M42 Sprocket Health

[noahds]

Time to replace my sprockets?

What's up R3v,
So I am about to put up roughly $1,000 to have my favorite mechanic rebuild this M42 as my replacement. This will include basic replacements before I drop it in at home, such as:
- Water Pump
- Thermostat
- Gaskets (Valve, Head)
- Fan clutch
- Everything rubber
- Sprockets
- Chain Guide
- Timing Chain
- (possibly oil pump)
But I was wondering if you guys think these sprockets are going to be high up in the priorities list. I am going for rebuild but if these will last another 30,000 miles I may just wait to do it myself down the line. Just hoping for some opinions as any advice for this process is welcomed. Thanks in advance! Noah

[roguetoaster]

Those need to be replaced, any time you see pointy teeth on the cam sprockets or the idler sprocket they should be changed. Yours even exhibits what looks like chunking at the bottoms of the tooth valleys, which is a rather extreme case of wear. That sort of appearance also indicates that the rest of the timing system may be worn out.

Just so you know, the crank sprocket looks point from the factory, but it's probably a good idea to replace it as well.

So, don't cheap out here, especially over $100 for the cam sprockets, or ~$350 for all of the sprockets. Also, don't be tempted to not do the lower guide as it is actually necessary, and when you get the new main guide there is a different bolt that is required when installing that guide.

[noahds]

Those need to be replaced, any time you see pointy teeth on the cam sprockets or the idler sprocket they should be changed. Yours even exhibits what looks like chunking at the bottoms of the tooth valleys, which is a rather extreme case of wear. That sort of appearance also indicates that the rest of the timing system may be worn out.

Just so you know, the crank sprocket looks point from the factory, but it's probably a good idea to replace it as well.

So, don't cheap out here, especially over $100 for the cam sprockets, or ~$350 for all of the sprockets. Also, don't be tempted to not do the lower guide as it is actually necessary, and when you get the new main guide there is a different bolt that is required when installing that guide.

ah bollocks, I was fearing my optimism for it's condition.

I see, well I have yet to take the timing case cover off to inspect the other guide rails, but will without a doubt now require their replacement in the rebuild process. I won't cut corners as I would really like to make this my daily driver. I just hope engine work on a stand is significantly cheaper than in the car... Crucial advice much appreciated!

[roguetoaster]

If you have the space, all of the repairs listed that you intended to have done are very much within the capabilities of someone who can swap an engine. So, if you wanted to save a few bucks you could, and in my opinion should, DIY the rebuild as none of those tasks require special tools.

Best of luck going forward with your M42. I can offer encouragement that an M42 treated to those repairs will be good for at least 7 years of complete thrashing as an on again, off again daily.

[Balleristic31]

If you ever need help on your m42 or e30 let me know! I'm in Santa Barbara as well and have done plenty of m42 work before!

[Mushroom Stew]

Hey all,

Don't mean to hi-jack your thread Noahds, but I'm new to the m42 game (previously had an m20 e30). I felt pretty comfortable doing the valve adjustments/waterpump/TB/ignition system refresh maintenance. I'd like to refresh my m42'd e30, possibly by preparing everything with a different engine. So here are some questions:

I know the e30 m42 is different than what the e36's use. However, it is much easier in my area to find m42b18's from an e36 than an e30. Is it possible to convert an e36 m42b18 to use in a e30? Any parts and work required would be really helpful. If not, perhaps I'll just wait till an e30 specific m42b18 comes up for sale, then try to refresh it like noahds is. I assume the repairs listed in the OP are still in the wheelhouse of a novice DIY'r like myself? I might even start a thread and see if I can the r3v m42 community help walk me through it......

[varg]

OP If you're tight on cash and need used sprockets that will last a while longer I have some that should be decent on my old M42.

[unixnerd]

I'm not sure it's a good idea to use newer sprockets with the existing chain. I'm a keen cyclist and I know that the chain and sprockets wear in together. If you replace the sprockets with a worn chain it may not end well.

I did this job about 17 years ago on my last 318iS at 122k miles, the previous owner had run the car too long on a worn tensioner. Current car has just over that mileage but sounds fine. I only do 2-3k a year in my current 318iS as she's a summer dry weather car so I'm hoping she'll be fine for a few more years. Put in a new tensioner years ago as a precaution.

[varg]

I never had any trouble with my used sprockets and new chain, and I beat that engine, my rev limiter was at 7,500rpm.

[noahds]

If you ever need help on your m42 or e30 let me know! I'm in Santa Barbara as well and have done plenty of m42 work before!

Much appreciated man! Will definitely have questions for you once I start ordering in the replacement parts. Something tells me I'm not going to take it to Granny's Garage this time around. I'm gonna tackle this list! And I guess my first question for you is, do you have a cam locking tool? haha -- anyways, thanks for reaching out man, will be asking you questions I'm sure to say the least

[noahds]

M42 Sprocket Health

Well I'm at a crossroad and need some wisdom:

These are the sprockets from my overheated engine



I was wanting to know whether you guys thought it would be ridiculous to take these internals (sprockets and chain) to use on the camshafts of the "new" engine posted above? I'm really not trying to cut corners in a death trap way, so knock some sense into me if I really should just wait another month or two to slowly fund the new parts. Thanks all

[roguetoaster]

Those look fine to me.

[jrobie79]

i see no issues with those

[jaredmac11]

Look great. I have some sprockets from an E36 m42 if you want em however.

[noahds]

Good to hear, thanks for the input everyone. Really appreciated -- started the tear down last night.



Much help from my buddy Nick, paying homage to his e30 days...


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