Hitchcocks Forum

Hi. 1945 WD/CO (same engine as a Model G) and the decompressor doesn't work. Opening up the tappet case shows that the exhaust pushrod is almost at it's fullest extension (tappet adjuster would right out) and the decompressor arms are not contacting the exhaust pushrod collar, ie not being able to push up pushrod/valve to decompress..
The pushrod is clearly correct and unworn, the valves appear to be un-modified (ie not shortened) which leaves the exhaust cam being worn, but the valve lift appears effective and correct. Before I have to start throwing money at replacement parts, has anyone experienced this before? Thanks!

The decompressor arm seems to be a weak component on these models and there have been several posters here in the past who had broken ones. I wonder if yours is bending prior to breaking or otherwise distorted? Our Hosts had new ones made recently so at least you can get them! I suggest you phone them and get them to send you a picture of a new one to compare? H's are very helpful like this.

REgards, Mark

Tman,

Firstly I have zero experience with these motors so apologies if I'm making a fundamental mistake, however. Since the tappets are set whilst at the base circle cam wear will have no effect on tappet adjustment. Therefore if the tappet adjustment is at it's fullest extent it would appear that the fault is not with the cam but between tappet, pushrod and valve stem ie something's too short and tappet adjustment is being used to compensate. Good look.

Hi Paul and Mark, the tappet arms are OK (not worn, bent or otherwise distorted), but there's a 4mm gap between them and the collar they push on. I discounted the cam etc (as said) as the valve was still opening correctly. As I've just cleaned inspected and reground the valves (the engine came semi-dismantled) I'm loathe to strip out the valves again to buy and fit new hoping that that's where the problem lies, especially as the top end is now all together. I'll have to find out an accurate measurement of a new valve length to compare. Thanks.

Hi Tman, There can be 2 possibilities :
1) Or the valve lifter cable is't properly fitted on the valve lifter arm (and that can be akward to fit, there isn't a lot of place, there is the inner spring that doesn't help either, and you don't see anything). In that case, check carefully that everything is in the place it has to be.
2) Assuming that everything s settled as it should be, just cut a part of the cable (at the decompressor end), and fit a new end stop. It oftenly happens because the decompressor lever isn't original, the valve lifter arm is a bit bent, and the cable has extended a bit (it's routing is too a bit akward).
I have made a modification on my WDCO to have more gap settling, if you are interested, I can send you some photos.
Hope it will help you
Claude

Hi. Again, the cable is properly fitted, and the decomp arm moves through it's working arc correctly, but at it's uppermost position it doesn't contact the pushrod collar. I have turned up a 4mm collar and press-fitted it onto the pushrod, and it works fine now, and will do until when/if I need to buy new valves and at that point I can revert to standard. Sometimes it's just easier to treat the symptoms rather than the cause, especially if the cause hasn't been ascertained! Thanks to all.