As the title suggests, what do most machinists/engine builders consider the max overbore for an OEM 88" Twin Cam Cylinder? .030, .040, .060, or more?

 

3.938" to make displacement 98"

 

The 3.75 “ 88 s are being bored to 98” that’s 3 & 15 /16s or 3.9375
An overbore of .1875 or 3/16”
plenty of room.

 

How thick is the cast in steel liner?

 

3.938 overbore leaves a wall thickness of approx . 060 in the “ spigot” that goes into the cases

 

Your other option is 3 & 7/8s ( 3.875 ) for a 95 incher

 

OP asked the biggest in a stock cylinder which is 3.938" for a displacement of 98" with the stock 4.00" stroke. S&S and HD sell 4.00" cylinders to make a square 100" but it is much cheaper to bore stock seasoned cylinders than pay for a new set. CP and Wiseco make pistons for the 3.938" bore. If one is already buying pistons and paying for a bore job why not get the extra 3ci for the same money? Free displacement is good!

 

Don’t disagree, but O.P. may read the s&s ad that claims the 3.938 bore is risky unless using their cylinders
just tossing in an option, no harm in choices

 

Thanks for the replies. I plan to open up the cam chest and check crank run out. I'm pretty sure I am going to find that I need to split the cases and true ,or replace the crank. I'm looking at about 90k miles right now and she's still strong but a little long in the tooth.

If I decide to pull the motor and split the cases most likely I won't go back stock, I'll spend the money on a new crank with a 4 5/8" stroke, chain drive cam etc. Once the bottom end is fresh again I can worry about the top end.

I can get the stock cylinders bored for nearly nothing and I can port and polish the heads myself. I'll probably do this much even if the crank checks out and I leave it stock.

 

Can you get the 3.938 without cutting the cases? If not that may be a reason to stop at 3.875.