M40 to M42 conversion - issues with knock sensors, cooling system, performance

[kanecvr]

Hi guys.

A couple of years ago I decided to convert the M40B18 in my E30 to an M42B18 using parts from several engines I've had in storage for a while now.

The primary reasons for this conversion were drivability, reliability and parts availability. The M42's engine management (at least the motronic 1.7.3 that comes on later e36 318is) seems to be a bit more flexible and more permissive when it comes to small vacuum leaks and other small issues. It also does not use a distributor for ignition, and all hoses and gaskets can still be found new, OEM and aftermarket - as opposed to M40 parts. Simple stuff like the M40 rubber intake boot are getting very scarce. I'd driven a couple of years with a taped over intake boot in my 318i because no retailer in my country would stock the part. After 24 months I lost patience and ordered one of aliexpress. I got the wrong part - they sent the E36 intake boot which is much longer then the E30 one. Then I caved AGAN and ordered an original BMW part for almost 200$ - as well as a double water and air hose specific for the m40... but still no luck. The intake boot was sealed, and already cracked. The other hose was fine. BMW refunded me for the intake boot and said the newest lot for that part number is dated 2004... so take it or leave it. I left it.

One day I was taking inventory of engine parts and came across two sets of e36 M42 intake manifolds, 3 wiring harnesses, all e36, one pre 94 and two post 94, 3 cilynder heads, 10 pistons, two crankshafts, timing chain covers, oil pump, 4 DMEs, everything I'd need for the conversion. I had a look at the part number on M42 and M40 engine blocks, they are the same. The only difference is the lack of bosses in the block for knock sensors on the M40.

And here is issue number one: my engine is finished, the car runs, but I don't have any knock sensors installed. I haven't tried connecting any scan tools to the car, I think maybe BMW scanner MIGHT work. The engine runs fine, idles well, revs well, no weird noises, minor oil leak at the timing chain cover despite using new Elring gaskets all around (should have added a dab of RTV I guess) - but the car seems slow... not "there's something wrong" slow, just... M40 318i slow... keep in mind since I did just rebuild the engine, I'm not willing to rev past 4k RPM just yet, and I am taking it easy on the old girl until it does at least 2000km, but so far, up to 4k rpm, I can't feel any difference between my old setup (M40b18 with M42 fuel rail, injectors and AFM) and the new setup.... Is it possible that the lack of knock sensors is causing the engine to run in a "safe mode" of sorts? Would it be possible to "code out" the knock sensors from the DME? I really don't want to drill holes in the M40 block, and even if I did, I read the knock sensors are finicky and need to be placed on the block exactly where BMW put them - that won't be possible. I can't glue them on - I could drill into the block or weld a nut in the same location as on the M42 block and screw the knock sensors in... any opinions on this idea?

Issue 2 - my engine runs a bit hot. The needle sits in between the center mark and the one further to the right... If I push it a bit harder, it will move closer to the 4th mark on the gauge (to the right) - if I take it slow it stays nearer to the center. If I turn the heat on it will move closer to the center mark. Could it be a gauge issue? I know e30 gauges are problematic. I tried reading engine temp with an IR thermometer and the radiator is 70-78C while the head reads 88-90c. I'm using a brand new NISSENS E36 318is/320i radiator. New water pump, thermostat, fan clutch and hoses of course.

Issue 3 is, as mentioned above, performance - seems similar if not identical to the M40, at least up to 4000rpm. I don't particularly mind if I don't get this one sorted, as I plan to be gentle with this car. It's purpose is leisurely weekend driving for relaxation so It's OK if performance stays the way it is, but it would have been nice to be able to feel some extra power after all that work.

