M42 head on M44

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B86un2003

Regular Member
Joined
Jul 15, 2024
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Hello all,

So the headgasket has gone again on my M44 after replacing it a couple of years ago. When I got the head skimmed the first time, the guy said he could not skim it again because of the amount of material he removed.

Rather than doing a headgasket again, I went out and bought (what I thought was) a replacement m44 to put in the car. Got it home anddd it has a metal Thermostat housing. Its an M42, which adds a whole level of complication.

Now, as far as I understand, the M42 has a more desirable head, including but not limited to higher lift/longer duration cams. What I want to know is, how involved is putting an M42 head on an M44? I'd rather not, but I can put the car on a standalone. The wiring side of things are of larger concern to me. Any new information will be much appreciated.

Thanks in advance,
Jonny
 
B86un2003 said:
Hello all,

So the headgasket has gone again on my M44 after replacing it a couple of years ago. When I got the head skimmed the first time, the guy said he could not skim it again because of the amount of material he removed.

Rather than doing a headgasket again, I went out and bought (what I thought was) a replacement m44 to put in the car. Got it home anddd it has a metal Thermostat housing. Its an M42, which adds a whole level of complication.

Now, as far as I understand, the M42 has a more desirable head, including but not limited to higher lift/longer duration cams. What I want to know is, how involved is putting an M42 head on an M44? I'd rather not, but I can put the car on a standalone. The wiring side of things are of larger concern to me. Any new information will be much appreciated.

Thanks in advance,
Jonny
Click to expand...
I imagine its quite a lot of work. Head bolts to block might fit but Manifolds might not so you might need to use much of the m42 intake and do some head scratching about the ECU. Timing chain might need some thought too.

Some people also like the m42 crank too which apparently is stronger especially if they're planning on tuning, turbo etc.

But for a standard runaround I'd stick with a proper m44 head. Can't be hard to find. Lots of 1.9 z3's falling by the way side.

But why does the gasket keep failing?
 
Duncodin said:
I imagine its quite a lot of work. Head bolts to block might fit but Manifolds might not so you might need to use much of the m42 intake and do some head scratching about the ECU. Timing chain might need some thought too.

Some people also like the m42 crank too which apparently is stronger especially if they're planning on tuning, turbo etc.

But for a standard runaround I'd stick with a proper m44 head. Can't be hard to find. Lots of 1.9 z3's falling by the way side.

But why does the gasket keep failing?
Click to expand...
Thanks for your reply.

ECU is my biggest problem I think. As far as I'm aware, you can use m44 timing stuff on an m42, so it'd be a case of fitting the m44 timing gears to the m42 cams. Use the m44 timing cover (also supposedly viable) to keep the m44 cam sensor. Exhaust manifolds are interchangeable. I'd need to use the m44 intake manifold, as I'm assuming the injectors go into the manifold and not the head but can't remember now, but whether or not the m44 manifold fits is a different matter. I believe theres a change in coolant line routing, an extra oil passage in the m42 head, and two temperature sensors on the m42 head (one for the ECU, one for the temp gauge) vs one on the m44 head. The m44 temp sensor supposedly fits the m42 head.

As to why it keeps doing headgaskets, both are negligence. The first, it sat at a very high speed for a couple of hours on a French motorway late at night, and ended up getting hot. Got home, and it started chuffing smoke. The second and most recent, the car has an ebay aluminium radiator, and the cap where a coolant level sensor should be worked its way loose. Car lost all of its coolant, and I didn't notice until the car shut off. End result, head warped again
 
Nearly everything swaps over as far as I remember.
Do make sure it’s a later head with the 6mm stems. Early ones, pre 93 (or 94?), have 7mm stems. Valve sizes are the same in both 42/44 heads.
The 42 has higher lift at 9.7mm v the 9.5 of the 44, though the 44 has longer duration cams, that’s helped by the roller rockers. If I remember correctly the 42 has solid buckets, so it’ll rev higher, but you’ll need to balance the whole motor to do that.
Both heads can stand a little more compression, 10-15 thou comfortably.
Do replace the stem seals, they’ll be hard as rocks.
 
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I broke up a 1997 Z3 last year with an M42 head fitted. It ran fine.

I only noticed when I pulled the engine out. I was annoyed with myself for not noticing - M44's are next to worthless but a good M42 head now has a value. Oh well.
 
The M44 is a tough little engine. Mine has now almost 150K miles, uses no oil and is on the original head gasket.
Some mechanical sympathy is required with all engines if they are to last. I would fit a replacement M44 head given the history.
 
As would I.
Nothing wrong with the M44 head really, ‘uprated’ M42 i believe uses quite a few M44 parts.The M44 gives better midrange because of the longer duration cam, BMW claimed 70% less valvetrain friction.

Metric Mechanic in the States mix-n-match parts in their engines. The 44 crank and rods are lighter, allowing the engine to spin up faster.



The only real advantage I can find is the 42 will rev higher using standard parts, the 44 needs different valve springs once you go above 6K, though if you want reliability approaching/above 6k in either engine there’s quite a bit of work required.

There are quite a few folk ( including me), building hotter M44, M44/2 M42/4 hybrids, most have gone away from S50/54 piston route (also including me), unless you have unlimited funds. 230hp is common nowadays with a big budget and the right parts, 350-400 with a turbo.
 
I must confess I'm no expert on this. But I gather maybe the best bit of the M42 is the crank shaft. Forged steel whereas the M44 is cast iron (i think) . Also M42 has 8 counterweights spaced along the length of the crank. M44 only has 4 counterweights. Make it lighter so spins a bit easier but more flexing at high rpms. So if you're going to turbo or super charge them maybe the M42 crank would be a good bet.

On the other hand I think if I really wanted more horses I'd just go for bigger 6 cyl which will likely be cheaper and get the hp without squeezing 1.9 till the pips squeek.

On the other other hand I do like my stock M44. Its plenty quick enough for me. But I can't shake off the idea that my 507 Rebody really wants a Rover V8
 
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