Slip-in 94's, or bore the case proper.

[Splitdog]

Which way is best? If you have 8mm studs and savers.

[madmike]

It's called step boring

[Splitdog]

I know. But I wonder which way is strongest. Leave the meat all on the case and go slip-in, or machine it out for 94's and leave the meat on the spigot.

[Piledriver]

IIRC the reduced base 94s and 92s "slip in" to the thickwall 88/90.5 hole, not the stock one, so you will be machining the block some regardless.

You can afford to lose some meat at the bottom of the cylinder as long as the rod/stroke keeps the piston in the bore properly.

I'd personally machine a mag block as little as possible.

[Splitdog]

Yes, it has been bored for 90.5's by Berg. I was thinking the slip-in route might be better. More meat around the case savers. The 94's hit the bottom of the bore step at BDC.

[Marc]

I'm with Piledriver, you don't want to remove any more material from the case than is absolutely necessary; now that 94s are available with the classic "92" skirt O.D. there's no need to have them turned down on a lathe, but you will need to have the case step-bored to clear the skirts at BDC (there may be some short-skirt pistons that would work without that, and without a big stroke).
The thin spigot of the "slip-in" jugs has been proven to NOT be an issue. They're fragile on the bench, but once assembled they hold up fine...it's not a highly-stressed portion of the cylinder.

Note that 94 jugs tend to be slightly taller than the smaller bores', because at that 97.3mm bore the case ends up needing to be decked considerably. In fact, even at 96mm you'll sometimes have to mill quite a bit off of the case to establish a decent seating surface for the cylinders. Take a good look at your case, if the "rim" around the cylinder opening is thinner than the step on the bottom of the cylinders you may as well have the case decked down while you're getting it step-cut.

[Marc]

IIRC the reduced base 94s and 92s "slip in" to the thickwall 88/90.5 hole...

The first machine-88s were ~95.3mm at the top and ~91.7mm at the spigot. Berg may still have some Birals on the shelf in this size, but for all practical purposes they're obsolete.
Late 88s have the same external dimensions as the original 90.5s (97mm top, 94.4 spigot). Early 90.5s are also obsolete.
Late 90.5s have the same external dimensions as the original 92s (98/96mm). Classic 92s are still available (if not advisable).
"Normal" 94s are larger than 92s (101/97.3mm)

AA makes 88s that slip in to the stock case openings but require the heads to be opened up to late 90.5/classic 92

Their thickwall 92s originally had the same outside dimensions as 94s, but I hear they're now made "92" on the bottom and "94" on the top

94s can also be had (or made) with "92" diameter spigots - the "slip-ins" Splitdog wants to use.

[Splitdog]

Thank you for your replies. By step-cut, you mean cutting only the remaining step that is there? I mocked up a 94 P&C and the piston hits at the 11:00-1:00. and 5:00- 7:00 positions as well as the little bit on the 'step' going around the existing bore. The piston would clear the existing large part of the bore.

[Marc]

Yes, you just need to increase the depth of the cut enough to take down that ledge to clear the skirts at BDC (by ~1mm to be safe). It can be done at the full 96mm diameter; where the "step" comes in is when you do it right and take out no more material than necessary, say at ~94½mm diameter.

I presume your 8mm case savers are factory-installed, so you have the "sunken stud" (top-front stud on #3 is anchored more deeply into the case, so it uses a stud the same length as the 8 lower ones). That's vital.

[Splitdog]

Yes, I have the sunken stud.
Thanks guys, i will simply hand grind the ledge. Slip- in it is!