Guinness
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| posted on 23/7/09 at 03:21 PM |
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Skimming a head - have I just made a fool of myself?
Took my cylinder head into a local engineering workshop this morning to get it skimmed.
The tollerance in the manual is 0.002".
They agreed to skim 0.004" off it and surface it. They knew it was a Kawasaki bike engine head.
Just been round to collect it and I wasn't (at all) impressed by the finish.
Basically either end of the head was absolutely mirror smooth, like glass. But in the middle (cylinders 2 and 3) it was like a record!! You could
clearly see and feel the circular tracks where it had been cut.
They said that the gasket would cope with it. I said it was a multi layer steel gasket, and thought it would leak like a sieve. Honestly the groves
were easily felt with a finger nail and right across the face of the head, connecting oil ways / water ways and the combustion chambers.
They have agreed to re-finish it and it'll be ready in the morning.
Question is, have I got them to do un-neccessary work, and made myself look like a tit?
They are the experts and have probably done more cylinder heads than I've had hot dinners, but, I just wasn't willing to risk the time /
money in re-building the engine to find out that I was right and the head gasket couldn't cope with the grooves.
Mike
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pewe
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| posted on 23/7/09 at 03:28 PM |
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I would have thought it should have been equally smooth all the way across otherwise it's not dead flat, espec if they have put it on a surface
plate.
Having said that its your money not theirs so your perogative to have it as you want it.
Hopefully they won't end up taking too much off - suggest you dry fit first to check clearances in case they have.
HTH.
Cheers, Pewe.
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dinosaurjuice
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| posted on 23/7/09 at 03:30 PM |
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your not an idiot.
youve seen how good the surface finish is at the ends. theres no good reason they shouldnt replicate that in the middle.
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coozer
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| posted on 23/7/09 at 03:34 PM |
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No Mike, you very clever and sensible...
Head skims need to be perfectly flat and mirror smooth. The grooves you describe may make the head gasket fail prematurely..
1972 V8 Jago
1980 Z750
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Andy D
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| posted on 23/7/09 at 03:51 PM |
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I had exactly the same with mine. OK, it's a pinto, and the grooves must be for a 78 record! 
Didn't notice when I clapped it together, but it would'nt seal. Had to have it skimmed again.
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gaz_gaz
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| posted on 23/7/09 at 04:35 PM |
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the finish is very important when using mls gaskets.
you done the right thing.
i machined a head for a customer a while back but it was porous, i told him it wasn't going to seal properly,
he told me he was going to use a mls gasket and hylomar blue on it,
week later he brought a replacement head in for a skim 
[Edited on 23/7/09 by gaz_gaz]
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balidey
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| posted on 23/7/09 at 04:44 PM |
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difference in finish across the head shows its been done wrong / badly.
grooves you can feel with a fingernail are OK, but the smoother the better. They may have traversed too quick.
[Edited on 23/7/09 by balidey]
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AdrianH
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| posted on 23/7/09 at 04:45 PM |
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Not in anyway an expert, but I would have thought some roughness to the surface rather then mirror finish, reason for saying this is that when clamped
down the gasket would be filling so,e of the imperfections and having more resistance to move under pressure. I would have thought that a mirror
finish would not provide this, hard for me to describe so sorry if this is not making sense?
But groves over say one or two thou would be too much for the gasket to fill.
I may have something about finishes some where?
Adrian
Why do I have to make the tools to finish the job? More time then money.
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scottc
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| posted on 23/7/09 at 05:47 PM |
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Where was this Mike? I received good service from Northern Rebore.
Though this was about 2 years ago.
http://www.sotoconnect.com
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Guinness
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| posted on 23/7/09 at 06:34 PM |
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Hi Scott
No, not Northern Rebore.
I'll not name the company. Unless of course I don't get my head right!
Thanks for the rest of the input guys. I'll see what the morning brings.
Mike
[Edited on 23/7/09 by Guinness]
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perksy
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| posted on 23/7/09 at 07:43 PM |
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As has been said above if your using a steel 'layered' head gasket the surface needs to be Machined to the correct finish
I'd be taking it back and having a 'chat' with them 
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02GF74
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| posted on 23/7/09 at 08:15 PM |
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I reckon you are correct.
can't see how you can possible get gooves that you can catch your finger on unless there is some problem with the process.
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Peteff
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| posted on 23/7/09 at 10:18 PM |
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I just had a Corsa head skimmed locally, it cost £25 and it was like a mirror finish. They pressure tested it as well and said it was o.k.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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NS Dev
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| posted on 24/7/09 at 06:15 AM |
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yep wot they said.
There almost certainly will be cutter marks, but you shouldn't be able to catch them with your nail.
That said, 4 thou isn't much, a lot of heads won't clean up at that, and if it was ok at the ends is could be that they have taken you
literally on the 4 thou, rather than going a touch further to get decent cleanup
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Guinness
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| posted on 24/7/09 at 11:48 AM |
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Well head collected this morning. It's about 10x better.
However, I have to admit to a distinct loss of confidence in it, so I took it to Northern Rebore for a second opinion.
They passed it as an acceptable finish, but said they would have done better!
Just waiting on the gaskets arriving now, so I'll be spending most of the weekend lapping valves in and fitting them back into the head.
Cheers
Mike
Mike
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