Boring original cylinders for larger pistons

[silvercab996]

It's my understanding when having cylinders bored out for say a 95" kit, that the machinist have the pistons on hand that are going to be fit and also a perfered clearance based on ultimate usage that may override the manufacturs recommendation. Also I have found pistons in the same oversize can vary nearly .002" from one to another. Size will also vary from one manufacturer to another.

A guy that is looking for longivity and willing to do some careful breakin that will be using the bike for touring may opt for fitting on the tight side of the recommended clearance.

The other extreme, for a hot rod, and an impatient type of owner, and one that like to be heavy on the throttle all the time, it only makes sence to give it an additional .0005" or even a .001" or .002" in addition to the factory spec.

Forged pistons are generally fit looser, and including early 3" bore XLs, I've seen fits as large as .006"-.008" and as tight as .0005" on some Big Twins.

If you by S&S pistons and cylinders they are marked indivually with the size in tenths and should not be mixed. Some other manufacturers will ship already bored and finish honed cylinders based on the factory bore size. If you are fitting pistons, it becomes your responsibility to find pistons that will fit with the proper clearance, of if more is needed, make allowances.

What are your experiences with this?

[02FYRFTR]

I buy the pistons then take the pistons with the cylinders to my machinist.  I specify the fit with a tolerance to the plus side and make sure that torque plates are used for boring and honing.  Final measurement and any adjustment must be taken with pistons and cylinders at room/ambient  temperature.  Pistons must be measured at the point from the bottom of the skirt as specified by the piston manufacturer.  I have yet to take a motor down for piston problems if procedure is followed.  Seldom does a freshly built motor come down for loose fit, tight fit/dirty  however is more common.  JMHO

[Admiral Akbar]

Sick'em Red...    Max

[Ultrashovel]

There was an extensive thread on this a couple of weeks ago. Incoming!

[crazycalvin]

 

[Hillside Motorcycle]

Entry level basic engine building skill.
Been performing that operation for over 20 plus years, without issues. Piece of cake.

[ICANTD55]

Sick'em Red...    Max

LMAO

[PanHeadRed]

Sick'em Red...    Max

LMAO

It was funny, even comming from the cheap seats.

[silvercab996]

Thanks guys, found the thread.

entertaining!