I"m not building this engine. I saw a project advertised with what I thought were some wrong info and wanted to advise the seller.

Spank, thanks for the link.

good conversation here.

I've got a floor full of 1275 engines and some 998's so my preference is to use the 1275's first.

I just need mini bodies for them.

And don't we all?

Mike.... what about fitting a 1098 crank.

I bored my 998 out .040.... with 1098 crank, that's 1130cc I believe

Does anyone know when the late 998 s went to the press fit rods? I have only been able to locate three sets so far. If you ( anyone ) has a set spare please let me know. Steve (CTR)

https://www.minimania.com/msgThread/114004/1/1/How_much_can_a_998_block_be_bored_out

I'm just starting to collect parts for my 998 builds this spring. I have one already spoken for and plan a second to have on the shelf. Having a block, rods, pistons and balanced rotating assembly done with only a cam and cyl. head choice to complete. Doing a full and complete lead free 295 cyl head is not cheap and getting the chambers down to size adds to that cost. Unless I find some good 1100 cranks I'll be sticking with 998 s for now. Steve (CTR) 

ROO's 1098 bored (without offset) to +100 (with 0.00175 running clearance) will yield 1185cc...with RE flat top pistons, mildly modified 12G295 head with larger Ivey race valves & S springs and RE 266SS cam, HIF 44 on RE long runner intake & with Cooper Freeflow exhaust should punch out interesting numbers.  I will look to seeing what a dyno sees later this year.

After I had a ride in Matt Russell's Mini with GR worked 998 way back in 2011 my view about the potential of the small bores was...expanded.

Mine is at 68mm or +.135" and gives 1107cc.  GLF too.

A 1098 at 68mm gives 1215.

I believe it is possible to go to 69mm, possibly with Fiesta pistons.

Kind of wonder why I even bother any more? I call my big bore 998 s with 940 cyl. heads Baby Cooper S. They can be drilled and tapped for the extra studs and with tappet covers they look the part. It is best to pocket the blocks for the exhaust valve when fitting a 940 cyl. head. I contacted Calver yesterday about the .100 O/S pistons listed on his site. I believe that is about as big as you can go and that requires off setting the bores. Even a std bore 1300 piston would require .243 give or take to come out and there is just not that much room. There is a .125 difference in the 998 and 1275 crank mains and a .200 difference in stroke. 

It seems the last batch of .080 and .100 O/S 998 pistons were never made and it will be months before more are produced and on the shelf. There were pics. of the baby Cooper S engine I did a couple of years ago. Many of the pictures are no longer hosted as I never posted myself and the guys who did my posting for me are gone also. 

Thinking out of the box I have looked at having 998 cranks machined to fit a 850 block. I'm still having issues with getting the 2.5 + - blocks bored local. There just are not that many boring bars still in operation now. The one I found had to be rebuilt before it would bore a round hole. I tried to buy it but no deal. 

It would be fairly simple to take a 998 put a 1100 crank in and find a piston to get it to 1220 I think. Adding a 1300 head does not make it anything but a 998 with a 1300 head. Steve (CTR) 

Here's the deal, I saw a project advertised saying the engine was to S specs. It's a 998 block with a 1300 head.  I'm not sure this can be assembled as the seller thinks. Hence I was wondering how big you can bore the 998 and if one could stuff the 1300 pistons into it.  So Steve says no to the 1300 overbore, and no to fitting big bore pistons.

What's the max a 998 can be opened up?

i know it won't be an S spec lump but would like to advise the seller what he has.

How long is a piece of string Steve?

So what's the cc of a finished big bore 998 Steve?

No and No. close to .250 to come out and the stroke  would be wrong and 1300 s have a 2 inch main. Steve (CTR)

Can you fit a 1300 sized piston into a 998?

And would it then be a 1300?