M10 Engine Rebuild

[walter_middie]

I’m starting this blog to document my engine rebuild. I bought a 1976 BMW 2002 for my daughter after she graduated from college. I’ve liked having older cars most of my life, and I think it’s rubbed off on my daughter, as she really wanted a 2002. This one didn’t look too bad and was fairly cheap. After driving it for a few months, the head gasket let go.

It looks like the PO may have thrown this motor together for a quick sale, as it was not the original engine, the head was cracked, and the block cylinders were scored so bad it could not be bored out.

I got a couple of very good recommendations from the BMW locals on a machine shop and an independent repair shop:

Gary at Pacific Auto Machine in Renton, Washington

Patrick at Midnight Motorsports in Seattle, Washington

Help from Gary and Patrick has been extremely helpful. I’ve rebuilt a couple of engines before (small block chevys, a Triumph TR3, a Porsche 911, and a Yamaha RD400). I’ve made a lot of mistakes in the past, but I’ve learned a lot. I guess I’d rather jump in and try it myself as opposed to having someone else that I know will do it right the first time. So I’ve once again decided to assemble the engine myself.

I found a good core under a tarp in someone’s backyard. It was a good core that only needed boring to get some minor rust cleaned up. Good parts were the head, valves, valve guides, crank, and rods.

I decided to stay with 9:1 pistons for the new ones as the old ones were also 9:1. I’m also having my cam re-ground to 292 specs by Delta.

Yesterday (Friday Feb 3rd, 2012) I picked up my freshly machined block, my balanced pistons, rods, crank, flywheel, clutch pressure plate, front pulley, and miscellaneous gaskets. That night I painted the block, installed all 8 of the 36 mm freeze plugs, and installed the crank seals into the front cover and the rear crank bearing oil seal retainer.

Saturday started with ring sizing. Each ring is pushed into its cylinder with a piston and the gap is measured.

I like to double check things, and I have a Haynes manual, the blue factory manuals for a 320i, and the rule of thumb. They all come up pretty close, so that’s good (all measurements given in mm unless otherwise noted).

Haynes / Blue Book / Theory

Top Ring 0.30-0.45 / 0.30-0.50 / 0.36 (0.004” *Bore)

Middle Ring 0.30-0.45 / 0.20-0.40 / 0.45 (0.005” *Bore)

Bottom Oil Ring 0.25-0.40 / 0.25-0.40 / 0.38 (.015”)

After sizing all the rings I went for a quick run and had the rest of the morning off to relax. By 1:00 I had a rented engine hoist and an engine stand in the garage. I mounted the bare block on the engine stand, and assembly began.

It’s my daughters’ car, so she assembled the engine.

We dropped the crank into the block on dry bearings (no oil yet). Plastigauge was inserted and the main caps were torqued to spec and then removed to read the squished Plastiguage width. After confirming the bearing clearance, the bearing saddles were oiled and the main caps torqued for the 2nd and final time.

The process was repeated for each piston – install piston with dry bearings, tighten rod caps to spec, remove and read plastigauge, clean, oil, and reinstall rod end caps for the final time. Repeat 4 times.

Now we have a short block rebuilt!

It was dinner time, so we took a break. After dinner we started lowering the completed short block into the engine bay.

I knew it was going to be difficult to line up the engine and transmission, so I installed a couple of guide pins – bolts screwed into the block bell housing with their heads cut off. It still took quite a while to get them lined up just right. About the time I was wondering how much trouble it would be to remove the transmission, the clouds parted, the sun shown, angles sang, and the engine and transmission came together. Hallelujah.

[walter_middie]

I just found out that my head and cam are ready to pick up - so I should be able to finish this up by this weekend.

[roadhog0]

Very nice! I'm glad my old motor came out good for ya! Should be a nice runner when it's done! Keep up the good work Rex!

[walter_middie]

Thanks Nathan.

I picked up my head, cam, and new head bolts today. I'm taking the day off from work tomorrow so I won't be hurried, and can spend my time making sure everything is done the way I want it. Sometime this weekend we should be able to start it.

[walter_middie]

Long weekend. Friday was spent getting the fan, radiator, and alternator back in. Then I put the head back together. Once that was done, I attached the intake and exhaust and called it a day.

