Kicking through without a compression release puts a big strain on the kick start components. be prepared to replace these regularly especially the kickstart quadrant (15-4121), kickstart ratchet (66-3079) and pinion (66-3080).

email (option): cas.vanderwoude@gmail.com

Yes, and not to mention the strain on the fragile gearbox endcover. I try to spare these as much as possible.

Cheers, Michiel

email (option): m.wijbenga@hotmail.com

I am listening to all of your inputs, much appreciated I can assure you!

Ian, Cas and Michiel are absolutely right. The valve lifter reduces strain on the valve train when starting. It's not just about being a hairy-arsed biker who can kick anything over.

Anyone who intends to use a WD motorcycle for the purposes for which it was intended should watch the 'Army Motorcycling' films and understand how a valve lifter can be utilised in assisting the negotiation of a difficult, slippery downward slope.

We are privileged to own something which, in its day was almost more all-terrain capable than any other vehicle available. Any modern-day owner who wishes not to avail himself of that potential is of course free to do so...but for me at least, sharing the experience of those who rode them for real more than seventy-five years ago is part of what it's about.

That said, any hint of 'bobbing' and wrapped exhaust pipes is enough to make me reach for the Boys Rifle so perhaps I'm not typical.

A handly device, but not vital.

You can easily bump start a Manx/CCM/etc. on 12:1, at walking pace - with the throttle closed.
Open the throttle too much, too soon and they stop dead!

Reason - closed throttle = limited air in cylinder, hence limited compression.

Racing yesterday - lots of dope burning CCM's (250-580) - not a decompressor among them - close throttle, get it over compression then swing, opening throttle very gradually as you do so.
Snap throttle open as soon as kicking - instant dead stop!

Thats why we spend so much time getting the low speed jetting right!

Watch someone swinging at a high comp 750 triumph twin - they ALWAYS (inknowingly ?) open the throttle as they do it - watched same thing yesterday.
I had no problem kicking it over and eventually starting said bike in my trainers .....?

Would i fit a decompressor - yes, if there was provision and it required no effort.
Must get round to fitting one to the '32 norton - yes i can stand all day on the kick-start, but it would be much easier with a decompressor, for when i get it wrong.

For:
Easier starting ritual
Easier to check tappets and timing
Reduces strain on gearbox components
Reduces wear and tear on ageing knee joints
Helps in clearing a flooded cylinder
Easy way to stop engine safely


Against:
You will have to fit it and adjust it…once!
A good excuse for not losing weight

Fit it and if you don't like it take it off again.

Add to "against": I don't have one for this bike and it would cost me my right arm IF I could find all the parts to reconstruct one - which I can't.

PS: They are not conflicting views. Ian references a 720 with a 7:1 compression. I was referring to a standard M20, 500 with 4:1 compression. The total pressure on the piston crown in Ian's bike is probably more than twice that of a standard M20, and that's the pressure you need to overcome when kicking.

As for the 750 Triumph, it's not comparable. I presume you're referring to the 3-cylinder, which means that you're only kicking through one 250cc cylinder at a time. It does not compare to Ian's 720cc single-cylinder.

email (option): jonny.rudge@verizon.net

Personally I think life is easier with the valve lifter rather than without for all the reasons listed in the various posts and I would always fit one myself even to a standard engine...

As always there are plenty of conflicting views and I suppose each individual has to consider them and make what he thinks is the right choice...Ian

email (option): ian@wright52.plus.com

Woah, seems I started something of a debate here.
Some comments from me:

- My sole reason for not mounting a compression release is that I don't have one. Not having endless resources I try and save money where possible.

- Was thinking for instance of my garage buddys Yamma SR 500 that has a compression release that is to no use what so ever, the bike is easy to kick. So I thought perhaps I didn't need one on the M21 either. Some good points here as to why I do.

- If going without the compression release I would have constructed something else for stopping the bike, like a button for shorting out the spark for instance. Stalling it by putting it in gear and releasing the clutch just feels wrong. Did that for a short period of time on my Vespa (Purple 1966 180 Super Sport) and I felt like a blithering idiot every time. Made sure to fix the kill switch as soon as I could!

