Ajs 16m

[got2BaSBT]

Afternoon All,
Just wanted to run this by you. On a ride today 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. After checking over everything briefly I tried kicking it over again and compression had come back? I was half way up a hill so bump started it and rode it 3 miles home. When I got home I pulled the valve lifter to switch it off and nothing happened.Any ideas folks before I start pulling timing covers off?

[Mick D]

Hi

Now things have cooled down:

Do you have compression?
Does the valve lifter work correctly?

I'd check:

The free play on the valve lifter is good.
Valve clearances.
Position of the inlet valve oil screw is good.

What maintenance has been carried out on the engine recently?

Regards Mick

[ajscomboman]

Spitting back through the carb and a loss of compression indicates that the inlet valve could have got stuck. As Mick has stated it's worth looking at the oil regulator screw setting for the inlet valve and also the decomp cable.

[got2BaSBT]

I wondered if the inlet valve had momentarily seized too. Things is though it must have freed itself after a minute because I rode it home.
Now its cool it's got the same compression as normal but although the valve lifter can be seen to move externally, it doesn't do anything now?
Maintenance wise I've recently purchased it from a member of my family. The oils are all clean and the levels are all topped up. The oil is returning well into the oil tank and it's been well looked after.

[Mick D]

Hi

From what you report I'd first go to the valve lifter. You can remove it quite easily - disconnect the cable and undo the screw that retains the spring to the rocker box, you can then withdraw it from the rocker box and examine it. Is the arm still firmly attached to the spindle? does the spindle show any abnormal marks? (it should just be a cylindrical shaft with a flat on the end.

Hopefully you'll see something untoward, if not check the valve clearances - I hope you don't have an exhaust valve seat which has moved.

Regards Mick

[ajscomboman]

Hi

From what you report I'd first go to the valve lifter. You can remove it quite easily - disconnect the cable and undo the screw that retains the spring to the rocker box, you can then withdraw it from the rocker box and examine it. Is the arm still firmly attached to the spindle? does the spindle show any abnormal marks? (it should just be a cylindrical shaft with a flat on the end.

Hopefully you'll see something untoward, if not check the valve clearances - I hope you don't have an exhaust valve seat which has moved.

Regards Mick

You don't have to remove the spring from the rocker box to remove the lifter, once the cable is free you can slip it out with the spring in situ, same goes with replacing it.

[56G80S]

It may be possible, although difficult, to do this without removing the tank.

I bent an appropriate size spanner for the adjuster and locknut to a bit over 45 degrees and with patience was able to fit a new cable.

Johnny B

[got2BaSBT]

Thanks for the replies chaps. It's not looking good, I went straight in for the kill and took the tappet cover off...The exhaust valve has suddenly developed a clearance of about 5 mm!
So what would you recommend now...have a new seat put in or new head time?
Is this common on these old brit bikes, I've had all sorts of vehicles and engines but never experienced this

[SPRIDDLER]

The exhaust valve has suddenly developed a clearance of about 5 mm!

What clearance is that? Is it between the top of the p/rod and the rocker arm (which should be 'nil' when engine is just warm)?
If so, and you have good compression, it may just be that the adjuster at the top of the p/rod has come loose (the pushrods rotate when the engine runs) but that wouldn't account for the lifter not working. A stuck open zorst valve would, but you have compression......

(Edited twice as I cocked up my first edit )

[ajscomboman]

If the lifter is no longer working and the valve clearance has suddenly increased you really need to look at that first as if it's holding the valve slightly then the clearance will be more. Are you sure compression is right back up? If it is, then that'd indicate that the seat hasn't moved but equally so that the valve lifter isn't holding the valve. I'd reset the adjuster and see. Always go for simple first then if nothing is obvious go in for the kill.