Reboring & Finishing a Cylinder at Home

[Frank Martin]

I have an old Lauson RSH that I've finally gotten all of the parts for that I need in order to restore/rebuild. I need to bore out the cylinder to 2.020" to accomodate the .020 over rings and piston I will have. Originally, I anticipated only going .010 so I had a local vo-tech bore it out that far but as it turns out, the only parts that I could find were .020. The kid at the vo-tech used a milling machine and a brake cylinder hone, much like the average guy could do at home with a drill press. I'm sure that there is a better way to do this, even at home. I tend to be a perfectionist and consequently, I want it done correctly. However, at this point I also think I'd like to do it myself as opposed to farming it out to a machine shop. Does anybody have any thoughts regarding how I might pull this off. I am willing to invest in some tools and or equipment if necessary and although they might only see limited use on this project, I'm sure I will get much more use out of them on something else later on.

Thanks,

Frank

[cabinetcrafter]

Sure you can do this at home, You can find a boring bar , I gave about 450 for my old model F, then you need a good rigid hone, thats another 100. You still need a way to support the engine block and hold that heavy boring bar on top so unless you have welding capabilies add that to the expense. In other words, to get a first rate job, take it to a machine shop. There are loads of shops that specialize in small engines and bikes. They can do the job, it will be accurate and quick, well accurate thats for sure maybe not on the quick part. Save yourself a load of grief and sub it out.

[Peter]

There are vendors right on this website that will make custom rings to any size. The 20/1000 over piston can be turned down 10/1000 much much easier than boring the cylinder out. if you dont have the lathe to turn down the piston, then you are probably over your head in the boring dept. I imagine the trade school could turn down the piston and get a perfect fit for you.

But, if you just want to do it for the experience of doing it. You can uses a sunnen hone and no problem removing 10/1000 from the bore. this is a legit professional (aka proven) method. The hone can be setup in a drill press, that might be how the trade school did it. The hones are expensive, perhaps a good item to have if you want to make some engine friends.

The beauty of the sunnen hone is that they are made in sizes to handle the big bores like 10 inch diameter and if careful and patient the hone can be run off a big hand held drill.

I never used the sunnen hone, this is what some engine friends told me at one of the shows. very reliable sources, with some big engines running to backup the advise.

[Frank Martin]

I watched the kid at the vo-tech do it and he used one of those little flexible brake cylinder hones that KD Tools makes and while I appreciate his effort, I remember thinking that I was hoping for something a bit more professional as I could have easily done the same thing myself. While the brake cylinder hone is good for its intended purpose, I'm sure it leaves quite a bit to be desired as a tool to be used for overboring a cylinder for an internal combustion engine. It has always been my understanding that overboring and honing are two separate operations. Boring removes a substantial amount of material and enlarges a cylinder to a uniform shape very near its final dimension while honing removes only a small amount of material to create a fresh finish to aid in ring seating on a cylinder that will not be overbored during a rebuild or to finish a cylinder that has just been bored or overbored. I haven't actually measured it but I'm sure that the cylinder is still tapered or out of round to at least some extent because I don't think a flexible hone would fix those imperfections. I suppose it would be possible to use a hone for the entire operation, but it would have to be a rigid hone as opposed to a flex hone.

I can cut and weld as need be. Where is a good place to look for a boring bar and what does it look like/how does it work? The bore on this engine is only 2" so I shouldn't need anything terribly big. I do have a lathe, and theoretically I could turn down the piston, But I'm hesitant to remove that much material from such a small piston and also doubtful that I could reproduce the taper that the piston is supposed to have from top to bottom.

[J.B. Castagnos]

Get a Sunnen hone for this job. The Sunnen is a precision tool, it will leave a true hole with no taper. Trying to bore .010 is pretty tedious, you're going to bore .008 and hone .002. This leaves .004 on each side, not much room for error. You'll need a Sunnen Jr. for this small bore, a set of 100 grit stones used dry will remove stock in a hurry, finish with 400 grit wet. I have my fathers Sunnen hones, he was in the outboard-lawnmower business, this is all he used for reboring. I bored an Aermotor headless engine .060 over with this and it went well. I've seen the Sunnens on Ebay, check there.