Richard Jenkins
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| posted on 17/5/08 at 02:50 PM |
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Checking valve seats
With the head off and on the bench, on blocks so I can see underneath, when I put petrol into the inlet and exhaust ports is there a problem if I see
any seepage / leaks?
Best is no.1 inlet which has a slight dampness at one point around the seat, worst is no.3 exhaust which has seepage all way around the seat and drops
of petrol form after a minute or so.
All valves show some seepage, inlets are generally better than exhausts.
Engine is a 1300 x-flow (for the 750MC series)
thanks
Rich
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mookaloid
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| posted on 17/5/08 at 02:54 PM |
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I would be suprised if petrol didn't seep past TBH. If you take the valves out and inspect the seats and valves for wear and either relap the
valves in or take the head to a machine shop to have the seats recut if neccessary.
Cheers
mark
"That thing you're thinking - it wont be that."
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Chippy
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| posted on 17/5/08 at 02:58 PM |
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Yes! the valves should be gas tight, (which is thinner than petrol, :-) ), so looks like a strip down and at the very least a grind in job. If the
seats are too bad you will need to get the them recut, but just a little. If the valves are too pitted, chuck them and get some new ones. Also while
it's in bits check the valve guides for wear, if they are badly worn I think you have to have the head bored and shimmed, as from memory the
guides are not removable on the Xflow, (may be wrong on that). HTH Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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rusty nuts
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| posted on 17/5/08 at 03:07 PM |
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It is possible to bore out the "valve guides" on a crossflow and fit aftermarket guides . The valve seats will need recutting afterwards
to ensure they are concentric with the guides . You may be lucky as already suggested and get away with a light lapping in. I tend to use engineers
blue to check the seats , any parts that don't seal show up. Petrol down the ports will only leak through if the valve is not seating
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Richard Jenkins
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| posted on 17/5/08 at 03:10 PM |
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Engine was rebuilt over the winter and the valves were refaced to the head then. I've only done 3 meetings so far this year.
Rich
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RazMan
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| posted on 17/5/08 at 03:31 PM |
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IMO you would expect to see some seepage, as the valves are only under spring pressure. When you subject them to hundreds (thousands?) of psi from the
combustion process they will probably not leak, although as mentioned, it is a good idea to lap them while you've got the head off anyway.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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britishtrident
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| posted on 17/5/08 at 03:52 PM |
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Best test is to turn the head on its side and fill the ports with kerosene, then point an airline jet at the combustion chamber side -- you
don't need to go too close to valve but work you way round the rim of each valve seat in turn --- a few very tiny bubbles is ok but if you get a
stream of bubbles its a fail.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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BenB
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| posted on 17/5/08 at 06:05 PM |
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I wouldn't be worried about a little seepage. As already said, they are only being held in place by spring pressure. When the car is actually
running they'll be a few hundred PSI in the cylinder helping them stay closed....
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