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Valve clearances


gfewster

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[quote by=gfewster link=Blah.pl?b=spit,m=1180867520,s=2 date=1180869247]The valves are in great shape, I've just done a de-coke.

I reckon any wear is probably in the rocker gear, so should I tighten them up until it's quiet?[/quote]

Hmm, could do that (I'm not too knowledgeable I'm afraid!) but is your timing set up correctly?

It's 13 degrees BTDC for MK1 and MK2 Spitfires, 6 degrees BTDC for MK3 and early MKIV Spitfires and 8 degrees BTDC for later MKIV Spitfire and 10 degress BTDC for 1500 Spitfires.

Of course, this information can be found in your work shop manual too!

Hope this helps!

David

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Thanks Dave. That's even larger gaps than the book spec, right? Then will it be even louder?

I was driving it yesterday (at book spec) and the chatter from the rockers was really loud and irritating. I guess I need to change the rocker gear?

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The noise might be caused by worn tappets.  If worn, they can go convex and tightening them up does not really help.  What happens is that you set the gap with the tappet on the back of the cam and if there is wear it will be the crater rim of the convex tappet which will be in contact with the camshaft.  In operation the cam lobe comes round and slaps down into the crater of the tappet causing the noise.  The effective valve clearance with worn tappets is what you set it to plus the depth of the worn crater times the rocker gain.

That's my theory anyway (from experience).

You can probably tell which tappet is worn without taking the head off by pulling the tappet up and down with the pushrod when the tappet is on the back of the cam, preferably when the oil is cold and thicker.  Best if you take off the rocker gear.  If you get a dull thud then there is a nice oil film between tappet and cam.  If you get a sharp tick then you are probably hitting the cam with the crater walls of a worn tappet breaking through the oil film.

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Had the same problem with mine got advice to try a click adjuster and it does work ,instead of using a feeler gauge which wont account for the concave or worn rocker as it bridges across the hollow

BAZ

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