What is needed for a m42 stroker to a 2.0/2.1L?

[318istourer]

I’ve got a m42b18 sitting waiting to be restored, I have my dream build it’s making a e30 318is touring, I do want the engine bay to look original as it will be a daily/show car so will keep the original ancillaries, coil plugs air box etc. This will replace the m44b19 I’ve currently got in it as the m42 appeals more to me for what it can do.

What do I need to make this a reliable 2 liter stroker? Because I want that extra power to about 170-200hp.

I’ve seen people use the N47 camshafts, which this will need as it’s forged steel - best for the m42, what parts is best recommended for this build?

Thanks,
318istourer.

[TobyB]

Having looked into it just a little,

there's not much out there....

https://www.google.com/search?q=bmw+s42

Good luck!

t

[bmwman91]

I have a 2.1L M42. It was built by Metric Mechanic Inc. Long story...had one built in 2012 which had some issues and I eventually had a HG failure in 2019 (which I do not think was their fault). They rebuilt one for me at cost of labor after discussing it with them, and I put it in at the start of 2020. It has been AMAZING, and I am super duper happy. The issues with the first one were what I'd call a mix of problems caused by a former supplier getting acquired by an overseas company, and something along the lines of a staffing issue back in 2012. The second / rebuilt one has been totally trouble free, and I've been driving the absolute dogshit out of it for the last 5 years.

The main item that you need is an M47 crankshaft. It has an 88mm stroke while being fully forged and fully counterweighted. There are a couple of variants of it, and IIRC only one of them will work. In addition, that "working" variant requires machining to the front snout to be compatible with the M42 crank sprocket and damper hub. It is not a DIY thing unless you are a competent machinist. There is also a partially-counterweighted 89.6mm stroke version, but it was intended for use with a balance shaft system and I have no idea how nice it feels when it runs.

My block was bored out to 87.5mm, which is about the max you would really want to go since it only leaves a 3.5mm web between bores. I think that Metric Mechanic switched to an 87mm bore at some point after mine was built. Obviously you will need custom pistons and rods to go with it. MM published a little booklet for the build that they do here:

https://metricmechanic.com/wp-content/uploads/2016/07/M42-Engine-Booklet.pdf

The booklet is pretty old, and as of now they have changed / improved many things. The internals are much lighter, and they reduced the peak lift of the cam profile to prevent some issues with excessive wear due the cam lobes overhanging the outside diameter of the lifters.

You will need a custom tune for the build, and I recommend Sssquid Tuning. While MM sells a tune, it is my experience that the Sssquid one is better, having run both. I worked extensively with Sssquid for a few years to reverse engineer the Motronic 1.7 unit, and I do not think that anyone else knows it as well as them. They have done many of the MM 2.1L M42 engines at this point.

https://shop.sssquid.com/product/mm42-19-20-21/

I also recommend the RHD Engineering ultralight flywheel: https://racehead.com.au/product/bmw-...254-m40424344/
It is what I am running in my setup and it lets the car rev like a coked-up badger. I had the lightened MM flywheel prior to this, and it was nice, but the RHD one is better. Again, the tune form Sssquid got it idling better than stock even with this absurdly light flywheel while only increasing the target RPM by 20!

You can ask Sssquid about the power numbers that the engines are putting down since they have dyno'ed several. I think that they generally make ~200bhp, with a nice wide powerband. Street drivability is excellent and I do not find myself constantly needing to downshift like with the stock M42.

MM is not cheap and they charge a heck of a premium. If you know of a competent engine builder in your area, you could probably work with them and get good results. I am not sure if you would be able to get the same output as MM since they have custom cam profiles and a lot of thought went into making the design pleasant on the street (versus track / racecar). They could probably modify and sell you the M47 crank, and they are the only shop that I know of personally who knows what to do. 12 years ago the crankshaft alone was $1250 new from BMW, and it had to be imported from Europe since the M47 was never sold here.

You should also consider changing over the the M44 timing case and oil filter housing. It is mostly a bolt-on change, although you need a custom machined bracket (MM makes and sells them) to hold the crank position sensor since the M44 did not have it on the front of the engine. The M44 case eliminates the failure-prone deflector sprocket in favor of a plastic guide, and it also has an 11mm thick oil pump rotor (vs. 10mm for the M42) ensuring 10% more oil flow. The M44 OFH is just a cleaner setup IMO. If you are trying to look 100% stock, then the M42 OFH is fine I think.

