Jules’ favorite bike 1928 101 Scout

[gharper]

Joe,

I wouldn't worry about different size pistons, the engine won't know or care. I would however, do the best I could to get the total piston assemblies the same weight. That will help your balance issues and make the engine a bit smoother. You can often remove some material from the underside of the heavy piston if the tops are thick. Otherwise, add some lead weight into the center of the wrist pin on the lighter one as needed to get them equal weight.

I had many long discussions with George Yarocki about oil control rings. He was adamant about not using them. His argument was "These engines were designed to burn oil so the top end gets lubrication." I disagreed, arguing that the early engines burned oil as a consequence of the design, Good oil control methods hadn't been figured out yet. In my mind, if burning oil is such a good thing, why do modern engines go to such great lengths to prevent it? Oil burning in the combustion chamber is not good, it leaves carbon deposits which break off and move around, causing damage to the bore, pistons, rings etc. Also builds up on the exhaust valve stem and can stick the valve open. I've always run cast iron oil control rings with cam ground aluminum pistons. Over the decades I've put an honest 15,000 miles on my 24 Chief w/ sidecar and 5000 on my 24 Excelsior. They both will use less than 1 qt of oil in 300 miles, most of which I dump out at every gas stop and reset the level in the crankcase. It's cheap insurance to dump a couple ounces of oil every 75 miles or so. I fit the piston clearance on the Chief (3 1/4" bore) at .0065". The Excelsior I fitted at .006". These numbers are for cam ground pistons, which Indian didn't have back in the day.

Of course oil control also needs to be managed at the oil pump. With Oil control rings, the mechanical pump needs to be turned way down, unless your engine is leaking all over the place! This is another reason to change oil every gas stop. The small amount of oil in the engine does a lot of work and breaks down quickly, so replacing frequently is a good idea. I like my engines tight and clean, I hate oil leaks! Good oil control rings and proper pump adjustment go a long way here, plus I put a lip seal on the magneto gear...

Hope this helps.

Gene

[FLFD7]

I agree, and I wouldn’t mess with the .020 over cylinder. But if I got a set of .030 cylinders that’ll work makes sense to use them.

[T. Cotten]

Seriously, Joe,...

Jules knew that the motor doesn't care if the cylinders are the same bore.

Hogging one out to match the other is a waste.

....Cotten

[FLFD7]

Just some pictures comparing the pistons…
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Notice how thick the original pistons are, and the later pistons a bit taller.

The recommendation in the 101 R&O manual is to use the later pistons and all three compression rings but either leave off the oil ring or use the oil ring but leave a big end gap. Since Jules used the oil ring on both these motors that’s what I’ll do.

[FLFD7]

One note is that the black painted cylinders had original 101 pistons. They have two thick compression rings and no oil control ring (total loss oil). They also are sized for .010 clearance in the bore for aluminum pistons as opposed to .003 clearance for the later Sport Scouts. If they were iron pistons, then .003 clearance.

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So the original pistons measure .007 smaller then the later ones.

[FLFD7]

But wait, there’s more…

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Not only did Jules use two different pistons, they are different size bores…ugh. The front cylinder .020 over, the rear cylinder .060 over. C’mon man…..

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The cylinders originally on the bike are .030 over.
I have another set of cylinders that also measure .030 over and look to be in better shape.

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They look good but have been painted black. I got another set of cylinders that the .030 pistons drop right in but the .060 piston doesn’t, so they are either .040 or .050 over.
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So I’m going to mull over what to do. I don’t want to bore the spare motor front cylinder to .060 over, if nothing else but for time and expense. I’m leaning to using the black painted cylinders, I have new .030 over pistons, but no rings (I looked and Greer out of stock on all the Scout pistons and rings).

[FLFD7]

Well, I pulled the cylinders to see what’s what and, well, not great news… IMG_2267.jpeg IMG_2269.jpeg

Yep, two different pistons…

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On the plus side the bores looked good, no gouges…
But on the bad side….

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A lot of rust, so this gotta come apart, something I was hoping to avoid. I’m guessing this spare motor was under water at some point, just like the bike.

Sigh….its always something….

[grease monkey]

I remember seeing that beautiful sidecar at Brookfield several times At the time it looked like it was new old stock and had just been uncrated. .
Interesting to read the story. Good luck with the refurbishment.

[FLFD7]

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