Possible to replace gaskets without removing engine?

[nathancitox]

Have you swapped the push rods. Have you re adjusted the tappets. That exhaust tappet looks like it is adjusted up very high compared to the inlet tappet. You must adjust the tappets. Turn the engine over until both valves are shut, check the tappet adjustment. If you have not done this, maybe you swapped the push rods, Now the exhaust is too tight and the inlet too loose.

I haven't swapped the push rods, I labeled them so I won't swap them.

I've re adjusted both tappets, but the exhaust rocker is higher than the inlet rocker (both valves closed). Could this be a worn out rocker? rocker axle? As I'm looking in the manual, it's not possible to adjust the rockers, only the tappets. I think the problem was that it had fitted a slightly thicker gasket, and upon replacement for a correct one, now it's not possible to adjust it. I've also noticed some bending on the exhaust push rod.

Checking the manuals looks like I need a press for removing the rockers? I would like to check for wear.

Thanks again

[REW]

If your bike was running fine before you changed the gasket then the problem is something you have done since. Was the engine at top dead centre on the firing stroke (both valves shut) when you adjusted the push rods?

[nathancitox]

If your bike was running fine before you changed the gasket then the problem is something you have done since. Was the engine at top dead centre on the firing stroke (both valves shut) when you adjusted the push rods?

Yes, it was at TDC , when I've adjusted it, valves closed.

I do remember that the last time I've adjusted them, the exhaust rocker was too loose, so I adjusted it, but I started to hear a sound like "loosen little piece of metal" from time to time.

So maybe the tapet broke a piece of the rocker box and that's why the push rod is bended.

I rode 100km with the motorcycle like this.

Tomorrow I'll take a better look at it.

Thanks



Enviado desde mi iPhone utilizando Tapatalk

[clive]

looks to me like you may have a problem with a missing valve cap. The earlier valves were shorter and had a hard endcap fitted. The later valves were longer and the end of the valve stem was hardened. Either can be fitted to your bike but if the earlier valves are used you must use the end cap.
I would suggest what has happened is that your exhaust valve is the earlier type and has been fitted with no end cap. As there is no hardened seat the pushrod would have needed regular adjustment. At some point this adjustment, set at TDC when the rocker arm is down has resulted in the arm hitting the top of the rockerbox at full lift. This would bend the pushrod.

DSC00510comp.jpg

So I suggest you check the lengths of the inlet and exhaust valve, they would normally be the same. If the inlet is longer it is probably a later valve and does not need the endcap, if the exhaust is shorter it is probably the earlier type and needs the endcap or replacement with the later type.

[nathancitox]

Hi Clive,
As you said the problem was a missing valve cap.
When replacing the rocker box I must have hit it and it fell.
I found it inside the cylinder head.
I was able to straighten up the bended push rod.
Machine is working fine again with the correct carb!

Thanks



Enviado desde mi iPhone utilizando Tapatalk

[Rob Harknett]

Sorted. There had to be a reason why that Exhaust tappet was adjusted up so high.

[bjork]

Sorted. There had to be a reason why that Exhaust tappet was adjusted up so high.

Quite right, we also found another reason for it recently. The rocker shaft was twisted! I guess a gorilla had fitted the rocker arm sometime in the past and overtightened the nut. The splined part was no longer straight and the effect was the same as on this bike, one arm at a different angle. all fixed now with new parts from the club spares scheme. That G3 is now chugging happily round the Cambridgeshire fens.

[Trefor]

I use 36ftlbs for the head bolts on my G80s- as recommended in the 'Motor Cycling' Maintenance Series covering the Matchless 1939-1955 published 1955. Seems to work fine.

[clive]

Hi Clive,
As you said the problem was a missing valve cap......
Machine is working fine again with the correct carb

Great, enjoy the ride.

[56G80S]

There's a lot of threads about tightening head bolts, do a search and see.

I used to wind up as tight as that and had the pillars in the head deform and crack as a result, so after expensive repair now using largest thickest washers I can slot in under the bolt heads.

My personal belief is it's less about being super tight than getting all the bolts at the same tighness and that involves cleaning threads, making sure the bolts don't bottom out, annealing gasket properly and using expert touch/feel or (if like you me you are too heavy handed) a torque wrench.

Johnny B