Some details on the build:

The engine is completely rebuilt with new parts, took me 2-2.5 years to finish. All gaskets, sensors and hoses are new (with one exception - the crank ventilation hose). New rings, new shell bearings, polished crank, rebuilt cylinder head (valve seats, decked, valve stem seals). I also did a coil over plug conversion so I would not need an ignition coil bracket witch my car did not have and so I can get rid of the spark plug leads. I'm using M52TU ignition coils. I'm using the DME from a '96 e36 + the wiring from the same car. I kept only the engine block and oil pan from the M40. I installed the flat belt pullies and power steering pump + alternator from a post 95 e36 to get rid of the constantly squealing v-blets and to make it easier to install a modern AC compressor on the car. The gearbox and final drive are original to the car, and I used the single mass flywheel + clutch kit I had on the M40 as they are in near mint condition. I used the oil pump/timing case setup from a later 96 engine that uses a plastic slider instead of the pinion for the lower left side of the timing chain, as I've had issues with those pinions on early M42 engines in the past.

Any advice and input is welcome!



Test fitting the M42 head and timing chain cover / oil pump on the reconditioned M40 block and oil pan:



Engine in the car:

[kanecvr]

Here's how my engine bay looks like right now:

[82eye]

nice clean install.

i don't think any north american e30 m42s had knock sensors. on an e36 they are below the intake on the side of the block. one measures cyl 1/2 the other 3/4. depending on your block you should have two blank bosses that would get drilled and tapped for the sensors. you'd have to run the e36 dme to use them. i'm not sure when the bosses got added, some early blocks may be missing them.

warm temp running issue doesn't sound like much of a problem and is likely easily solved with a thermostat.

as far as running i'm not sure the lack of sensors would cause a low power response. usually, the dme would pull timing when it gets a knock signal, i don't think it looks for a constant reference.

[bmwman91]

E30 M42's used Motronic 1.7 and did not have knock sensors. As noted above, the block has the bosses cast into it. The bosses should have untapped holes in them which may or may not need a quick pass with the appropriate drill bit before tapping. The front knock sensor is fairly easy to get at since it is just behind and to the right of the oil filter housing. The rear one is a little more work and requires you to remove the intake manifold and the big plastic wiring box which under it. You probably need to pull the heater coolant return hose out of the way too. Basically, the bosses are between cylinders 1+2 and 3+4.

I do not know all that much about Motronic 1.7.2 and 1.7.3, but since they were designed to have knock sensors installed in the OEM setup, I think that it is is probable that ignition timing is being retarded by some amount in their absence. I have not heard about the sensors being troublesome to be honest. You just need to install them with the OEM fasteners, with the specified torque in the repair manual, and if there are any notes about which way to orient the wires then that should be obeyed. If your block is painted, then make sure to scrape all paint off of the boss faces where the sensors mounts so that they are directly on the metal. Other than that, you should be fine.

Performance-wise, the M42 should feel a bit more lively than the M40 lol. Some of the lack of sportiness is potentially from a lack of ignition advance due to missing knock sensors. The rest is probably due to the RPM limit that you have set for yourself. The E30 M42 makes its power up top, being a small 4 cylinder. Also, the E36 is sort of known for being a bit less sporty due to the intake manifold design. You get a bit more mid-range power from it, but it suffers at the top end versus the E30 setup.

So, you can hunt down the knock sensors and install them, or you can find an E30 ECU, harness, and intake manifold. Personally I think it is really cool that you are running the late E36 setup. M1.7.3 did have several improvements over the original M1.7.

2000km is very likely a much longer break-in period than needed before revving it. The rings will seat 90% during the first 50km, and there really is not anything else in an engine which is supposed to "wear in". Just make sure to change the oil after 100km and only use high quality stuff. Based on the input from the company that built my high performance M42, you should be good to rev the crap out of it after ~700km of normal+moderate driving. But you are of course free to do what you want since it is your engine, and break-in is one of those things that nobody agrees on lol.

[kanecvr]

E30 M42's used Motronic 1.7 and did not have knock sensors. As noted above, the block has the bosses cast into it. The bosses should have untapped holes in them which may or may not need a quick pass with the appropriate drill bit before tapping. The front knock sensor is fairly easy to get at since it is just behind and to the right of the oil filter housing. The rear one is a little more work and requires you to remove the intake manifold and the big plastic wiring box which under it. You probably need to pull the heater coolant return hose out of the way too. Basically, the bosses are between cylinders 1+2 and 3+4.

