Reusing the Original Pistons, etc. ???

[danf19]

I've been asking a few questions about rebuilding a 1917 excelsior motor . I have nice resleeved (I was told) cylinders measuring 3.3545" (measured by myself using a bore gage). I also have a few original pistons 3.3285".
a few questions...
1) why not use the original pistons assuming they are crack tested and checked over. how about the rings and pins ?? Im not sure if I have a complete set of pins , wristpins etc. If either rings, or pins, wrist pins etc should be replaced, can anyone recommend a provider ??
2) are the cylinders the original bore size ?
3) would the pistons have the proper tolerances for the cylinders ??
4) Since all else is original , I assume I would not have to rebalance the flywheel and be concerned about where to remove the weight- only true it ??
5) this will only be a rider and don't plan on any grueling rides like the cannonball.
your thoughts ??
thanks and stay safe,
Dan

[gharper]

Dan,

I doubt that your cylinders are re-sleeved, picture of that?

If your bore and piston measurements are correct, that is way too much piston clearance, .026". Sure, the motor would run but it would sound like hell, lots of piston slap there! As I've mentioned before, HD UL pistons work well. That standard bore is 3.3125, or 3 5/16". I've done all the math and using a +.020" over UL piston will fit a standard bore X cylinder that gets honed about .005" oversize. The compression height is the same but the HD wrist pin is larger. That can be used by boring and honing the X wrist pin bushing to fit the new pin. You will also need to increase clearance inside the piston a bit for side play of the rod.

If using UL piston, bore sizes should be as follows, giving about .005" clearance for each oversize.

Piston size Bore
Std 3.310"
+.010 3.320"
+.020 3.330"
+.030 3.340"
+.040 3.350"
+.050 3.360"

Based on this, I would get +.050" pistons and hone your cylinders about .004-.005" OS. If you don't want to hone, guess you use +.040's and listen to it knock.

Also, you will never find any original pistons bigger than .+020" OS. X didn't even offer oversize pistons until 1920, and then only in .005. .010 and .020 OS.I always thought they were too thin to bore bigger than that but not true. I know one cannonballer who successfully went all the way and still rides the bike with =.060" OS high compression pistons.

Yes, you will need to re balance the motor......

I'm currently dealing with pistons right now on my 24 X. I"ll be using EL pistons and the numbers above are exactly the same, as EL and UL bores are the same. Of course using EL pistons will raise compression significantly. I did volumetric measurements and calculated the stock X compression ratio at 4.4/1. Using an EL piston gives 5.45/1 compression. That and a new cam will make the old X wake up and go down the road much better and should also increase fuel economy. Building this bike for a cross country trip in 2021.....

Gene