built-in decompressors in the process of bringing it back to life. Most big singles have a similar device, which alters cam timing enough at low (starting) engine speeds with a bobweight on a spring and a flattened pin that rotates to the round part when the bobweight flies out. Suzuki's initial design was cable-operated, replaced by a solenoid-operated device. In the late '90's, they devised the automatic decompressor, which is what they use to this day. A Norton twin with super-high compression could surely use such a device and for those considering an e-start conversion, one might be a path to keep kicking it for a while
 
Try kickstarting a Harley Ironhead Sportster. Two long-stroke 500cc singles with 9.5 to 1 compression joined at the hip, and not a decompressor in sight. After than, Nortons seem like nothing.
 
In my experience decompressors are really only useful for speeding up the time it takes to get "just" past TDC - biggest run-up possible.
Not much use on a 360 twin when the next compression is close.
Forget it and just kick the thing!
 
FWIW-Briggs and Stratton has decompressors on their pull start lawn mower engines.
 
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