r/EngineBuilding • u/[deleted] • 3d ago
BMW M10 Block Crack?
Hey all, I’ve seen this before while searching and usually the general response is the block is garbage, but I’ve got this M10 engine that I’m refreshing to put back into a project BMW 2002. It came with the car and seemed in good shape before I starting tearing it down to replace the head. After cleaning off the old gasket material and prepping the deck surface I noticed the dreaded head bolt crack shown in the photos. The thing is it looks like the crack doesn’t propagate into the water jacket if you look in the second photo and you can’t really feel it running a fingernail over it. I’ve got no history on it unfortunately since it was purchased from an estate. Not sure if this thing is cooked or not, I’ve got a lead on another block but obviously it’s cheaper to keep this one. Just looking for some opinions. Thanks!
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u/surewriting_ 3d ago
Time to put an m30 in there instead
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u/NFS_Jacob 3d ago
M30 would rock, but just really big for the chassis. The M20 is a great documented engine for the 2002 though
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2d ago
If all else fails would probably do an M42 swap on this. My E30 is the M42 and I love the engine.
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u/Legionof1 3d ago
I feel like German engines are one time use, you only open them to see why you are throwing them away.
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u/Rus-t-bolts 3d ago
Youre out of your mind. The m10/20/30/50/52 are all absurdly robust and hold up to huge horsepower numbers. Very hard to kill them without gross negligence. Source: i build/boost/tune them for a living
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3d ago
Any experience with this type of cracking?
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u/Rus-t-bolts 3d ago
Yeah it tends to happen when the m10/20/30 is serially overheated. Based on what I see(limited via phone screen obviously), if its just an na stock motor, if the headstud torques, run it. But first thing id do is check the cylinders for round and check to see if your head has cracks in the coolant passage below the cam from overheating. But ive run a few of these with minor damage luke this on "just for fun" cars for lemons or rallyx that never had an issue at all. If it was from oil passage to coolant passage it would be a different story but that crack is superficial, doesnt touch any other gallery, wont mix fluids or leak compression. Check other vitals and make a decision.
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3d ago
I appreciate this info. I did run a leak down test before disassembly and it passed but I’ll check the cylinders as stated and make a decision on it. Was hoping to run some boost at some point but maybe not with this going on.
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u/Rus-t-bolts 3d ago
Yeah i mean truthfully it would probably still be fine but for peace of mind if youre going to do boost later, maybe pivot to a block that doesnt have cracks. But these m10's are notorious for being wildly robust in the vintage bmw community. Bmw raced with these motors a ton in the early days to great effect against some gargantuan competitors.
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u/ZMAN24250 2d ago
Throw some thread sealant on the threads too or you'll find a very slow coolant leak.
Had the same thing happen do my trucks motor. I sent it and it's been fine so far.
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2d ago
Just went through that thread thanks! TBH this car won’t really get beat on so leaning toward just getting it in the car to get it on the road. What thread sealant did you end up using?
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u/ZMAN24250 2d ago
I had some ARP thread sealant on hand so used that. Probably overkill but I would think any about any Teflon paste thread sealant should be fine.
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u/howsitallwork 2d ago
Helpful that you share with us, that you feel that.
I suggest instead, you know, that this engine block was the basis for a 1500cc F1 turbo engine making circa 1400 bhp in the early 1980s?2
u/m0arducks 2d ago
To be fair that was the era of F1 where they’d chuck the engine after practice, chuck it after qualifying and chuck it after each race.
Usually they were rebuilt though, to your point
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u/its_kinda_hmm 2d ago
Actually the blocks they used for the f1 engines were the ones that already had lots of miles on them, because “if they were going to fail then they would have” they used to leave to blocks out behind the shop and piss on them because they were German and even the cars have piss kinks. These cast iron blocks were and still are incredibly resilient.
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u/FckXFckMusk 2d ago
It has been like this for a while from BMW, Mercedes et al.
I've seen a 2006 Mercedes slk collapse on the road due to a collapsed sub frame assembly, completely rotted away due to sub standard steel being used.
Mercedes knew about this and did no recall, if this happened on the motorway we'd be looking at severe casualties.
Germany engineering my arse...
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u/AllAboutYoButt 2d ago
i agree with you with any engine newer than this family of engine, at least for bmw. our M10s were high miliage when we got them and they just keep going. were not kind to them either.
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u/Oak510land 2d ago
The legendary thing about the m10 is in the 80s bmw cranked 800hp+ out of them by destroking to 1.5l and turbocharging. They took first in F1 with this setup. They specifically used salvaged blocks, the theory was the heat cycling made them stronger or something.
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u/TyrannusourR3X 3d ago
Only newer bmw engines, 2010+ are notoriously bad. Older bmw engines were bulletproof. Great for tuning with simple swaps from other engines instead of custom builds. Don't even get me started on ford engines nowadays. Even new hondas now are having head gasket issues & egr issues. Toyotas with wiring issues etc. Emissions is the real killer that's bringing all of automotive down.
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u/Legionof1 2d ago
I have abandoned all new vehicles... my newest is a 2012 LS3.
But damn the Germans with their coated aluminum cylinders...
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u/FckXFckMusk 2d ago
Porsche are the same with their crapppy engines, scoring on the cylinders....
Everything German now is dank, its wasn't allways this way.
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u/Nervous_Smell710 2d ago
I will say the B58 has a great reputation minus the generation they had a plastic oil pump housing that would break when running 5w-40 but every other engine that they've made that isnt a L6 has been trash
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u/Cheapskate3000 3d ago
Get it magnafluxed or grind it out, weld it back up and mill it
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3d ago
Seems like more effort than picking up another block at this point, I’ve got a lead on a solid one for $100. Probably cheaper to just take that one and get it machined for use
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u/Vic2Quick 3d ago
so what are we doing having this convo
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3d ago
Just killing time on a Saturday I guess. But really just trying to save time and money on this if someone thinks it’s still useable.
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u/masterteck1 3d ago
Put it back together and use liquid Teflon tape or some silicone on that bolt when torquing it down just to prevent coolant from getting into wherever that bolt goes to after the head gasket. Just don't beat on it for a while and everything break in it should be fine
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u/zardvark 3d ago
IDK, it looks like it's into the water jacket to me, or at the very least will be as soon as you attempt to torque the head. A competent machinist could weld it up, but it might be cheaper to find a sound donor engine. Frankly, IDK, I haven't priced these used engines lately.
Bottom line ... I wouldn't trust it, if I intended to keep the car.
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u/TheMilchkanne 2d ago
Hi, I‘m sorry to see the cracks. I‘ve got the exakt same one in the M30 block, which is basically the same. I and some other mechanics that are familiar with these engines never heard of it before (because everybody says they are bulletproof), but found some other guys online that had the same problem - there is a little info out there in some forums. Apparently you can try to get away with it if you just send it. One E34 guy on youtube did that. I looked for a used block and replaced it. Mine was already opened from the owner before me, so maybe he did some errors while torquing it down or some fluid left in the holes. But I talked also with some guy that had this problem in a never opened engine. Still don‘t know why this happens.
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u/Apprehensive_Mix1093 21h ago
Just found out the same thing on my freshly rebuilt m20 stroker. I was supposed to go to the dyno and saw water in my engine...
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u/sam56778 3d ago
Being cracked on both sides of the bolt hole leads me to believe someone, possibly even the factory run the bolt down rapidly with liquid in the hole.