HarleyTechTalk

Hey all , bought Vtwins New manufactured Standard Barrel Piston and Ring Kit for my 51 Panhead FL 1200 which has STD Panhead cases so an upgrade on the old originals !
 I pulled the whole engine down, split the cases and resealed and put them back as they had a minor oil seep down the bottom of the cases while waiting for the piston barrel set to turn up which was a month later as i'm Australia .
When they did arrive I proceeded to install them , got piston on the conrods all went well so I hand rotated the piston and crank gently and when one of the pistons got the bottom and in no uncertain terms it just stopped , having a better look I realised the bottom of the piston had contacted the flywheel therefore I realised they bigger then my originals that already packed away not thinking a have to cross check them with the new ones , should never assume ..
Long story short I need to buy new pistons now with right length size like the ones I removed from it , i've added a few pics of my new and old pistons with a manual micrometer as I can't find my digital ones ..
Any suggestions as to what piston's of the correct size length wise would be much Appreciated . I'd like a quality brand of pistons .. Ring wise I have Hastings rings waiting to be instal with spiral circlips !!

New Piston

New Piston

Old Piston

Old Piston

Old Piston

 

What's the brand and part number of the pistons that were purchased?

You are measuring from the wrong reference point. For pistons the center of the wrist pin is where all measurements are taken from. Your measurement from the end of the skirt to the top of the dome is irrelevant. What is relevant is from the center of the wrist-in to the end of the skirt and from the center of the wrist pin to the compression deck. In this case that is the flat surface at the base of the dome. The dome height has relevancy but only as far as compression and valve to piston clearance goes. Nothing to do with the issue you are having. 

I bet a local engine machine shop can machine the skirts of the pistons you already have. Of course, once the skirts are cut and you mock up the engine there may be other issues that present themselves.

Do you have the numbers for your bore and stroke? It looks like the new pistons are for a shorter stroke crank.

As above measure stroke. If Stock I have fitted Wiseco pistons . They fit 74" pan and shovel. Not a fan of Vtwin parts. S&S or stock for me 

If the flywheels looked like stock HD parts, you may have 80" flathead wheels in it. That was a cheap and easy stroker kit way back when.

It might not matter in this particular case, but IMO plastic calipers are for wood working.
Good advice about checking flywheels might be 80".

I believe the 80" wheels were smaller O/D.  Installing them required building up the scraper boss in the case to prevent over deflection / slinging of oil up into the cylinders. The extra stroke required stroker plates to lift the barrel so the piston didn't hit the head but they did clear the wheels.

It may just be the camera lens but the pistons appear to be different diameter size.  The compression dome is taller too.  Do they fit the new (or old) barrels? Wrong pistons? 

QuoteI hand rotated the piston and crank gently and when one of the pistons got the bottom and in no uncertain terms it just stopped

Funny thing, this same thing just happened to me on a 1200 Shovelhead with new V-Twin pistons. They forgot to chamfer the skirts at the bottom for piston to piston clearance. I sourced another set from Drag Specialties. The DS pistons did have the proper clearance chamfer, and the problem was solved.

Out of curiosity, I checked all of the 1200 Big Twin piston kits in the parts storage room. None of the V-Twin kits had that little chamfer, but pistons from a different source did. All of the pistons have the same "JCC" logo cast on the inside.

I'm going to set up my piston fixture on the mill and cut them all while I'm thinking about it. That would be faster and easier than trying to get a return authorization, boxing them up, and shipping them back.

OP you still there?

Quote from: JSD on July 30, 2024, 10:18:27 PMOP you still there?

I noticed he had been absent too.  He posted for a solution on July 6 and hasn't been active on the site since 3 days later on the 9th.  This is another 22 days since then.