I am just thinking out loud here...

Seeing as oversize 850 pistons are hard to find and 998 pistons are plentiful is it possible to fit 998 pistons onto 850 rods? If not how hard would it be to make them fit

Cheers,
Alex

They will go straight on, but note the following:
1. You will need to deck the block about 4.0mm.
2. 850s have a clamp type little end, you will either have to get the 998 gudgeon pins grooved to suit, or use 998/1098 fully floating rods instead. Yes they are the same length. You can then either use the 998 circlips, or better yet get some PTFE buttons made.

Whichever rods you use, get them checked for straightness as 99% of s/h ones have a bend in em.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Wow quick and great response however that raises another question, will 998 rods fit a 850 crank?
And what oversize pistons can an 850 block take? any chance a 120 thou over 998 piston will fit without hitting water galleries or whatever is there to hit?

Cheers,
Alex

Q1. yes they fit, the rod bearings are all the same size (1.625"), 850-948-998-1098-1275 (early).
Q2. I doubt you will cram in .120" oversized 1098 pistons, but .080" would be OK I reckon. Ask Graham Russell to be sure.
To really tell before boring it you need to measure the cylinder wall thicknesses, there are now electronic ways to do this.


Don't forget, an 850 block only has ONE cam bearing. if you are going to use a decent performance cam and valve springs, get the block line bored for 2 more cam bearings like a 998/1098 has.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.