Hitchcocks Forum

All, I just completed a full top-end rebuild (with cylinder and valve head assemblies from Hitchcock’s making it much more straight forward) and took the bike around the block a few times.
The decompression release is ‘not working’. In quotes because:
Down at the cam/push-rod access area you *can* decompress using the exhaust rod’s inverted top hat.
It takes tremendous pressure. However, regardless of cable adjustment or position of cable fitting (4 o’clock, 6 o’clock, etc.) there is too much tension on the thumb lever on the handlebar. Not only will it snap (btdt) but it just doesn’t turn the cam enough.
It’s a relatively new cable assembly (and expensive too) but the cable might need to be replaced.
Ideas?
Tia, Matt

Sounds like an Electra-X/AVL set-up. Best thing to do is bin the valve lifter and machine the cylinder head to take a proper decompressor valve off the classic Bullet. I did this a few years ago and it works a treat, I know of two more that have been done since, both owners very happy with the modification. Pictures on request.



A.

Can you lift it by moving the bottom the torque-arm on the tappet cover manually? If it's very stiff here too, then it's not the cable.



Trying to understand what might have changed since before the rebuild (when it was presumably working). Have you fited stronger valve springs? Is the decompressor cam the right way round?



For what it's worth, there's one sat in my box of junk that came fitted to a classic engine 500 bullet I bought (it had been twin-plugged). I couldn't get it to work worth a damn either, first snapped a metal decompressor lever, then snapped the cable so I shitcanned it in favour of a conventional decompressor valve



If it's never worked for you, perhaps a bit of technique too? I found I could only get that one to work if I pre-loaded the lever as I turned the engine over. The opening of the valve by the exhaust cam asisted the decompressor to then hold the valve open even though it wasn't man enough to initiate the opening itself. This was unhelpful if you were stopped on a compression stroke though.

Adrian, thanks but if I cannot implement the fix myself then it will remain ‘unfixed’.
.
Stinkwheel, thanks. All installed/reassembled correctly and yes, it worked before the rebuild. It’s quite possible that the new valve springs are that much stiffer. “I shitcanned it in favour of a conventional decompressor valve”

I agree with previous comments. On my Electra X I kick it slowly with the ignition off until the valve lifter can be operated. (It makes it a lot easier to free the clutch off.) I also stop the engine using the valve lifter. (Relates to starter sprag problems.)

Matt,



are you the same Matt who contributed the Electra-X Mk1 Concentric carburettor fitting notes to our hosts' technical section?



OK, try a decent lever on the cable FIRST as per the suggestions above, and if it works, ignore the rest of this!



If not and you want to give the decompressor valve a try, I managed it with fairly primitive tools, not as neatly as I would have liked, but it works. Here's what you end up with, unless you have a milling machine or know someone who has, and it comes out nicely machined. You have to lose a bit of finning on top of the head, but it's a huge chunk of alumin(i)um, second only to the Big Head, and will still run fine. You have to drill a 1/2" or 12.5mm hole throught the top of the combustion chamber, this is the tapping size for the 14mm x 1.25mm spark plug thread used by the decomp valve, tap the thread (taps on ebay and elsewhere), and counter-bore the top of the hole deep enough for the end of valve to sit level with the top of the combustion chamber.















A.

The one I had was fitted to a 500 bullet where they'd fitted an extra sparkplug where the normal deconpressor valve goes so mine was a simple matter of just refitting the decompressor in place of the second plug.



Just thought it's nice to have reassurance it's not just you.

Adrian, RE: “are you the same Matt who contributed the Electra-X Mk1 Concentric carburettor fitting notes to our hosts' technical section? ”
Yes, a lifetime ago it seems.
Papasmurf: I’ll try your technique. Thought I knew them all but...
....All: thanks for the help and ideas.