J Model Piston/Cylinder Setup - AMCA Forum

I have built a few J motors over the past 15 years or so. Luckily for me I had some high quality help as I joined the Omaha Chapter about the same time and met Howard Wagner. Even though I was working on Brand X as he called it, Howard was always willing and able to offer his expertise regarding anything Antique motorcycle. He influenced me greatly. So when it came time to decide how to set up my first J model motor, it was a very straight forward approach. We’re not reinventing the wheel here. The only question was how did they do it originally? So with that in mind I went with a forged piston from Competition Distributing for maximum strength. Then a call to Hastings for some tech help which led me to a pair of 3/32” cast iron compression rings in the top lands and a 3/16” compression ring in the former oil land ring location with 006” clearance on the piston to cylinder. I’ve got almost miles on that motor now and I get about 700 miles to the gallon of oil. I’ve always ran Aeroshell 100 Straight Mineral Ashless Dispersant for oil. On a cold start, the motor has a distinct piston rattle. Upon warm up the noise dissipates completely. Spark plugs run a nice tan to chocolate hue. No noticeable smoke out the exhaust but a very distinct smell if your behind me I’m told. I’m convinced it’s the best setup for long motor life as I think the oil is key to the top end lubrication and cooling of the exhaust valve and guide. Look forward to others thoughts and opinions. Thank you for starting this, imho, much needed thread about how we set up the upper ends on our IoE J/JD (and pre-J) engines. I am looking forward to what fellow members share!
Jon Neuman did or had done the boring work of my cylinders. I am running Venolia forged domed pistons, with .005” skirt/wall clearance. The bore is straight, not tapered. Rings are the ones that came with the pistons, top two rings are the compression rings, the bottom ring is a three piece expander oil ring, so I am running a “dry” upper end, so it is not constant loss, oil accumulates in the crankcase. I have removed all the adjustment shim washers for minimum oiler output and as a result accumulate about 20 cc oil in the crankcase in 30 miles of riding at speeds of 35-45 mph. In hindsight, I would like to have set up the upper end “wet” for constant loss, however knowing nothing about these engines when i started out, I was on a huge learning curve not only getting a decent basic understanding of them as well as finding the information I could about them as well as the folks that could help me along my way. I run Phillips 66 100AD (SAE 50 weight) ashless dispersant in the oil tank and 2 ounces of Amsoil Interceptor synthetic 2-cycle oil per gallon of gas during the break in period. I now have just over 200 trouble free miles on my engine. My crankcase halves have their original baffles intact. The spark plugs are burning a light chocolate to dark tan. I would also like to make this post with the hope we can establish a concrete baseline for the upper end setup came originally from the factory. My only point of reference is the factory “Motor Repair Manual for the Guidance of the Motorcycle Repair Man.”

Per the Manual, the factory bore “tapers .003” inch,” the small diameter of the bore of a new cylinder will be found to be 3.307 and 3.308 inches. This measurement can be taken about ¼ inch from the upper end of the bore.” The Manual states “shop practice is to refer to a .003 inch loose piston fit if the small (upper) bore diameter of a cylinder is .003 inch larger than the large diameter of the piston which is at the bell or skirt shaped end.” i am assuming the tapered bore had to do with temperatures and expansion rates of the piston going up and down in the cylinder and maybe? something to do with allowing oil to work its way up the cylinder past the piston rings to get some oil to the valve stems and guides...?

I realize unless we are talking about and working with original pistons these instructions do not apply to pistons we work with today unless one has cast iron pistons available or made to order –and- most of us are not running a tapered bore or it sounds like in the case where "sswaney" is running a compression ring in the bottom land as a sort of oil control ring...? My understanding of the upper two rings, they were compression rings and the bottom ring was an oil ”control” ring, designed at least in part to allow oil past the ring in the tapered bore as a means to keep oil from accumulating in the crankcase as well as give some lubrication to valve guides/stems. The Rider’s Handbook says oil consumption is 700 mpg when the mechanical oiler is proper adjusted.

In any event, I am going to stop here because my ”knowledge” with original factory set up is confined to factory literature only and my personal experience is nil, nada, nichts, zero with a ring knocked off. As I stated at the beginning, I would like to establish a baseline of the original factory set up as well as an understanding how the oiling/lubrication “system” was intended to work when it ca me new from the factory.

I have a set of Stuart’s new repro ’29-type cylinders in the box. I am thinking I would like to, if I ever do, set them up to constant loss specs. Another person I would love to hear from is John Brookes in England, he is working on a ’20 F model, has had pistons cast from iron and if I understand correctly will be running a same as original setup.

Thanks again for starting this, imho, much needed thread! I love learning about these venerable IoE twins as I plan to ride mine ‘til I no longer can. To Steve's Point: How is everyone setting up their top ends?

I'm running the dry set up with oil rings, I mix in marvel mystery oil or two stroke oil like Steve. I have no washers left on my oil pump adjustment. UL aluminum pistons (the style with the steel support). Viton O-Rings on the bottom of the pocket and the top. 0.007 clearance on the pistons. I can push 20lbs into the intake with only leak around the valves. Valves have .004-.006 clearance on the bronze guides and .002 on the cast iron guides. No Baffles. Original large base 61" J cylinders with a sleeve in the front cylinder. Running a magneto with timing set to align all of the gear marks and then set the breaker for the rear cylinder. DLX36 Carb. Aeroshell 100 like sswaney.

I agree with sswaney that not using the oil rings may extend top end life, especially the exhaust valve. This winter I may remove the oil rings and replace it with another compression ring. Wonder what the cannonball guys saw, I feel like a small book could be written based upon their last two weeks. Yes Steve
My setup is as originally designed or "Total Loss" as its known.
Straight bored with no taper. I'm using Plumbago to seal the inlet housings. I'm currently building another J motor and regret not condsidering nikasil as an option. The cylinders were too worn for oversize pistons so I've gone with sleeving it down to 3 5/16" bore so it will be a 68 inch motor.
Interestingly my friend who does the final honing for me works in a very busy small airplane motor rebuilding shop.
We built a cylinder mounting plate that fits into their power stroke hone. They do a lot of blind hole cyclinders and their way of compensating for the natural taper which occurs in this machine when honing blind holes is to modify the honing stone sets by removing the upper half of the stone insert.

It seems to me that folks go through a lot of unnessisary effort when running oil rings. Reducing the amount of oil feeding into these motors to avoid oil accumulating in the crankcase then having to add an additive to the fuel to assist the top end cooling just seems like the wrong approach to me. It's never going to be a "modern" motor so why treat it as such?