Sand blasting gasket surfaces?

[mattyo]

Blasting gasket surfaces? I'm aware that will be a pretty obvious "don't do it!". I know the "correct" way to prepare a gasket surface but I'm curious about the theory/reasoning. I've done some research and apparently there are some people who do this all the time on car engine heads (aluminum) and don't have any problems. The key commonalities are to blast at 40-50psi and only give the gasket surface a very light "dusting" holding the blast nozzle about 8-12 inches away. What has been failed to be mentioned is the size of their blast media. I'm assuming it's small like #13 but no one has actually said. In some cases people said they would apply some spray-on copper gasket after blasting to smooth out the surface, but some people said they'd never done that and haven't had an trouble.

I'm well aware of the dangers but am curious if anyone on this forum has ever tried and what the outcome was.

I'm also a bit skeptical of the flat out "don't blast gasket surfaces" and I'll explain my (possibly flawed) reasoning. I have a parts bike and decided to blast the (parts bike) left-crankcase gasket surface (lightly) as an experiment. I didn't get a picture but that surface had some scratches in it that were in my opinion pretty deep, but the gasket still held the oil in. (Long story, I swapped engines and ran the parts bike engine this summer) The blasting gives the surface a matte finish but the depth of the graininess is not anywhere near as deep as those scratches were. One of those scratches in particular was all the way across the gasket surface and looked like it would have been leaking oil for sure but wasn't. So in my reasoning, if the gasket can compress to fill that scratch and keep it from leaking, it should be able to compress into the matte finish just fine and keep things sealed up.

One possible flaw with my reasoning is:
The oil pressure on the engine head gaskets is probably higher than on the left crankcase? I don't know that much about engines but that's my best judgment since the pistons are compressing to 150-200psi. I don't think the piston compression translates through the whole engine case. If that's true then that probably makes the requirement more stringent for a clean smooth gasket surface for the engine heads. I'd appreciate anyone to confirm/deny that reasoning.

But even if the heads experience a higher oil pressure, there are still some nasty scratches (not as bad as on the left crankcase) on those gasket surfaces that were holding oil. I guess the point I'm trying to get at is what makes a good gasket surface? Obviously the gasket is able to compress to some degree to fill in little nicks and scratches so as long as the blasted matte surface doesn't have a "graininess" that's deeper than the scratches I've observed, why wouldn't a matte surface work? I understand that over-blasting can cause valleys on the surface that the gasket cannot conform to and that would be a problem. Is that the point behind not blasting? Because it's too easy to create those valleys that the gasket cannot conform to? Or is there something about the matte surface that gaskets don't like? I don't know, I'm just curious about this.

[gmck]

very likely if you could blast perfectly even. there would be little problem. but a gasket surface has to be as flat as possible. if you blasted a. bit more here or there the gasket would be weaker in places because of weakened clamping pressure. also blasting tends to round off edges, making the clamping surface a bit smaller. Bottom line, might not bother but might. why take the risk. prepare the surfaces as clean and flat as possible, use appropriate sealer and gasket and torque correctly and you have the best chance of a leakless gasket for a long time.

[tubes_rock]

I agree with gmck. Blasting is not likely to cause leaks, so long as it's uniformly done and done in an area with a standard paper or rubber gasket. An eare with a metallic gasket (cylinder heads, etc) will probably give you grief.

That being said, I will caution against it for a more unlikely reason: future disassembly. A matte surface will bond with well over double the bonding force of a smooth surface. If you've ever removed a 20-year-old gasket from a machine, you know it's a bear to do. Cleaning the surfaces afterward is cumbersome at best. You make those mating surfaces matte prior to assembly and I would dare say those pieces are bonded for life.

--Justin

[Earthling789]

Originally Posted by tubes_rock

You make those mating surfaces matte prior to assembly and I would dare say those pieces are bonded for life.

--Justin

Agreed ^^^

I've had to clean gaskets from poorly machined surfaces before = NO FUN!
I would imagine a matted surface would hold that gasket in hundreds/thousands of pores per square-inch, which means more blasting if you ever had to remove it.

I've never had to do this myself, but I can remember my dad filling scratches or chips in mating surfaces (when rebuilding car/truck engines) with JB-Weld, if the scratch or chip was too big for the gasket to fill on its own, that is.... Apply a drop or two, smooth as best you can while "wet" (leaving excess is better than not enough), let harden for 24-hrs (will shrink a bit), sand/file/grind back as smooth as possible to the rest or the mating surface. I've even seen him use a polishing pad on a drill or dremel to "shine" a surface before re-assembly.

[jpr1968]

The biggest problem I see with blasting a head is that you could wear the whole surface down and not realize it. Could be a good thing as it could increse compression but you could never get it even not matter how careful you are and you would also decrease the distance between valves and pistons. How hard is it scrap a small head anyways. It not like it takes a long time.

[mattyo]

Originally Posted by gmck

why take the risk. prepare the surfaces as clean and flat as possible, use appropriate sealer and gasket and torque correctly and you have the best chance of a leakless gasket for a long time.

Agreed, I just have a load of gasket surface to clean up and I'll be sand blasting the exteriors for a new paint job anyway and figured maybe I could prep the gasket surfaces while I'm at it.

