FFTS
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| posted on 15/9/10 at 08:47 AM |
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K Series valve lapping and sealing
OK now I'm learning to be such a amazing grease monkey I have got all new valves and stem seals for my head and cut them in with course then
fine paste. Reassembled and all look good but the question is..
How good a seal should the valves make? I stood it on each side and poured water in to check the valve seating. Water did seep through after 5 to 10
secs but only a tiny trickle. Would this be ok when the cylinder is under pressure of combustion instead of just the spring pressure?
Adi and British trident are da boyz hehehe.
Chris.
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Strontium Dog
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| posted on 15/9/10 at 09:01 AM |
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If the springs are on it shouldn't leak! Use paraffin (heating oil) to test and not water as well The trick is to get the narrowest seal
around the valve as reasonably possible with NO black pits. The wider the cut area the worse the seal will be.
If you think about it, if fluid leaks past the seal then gas under pressure certainly will!
[Edited on 15/9/10 by Strontium Dog]
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daviep
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| posted on 15/9/10 at 10:25 AM |
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I personally wouldn't be using course lapping paste with new valves. If the seats will not clean up quickly with fine paste then I would look at
re cutting them.
As mentioned above you do not want a wide area of contact between the valve and seat, it's a bit of a compromise between sealing efficency and
valve life.
If the sealing face is too wide then you will not get a good seal, if it is too narrow then the vavle will overheat as the path for disipating the
heat in to the head is too small.
Valve and seat are cut to different angles, typically 45 degrees for the valve face and 46 degrees for the valve seat, they are then lapped in to
create the desired seat width.
Davie
“A truly great library contains something in it to offend everyone.”
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britishtrident
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| posted on 15/9/10 at 10:31 AM |
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Grinding in valves is a bit of chore no real short cuts except using a valve lapping adapter (Gunson Eezi-Lap) for a drill.
The important thing is not to let the valve spin through more than about 120 degrees without lifting it clear of the valve seat and giving it a 60
degree turn.
When grinding in tiny spot of paraffin or wd40 it will help keep the lapping compound from getting too sticky.
When you are finished you should get a nice even matt finnish for a full 360 degrees on both valve and seat.
To test lay the head on its side fill the port with paraffin and if no obvious leaks point a compressed air jet round the rim of the valve and look
for bubbles in the port.
[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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FFTS
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| posted on 15/9/10 at 10:32 AM |
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OK Thanks,
So that said what now?
More fine paste and swivelly stick?
Where would cut them at reasonable price if needed? Theres a place near me but he calls it a refurbishment and wants to charge £200+ if I had that
money I wouldnt have bought valves for a diy.
Chris.
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adithorp
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| posted on 15/9/10 at 10:32 AM |
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You should have an even grey valve seat when you've finished grinding with no variation or polished areas. To be certain you can mark the seat
by drawing radial lines across it with a pecil. Then put the valve in and give it a quick, light turn with a lapping rod. You want that to rub out the
pencil marks evenly.
With it assembled you'd expect it to hold parafin in the ports. You might see some seepage but not running. Personally never do it though.
I've always assembled with the valves and seats oiled to ensure a good intial seal when starting. Don't forget to tap each valve (stem
end) with a small hammer to make sure the collets are seated as you rebuild.
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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FFTS
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| posted on 15/9/10 at 10:40 AM |
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Hehe told you Da boyz would be right up with some K series knowledge 
Adi, would you U2U me your mobile number please.
Chris.
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adithorp
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| posted on 15/9/10 at 10:40 AM |
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quote:
Originally posted by FFTS
OK Thanks,
So that said what now?
More fine paste and swivelly stick?
Where would cut them at reasonable price if needed? Theres a place near me but he calls it a refurbishment and wants to charge £200+ if I had that
money I wouldnt have bought valves for a diy.
I'll have a look for you if you want. Only 1/2hour down the m-way. Joe's got my number. Not ground any valves for a while but it soon
comes back. It's all about rythem... and practice. If you get blisters, you're doing it wrong.
u2u now sent
adrian
[Edited on 15/9/10 by adithorp]
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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FFTS
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| posted on 15/9/10 at 10:44 AM |
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There's only one way thats worth getting blisters 
I think popping over would be a good idea. I could have them in and out too many times.
Chris.
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britishtrident
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| posted on 15/9/10 at 10:51 AM |
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Get one of these
http://www.ahspares.co.uk/products/GUNSON-EEZILAP-VALVE-LAPPER-MSC226.aspx
[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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adithorp
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| posted on 15/9/10 at 11:03 AM |
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You do need the right tune in your head to grind valves, but the only tune that goes with one of them is YMCA...
Just because they work doesn't make it right. You'll have him wearing rubber gloves next!
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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02GF74
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| posted on 15/9/10 at 01:02 PM |
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quote:
Originally posted by Strontium Dog
If you think about it, if fluid leaks past the seal then gas under pressure certainly will!
You have not taken into account the force on the valves from the gas pressure - that will tend to push them from inside the head.
but back to OP not sure what you have done here - head with crappy seats and got new vavles?
for a proper job, the vavle seats need to be recut and then new vavles ground in using fine paste. once you have a matt grey cricle about 1 mm wide
on the seat you can stop grinding - you cenrtainly don't want the whole seat.
if doing by hand, the whole process is a grind (pun intended) but then you are unlikely to have to do it for quite a number of years, if ever.
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Strontium Dog
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| posted on 15/9/10 at 06:01 PM |
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quote:
Originally posted by 02GF74
quote:
Originally posted by Strontium Dog
If you think about it, if fluid leaks past the seal then gas under pressure certainly will!
You have not taken into account the force on the valves from the gas pressure - that will tend to push them from inside the head.
I think you'll find that if the valve doesn't hold paraffin with the springs on no amount of pressure generated in the cylinder is going
to hold the valve tight so that no gas leaks.
Then of course there's the induction and exhaust strokes to consider..........!?
[Edited on 15/9/10 by Strontium Dog]
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