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Old 02-03-2015, 11:09 PM   #1
Hsquad12
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Default M42 timing case rebuild

Ladies / Gentlemen,
I am in the middle of tearing down a M42 engine that was parked 10years back with an overheating problem. Whilst i wait for the E12 socket to arrive required to pull the head i am contemplating what to replace/service within the timing case. The BOM makes for a frightening read if the sprokects and chain are replaced, so I am also considering the pros/cons and cost implications of upgrading the case to the M44 unit in order to delete the idler gear sprocket.

Oh, and the engine looks clean and has 131K miles on it for whats thats worth

If I have unlimited funds i'd replace everything however my inner Scot tells me the sprockets looks in great shape and a duplex chain wont be stretched. (it also looks in good shape btw)
So at one end of the budget I replace everything and dump $700+ into the timing case internals based on a used M44 timing case and oil pump and pray for a sub $300 bill on the head repair. this option does not make a lot of sense to me on a $2500 car....

Plan B is to be frugal and replace only the chain guides, c/shaft oil seal and stick with the idler gear and M42 case. if of course the idler gears checks out nice and smooth. otherwise it can be replaced.

trying to rebuild an engine on a budget is never fun and yes, i know an engine rebuild is never a place to save money so i'd appreciate some input on the "must have items" and the "nice to have" items.

Oh, and does the forum believe that the idler sprocket is a huge failure mode on this engine, or only and issue on engines that have been abused?
So many questions.....
thanks in advance.
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Old 02-04-2015, 12:06 AM   #2
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I would personally do plan B. I like plan B... For 700bux you can probably go M50 or most of it. Now there's food for thought.
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Old 02-04-2015, 12:50 AM   #3
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I would personally do plan B. I like plan B... For 700bux you can probably go M50 or most of it. Now there's food for thought.
Not going to argue with that.

What are you looking to get out of this E30... What are your long term goals?
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Old 02-04-2015, 02:16 PM   #4
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Wink

thanks inkk, i'm also leaning very much towards planB.

as for my plans - I was looking for a project vehicle for some time to rebuild and this car turned up over xmas on craigslist. this is my first BMW btw so i'm not an enthusiast although i will say i'm very impressed with the quality of both the design and manufacture.
the car looked too good to pass up or part out, and i hate parting out out solid cars so i bought it for grins.
i'm looking to put the car back together as a project to do with my Son and have a fun beater car to drive back and forth to soccer plus i miss driving a proper car with rwd and a manual box.
the body is straight, slightly faded paint and the interior is mint so once running i would think id be able to get $2500+ for it if i hate driving it.
before i make a financial decision on the timing case parts i need to get the head off and see how much it will cost to replace bent valves etc.
I also too a closer look at the sprockets over lunch and whilst the cams and idlers sprockets look almost new the crankshaft sprocket has a far more pronounced V shape with the peaks coming almost to a point. there are 15 links of the chain which i think will clean off so that could be reused along with the cam sprockets and possible idler gear.... or i could put an M44 case on and delete the idler gear for the same price as buying a new idler gear.... too many choices really.
Bottom line i wont be gunning the car to 6Krpm or driving like a maniac on the street. if i love the car and decide to upgrade the brakes, engine and suspension that will be long term project during which i will probably rebuild the engine again.
So anything thoughts on how much (& what) should be done to the engine to make a simple serviceable run around car out of this project?
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Old 02-04-2015, 04:50 PM   #5
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I would say you should be able to find a m42 that runs and you could just drop in for under $400. But like Inkk said, an m50 swap isn't far away from your budget, and if you want to sell it people will pay more.
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Old 02-05-2015, 12:02 AM   #6
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Default sprocket check

so i've taken a fresh look at the sprockets, chain, tensioner, chain guides and idle gear and given some more thought to the timing case rebuild.
looking at the condition of the hardware i'd have to say that i don't see much point in replacing anything other than the tensioner, and possibly the chain (if it does not clean up).
The idler gear is spinning really nice and the teeth on all the sprockets appear to be in my opinion in decent shape. I have no plans to race or rally the car so considering i'll be lucky to do 2K miles a year i think i can nurse her along for a while and maybe come back and upgrade the engine in a couple of years. Can you guys please take a look at the images below and let me know if you see issues that i might be overlooking? specifically, is the tensioner bar in good enough shape to reuse?

oh, and one last thing - i removed the upper chain guide between the cam sprockets to check the tension and the darn chain is 'bar tight' with barely 1mm of deflection at the midpoint. i hope this is normal but if not please let me know what should be expected!!!
cheers!
e
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Old 02-05-2015, 01:43 AM   #7
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idler looks good, and cam sprockets look like they have been replaced. They should be much more worn out.
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Old 02-05-2015, 08:15 AM   #8
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Default M42 timing gear

Thanks Nomade30. You made my day but it still early

I was of the same mind. In addition I think that the head has been off before as it does not exhibit the same amount of staining as the lower section of the timing case, which actually comes shinny clean with a light rub with a rag. The darn thing looks new once wiped down without a solvent.
The PO was insistent that the head was cracked when I bought the car and told me he had replaced the water pump (which is literally brand new btw) and a second hand radiator. He could not cure an overheating issue and gave up when water appeared in the coolant. At the time I was more inclined to think that the issue a profile gasket failure that resulted in a blown/cracked head due to overheating.
As an aside, I also noticed that the engine was air locked as the rear bleeds crew was dry while the thermostats housing chamber was full of coolant.

Anyhow, getting back on topic: what do people think about the condition of the crankshaft sprocket and tensioner bar/ guide?
And, should the chain be rock solid with minimal flex between the cam sprockets?

If the concensus is that I can re-use most of the timing gear then I think with a new chain, gaskets and M44 tensioner the case rebuilt will be $88, which is far more inline with my original gamble when I bought the car
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Old 02-05-2015, 02:39 PM   #9
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The crank sprocket teeth are supposed to be pointy (but this is not true for the cam sprockets).

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Old 02-05-2015, 08:15 PM   #10
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Default Crankshaft sprocket

Thanks for clarifying the unusual pointed form of the teeth on the crankshaft sprocket. I think there is enough evidence inside the case to convince me that some did a timing service and replaced a lot of parts before me. Once I get the head off I plan to pull the back half of the timing case and replace the gasket between the block and aluminum case. I will no doubt have more questions when I start to put things back together once I have a better understanding of the condition of the guides and chain.
Fear of failure or the failure of parts can be a paralyzing sometimes so thanks for the replies and sanity check. I'm back in common sense mode for at least a couple of days now so thanks guys.
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