Thank you for the input. I had a look at the engine I took out of my '92 318is e36 (which is now a 320i) and measured the depth, size and position of the bosses the knock sensors sit on.



Here are the two knock sensor bosses:


They stick out the sides of water passages running between cylinders. The rear one is between the rear most freeze plug and a water passage, while the front one is inconveniently located between the top most engine mount point and the oil filter housing. They are 20mm in height (from the exterior of the engine block) and threaded for an 8mm bolt with a 13mm head. Thread depth is 18mm. In the pic above you can see the rear knock sensor (yes I know it's backwards, I had it off the engine and put it on just to take some photos and measurements). The front boss is the one with the 13mm bolt sticking out.





This is my M40 block:



As you can see, the bosses are completely missing. Therea are two flat spots on the block, you can see one of them in the pic above, similar in diameter to the bosses on the m42, but they're not in the correct location and are not nearly high enough. One of them is on cylinder 3 and the other on cylinder 1, behind the oil filter housing. On the M40 block they serve no purpose - they're probably marks left from the mold / casting process. They are 1.5-2mm in height and looking inside a spare m40b16 block they're about the thickness of the block + 2mm - not enough to drill into and tap. Interstingly they're also present on the M42 block - in the same exact location, with the rear on right under the casting number and the front one to the front of the knock sensor support, right next to it.

So drilling is out. My only option would be to fabricate bosses out of nuts or spaces and weld them to the engine where the ones on the M42 block would be... that or have the DME software modified to ignore the knock sensors entirely.

Welding onto the block would mean a lot of disassembly (oil filter housing, belts, alternator, intake manifold, starter) and draining the engine of oil - I'm not really willing to do it If I'm not certain it will yield any positive results as it's a lot of work....

Performance-wise, the M42 should feel a bit more lively than the M40 lol. Some of the lack of sportiness is potentially from a lack of ignition advance due to missing knock sensors. The rest is probably due to the RPM limit that you have set for yourself. The E30 M42 makes its power up top, being a small 4 cylinder. Also, the E36 is sort of known for being a bit less sporty due to the intake manifold design. You get a bit more mid-range power from it, but it suffers at the top end versus the E30 setup.

It's that extra mid-range power I was betting on when I chose the E36 intake

Personally I think it is really cool that you are running the late E36 setup. M1.7.3 did have several improvements over the original M1.7.

As far as I can tell the 1.7.3 version does away with the daughterboard for knock sensors, integrating both DISA and knock functionality into the main PCB - it's also a bit faster to process engine sensor input and a bit more permissive fault wise - and it has independent injector control as opposed to having the injectors wired up in banks of two like motronic 1.7 and 1.7.2 - witch should technically give better fuel economy...

2000km is very likely a much longer break-in period than needed before revving it. The rings will seat 90% during the first 50km, and there really is not anything else in an engine which is supposed to "wear in". Just make sure to change the oil after 100km and only use high quality stuff. Based on the input from the company that built my high performance M42, you should be good to rev the crap out of it after ~700km of normal+moderate driving. But you are of course free to do what you want since it is your engine, and break-in is one of those things that nobody agrees on lol.

That's good to know. I chose 2000km as that's what is written on the clear sticker that comes on E30 windshield - driver's side (this car still has it on) - "be sure to drive moderately and not rev the engine past 4000 rpm in the first 2000km in the engine break-in period" or something like that :) I will be sticking to what the sticker sais. Despite keeping this as a weekend car, I'll be driving it to work the next couple of months - that's a 45km commute. 2000km shouldn't take that long.

I will be changing the oil and filter this weekend tough.

[kanecvr]

nice clean install.

i don't think any north american e30 m42s had knock sensors. on an e36 they are below the intake on the side of the block. one measures cyl 1/2 the other 3/4. depending on your block you should have two blank bosses that would get drilled and tapped for the sensors. you'd have to run the e36 dme to use them. i'm not sure when the bosses got added, some early blocks may be missing them.