Whether you build your own or not, I recommend calling up Metric Mehcanic. They will of course want to sell you on their engine, but I think that they would probably be willing to give some advice too. You'd need to buy a crankshaft from them anyway, most likely.

[jsnppp]

Makes me want a MM 2.1!

[318istourer]

I have a 2.1L M42. It was built by Metric Mechanic Inc. Long story...had one built in 2012 which had some issues and I eventually had a HG failure in 2019 (which I do not think was their fault). They rebuilt one for me at cost of labor after discussing it with them, and I put it in at the start of 2020. It has been AMAZING, and I am super duper happy. The issues with the first one were what I'd call a mix of problems caused by a former supplier getting acquired by an overseas company, and something along the lines of a staffing issue back in 2012. The second / rebuilt one has been totally trouble free, and I've been driving the absolute dogshit out of it for the last 5 years.

The main item that you need is an M47 crankshaft. It has an 88mm stroke while being fully forged and fully counterweighted. There are a couple of variants of it, and IIRC only one of them will work. In addition, that "working" variant requires machining to the front snout to be compatible with the M42 crank sprocket and damper hub. It is not a DIY thing unless you are a competent machinist. There is also a partially-counterweighted 89.6mm stroke version, but it was intended for use with a balance shaft system and I have no idea how nice it feels when it runs.

My block was bored out to 87.5mm, which is about the max you would really want to go since it only leaves a 3.5mm web between bores. I think that Metric Mechanic switched to an 87mm bore at some point after mine was built. Obviously you will need custom pistons and rods to go with it. MM published a little booklet for the build that they do here:

https://metricmechanic.com/wp-content/uploads/2016/07/M42-Engine-Booklet.pdf

The booklet is pretty old, and as of now they have changed / improved many things. The internals are much lighter, and they reduced the peak lift of the cam profile to prevent some issues with excessive wear due the cam lobes overhanging the outside diameter of the lifters.

You will need a custom tune for the build, and I recommend Sssquid Tuning. While MM sells a tune, it is my experience that the Sssquid one is better, having run both. I worked extensively with Sssquid for a few years to reverse engineer the Motronic 1.7 unit, and I do not think that anyone else knows it as well as them. They have done many of the MM 2.1L M42 engines at this point.

https://shop.sssquid.com/product/mm42-19-20-21/

I also recommend the RHD Engineering ultralight flywheel: https://racehead.com.au/product/bmw-...254-m40424344/
It is what I am running in my setup and it lets the car rev like a coked-up badger. I had the lightened MM flywheel prior to this, and it was nice, but the RHD one is better. Again, the tune form Sssquid got it idling better than stock even with this absurdly light flywheel while only increasing the target RPM by 20!

You can ask Sssquid about the power numbers that the engines are putting down since they have dyno'ed several. I think that they generally make ~200bhp, with a nice wide powerband. Street drivability is excellent and I do not find myself constantly needing to downshift like with the stock M42.

MM is not cheap and they charge a heck of a premium. If you know of a competent engine builder in your area, you could probably work with them and get good results. I am not sure if you would be able to get the same output as MM since they have custom cam profiles and a lot of thought went into making the design pleasant on the street (versus track / racecar). They could probably modify and sell you the M47 crank, and they are the only shop that I know of personally who knows what to do. 12 years ago the crankshaft alone was $1250 new from BMW, and it had to be imported from Europe since the M47 was never sold here.

You should also consider changing over the the M44 timing case and oil filter housing. It is mostly a bolt-on change, although you need a custom machined bracket (MM makes and sells them) to hold the crank position sensor since the M44 did not have it on the front of the engine. The M44 case eliminates the failure-prone deflector sprocket in favor of a plastic guide, and it also has an 11mm thick oil pump rotor (vs. 10mm for the M42) ensuring 10% more oil flow. The M44 OFH is just a cleaner setup IMO. If you are trying to look 100% stock, then the M42 OFH is fine I think.

Whether you build your own or not, I recommend calling up Metric Mehcanic. They will of course want to sell you on their engine, but I think that they would probably be willing to give some advice too. You'd need to buy a crankshaft from them anyway, most likely.

This is absolutely GOLDEN!!! Thank you so much, this is definitely what I was looking for and will be following this for the ultimate fun daily!