Noisey rockers

[Kamran]

Hi all, just purchased a sport for the winter as the cabs just got painted and would rather leave it in the garage till summer comes round again. Anyway the engine sounds a bit tappety and i've been told to adjust rockers out. Anyone confirm the clearance when hot/cold. 10/10 10/8.?
Any advice appreciated. Thanks

[kam-325i]

What engine.....

[Templ8e30]

It's a sport so must be an M20, 0.25mm cold / 0.30mm hot.

Cheers,

Iain T

[Kamran]

yep its a 2.5 m20 guys. Cheers for the info. Iain T. Get that sorted out

[FBF]

BAHH and i thought this thread was about the rolling stones!

[Simon13]

if it's still a bit noisy get a new spray bar Ԛ£10 from the dealer, made good difference to one of mine before

[Kamran]

if it's still a bit noisy get a new spray bar Ԛ£10 from the dealer, made good difference to one of mine before

whats that about Simon, Just ask for spray bar and the guys at the dealer will know what I'm on about, How's it work mate?

[Chris-W]

Run's above the cam, front to back, and sprays oil on the lobes. Dealer will know what you mean.

[deano325t]

lol @ fbf

[Simon13]

just ask for an M20 spray bar they are all the same, all u need to fit it is an 8mm spanner after removing the rocker cover. Hey presto

[Turbo-Brown]

Never understood why the hot adjustment value is higher than the cold!

Metals (and indeed most engineering materials) expand when hot, that's why we have the valve clearances: so when the stems and whatnot have expanded due to heat, the valves can still close.

So why on earth is the hot adjustment value not less than the cold?!

[Kamran]

Thanks for the advice guys much appreciated.

[Simon13]

i would say because if u set them too tight eg .20 when hot they would be way too tight when the engine is cold and this is not good and when rockers snap

it could of course be smaller than .20 when cold get me!?

[Turbo-Brown]

No, it's the other way around by my reckoning.

The gap is there, say 0.2mm when cold to allow the stems to expand and close up the gap as the engine gets hot.

Lets say that you set your clearances with the engine cold to 0.2mm and then went for a drive. If you whipped the rocker cover off and measured the clearances, they should be practically non-existant as the bits of metal have expanded into the clearance.

Now lets say that with the engine hot, you set the clearances to 0.3mm and then left it over night to cool off. If you checked them in the morning, they should be around 0.5mm!

I know I'm ignoring the expansion of the head here, but that doesn't get as hot as say an exhaust valve, although ali does expand more per degree than steel.

Can anyone else see my confuzzlement?

[Simon13]

i can see what your saying but by my logic setting them bigger makes sense to me. So when the engine is cool they are still with in tolerance. Maybe the engine expands in a different way to your theory?!

[Turbo-Brown]

Guess it must do!

You're quite right that the books say to set them larger for hot, just strikes me as being arse about face that's all.

Shame they're such a pain to get at on mine, would be an interesting experiment.

[eRgal]

I may be wrong but are these settings not to make sure your valves open the correct amount, So if hot and expanded if you set them same as cold your valve would be opened further than spec.

So your hot size is a larger gap so that when metal items expand the valv e only opens correct amount.