smart51
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| posted on 7/11/06 at 06:55 PM |
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Head off - how black should the pistons be?
I've just taken the head off my engine. Quite easy really, apart from the bolts being so tight that I bent my allen key through 50° before the
bolts budged.
The valves all seem to be seated nicely and the gasket is in A1 condition.
How black should the pistons and combustion chambers be? There seems to be about 0.2mm of black tar fading to really dark brown by the edges. Is
this OK for an 8 year old engine?
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DIY Si
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| posted on 7/11/06 at 06:57 PM |
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Seems fine. Wouldn't expect much different really. When you say the valves all seem to seat nicely, what do you mean?
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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Catpuss
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| posted on 7/11/06 at 07:09 PM |
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With all the WD40 and stuff thats been put down those bores to get the thing going I wouldn't be supprised if its black and like tar
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rusty nuts
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| posted on 7/11/06 at 07:13 PM |
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The only way to check for valve seating correctly is to remove them and check with engineers blue. Vacuum test and testing by pouring petrol/degreaser
down the ports will test for leaks but will not be as reliable . Is it a black oily deposit or is it carbon caused by overrich mixture?
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stevec
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| posted on 7/11/06 at 08:04 PM |
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Checking them with blue is fine when they have been cut or lapped in, but unless a valve has been rotating regulary when running it may have a non
uniform seat with a irregular contact area.
Steve,
[Edited on 7/11/06 by stevec]
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rusty nuts
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| posted on 7/11/06 at 08:15 PM |
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In which case it's not doing it's job properly - sealing.
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stevec
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| posted on 7/11/06 at 08:34 PM |
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It can seal providing you dont fug with it.
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rusty nuts
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| posted on 7/11/06 at 09:30 PM |
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Whats the point of having a valve if it doesn't seal? Try doing a cylinder leakage test with a valve thats not sealing!Compression test may not
show up a leaking valve but it will cause an engine to run rough
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smart51
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| posted on 7/11/06 at 10:29 PM |
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Acetone down all the ports produces no leaks. OK, so they may not be gas tight, but its a good sign.
I put a bit of oil down the bores doesn't appear to leak. that said, the engine is on a slant and I only filled half way up the piston. I
cleaned the mating surfaces with the acetone and in that time no oil seemed to leak.
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rusty nuts
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| posted on 8/11/06 at 08:25 AM |
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Any signs of head gasket failure?
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smart51
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| posted on 8/11/06 at 09:25 AM |
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No, the gasket looks to be in great condition. The mating surfices of the head and block are fine and have cleaned up a treat. Even the oil that I
poured into the bores last night is still there this morning. It all looks loveley.
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britishtrident
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| posted on 8/11/06 at 11:13 AM |
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Yep checking the valve sealing from the port side by filling it with a light solvent is a good test for checking the seal -- kerosene is easyiest
cheapest to use as it dosen't evaporate quickly.
Another trick is to fill the port with kerosene and aim a jet of compressed air round the circumfrence of the valve, if you get bubbles it
isn't sealing.
quote:
Originally posted by smart51
Acetone down all the ports produces no leaks. OK, so they may not be gas tight, but its a good sign.
I put a bit of oil down the bores doesn't appear to leak. that said, the engine is on a slant and I only filled half way up the piston. I
cleaned the mating surfaces with the acetone and in that time no oil seemed to leak.
[Edited on 8/11/06 by britishtrident]
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MikeRJ
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| posted on 8/11/06 at 11:28 AM |
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Mr Smart, just a thought. What exhaust system are you running?
If the primaries (or the secondary for a 4-2-1) for the middle two cylinders were partialy blocked it could cause the symptoms you are seeing, i.e.
glowing headers, misfiring, lack of power etc.
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smart51
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| posted on 8/11/06 at 12:08 PM |
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I'll check the exhaust then. Now that the head is off I can get into the headers from both ends.
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rusty nuts
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| posted on 8/11/06 at 03:47 PM |
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Check the valve clearances, tight tappets will cause problems/rough running etc
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