1929 JD- Getting Ready To Fit Pistons To Cylinders

[JC Hixon]

Greetings-

I've got my '29 JD cylinders at a machine shop and have been researching pistons. I've been told that VL pistons will work ok if the skirts are trimmed down to clear the crankcase baffles. I haven't found a source for cast VL or JD pistons yet. Competition Distributing sells forged JD pistons for $300 a set but the standard bore size listed on their website doesn't correspond with the bore size listed in the Service Dept. Bulletin Volume 1 book I've been studying. The correct piston size can be selected from their list but why would they change the original bore size to something other than what Harley's factory service book has listed and make it more complex than it has to be? The cylinders I have were .030 over and had a set of +.030 steel pistons with them. If the bores hadn't been so pitted I would have tried running them.

I did a search for related threads in this forum but couldn't find any.

If anyone would like to recommend or warn against certain sources for pistons I'd be interested in reading your opinions. -Jim

[Steve Swan]

i sent my 27 cylinders to Jon Neuman for him to fit Venolia forged domed pistons he ordered from Venolia, 180 miles so far so good, and as i've mentioned in previous posts, i am running a "dry" engine. i don't know what you mean by "correct finished bore size can be determined and the correct piston set selected." my cylinders were standard bore, Jon took them to the minimum o.s. to fit .005" o.s. pistons. i don't know as much as some folks on this forum, but i am pretty sure you want to bore your cylinder to fit the smallest available o.s piston. i may stand corrected, but the factory, back in the day, ran "wet" motors or constant loss, and part of the "wet" equation was a tapered bore in the cylinder, and no actual oil ring on piston, in part to lubricate the cylinder wall to prevent seizure and to lubricate the valve guides/stems. i don't know if this has anything to do unrelated to what Comp.D is doing with their piston sizing, but as i understand it, Comp.D pistons are run with "dry" motors and the bore is cut to fit their piston sizes. i don't know anyone who is running a tapered bore, i know John Brookes is having cast iron same as original pistons in his 20, so i am guessing he is running a tapered bore. anyone please feel free to correct me, as i will always be on a learning curve here on this forum.

[JC Hixon]

i sent my 27 cylinders to Jon Neuman for him to fit Venolia forged domed pistons he ordered from Venolia, 180 miles so far so good, and as i've mentioned in previous posts, i am running a "dry" engine. i don't know what you mean by "correct finished bore size can be determined and the correct piston set selected." my cylinders were standard bore, Jon took them to the minimum o.s. to fit .005" o.s. pistons. i don't know as much as some folks on this forum, but i am pretty sure you want to bore your cylinder to fit the smallest available o.s piston. i may stand corrected, but the factory, back in the day, ran "wet" motors or constant loss, and part of the "wet" equation was a tapered bore in the cylinder, and no actual oil ring on piston, in part to lubricate the cylinder wall to prevent seizure and to lubricate the valve guides/stems. i don't know if this has anything to do unrelated to what Comp.D is doing with their piston sizing, but as i understand it, Comp.D pistons are run with "dry" motors and the bore is cut to fit their piston sizes. i don't know anyone who is running a tapered bore, i know John Brookes is having cast iron same as original pistons in his 20, so i am guessing he is running a tapered bore. anyone please feel free to correct me, as i will always be on a learning curve here on this forum.

Thanks for sharing that info Steve. I'm wanting to run flat top pistons to keep the compression ratio low. Those old castings can get weak with metal fatigue so I want to stay as close as I can to stock specs and keep stress levels to a minimum. I've discovered since posting this thread last night that ULH 80 pistons have the correct o.d., wrist pin size and piston height for JD cylinders. My cylinders are going to be very close to 3 1/2 inch ID after being bored.

[DanM]

You may be done, but I obtained VL piston s from Harbor Vintage. I recommend getting a list of available piston sizes from the supplier, then work with the machine shop to find the smallest clean up bore, then order the pistons.

I am running the Comp Distributing pistons which are forged, and 3 ring including oiul scraper ring. I set the engine up at .008" piston to wall per Comp dist. The VL pistons are a little tighter. With oil rings too.

I am not sure the comp dist compression really results in anything........

[Steve Swan]

i would suspect running a domed piston is somewhere in the equivalency of a Rici chip....? Jon told me the basic difference is the engine will not idle at a the lovely "chuff-chuff-chuff-chuff" rate, and the engine will have a little more get up and go. i'm glad i went with domed, as i like the acceleration i have, and hill holding power, but then i have nothing to compare my engine's performance to.