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reconditioning valves & valve seats
omega0684 - 14/4/09 at 07:12 PM

how do you go about reconditioning valves and their seats as i have managed to get a few of them out without using a spring compressor. the exhaust valves are obviously the worst, it was very difficult to get the hard carbon of the back of the valve the inlet valves are not that bad.

how do i get the sealing faces nice and clean? will i need to re-seat the valve seats etc?

any advice welcome, tricks of the trade etc


prawnabie - 14/4/09 at 07:26 PM

mount a drill in the vice and put the valve in the chuck. use emery cloth to clean the carbon off but don't go up the stem.

If the faces aren't badly pitted then just lap them back in.


omega0684 - 14/4/09 at 07:28 PM

how do you tell whether they are badly pitted?

y don't i clear the crap off the stem?


prawnabie - 14/4/09 at 07:34 PM

I was told that you can damage the stem quite easily with abrasives! dunno how true it is like!

Just clean the crud off and see if they will lap in, you are looking to make a dull grey line on both the faces (valve and head) without any gaps in the line - gaps are pits in the surface!

Shaun


D Beddows - 14/4/09 at 08:03 PM

To be honest a wire brush in a bench grinder is better (plus a pair of sturdy gloves and a certain delicateness of touch ) you almost always mark the valve stem if you tighten a chuck round it - even with tape wrapped around the valve. I would clean the stem as well and I tend to find a very gentle polish afterwards with autosol shows up how worn the valve is a treat. The parts of the stem that don't go anywhere near the guides will come up mirror finish and the rest should be a little duller in a used but ok valve - in a really worn valve the difference will stand out a mile!

Then you lap the valves in with grinding paste to get a good (or should I say better) seal - if after a couple of minutes with coarse grinding paste you haven't got a continuous line around the valve and seat then you may have a problem but to be honest the seats or valves have to be pretty knackered for it not to happen. In my experience though to start to notice any real difference once you've put everything back together (unless it was REALY nasty) you need new valves, guides, properly cut seats and a bit of porting..........


snapper - 14/4/09 at 09:11 PM

The thought is that if carbon has built up on the stem, it effectively seals the guide, if you remove the build up you can get excessive stem to guide clearance.
Another of those jobs that can end up with an expensive head rebuild if not carefull


D Beddows - 14/4/09 at 09:31 PM

It is one of those jobs that you should either do properly or not bother doing at all really


sickbag - 15/4/09 at 07:21 AM

If the valve seats have regressed so far into the head that you didn't need a spring compressor to remove the valves then you may as well get the head reconditioned by a professional company - or get a decent head.


g.gilo - 15/4/09 at 08:33 AM

one here if u need it.
graham


mcerd1 - 15/4/09 at 09:20 AM

Alex, got any photo's ?