My M40 block is 07/88 - no bosses for knock sensors...

warm temp running issue doesn't sound like much of a problem and is likely easily solved with a thermostat.

I installed an 85C mahle thermostat. Maybe swapping it for a 75C thermostat - like the M40 originally had would solve the problem... Thing is I recently read some forums - specifically about engine swaps and the E30 temp gauge calibration. It seems the M42 is designed to run at 90-95C (temp measured in the head) while the M40 runs 5-10C cooler. I'm considering the gauges might be tuned so that center mark is 85C. The rebuild engine runs at 89-96, witch might explain the slight offset of the needle... I also read the 318is and 320is have a different cluster - differences are the temp sensor calibration and fuel economy gauge. On the 318is (e30) cluster takes a signal directly from the DME, while on the M40 equipped 318i and M20 equipped 320/323/325/327e the signal comes from a ferrite core installed on one of the spark plug leads... The fuel economy gauge is no longer working correctly on my car since the engine rebuild, so this might be causing it.

[kanecvr]

[UPDATE] - After some more driving these past few days I noticed two of the fuel injectors acting up - one more often than the other. Occasionally, very rarely, usually when the engine is cold, it will run in 3 or even 2 cylinders, only under 2000 RPM. Not at startup - the engine starts and idles normally - the injector issue manifests randomly, usually after I've driven for a very short while and the engine is still cold. If I rev over 2k and hold it there for a bit it runs fine again. I've narrowed it down to injectors 1 and 2 by using the ol' ear'o'meter. When the issue occurs, the aforementioned injectors will stop clicking or click very faintly compared to the others. My car has a new fuel tank (the original one was full of holes at the top) and new fuel filter, so 0 chance of crud making into the fuel lines. The injectors are from my '92 coupe. I'll be swapping them out for a set of black 19lb M44 injectors over the weekend, see if it makes any difference.

I think it's very likely this is the cause of the performance issue as I've noticed it is intermittent. Sometimes the car feels like a 316, sometimes it feels like a 320....

[bmwman91]

Got it, so I guess I was thrown off by the initial post where you said that the part numbers were the same for M40 and M42 blocks. Apparently the castings are different.

And yeah, if the injectors are being weird then that is very likely going to be the main culprit here. Did the ones you are using sit on a shelf for a long time? Sometimes the old fuel will varnish them up and make the pintles sticky when they dry out. Either way, hopefully the M44 injectors sort things out for you.

[kanecvr]

Got it, so I guess I was thrown off by the initial post where you said that the part numbers were the same for M40 and M42 blocks. Apparently the castings are different.

And yeah, if the injectors are being weird then that is very likely going to be the main culprit here. Did the ones you are using sit on a shelf for a long time? Sometimes the old fuel will varnish them up and make the pintles sticky when they dry out. Either way, hopefully the M44 injectors sort things out for you.

Oh yeah they've been sitting for a while - 3 years at least. And I can't remember witch engine they are off. Either a blown up late 96 M42 or an early 92 m42 with a cracked valve...

I've been rummaging around in my box'o'injectos and came across another set of M42 Lucas (I think) black top / orange line injectos, just like the ones I have installed right now. These have also been sitting for almost 2 years - and I also came across the odd, also M42 (I think), also Lucas black top / blue line fuel injectos I had on my M40 before I upgraded the engine to an M42. I had these blue line injectors in the M40 because I couldn't find replacement Bosch blue tops for my engine, and two of them were leaking externally (rusted case) so they had to be replaced. After installing the blue line Lucas in the M40 the engine changed significantly. I had to re-adjust the AFM to get the car to idle and it pulled all the way up to near-redline, something un-characteristic for an 8 valve M40, engines known for their mid-range and lazyness up top.

Looking around the interwebs I could not precisely identify the blue line injectors, but if they follow the BOSCH rating colors they'd be 21lb or 22.5lb, while the orange tops are 19lb. I believe the original bosch plastic blue tops that come in the M40B18 and the M20B25 are 17lb - but I don't think this is the case for the blue lines...

