350/450 exhaust valve compression release

[themoudie]

Aye David,

3 images of the de-compressor set up on my 1974 450 MKIII. I am the 2nd owner from new, having owned the machine since 1976 and at the cylinder head nothing has been modified. The operating cable is home made. Whilst the lever on the clip-on is a modern motoX decompression pattern lever. Beware! Many of the 'Classic', ball end pattern levers do not have a sufficient throw to enable the de-compressor to be fully activated! And they are more expensive!

Hope this helps with your rebuild, Bill

[graeme]

Hello David
My 450 Scrambler has a hole drilled in the exhaust rocker cover same as Bills to capture the cable end.
I’ve never seen the bracket you have on the head bolt before
If you don’t have the handle bar lever you could look for a bmx brake lever
Cheaper than motorcycle items.

Bill, in your 3rd picture, what is the spring for?

Graeme

[Jordan]

I put a non-Desmo head back on my single, with a valve lifter.
The handlebar lever I use is a standard Ducati choke type, on the left side. It looks neat and works fine.

[themoudie]

Aye Graeme,

The spring has a swivel hook at either end and is hooked into one of the holes on the front down tube bracing plate, whilst the other end hooks through a stainless steel locking wire loop that goes through one of the four drillings through the threaded exhaust ring. This keeps the ring in place, yet enables easy dismantling if required, without having to remake the lock wire loop if it was directly wired to the bracing plate.

Aye Jordan,

Having written off the original clip-ons in 1978 after low siding on a roundabout, with diesel trailed around it and at the time being a penniless student, with no other means of transport, cheap fixes and a loss of originality were a way of life. However, I like the idea of using a rotating choke lever, rather than a straight lever. I'll need to have a rumage!

My regards, Bill

[dlearl476]

I don't have a spare lever, but do you need the ferrule we talked about?

No, I went through my boxes Friday and found 4-5.

Thanks, though.

[dlearl476]

Hello David
My 450 Scrambler has a hole drilled in the exhaust rocker cover same as Bills to capture the cable end.
I’ve never seen the bracket you have on the head bolt before
If you don’t have the handle bar lever you could look for a bmx brake lever
Cheaper than motorcycle items.

Bill, in your 3rd picture, what is the spring for?

Graeme

Per the parts list, that bracket is OEM for the compression release. (#840) It's in Snakeoil's pic in the OP, and it's on mine.

I bought my Scrambler as part of a "lot" but, other than sitting in the sun and heat of the Nevada desert for 25 years, it was original and unmolested. The rest of the stuff, not so much. When I started the project back in 2006, I was pretty methodical about bagging and labeling the bits, as it was my first "restoration." When I had to put everything in storage in 2010, I separated out what I thought I needed to complete the Scrambler, and the bits to build the 250 Monza, and as I had the Barnett cable which I thought was correct, the original comp release cable went in the Monza boxes.

I have the original perches, throttle/brake/choke on the right hand, clutch/comp release on the left. What I was missing was the stepped end that fit in the actual compression release lever on the head, which I noticed when I got a good look at an actual Ducati cable. And then I found mine which is in pretty good shape.

image.jpeg

PS: Thanks for the insight, Bill. Maybe by ‘74 the pencil pushers realized they could save 3¢ per bike by eliminating the compression release bracket and drilling a hole in the valve cover instead.

[themoudie]

Aye David, no problem, pleased to help.

Bill

[dlearl476]

The critical bit is in this pic, second from the top on the right. It's a stepped bit that fits in the 4mm CR lever in the head and accepts the larger (5-6mm?) cable end.

image.jpeg