Originally Posted by tubes_rock

That being said, I will caution against it for a more unlikely reason: future disassembly. A matte surface will bond with well over double the bonding force of a smooth surface. If you've ever removed a 20-year-old gasket from a machine, you know it's a bear to do. Cleaning the surfaces afterward is cumbersome at best. You make those mating surfaces matte prior to assembly and I would dare say those pieces are bonded for life.

Yeah, that's a very good point. That hadn't crossed my mind.

Originally Posted by Earthling789

I've never had to do this myself, but I can remember my dad filling scratches or chips in mating surfaces (when rebuilding car/truck engines) with JB-Weld, if the scratch or chip was too big for the gasket to fill on its own, that is.... Apply a drop or two, smooth as best you can while "wet" (leaving excess is better than not enough), let harden for 24-hrs (will shrink a bit), sand/file/grind back as smooth as possible to the rest or the mating surface. I've even seen him use a polishing pad on a drill or dremel to "shine" a surface before re-assembly.

Thanks for that info earthling. That's definitely going down on a mental note for gasket prep.

Originally Posted by jpr1968

The biggest problem I see with blasting a head is that you could wear the whole surface down and not realize it.

Yep, it's pretty easy to blast away a few mils of aluminum. Definitely don't want the 750cc to turn into a 745cc. Also would have to start worrying about piston clearance. Not good.

At this point the most detouring information was how the gasket might stick TOO well to the matte finish and make it very very difficult to remove in the future without having to blast it again. Which then means a little more aluminum is lost and then the head clearances start to become, well, not clearances anymore.

Well, has anyone ever tried this copper spray-on gasket stuff to smooth out a surface. A few people on the auto forums said that after they blasted the engine head they would spray on this copper gasket to make the surface smooth again. If you haven't noticed, I'm trying to be as time efficient and lazy as possible. Sand blast the surface, spray on some copper and BAM, done.

[93gc40]

Seems to me the most efficient and lazy way to do the job is to do it correctly using correct materials. Takes alot of extra effort and time to redesign and engineer your bike. Even more time and effort, if said redesign doesn't work. Use the correct gaskets and gasket materials and installation methods. In theory you could use a spary, if you can get the coating thick enough and even enough to mimic the thickness of the stock gasket. Gasket thickness has affect on clearances.

[jpr1968]

Originally Posted by mattyo

Agreed, I just have a load of gasket surface to clean up and I'll be sand blasting the exteriors for a new paint job anyway and figured maybe I could prep the gasket surfaces while I'm at it.


Yeah, that's a very good point. That hadn't crossed my mind.



Thanks for that info earthling. That's definitely going down on a mental note for gasket prep.


Yep, it's pretty easy to blast away a few mils of aluminum. Definitely don't want the 750cc to turn into a 745cc. Also would have to start worrying about piston clearance. Not good.

At this point the most detouring information was how the gasket might stick TOO well to the matte finish and make it very very difficult to remove in the future without having to blast it again. Which then means a little more aluminum is lost and then the head clearances start to become, well, not clearances anymore.

Well, has anyone ever tried this copper spray-on gasket stuff to smooth out a surface. A few people on the auto forums said that after they blasted the engine head they would spray on this copper gasket to make the surface smooth again. If you haven't noticed, I'm trying to be as time efficient and lazy as possible. Sand blast the surface, spray on some copper and BAM, done.

Seems to me that you want to screw that engine up. Do it the right way and get it running right. Do it the wrong way and take extra to time to repair your F&*k up the second time. For the short cuts you want to take you mught as well take a sledge hammer to the engine now and save yourself all the added problems you want to create.

[mattyo]

Originally Posted by 93gc40

Seems to me the most efficient and lazy way to do the job is to do it correctly using correct materials. Takes alot of extra effort and time to redesign and engineer your bike. Even more time and effort, if said redesign doesn't work. Use the correct gaskets and gasket materials and installation methods. In theory you could use a spary, if you can get the coating thick enough and even enough to mimic the thickness of the stock gasket. Gasket thickness has affect on clearances.

Point taken. I had the impression that the copper spray was just to smooth out the blasted matte finish and they still used a stock/aftermarket gasket, not just the spray as the gasket. You still have to factor in the loss of aluminum from the gasket surface as an overall downside to blasting but I'm still curious about the effectiveness of said method.

Originally Posted by jpr1968

Seems to me that you want to screw that engine up. Do it the right way and get it running right. Do it the wrong way and take extra to time to repair your F&*k up the second time. For the short cuts you want to take you mught as well take a sledge hammer to the engine now and save yourself all the added problems you want to create.

Would you suggest a copper sledge hammer? Don't get me wrong, I like shortcuts but I still want them to be effective shortcuts, hence why I'm questioning traditional gasket prepping and also the methodology behind blasting. It has been done before and it has worked so I'm curious why it works for some people and others strongly oppose it (even though they've never tried it (generalization)).

[Schattenreiter]

One thing to note. If you decide to blast any part of an engine you need to make absolutely certain that you clean out all of the blast media. Engines have all kinds of nooks and crannies that can hid residue from the blasting process. This will be a very bad thing when you reassemble the engine.