- The 750cc Triumph is a twin. Originally, if such a thing can be said about a motor that was assembled from various parts, it was a 650cc, meaning that the cases once had such cylinders fitted to them. It now has a big bore 750cc kit. But like I said its not an original bike. Parts from all over. Runs sweet and strikingly strong though with its modern designs such as OHVs and all.

- I do not in any way have any intention to pass myself off as being a tough guy who can kick any big bike. If anything I am a cheap little fella who will not spend money unless it is called for.

Thanks for all your input! Much appreciated.

On the other hand, click it into second gear, roll backwards until at the good side of TDC, back to neutral and give her a kick.

email (option): cas.vanderwoude@gmail.com

I ran a B31 for years without a decomp but I would recommend putting one on. It isnt kicking it over that is the issue which is definitely easier with decomp but it is killing the engine in emergencies. There is the risk of fire especially with no air cleaner, broken clutch cable which has happened to me several times in busy traffic and stuck throttle either because of carby issue or kinked cable for whatever reason. Im sure there are other reasons that I cant think of at the moment. You dont want to be reaching down for the spark plug lead to kill it especially in wet conditions.

It seems the list of reasons for fitting a valve lifter is a lot longer than the list for not fitting one....

Not having one has to be a compelling argument for the latter though... ..Ian

email (option): ian@wright52.plus.com

Think that about sums it Ian

Careful, there are more than 10,000 volts in there. If you don't set it up right and do the kill procedure right each time, you're liable to get zapped. A magneto ignition is not the same as a regular coil ignition. In the latter the kill switch shorts the low-voltage primary circuit, not the high-tension spark wire. Also, if your switch and wiring are not right the spark may jump the switch contacts or the wiring when operating, instead of the spark-plug gap. This would be bad enough if it jumps all the time (engine doesn't start) but what often happens is that the shorting out of the switch or the switch wire happens intermittently, usually at high revs. If you don't keep this potential problem in mind it will drive you crazy to find out why your engine is coughing.

Obviously, I see no shame in stalling out a 70-year old engine, having done it hundreds of times myself. BTW, no one will notice.

email (option): jonny.rudge@verizon.net

BTH racing mag's have a machined alloy points cover with a carbon brush in the center that runs on the points (low voltage)- you fit a wire from this via a stop switch to earth.

I have seen a similar system for the Lucas face-cam mag. with the brush bearing on the center mounting screw - i think it worked?

It works on my 'non racing' BTH fitted to the TRW... ..

Also fitted to early Lucas K2F mags as used on the A10 etc....

Do these earth the high tension side though?....Ian

email (option): ian@wright52.plus.com

A while back I had for the first time assembled the magneto (new bearings, brushes, points and so on) and mounted a piece of ignition wire to it. I was sort of pondering what would be a good way to connect it to a drilling machine or something to make it spin and find out if it worked. As I was thinking and looking around me I was sort of absent mindedly slowly turning the magneto by hand and ZAPPP! Not the first time I've been zapped by electricity I can tell you, but the first time I tested a lucas magneto on my left hand fingers.

Having just done this work I of course know that it works differently than a coil ignition. Have not yet figured out how to make a kill switch but something along the lines described above was what I had in mind.

Not a question of shame, it just feels a bit unsofisticated.

Thought i'd seen a similar arrangement on other machines.

I don't think they earth the high tension side, as a standard ignition cut-off (better still a jet-ski one) works without any arc'ing to earth.

Mind you even the 'low' tension side can show ~300v when running ....

We only fit them because we have to - for any machine racing, most of the time they are not actually connected as they cause so much trouble.

You got any links to where I can obtain one of these? (still thinking of building my own though)

/s

They were never fitted to magdynamo mags as used on the M20...Ian

email (option): ian@wright52.plus.com

Was more thinking more along the lines of the ones for jet-skis that was mentioned. All this is just me letting my thoughts wonder of really... best option appears no doubt to be fitting the compression release. If I can obtain one at a reasonable prize that is.