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Valve grinding: when is it enough?
by
oris
on 20 Jan, 2010 02:51
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Hi,
First a short introduction:
Allthough this is my first post on this forum, I've been reading quite a lot here for the past year, and have been learning a lot!
My problem:
I'm rebuilding a JR 1.6 TD engine, and at this very moment working on the head.
I've replaced the valve guides an all valves looked great.
So no valves have been replaced and now I've grinded the valves in the valve seat.
But the problem: how well should they seal?
I've filled the ports with white spirit and let it rest for a day.
There was not much leakage, but some, a few milli liter probably.
Will this be tight enough or should I continu grinding until there is no leakage at all?
Thanks!
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#1
by
Rabbit on Roids
on 20 Jan, 2010 09:06
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how perfect do you want them?
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#2
by
600K
on 20 Jan, 2010 09:25
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Did you grind the valves and seat or hand lap them? If you ground them, you should finish with a hand lap to get a final seal. If you just lapped them, then it should show a complete circle around the valve face.
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#3
by
oris
on 20 Jan, 2010 10:25
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how perfect do you want them?
Well, I would like to use the engine for a long time, and it should be reliable..
I'm assuming that the better the seal, the higher the compression, thus higher MPG and better cold starts, so a leak would be a bad thing.
But how much would the effect of a small leak be on the real life compression?
Did you grind the valves and seat or hand lap them? If you ground them, you should finish with a hand lap to get a final seal. If you just lapped them, then it should show a complete circle around the valve face.
I hand lapped them, first with a rough compound, followed by a fine compound.
The dirty spots on both the valve seats and the valves themselfs disappeared, and the seats and valves look clean, but they do leak a tiny bit..
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#4
by
smutts
on 20 Jan, 2010 13:31
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Dont go too insane, a continuous ring of matt area all the way round the valve seat. Too narrow, and the valvehead runs hot, too wide and the contact pressure is lower, possibly allowing combustion pressure to force the valve off the seat. Make sure you wash all traces of the paste away, as it's hungry. But someone else might know better, theories change. The world used to be flat once.
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#5
by
oris
on 21 Jan, 2010 04:43
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Allright!
Just to be sure I've ordered a compression tester,
I'll do a compression test as soon as I've finished working on the head and be able to pre-mount it.
If the numbers are right I know it's ok!
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#6
by
745 turbogreasel
on 21 Jan, 2010 05:44
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Edge of intake valve must be 0.5mm 0.02in or thicker
do not grind stellite coated exhaust vales by machine
Valve seats 45*, contact surface:
2.0mm 0.08in for intake valve
2.4mm 0.09in for exhaust valve
use 15* cutter to reduce size
installed gap between valve face and head surface should be less than 1.5mm 0.06in replace eat, and possibly valve if gap is too large.
or so says my book.
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#7
by
oris
on 21 Jan, 2010 09:48
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Edge of intake valve must be 0.5mm 0.02in or thicker
do not grind stellite coated exhaust vales by machine
Valve seats 45*, contact surface:
2.0mm 0.08in for intake valve
2.4mm 0.09in for exhaust valve
use 15* cutter to reduce size
installed gap between valve face and head surface should be less than 1.5mm 0.06in replace eat, and possibly valve if gap is too large.
or so says my book.
Thanks, but that's for cutting the contact surface, I didn't cut it by machine,
I only used a grinding compound to lap the surfaces by hand.
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#8
by
oris
on 24 Jan, 2010 05:49
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The seats (and valves) were all matt.
I've placed the head on the block for a short test (reused the old 3 notch gasket, new one will be 2 notch) and found out that the compression was a bit low, but uniform. (something like 20 Bar, 290PSI, cold engine offcourse: still on a stand)
Could this be caused by the fact that the cylinder walls have been honed and the pistons re-ringed and they should run in first or should I expect it to be caused by ill sealing valves?
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#9
by
macka
on 24 Jan, 2010 08:00
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The old head gasket for the test is inconclusive as it is pretty much molded to the head before you decked it (you did have it resurfaced right?).The pressure will jump up when you get the rings seated properly. I use dino squeezings for the break in then switch to synthetic oil at the second change interval. Just remember that the oil will be changed twice rather quickly to eliminate metal bits that will be found during the break in. If you can go with a 1 notch head gasket, I'd go that route
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#10
by
oris
on 24 Jan, 2010 09:25
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But I might have to remove the head again, will using a new gasket not result in having to throw a new gasket away once I've used it?
Or isn't it a problem (tightening and loosening) if it hadn't heated up?
Nice to hear the compression will go up once the rings have seated
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#11
by
macka
on 24 Jan, 2010 19:10
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the old gasket will be different, especially when you go from a 3 to a 2 holer compression wise. WHy would you need to pull the head again? If you are doing lots of stuff, just wait until you are ready to button it up for good to do a compression test. I'd say with those numbers on a 3 holer that is used you should see way better numbers with the new 2 holer once you are buttoned up for running. Don't waste your time this early with a compression test, as it really isn't close to a final proper number. Get the valves sorted out and be ready after its been ran to test. Right now you are distracting yourself with unnecessary self made worries.
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#12
by
Rabbit on Roids
on 25 Jan, 2010 10:32
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the old gasket will be different, especially when you go from a 3 to a 2 holer compression wise. WHy would you need to pull the head again? If you are doing lots of stuff, just wait until you are ready to button it up for good to do a compression test. I'd say with those numbers on a 3 holer that is used you should see way better numbers with the new 2 holer once you are buttoned up for running. Don't waste your time this early with a compression test, as it really isn't close to a final proper number. Get the valves sorted out and be ready after its been ran to test. Right now you are distracting yourself with unnecessary self made worries.
SOOOOOOOOOOOOOOO many people have this problem on this forum. i occasionally do too, but then when i have all the self made worries, usually something goes wrong. if i dont worry about anything, things go as planned.
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#13
by
oris
on 26 Jan, 2010 00:46
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I guess you're right, it hard to determine what's right and what's wrong if you haven't got a lot of experience, asking more experienced people can help in those occasions
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#14
by
smutts
on 26 Jan, 2010 07:24
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I guess you're right, it hard to determine what's right and what's wrong if you haven't got a lot of experience, asking more experienced people can help in those occasions Smiley
As the old saying goes, "We learn by our mistakes." So why am I not a genius, with lots of broken engines?