Author Topic: Max. Bore for M42 (Read 8444 times)

M42_Jester · « **on:** July 06, 2009, 01:01:56 AM »

Does anyone know the maximum bore for the M42? i've seen people that are building a 2.0L M42, using the S52 pistons (bore 86mm) but i was wondering wat the maximum bore size actually is?

does anyone know if it is possible to use S14 pistons (94mm bore) instead of the S52?

Cheers,
Jester

dsm2002 · « **Reply #1 on:** July 06, 2009, 01:50:59 AM »

Metric Machanic do 87mm. This is the largest I have heard about.

1991 E30 M42 · « **Reply #2 on:** July 06, 2009, 02:44:59 AM »

I run 85.485MM pistons

fabe · « **Reply #3 on:** July 07, 2009, 06:01:55 AM »

87mm is the max of the max..

94mm??? hehe.. there won't be a cylinder wall left.. The S14 has bigger bore to bore spacing, hence it has big bore. and for the same reason, M42 can't use any performance parts available for the S14 ie camshaft, crankshaft....

It also helps if you do some basic research to understand more of your engine and options...

anyway, here are some calculation I did using spreadsheet on the various combo.. not rocket science, just basic school maths

bore x stroke : displacement (cc)
84 x 81 : 1796 (M42 stock)
85 x 83.5 : 1896 (M44 stock)
86 x 81 : 1883 (M42 crank, bore out 86mm)
86.5 x 81 : 1905 (M42 crank, bore out 86.5mm)
86 x 83.5 : 1941 (M44 crank, bore out 86mm)
86 x 88 : 2045 (M47 crank)

M42_Jester · « **Reply #4 on:** July 08, 2009, 12:57:47 AM »

That's good to know. I knew that 94mm was a bit a long shot.

so 87mm is the max? that's good. it means that my original plan of using the
S54B32 pistons with the M47 crank would still work. Displacement would be closer to 2.1L then aye?

just something i've been thinking bout

cheers for the info...

Jester

fabe · « **Reply #5 on:** July 08, 2009, 05:10:57 AM »

87 x 88 : 2093 (M47 crank, bore out 87mm)

there's one guy here who has this set up. Done by Metric Mechanic...