AJS & Matchless Owners Club

I do not think you need pull timing covers off yet. Take tappet cover off check tappets, watch push rods are working OK. If all seems OK except the exhaust lifter no longer seems to work. Has the spring broke? Has the lever gone out of position, so not reaching the part that will depress the valve. Perhaps it slipped past the position some how when your bike momentarily stopped. Having now past that point, it no longer seems to work. Test the lever on the engine, if nothing is felt of it touching anything. It may have got out of position, perhaps even broke off inside.

I tried the valve lifter and as you pull the lever I could see it lifting the pushrod at the same point as when it used to stop the engine. The clearance at the tappet is so big that it can't lift the valve now though.
Compression wise it's definately the same as it's always been, with a distinctive resistance on compression.
I take you're point on not jumping in, but with it having compression and even idling fine I can't understand what has suddenly created that excessive clearance.
If it is the seat dropping down and I keep running it I'm bothered it will end up hitting the piston.....I'm thinking maybe take the rocker cover off and measure the valve stem protrusion

Hi James, what year is your bike do you have an iron or alloy head?

Hi Duncan, it's a 1948 with cast iron head

If you have the hardened caps on the end of the valve stems, maybe one has dislodged.
Ray.

If it has had lead free inserts fitted in there past these could move otherwise there should be no seats to drop.

Your valve lifter should be on the engine case I think some of the above advice has been for later alloy heads.

Duncan wrote:Your valve lifter should be on the engine case I think some of the above advice has been for later alloy heads.

Ah, a '48 so guilty as charged mustn't assume, but not helped by no year details given or shown in the Profile.
It's obvious but have you checked whether the pushrod adjuster/locknut is loose allowing the p/rod top fitting to wind itself back into the pushrod?
Is everything in order in the rocker box?
As Yak mentioned, the hardened valve stem cap could have become dislodged.

got2BaSBT wrote:....all of a sudden the engine conked out with some spitting back through the carb. I kicked it over and found there was no compression.

Sorry to be a right PITA but just to avoid any confusion are you certain it was actually spitting back from the carb or was it misfiring in the exhaust (which would indicate a sticking exhaust valve)?

Hi

When you take the rocker box off have a good look for a broken / dislodged exhaust valve cap - this would explain the increased clearance.

Regards Mick

Duncan wrote:Hi James, what year is your bike do you have an iron or alloy head?

Now that Duncan was a very good point, most just assumed it was alloy as they are quite good at nipping the inlet for no reason then simply don't do it again.

Iron head is a different kettle of fish as unless it's converted with an insert there's bugger all to go wrong except the valve cap if it has one and hasn't been converted using a longer valve. If that's all good on inspection I'd be even more tempted to simply reset the tappet adjuster.