A4 Piston Movement

[bulldogbobby]

Hi all,

Long story but I'm trying to get my A4 100% 'right' before the weather gets better. I'm happy to have a go at most things on bikes but know my limits and a good mechanic mate popped over this afternoon to take the head off as he suspected a bent valve on no. 4 exhaust. The bike looks to have been running rich and the is also a bit of movement between the top of the piston head and the barrel (around 1mm I'd guess ). Maybe a daft question to those in the know but is this to be expected or do the barrels need to come off?

Many thanks in advance!

[gray]

Somebody else will be able to quote you the piston to bore clearance that is normal and acceptable ( which you will feel as a looseness of the piston in the bore) , for a cold engine ( which will tighten up as the engine heats up)
The questions I would ask are - does it smoke? Does it use oil? is it noisy compared to other engines? Did you check compressions with and without oil in the bores?

[zed1015]

Piston/bore clearance is measured at the skirt and the pistons taper towards the top so some rocking fore and aft in the bore is normal when cold.

[bulldogbobby]

Somebody else will be able to quote you the piston to bore clearance that is normal and acceptable ( which you will feel as a looseness of the piston in the bore) , for a cold engine ( which will tighten up as the engine heats up)
The questions I would ask are - does it smoke? Does it use oil? is it noisy compared to other engines? Did you check compressions with and without oil in the bores?

Thanks mate - doesn't smoke or use oil excessively, just poor running. Long story but the W shaped cam tool pinged out when checking valve clearances /shims and pretty sure it's bent the valve. Having a good look at things we can get to while the heads off and just wanted to get some advice on the piston movement - thanks for your help, pretty sure all's good

[bulldogbobby]

Piston/bore clearance is measured at the skirt and the pistons taper towards the top so some rocking fore and aft in the bore is normal when cold.

Thanks mate, that's brilliant - appreciate your help

[gray]

if the valve is bent , you may be able to test it now the head's off. With the park plugs in, Turn the head over, so the combustion chamber is facing up and pour a tablespoonful of something runny ( paraffin or white spirit might do ) into the chamber and see if it runs out. Fill all 4 chambers so you know what the "normal is. if it appears out the inlet or exhaust tract then that valve isn't seating well and the head of the valve may be bent. If that's Ok, then use a valve spring compressor to remove the valve and inspect the shaft of the valve- roll the shaft on a flat piece of glass to see if it seems bent

[Gus]

Long story but the W shaped cam tool pinged out when checking valve clearances /shims and pretty sure it's bent the valve

Cant see that being the problem, it would just be like the valve slamming shut.

No external forces applied apart from the closing force of the spring

Gus I could be wrong ( wife kids Etc. )

[bulldogbobby]

if the valve is bent , you may be able to test it now the head's off. With the park plugs in, Turn the head over, so the combustion chamber is facing up and pour a tablespoonful of something runny ( paraffin or white spirit might do ) into the chamber and see if it runs out. Fill all 4 chambers so you know what the "normal is. if it appears out the inlet or exhaust tract then that valve isn't seating well and the head of the valve may be bent. If that's Ok, then use a valve spring compressor to remove the valve and inspect the shaft of the valve- roll the shaft on a flat piece of glass to see if it seems bent

Thanks mate, did that and no. 4 exhaust valve is definitely passing fluid

[bulldogbobby]

Long story but the W shaped cam tool pinged out when checking valve clearances /shims and pretty sure it's bent the valve

Cant see that being the problem, it would just be like the valve slamming shut.

No external forces applied apart from the closing force of the spring

Gus I could be wrong ( wife kids Etc. )

Thanks mate - the valve is definitely passing and if nothing else, it gives me a good opportunity to check everything properly while the heads off!