Overbore pistons for HD 4.060 cylinders.

[838]

How much can the HD 4.060 cylinders be bored, and who makes overbore pistons for these cylinders? Thanks!

Rationale for the question is solely for a precision fit.

[rigidthumper]

Diamond pistons makes a 4.085" 8cc dome piston that works very well

[Geezer_Glider]

Don't know how good they were but HD made some .010 over SE pistons a few years back if you can find some NOS somewhere. Some were for the HTCC heads but some were for the open camber 103SE heads and had just a small raised dome with no special shaping to it.Also people have been known to take those cylinders to 4.125 giving same liner thickness as 107 from stock jugs(a bit thin for my taste). Sounds like Rigid has had good experience with the Diamond pistons.
Just saying,
R Meyer

[Hillside Motorcycle]

If refering to a 120R engine, pistons are available to bore to 4.125".
Certain cylinder spigot mods need to be performed at that time.

[HD/Wrench]

Well there is another option ... That is to not worry about new pistons get your cylinder straight and round .  Then send the pistons to Line2Line tell them what size you want the piston to be and your done .

I have done this and on my personal 124 that I raced put just over 21,000 miles on the piston with the skirt coat build up . leak down and CCP re test on the dyno and yes still have the 1/4 slips to prove the stated power .

I like it and we use the coating often .

[Don D]

If someone wants a 4.125" bore from us it is an S&S cylinder.
Harley offers a .010 4.060 piston for the 120r. Or line2line and a hone job.

[TorQuePimp]

Diamond pistons makes a 4.085" 8cc dome piston that works very well

Big as you should go

[Hillside Motorcycle]

T-man offers the pistons...........................we don't.

[Don D]

They did one thing wrong with the machining package originally.
They used an insert with a very sharp small radius to finish the spigot and base. This left a sharp corner where the spigot meets the base. They split right there horizontally. Wonder why?

[Hillside Motorcycle]

T-Man shares special spigot machining instructions, or at least to us.

[Don D]

Anybody qualified to hold them right with the proper tooling and machine can do this. It is no big secret.

[Hillside Motorcycle]

No secret implied, whatsoever.