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Is it safe to remove head scratch/grooves using valve lapping paste ?


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Hi all,

 

I've a stupid question but I'm asking anyway. I have an engine head which has scratches and grooves caused by sand paper on its surface (where you put the head gasket).

The scratches and grooves are not too deep but they may have a little impact on the head gasket lifetime. It is always better to have a clean flatten surface.

I can't afford to bring the head to a professional shop so I'm asking myself what if use some valve lapping paste to remove these scratches.

I have a flat piece of glass which is big and thick enough. So what if I put lapping paste on the head surface and put the glass above it ?

Then moving the glass left/right several times just like when doing valve break in until the scratches disappear.

I didn't find anyone doing that so I guess that's like some stupid idea. I don't have a sand paper big enough to cover the whole glass and head also.

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  • cedreex

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steveo3002

how bad is the damage ? feel it with finger nail?

i would prefer to use wet and dry sandpaper and oil ...i dont think it would matter too much as long as you make one whole pass over the paper in any direction

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The scratches are not deep but you can feel some of them on your finger nail. The finger nail won't fall deep within though but you'll feel a very little resistance as you try to pass your nail on them.

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Alternatively I was thinking of using scotch brite sponge instead of the glass and lapping paste combination.

But I find out that even the scotch brite sponge can scratch the surface if not using it very gently and smoothly.

 

1.jpg.3a363c880731763bc24e0bb6c55b9d1d.jpg

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steveo3002

you need the flat surface and abrasive to cut away at the surface , scotch pads wont cut

 

have you checked for flatness with a torch and steel rule?

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I'd move the head over the glass with paste like this guy using sandpaper.

 

Can you get HT8 floor sander paper?

About 20x45cm.

 

Looking closely he has taped 3 sheets to a bench, so you can use finer grades.

 

 

Edited by dvderlm
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@steveo3002

I haven't checked for flatness yet but I will. Unfortunately I don't have very precise tools like steel rule for such purpose so I will try to check the best I can with what I have. A feeler gauge and something like below (don't know the English word for it).

 

1.jpg.6fefb5621ab6cf8761435402cd0483e1.jpg

 

 

@dvderlm

What are the grade/grit specs of HT8 floor sander paper ? I've never seen HT8, is it equivalent to a 800 grit sand paper ?

I can try to find sand paper in the local shop arround me but If there are no HT8 then I'll need to know what grade/grit sand paper I should buy.

You suggest moving the head above the glass just like the videos also suggests. Can I get the same results if I move the glass above the head ? Just asking

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steveo3002

i think at least a good quality rule ...hold it against the head and shine a torch behind it ...if you see light its warped

 

if you never overheated it chances are its okay

 

Pro Art Stainless Steel Ruler 18 in. -- CreateForLess

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I think you are more likely to break the glass or make a rounded surface with glass on top. Let gravity help you?

 

He has the sand paper on top of perspex and says glass is fine too. 

Clamp it or have it against a wall.

 

100 grit then 240 grit is his suggestion.

Floor sander paper is definitely available in 100 grit.

 

Or, if mostly smooth and degreased, you could try, block all oil and water holes and valve seats,combustion chambers in head face with tissue and plasticine, then spray face with 2 coats of Glyptal 1201 Red and bake in the oven. It's not cheap stuff, mind.

 

Edited by dvderlm
not where petrol burns
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Good point. Would remove gasket traces, but may well score it.

 

Alloy wheels are refurbed with 400, 600 then 800 grit before painting.

 

 

 

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steveo3002

head skimming is pretty affordable here ...sometime its best to get it done right as doing it at costs the same and doesnt work well

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Ok I understand the problem of putting the glass above the head instead of the inverse. The problem I have is to make sure the sand paper doesn't move on the glass and using a glue I can easily remove from the glass after. I like this resurfacing method like they did the old days. As I said, going to a professional shop is definitely not possible right now. So I'll either try the resurfacing using the glass either I'll clean the scratches very smoothly using scotch brite sponge.

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