Head skim needed? Opinions please. - Alfa Romeo Forum
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(Post Link) post #1 of 14 Old 16-03-12 Thread Starter
pkr
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Head skim needed? Opinions please.

My cylinder head is off for reconditioning and I've got a few imperfections in the surface.

In each case the imperfections are at least 7mm from any water/oil/stud hole.

The first picture is near No4 cylinder inlet side. The second is near No1 also inlet side.

http://i1134.photobucket.com/albums/...2_DSC_0005.jpg

http://i1134.photobucket.com/albums/...2_DSC_0006.jpg

( Sorry, that second picture isn't as good as it should be ).

As near as I can measure them with a pair of digital calipers, one is 0.04mm deep and the other 0.14mm deep.

I'm inclined to get it skimmed anyway but advice please.
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i wouldn't bother Paul, they are going to be hidden below gasket and are well away from both oil and water pathways. IMO

If you really are OCD get the holes welded?
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I'd skim it pkr , any imperfection can cause probs at a later date or maybe not but is it worth taking the risk for saving £30 , plus the compression that drops of from wear from use raises a little with a skim , gud luk Nee .
 
(Post Link) post #4 of 14 Old 16-03-12 Thread Starter
pkr
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LOL!

1 all!


Although there appears to be plenty of metal left for skimming, I was a little concerned about the CR. How does wear reduce the CR? Erosion of the combustion chamber through normal combustion?
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I would skim it. It will reduce the imperfections and give as good a surface as possible for the new gasket. Part of the job IMO.
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Quote:
Originally Posted by pkr View Post
My cylinder head is off for reconditioning and I've got a few imperfections in the surface.

In each case the imperfections are at least 7mm from any water/oil/stud hole.

The first picture is near No4 cylinder inlet side. The second is near No1 also inlet side.

http://i1134.photobucket.com/albums/...2_DSC_0005.jpg

http://i1134.photobucket.com/albums/...2_DSC_0006.jpg

( Sorry, that second picture isn't as good as it should be ).

As near as I can measure them with a pair of digital calipers, one is 0.04mm deep and the other 0.14mm deep.

I'm inclined to get it skimmed anyway but advice please.
I vote for a skimmed surface and plane grinding : I'm not shure whether new stretchbolts for the head is recommended.
Last time I had to do that 30 years ago (FIAT 131 Mirafiore) I went to the grinding specialist with the head of the engine in my rucksac on a bike,hell my buttocks vere in pain after 15 kilometers!" The pain was due to the weight not the price tag

William LŁtken Alfa Romeo 156
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How about doing a compression test and comparing with a much younger engine?

I imagine that piston ring wear would be the cause of the most compression loss but I dunno really
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(Post Link) post #8 of 14 Old 19-03-12 Thread Starter
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Thanks all for the help everyone. I did get it skimmed in the end. Peace of mind etc.

Quote:
Originally Posted by wlu View Post
Last time I had to do that 30 years ago (FIAT 131 Mirafiore) I went to the grinding specialist with the head of the engine in my rucksac on a bike,hell my buttocks vere in pain after 15 kilometers!" The pain was due to the weight not the price tag
Ouch!

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Originally Posted by Turtle4288 View Post
How about doing a compression test and comparing with a much younger engine?

I imagine that piston ring wear would be the cause of the most compression loss but I dunno really
I did the compression testing prior to dismantling. No1 was around 230 psi ( 15.8 bar ), Nos 2 and 3 were slightly less ( 215 psi & 210 psi ) but No4 was the bad one at about 80 psi ( 5.5 bar ). If I'd had a leak down tester I would have used it before taking anything apart as well to determine where the problems lay. However the bores are good with no wear and original honing marks still evident. I poured oil into the bores and the majority of the oil was still in there after 24 hours so I'm fairly confident the bores and rings are good.

I really must make myself a leak down tester.
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I wouldn'a skimmed it... but I guess it's all shiny now.

Compression sounds okay (apart from #4 obviously).


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That is interesting... my compression test results are:

------Test 1--- Test 2--- Test 3---- Oiled
Cyl 1 186psi----- 180----- 182----- 215
Cyl 2 175psi----- 182----- 180----- 215
Cyl 3 190psi----- 186----- 186----- 225
Cyl 4 195psi----- 186----- 184----- 222

I considered this to be OK at the time...
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Hi All,
Just a note on compression, my 2000 105 series engine (S2 Spider) had low comp on one cylinder, about 25% down on the other three which were within a few psi of each other. With the engine still in the car, the oil-in-plughole compression test brought the compression up to the others so I guessed at worn rings or liner.

There is a 15 year old bit of paper probably under a cupboard in my garage with the psi figures on, but I guess it's not critical to my point, which is that the problem liner looked as good as the others upon removal, nice smooth sides, no steps or excessive wear etc, as did the rings, but the liner was worn in a shallow 5mm wide band, just around bottom dead centre, I guess this was allowing the pressure to escape. The overnight oil-in-cylinder test wouldn't have shown this up unless the problem cylinder happened to be at b.d.c., you would really need to turn the crank to run the rings past the worn part of the cylinder to detect any leakage.

I tried re-honing the liner as the worn area was very shallow, but it didn't get close to removing it completely, so I replaced with a 2nd hand liner. I now have a 105 series pen holder on my desk !
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What was the cause of the low compression in the end PKR?
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(Post Link) post #13 of 14 Old 16-11-12 Thread Starter
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A piston had self destructed. Aluminium between the piston rings had snapped off between the rings.

Photo :
http://i1134.photobucket.com/albums/...4_DSC_0008.jpg

No damage to the bore fortunately, so a used piston fixed it. I took the opportunity to re shell the bottom end and fitted new rings as well ( of course ).

That wasn't the end of the saga though. Some of the new valve stem oil seals were faulty and 6 of them ( I subsequently discovered ) on the exhaust side came off the valve stems. Sigh. So the head came off again to fit another 16 stem seals ( this time genuine AR ).
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Skim it down to the max marker and raise compression. More powerz!
Then run on high octane fuel ;-)
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