Compression Release Valve?

[Philly Eddie]

Guys and Gals: I have a spring head 450 which, of course, is a bear to kick (I am74). The valve lifting compression release is not getting me there. So, I am toying with the idea of installing a pop-up compression release valve in the cylinder head where the AHRMA guys install a second spark plug. Is this feasible? Thanks for any advice. Eddie

[graeme]

Hello Eddie,
Perhaps there is something wrong with the set up of your decompression device ?
I have the same on a 450 scrambler, works very well, no compression at all.
All it does is push the exhaust valve off the valve seat.
Letting the compression leak out the exhaust.
I also have an RT desmo that has a compression release in the head which just opens the head to atmosphere through a small hole.
The Scrambler type is easier than the RT type. (neither are hard to get the piston just top dead centre for kicking)

Graeme

[blethermaskite]

I have just refitted the decompressor to my 350mk3 ( after being remove by me about 40 years ago!) due to my aging hip causing starting difficulties, starting is now quite easy ........so unsure of why this isn't working for you, check yours is actually pushing the exhaust valve of its seat to waste the compression.
Cheers,
George

[themoudie]

Aye Philly,

I have a '74 450 MKIII, with the decompressor pin acting on the exhaust valve and have no resistance from compression whatsoever when in use. Like Graeme and George, I suspect that something is amiss with your de-compressor or the cable.

Has the your cable become slack where it is held in the cylinder head, or has your cable outer become shorter for some reason? It is the length of the cable outer that determines the effectiveness of the decompressor on my set up. If it is too short then the decompressor pin will not be depressed sufficientll to hold the exhaust valve off its seat.

I can post images if required.

Good health, Bill

[Ventodue]

Same story here, Eddie ...

Craig 450 SCR

[LaceyDucati]

There are two different pin lengths, I think to take account of screw adjuster and solid rocker variations. If someone has mixed and matched parts, it may be you have the shorter pin and it is not long enough to reach the rocker. Worth checking and it should be obvious.

Regards Nigel

[frankfast]

Have a question regarding the use of the compression release. Do you guys depress the compression release valve as you start kicking or do you release just after top dead center and then start kicking?

[Wolf]

Frank,

the latter one: find the TDC, pull the decompression lever, turn the crankshaft a tiny bit with the kickstarter and then kick it with force.
I've just replaced the old decompression cable with a new on and I've observed as well as above mentioned that the right length of the cable is critical for the operation of the decompression device.

Kind regards

Wolf

[frankfast]

Have a question since Nigel mentioned the use of two different length pins on the compression release. Were there any Ducati models that used both screw type adjustable rocker arms and a compression release and what was the reason for two different length pins - rocker arms or valve covers?

[themoudie]

Aye Frank,

I have a 1975 350MKIII widecase that was fitted with adjustable tappets rather than shims and had a valve lifter fitted that appears to be the same as that on my 1974 450 MKIII. I have not measured the pin lengths that bear on the rocker arm. Nor do I know the reason for a difference in pin length, but suspect that there maybe a difference in the profile of the rocker arm rather than in the rocker cover casting.

At present I am working on an SRX600, so would be a wee while before I can measure or compare things.

Good health, Bill