Black / orange line injectors part number: 173 9242
Black / blue line injectors part number: 173 1357

Here are some pics:


^Orange and blue line injectors side by side.



Notice the nozzles are different as well. The orange ones are open nozzle while the blue ones have a baffle plate of sorts, possibly to help with atomization.


This is the part number for the blue line injectors. Googling the part number did not yield any relevant specs.

The question now is - which ones do I install? I know the orange ones are stock for the M42, but they've been sitting for quite a bit and I don't know how well they run, as they might have come off a blown M42 or an M42 with a cracked intake valve that never ran OK. In contrast, the blue line injectors ran in my M40B18 for quite a bit - over a year - ran well, and seemed to increase that engines performance... but what are they off of? What specs?

What would you guys chose?

[UPDATE]

After adding the BOSCH specific 13 64 code in font of the blue top's part number I came across this page:

2023 BMW parts catalog 3' E36 318i Injection valve, Detail number 13641731357 (13 64 1731357) (bmw-etk.info)

Mystery solved, it seems the blue line injector are off a 1995 318i e36 with the M43B18 engine. Similar spec to the original blue tops in the M40B18 / M20B25, but in good condition as opposed to the rusty leaky ones I had before, witch is why I noticed a significant performance improvement.

Another site has specs:

Bosch 0280156346 / BMW 1731357 | INJECTOR PLANET CORP.

It seems the blue line injectors are 15.4lb injectors, and the orange like ones are 19lb. Both made by Lucas.

This means if I want my M42 to perform properly I need to use the orange line injectors. I'm also considering finding a set of equivalent orange/yellow or maybe even purple plastic top BOSCH injectors, maybe of a 328... those are newer and more reliable, while having a similar spec. I don't know if they will fit the manifold properly - they should... The old M30 3 nozzle yellow tops fit perfectly, and I have a set of 6, but they are OLD... and have been sitting forever... they worked when I put them in storage, I used them on a heavily modded M20B27 (323i 713 code shaved head with larger valves and 2.5L cams, b25 intake and throttle body, megasquirt) with great results, but that was back in 2008 or so.

[Andrew325is]

You could also use the M44 engine management on the M42 which is even more adaptable. It's also nice being able to view OBD2 data and you get the MAF instead of the AFM.

[murat]

hello mate, what is the latest situation after a long time on it, do you think the m40 engine is suitable for making m42?

[kanecvr]

hello mate, what is the latest situation after a long time on it, do you think the m40 engine is suitable for making m42?

The conversion has been completed a while ago - before I opened this thread. I did not solve the knock sensor issue, I'm simply running with no knock sensors installed.

To convert an M40 to an M42, you need a complete and functional M42 donor engine. Move over EVERYTHING from the M42 donor engine to the bare M40 block. The only benefit is keeping the car's original engine block with serial number and model (18 4 S1 vs 18 4 S2). This is useful in countries that frown upon engine swaps. You can upgrade any of the two M40's - the 1.6 and 1.8 liter, the blocks are the same, the difference is the stroke (rods, crank and pistons). The mod can be done on E30's and E36's. You can even cross between the two, as long as you keep the appropriate oil pan and dip stick. My build uses the internals and head from a 1992 E36 M42, with the intake manifold, timing case, timing gear, camshafts, DME, wiring harness and accessories from a 1996 M42 off an E36.


The issues I described at post creation have been resolved. The "slowness" was due to the fact that I did not want to rev the engine over 4k RPM and the M42 doesn't make much torque down low. It makes torque up high, over 4500 rpm. Below that it feels like a 316i M40. Over 5500rpm it feels a bit like a 6 cylinder. It's a kind of wierd, and I was not expecting this behavior, but I supposed I should have. The m40 8 valve makes peak torque lower down, and gives usable acceleration at 3-3.5k rpm, but kind of falls on it's butt at 5k. Bigger injectors and an AFM tweak help with that. The M42 will make good torque higher, and will happily make good power up to 7k rpm.

As for the overheating issue, I was using the wrong thermostat. I replaced the M42 e36 thermostat with the old M40 e30 thermostat that came out of my engine and the issue went away.