sandpaper heads

[sling]

Anyone ever hear of placing a sheet of sandpaper on a sheet of glass.....and gently rubbing your heads on it to clean and get a straight edge ?

 

[rjezuit]

Re: sandpaper heads

Yes, start with 240 grit and finish up with 400. Kind of go in a figure 8 pattern until it cleans up. Rick

 

[Bubonik]

Re: sandpaper heads

my Johnson manual says to do that
(Sandpaper on Glass)

I also heard of a guy that uses a cinder block

 

[boobie]

Re: sandpaper heads

Stick with the glass.

 

[sling]

Re: sandpaper heads

thanks, guys

 

[Tim Frank]

Re: sandpaper heads

It's called lapping and is useful in many other applications.
Truing a sharpening stone, a plane plade, plane sole...etc.

Not quite as accurate as a surface plate, but way cheaper.

 

[Rick.]

Re: sandpaper heads

Personally I would start with 100 grit and then to 180 max. I also have had good success using valve grinding compound on glass instead of sandpaper. Both work very well. Best of luck. Rick.

 

[Chris1956]

Re: sandpaper heads

Gee, I would be careful with any grade of sandpaper courser than 400 grit. The 400 grit may be too course.

We always used a new piece crocus cloth, which is real fine grit(1200 grit?). A piece of plate glass is pretty flat, however, you are using it to remove metal from a highly machined piece.

 

[robert graham]

Re: sandpaper heads

Depending on how much warpage you've got, a large flat machinist's file to use as a straight edge and to correct any big humps or bumps, then finish with the emory cloth on a flat surface. Aluminum is very easy to work with and you can get it flat to within a few thousandths of an inch, just take your time. Good Luck!

 

[MudLake]

Re: sandpaper heads

I have used a sheet of 1/4 inch glass and automotive valve grinding compound.

 

[Rick.]

Re: sandpaper heads

Gee, I would be careful with any grade of sandpaper courser than 400 grit. The 400 grit may be too course.

We always used a new piece crocus cloth, which is real fine grit(1200 grit?). A piece of plate glass is pretty flat, however, you are using it to remove metal from a highly machined piece.

I mean no disrespect but that seems like over kill to me. I've seen new heads that really aren't that polished. I think the main objective here is flat no so much shinny. Sometimes I think gaskets work better if the machine surfaces have a little tooth to bind to but I admit I'm no mechanic, but my Grandfather was a machinist. LOL. Anyway, either way will get the head done in the end I believe. Rick.

 

[Tim Frank]

Re: sandpaper heads

Gee, I would be careful with any grade of sandpaper courser than 400 grit. The 400 grit may be too course.

We always used a new piece crocus cloth, which is real fine grit(1200 grit?). A piece of plate glass is pretty flat, however, you are using it to remove metal from a highly machined piece.

Interesting comment, and I am not sure that I am qualified to disagree, but here goes anyway....

Judging by the number of opinions on grit size, actual choice may not be all that significant if people are using such arange and not having pro

In theory, surface finish can be really critical, and certainly in the automotive world most engine manufacturers will have a pretty specific and fairly tight call-out in that.

Too smooth can be as problematic as not smooth enough.

When I touched up the mating surface of the head on my $500- E/rude 6 HP, I just used a plate with progressively finer sheets of 3M wet/dry and got down to 600x.
It worked fine.

But if I had a $5000 E/rude, I'd try to find out whether there is an OMC preferred surface finish spec that I could aim for.

 

[Tim Frank]

Re: sandpaper heads

Sometimes I think gaskets work better if the machine surfaces have a little tooth to bind to but I admit I'm no mechanic, but my Grandfather was a machinist. LOL. Anyway, either way will get the head done in the end I believe. Rick.

This is an interesting thread, but probably one that would never see a consensus reached.
There is a lot of theoretical arguments that can be offered up, but IMO, for most of us in here, the practical takes precedence.
If it works, in spite of theory.... it still works! Smile and wave boys, smile and wave....

Given that a surface finish measuring device costs $1000- plus, for even an entry-level unit, it is unlikely to be found in many of our tool boxes.

Regarding "a little tooth...", the flip side of that says that if the head bites into the gasket, any lateral expansion ( likely to be at a different rate than the block mating surface) may work small tears into the gasket over time which can lead to failures.

My gut feeling would be for most O/B heads that 80x would not necessarily be too coarse....and 600x not too fine. Between those values is probably a safe range.

 

[tswiczko]

Re: sandpaper heads

Personally I would start with 100 grit and then to 180 max. I also have had good success using valve grinding compound on glass instead of sandpaper. Both work very well. Best of luck. Rick.

The problem with that is the valve grinding compound is usually harder than the glass and you are now wearing the flat surface of the glass away as well taking metal off the head, and there goes your flat surface.

Valve grinding compound is usually made from alluminum oxide(AKA corrundum) Al2O3 which is very hard, it is a hardness of 9 on the Mohs hardness scale and glass is about a 5.5 on the Mohs hardness scale.

 

[Chris1956]

Re: sandpaper heads

You are not interested in getting a shiny finish. You are also not interested in getting some tooth. The intent is to get the mating surface of the head as flat as possible. You want the best seal with the block, nothing more, and the block is milled to be absolutely flat (within some tolerance, naturally).

If you guys want to scratch up your heads with 100 grit paper, and pray the head gasket fills in the scratches so you get some compression, it is your motor.

Why do you think machine shops mill heads to fine tolerances. We are not working on B&S lawnmowers.....

 

[Rick.]

Re: sandpaper heads

You are not interested in getting a shiny finish. You are also not interested in getting some tooth. The intent is to get the mating surface of the head as flat as possible. You want the best seal with the block, nothing more, and the block is milled to be absolutely flat (within some tolerance, naturally).

If you guys want to scratch up your heads with 100 grit paper, and pray the head gasket fills in the scratches so you get some compression, it is your motor.

Why do you think machine shops mill heads to fine tolerances. We are not working on B&S lawnmowers.....

I beg your pardon but who in this thread ever deviated from "flat" being the main objective? The fine tolerance sought after by us and machine shops is flat not toothy/shiny mating surfaces. I do like shiny cutting tools but that's just me. Rick.