Bore And Stroke Questions

[318kid]

Well my engine is starting to get high miles and it might need a rebuild soon so I have a few questions. I know there is not much of boring and stroking for our engines, but what do you think is the most streetable set up. Im not looking for the most power out of our engines but something respectable.

I know that s52 pistons fit if you bore the block, but is it a direct fit or do you have to machine the pistons too? What bore and stroke does our engine have? I know about the m47 crank but I heard something about a m44 1.9l crank. If you had any choice to bore and stroke your engine what would you do? (besides the m47 crank) Any replies would be great. Thanks

[christophbmw]

i would personally stroke it (more torque). but if you want it streetable i would leave it stock, or maybe a slight overbore. just my 2 cents.

[Tor Arne Kaasen]

it poseble to bore it from 84mm org to 87mm and stroke it from 81 mm to 88 mm whit an m47 crank. i am i the bilding prosess on my m42 engine. have a m47 crank an m3 s50 piston 86 mm and rods from m50 b20 135mm lenghts org 145mm. lot of worke and excpensive. overbore and honing. must mod the fuel injectors for more fuel.

[steve321]

i would also like to do this on my M42, how much work is really involved i have been quoted about £120 to bore out my block, which i thought was quite cheap, and i can do all of the mechanical side of things myself, so is it just case of getting the M3 pistons and M47 crank, and the right rods and it will just all bolt together and work, or is there more too it than that

steve

[cecotto]

Well my engine is starting to get high miles and it might need a rebuild soon so I have a few questions. I know there is not much of boring and stroking for our engines, but what do you think is the most streetable set up. Im not looking for the most power out of our engines but something respectable.

I know that s52 pistons fit if you bore the block, but is it a direct fit or do you have to machine the pistons too? What bore and stroke does our engine have? I know about the m47 crank but I heard something about a m44 1.9l crank. If you had any choice to bore and stroke your engine what would you do? (besides the m47 crank) Any replies would be great. Thanks

I'm doing a project where im boreing to 86mm and stroking to 88mm, if you do the same and keep the camming conservative i see no problems with regard to streetability. Infact it will most definetly be more fun to drive, more low end and more top end performance.

So in my opinion all talk about keeping it stock will retain the streetability the best is rubbish more power will always be better.

My recomendation for you will be: Count your money and decice how muck of it you want to spend on your engine. If you decide on little money, this is okay but dont start the M47 crank and custom pistons route. On the other hand if you decide on spending what it takes i would recomend you start buying parts and i'm sure you will end up happy about your engine.

[Tor Arne Kaasen]

The S50B30 euro pistons dident work, the pin was 21mm not 22mm.

[steve321]

i thought the S50B30 pistons did work, what rods were you using

steve

[cecotto]

The S50B30 euro pistons dident work, the pin was 21mm not 22mm.

What you need is to have your pin bushing changed out to one with a smaller diameter. I think this is what people are doing..

[Tor Arne Kaasen]

i am using m50 b20 rods that are 135mm. the S50B30 rods on the euro is 50mm not 45mm on the crank.

4 custom M42 Turbo JE 2618 Alloy forged pistons is in the mail, 1,5 mm taler then og an comp 8,5 -1 for FI.

[Tor Arne Kaasen]

the us rod S50B30 is 45mm i think and 135 mm long 21mm pin