Smooth Engines


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The following comes from a recent topic on SmokStak, which can be found on the Internet at: smokstak.cgi. As ever, various individuals started, commented on and concluded the following bulletin board thread.

Visiting the Coolspring power museum in Pennsylvania a few years back, I noticed that most of the engines there looked smooth and free of any pitting from rust. I was wondering how they make the parts look so good and smooth; do they resurface the parts or put some kind of filler on them, or just a really good, thick primer? - Tanner

Most likely they grind the castings smooth using a floppy type grinding disk and then apply body putty over that. Then they use fill coat primers followed by several coats of paint. As always, the important work comes well before the pretty paint. - Doug

I'd advise not putting too much effort into smoothing cast iron engine parts. Some engines do end up more pitted than others (due to the elements), but original cast iron is supposed to have a somewhat rough look and feel to it. Its slight imperfections are what make cast iron from the olden days stand out as original. Casting outfits these days remake parts a little too perfect.

I've seen many engines that have been sanded and smoothed down to where the cast iron looks like glass. This is about as far away from original condition for the engine as you can get. When these engines came off the factory line the cast iron didn't look and feel like glass! In my opinion, engines that look like this have greatly decreased value. These days, collectors want engines in original condition. An engine that is over restored is not original and it will not have the same value on today's market.

I've been to Coolspring, and I'm not sure why some of their really old/rare engines look so smooth. I do know they are mostly restored and came from a single collector, so maybe that person did a little over restoration. However, when you walk around to the rest of the buildings, you'll see many of the engines are in original, unrestored condition and they have that slightly rough casting.

In my opinion, I'd highly advise against doing what Doug mentioned unless your engine has severe pitting you want to get rid of. I believe there is nothing more damaging to a historical engine than over restoring it to something it never was. Put on too much primer, put on too much paint, but don't grind down that original roughness and putty the whole thing up. You can always recover an engine from too much paint, etc., but you can never bring back the original surface and feel once it has been sanded and ground away. - Jeff

I have an 8 HP Field Brundage engine I bought 35 years ago. At that time the thought was to sand blast down to bare metal and start over. I wouldn't do that to that engine today, as it had a lot of original paint, even though it did have a tapped hole in the hopper for 1-inch pipe to circulate water to another tank. The original finish was smooth, and while sand blasting it you could see a thick layer of some type of filler used to fill in casting imperfections. This was a quality engine, and I think most engine builders made some effort to turn out a nice looking product. I took the effort when I restored this engine to fill it and sand it, and it looks smooth, just like it did originally. Don't be too quick to judge. -John

'There is nothing like an old engine all slicked up sparkling and bright. I just stand there in amazement as to all the hours of labor it took to get it that nice looking,'

There is nothing like an old engine all slicked up sparkling and bright. I just stand there in amazement as to all the hours of labor it took to get it that nice looking. That's on top of what it has taken to mechanically restore it. My engines start out all slicked and shiny and I even use car wax on them, but they don't look like that for long because I like to run them. That's another reason I like them slicked, they clean up easier. - Ken

I have never been to the Coolspring museum, but I have seen some pretty big engines (100+ HP) and one thing they pretty much have in common is they were used inside to power cider presses, line shafts, pumps etc., and they were permanently mounted. With that said, it is easy to why they wouldn't have any pitting after having spent 75 to 100 years sheltered compared to an FM Z that spent the last 40 years out in the fence row. Other than casting roughness, these sheltered engines would appear pretty smooth. - Keith

I have never seen an engine in original, unrestored condition with castings so smooth they looked like glass. However, I have never heard (or considered) that original manufactures took the time to putty up their engines to make them look smoother. I have seen many an engine with 90 percent original paint, stored inside all their life and with little wear, and they all have a slightly rough look and feel.

We have a 6HP Mogul that most likely never sat outside. It has smooth flywheel surfaces and the oiler and gas tank look like they were just riveted yesterday, yet the flywheel spokes, hopper, and base all have a slightly rough feel. We lightly sanded and brushed off the old red paint (even saw slight remains of the original pea green paint), applied a light solution to clean off the dust, and then put on primer and a few coats of paint. The engine looks great, yet it doesn't feel as smooth as glass.

I think there might be a mix up about what degree of smoothness we are talking about here. Original castings are all pretty much smooth, but they also have a slight roughness to the touch. I don't think the surfaces should be as smooth as glass, and I also can't imagine that many companies put on a layer of putty over their castings before painting. Of the 100s of engines I've seen, touched and restored, I've only seen a few that were restored and looked and felt as smooth as glass - and in my head I thought the engines couldn't have originally been like that. - Jeff

I also prefer the original cast look. Remember the 'help with Simplicity' thread that ran March 1? Take another look at the picture - the black areas have a thick putty-like filler over a very rough casting.

In the grease protected areas, the paint is almost automotive smooth over this filler, and on the base flange where I cleaned away some of the grease you can see the original dark olive paint.

I'm using a side grinder some places and a sanding disc in others while trying to retain the best cast appearance. This experience tells me that maybe the engine builders did use filler to cover rough castings. - Ralph

I agree with both sides -most engines are best restored back to original condition. For example, I wanted the little Ironwood I just finished to look like it did when originally finished by some young boy at Ironwood High School. I did remove the forging 'frost' that was under the original paint prior to repainting and I removed most of the pattern tabs, however. Even the hopper opening is rough and irregular and it will stay that way. In this case it is part of the history of the engine. The builders were not professionals and the engine reflects that. Some of the expensive engines - including many sideshafts - had a fancy factory finish and should, in my opinion, be restored accordingly. - Dean

Some manufactures did not take any pains removing flashing or pimples, and most engines I have collected needed some sanding and filling. When I restore an engine, I finish what was probably a production process of cleaning flashing and grinding high spots. I do use body filler to slick the finish up, and my reasoning is that it makes the engine easier to clean and highlights the lines the engine manufacturer designed into the engine. If you look at some of the old ads the engines appear clean and streamlined, while in reality they were not. Looks sell, and I like to see a smooth, streamlined engine. If people take the pains to do that, then normally they are as meticulous about the mechanical restoration. I don't collect engines to sell, so If I buy it, it's because I'm going to keep it. I do slick mine up a bit, but not like a new car finish. I'm going to keep doing it, too, but to each his own. Our main objective is to preserve these engines. - Pat

'I have never seen an engine in original/ unrestored condition with castings so smooth they looked like glass.

The above messages and many more can be found by visiting SmokStak on the Internet at

SmokStak is an engine conversation bulletin board with over 46,000 messages on file and is part of the Old Engine series of web sites that started in 1995 as 'Harry's Old Engine.' Harry Matthews is a retired electronic engineer and gas engine collector from Oswego, New York, now residing in Sarasota, Florida.