Question about Mastermind cylinder cleanup method

[RIDE-RED 350r]

Well, I'm going to be starting on my 394 overhaul after the holidays. I have not yet torn the saw down but I happen to have a spare 394 cylinder on the shelf that had some transfer and thought I would clean it up.

I made an arbor from a 1/4" bolt with a slot cut in it and the head hacksawed off and chucked it into a pneumatic die grinder. I wound some 120gr strip sand paper up in the arbor and largely it worked very well. BUT, as I was working around the exhaust port where all of the transfer was, I noticed that the sandpaper was enlarging the exhaust port on one side, the side the paper would drag out of. It actually looks like some nice, albeit excessive port window tapering. My concern is that I'm going to have to match up the other side with a burr and I have seen it said that one must use caution when thinking about widening the exhaust on the 394. I was also wondering what I'm doing wrong to cause that alteration of the port window?? I was able to remove all but a tiny tiny bit of transfer just above the port on that same side. It is almost gone but still visible, but cannot be detected by the fingernail test. This is the second time I have cleaned a cylinder using this method and had this result of altering the port window on one side as a side effect of the operation. Is this a problem or am I overthinking it??? I'm sure I can match it up and even things out with a burr, but how does one prevent this if widening the port is not intended to be done??? I wonder if I need a reversible grinder to avoid this... Maybe muriatic acid is the better method for me??


Thanks

Pics show both sides of exhaust port for comparison.. I'm afraid I just ruined my cylinder..

 

[stihl saws]

My first thought is the die grinder may be too fast. Or too much paper in the arbor. I've used a cordless drill with good success.

 

[RIDE-RED 350r]

Good points, but our die grinder can be turned down, which I did. I wound about a foot of sandpaper loosely in the arbor.

Maybe me and my OCD screwed me here. As I was getting the pics I took a second look at that little tiny bit of transfer I left, it really is pretty insignificant. Maybe I just pushed the issue too much trying to get that last little bit of transfer?

 

[tree monkey]

I think you over did it just a bit. yes you will have to match the other side if the skirt will cover it

 

[Jon1212]

I made a mandrel from a wood dowel(to prevent galling), and used automotive wet/dry paper starting with 120g and working my way to 800g. I kept the pressure very light, and my max rpm was 750.

 

[stihl saws]

I'll be the first to say it's very scary the first time you do it. My mandrel is brass and I use a very light touch.

 

[RIDE-RED 350r]

OK, I think RPM may be my issue. While the die grinder can be turned down, I'm not sure it will go that slow.

Thanks for the replies fellas.

 

[tree monkey]

don't throw it away, you can always have a custom piston made

 

[Mastermind]

Looks like you cut thru the plating pretty bad.

 

[David Young]

I think this shows how much you can do and really not hurt anything. I am +1 on the wood dowel.

 

[exSW]

I'm in the wood dowel camp also.

 

[Czed]

I use a bic pen with a slot about two inches deep emory or sandpaper with a cordless drill I'm always different.
The white ones without the gut's in it.

 

[BigRed96]

I use these chucked in a drill and use wd40. I have done a few using these and if there's any transfer left I finish it out by hand. The biggest one I have is probably an inch and a half. Even on high in a electric hand drill the speed is relatively slow so your chances of doing damage is very slight.

 

[PogoInTheWoods]

I use a piece of aluminum hydraulic/brake line with a slit on one side only with the end of the paper rolled up inside to keep it from flapping out. 'Bout a 5 inch piece of brake line chucked into a variable speed 3/8 DeWalt drill with 1 1/2 inch wide 120 grit welder's / plumber's paper for the initial session. It's aluminum oxide paper and both loads up and breaks down fairly quickly so you can't get too aggressive with it for very long. Going slow you can really lean into it without it getting away from ya and damaging the plating unless there's already some pretty obvious flaking. Shouldn't be able to get through NiSi even with 80 grit if you go easy in the beginning to get real nasty stuff. You'll know fast enough if the plating is trashed. I can't believe that port got so weird so fast, but high grinding/sanding rpm's without pinpoint control can obviously be quite unforgiving before ya know it. I've screwed up with a Dremel and a 3M 120 grit flap wheel before I barely even got going one time. Learned a lesson on that one.

 

[Al Smith]

You didn't fork it up I don't think .However just as an opinion you'd be better off to do like Randy with 3M
scotch bright than sand paper .And use some kerosene or something,don't ever do it dry

I got in a hurry once and used too course of a flap wheel,never again.It's not a race .

 

[jake wells]

a brush hone works well using brake cleaner also.
i do that to break the glaze in the cylinder.

 

[angelo c]

Wood dowel for me. Makes sure I don't use too much pressure. It just snaps if you do. I buy a bunch of different width to drive out wrist pins anyway. Use a Dewalt cordless. Sometimes I'll chuck the dowel in the drill press slow as well.

 

[Al Smith]

I do not hone them .Only a little swipe Scotch bright .I have a Lisle precision hone with hard stones for plated cylinders but the only thing I've used it on is cast iron McCullochs .That plating is only a few MM thick and it doesn't take much to eat right through it . If the cylinder is eccentric given enough time the rings will seat in .Best thing to do is clean it up and run the snot out of it . It will either come or bleed .If former comes before the later it will run better than factory fresh .Extremely tight is good in some situations but delving into that would be TMI .

 

[Magic_Man]

I think you just got too aggressive with it. Only use as coarse of a grit as is neccesary and only as many rpm's as necessary. Stay away from the edge of the ports or you will eat the plating like you did.As mentioned above last I knew Randy was using scotch brite balls instead of paper on a mandrel.

 

[Mastermind]

I use both. The key is to stay away from the port edges.