Saturday morning I installed the head, torqued the head bolts, installed the cam sprocket, hooked up the coolant lines, and adjusted the valves.

Sunday was spent priming the oil, installing the distributor, and adding coolant. It started easily. Unfortunately a dead battery made it hard to restart.

[Guest Anonymous]

Nice build

[FunElan]

How long did the whole engine rebuild process take you??

[bjbarbieri]

Great work! You didn't waste any time!

[jrkoupe]

I havent reviewed your posting dates but that sure seemed fast!

how would you compare the m10 vs the early 911 rebuild?.....

kudos to your daughter...and her red nails...lol..she is lucky to have a pops like you.

any pics of the 911?...

[delacruz7]

Hello Walter,

Your engine looks very nice! I am building a similar one as a mild racer. We are using 90mm cast pistons and was wondering what you had for piston to cylinder clearance. The books I have say that the factory spec is 0.0018". Mine came back from the machine shop with 0.003" clearance and the machinist insists this is what he has done in the past. What did you use and how's it working for you?

It would be interesting to hear how it feels to drive your car after all the work you have put in it.

thanks!

Rudy G.

[walter_middie]

Thanks to all for your replies. I'm sorry I haven't been on here for a while to update my progress. It has been a bit of a struggle, but I think I'm finally over the hump.

The reason that this blog stopped so suddenly was for 2 issues that came up right as the engine was ready to start. One was easy - that was a bad starter that would drain the battery every time you started the car. The engine that I bought came with a starter, and switching to that one fixed the starting problem. Now for the real issue - as I was doing the final torque of the head bolts (25 deg turn), one of the bolts did not not increase resistance. I removed the bolt and the threads looked fine, except for some metal shavings - from the block I assumed. I put the engine together and held my breath for a couple of weeks while I explored my options and got the tools together. I found a kit you could buy specifically for drilling and tapping a BMW head to fix a striped thread - but it was $400.

What I finally did was to buy a special tap, drill, and threaded insert like a Time-Cert, which is stronger that just a threaded coil of wire that is inserted. I used the old cracked head that I had for a drill guide by drilling out the offending bolt hole in the old head, and mounting the old head on the block after carefully taping off anything I didn’t want to get chips into. It worked great – the hole was drilled square and the threaded insert went in and held. Bolting the new head on for the final time, all the bolts torqued up correctly.

The engine has been running for about a month now, and the only problem I’m having is the points keep burning. I’m hoping to get it connected to a friends scope to see what the issue is. I don’t know if my new condenser is bad, connected wrong, or I have a bad match of coil and condenser. I’ll get to the bottom it or replace with Pertronix. All in all the engine is running wonderfully – no smoke – no oil consumption – no leaks – no funny noises.

FunElan – How long did it take me? I started just before Christmas, and it was running in early February.

Bjarbieri – thanks

Jrkoupe – it would be hard to compare the 911 engine rebuild with the 2002 rebuild. The 911 was a lot harder, a lot more complicated, involved a lot more specialty shops and mailing parts around the country – and a ton more $$$$. In short, the 2002 was a breeze in comparison.

Delacruz7 – I’d have to ask my machinist about the piston clearance used. The machinist I used knew these cars very well, and I traveled a long way to use him, but it was worth the trouble in the long run. How does the new engine feel? Pretty darn good. I am still using the old carb, and I have been told that a bigger carb would make a difference. However, at low speeds I really don’t feel much difference other than it is smoother and doesn’t smoke. The real difference comes when you put your foot down. Instead of running out of breath at 4,000 RPM, it now pulls really strong up to 6,000 RPM. Before, the freeway was about top speed or close. Now I can keep up with fast lane traffic without even trying.

[Guest Anonymous]

Hi Walter,

Very interesting information on your engine rebuild. Can you tell me who you used as a machinest since I have a 1971 BMW 2002 and I am considering trying to rebuild my engine also. Last question, can you give me an idea how much it cost to rebuild your engine?

Thanks,

Tom

[Guest Anonymous]

what size are the bolts that hold the engine to the stand thanks

[Guest Anonymous]

dear SIR

I have a BMW 2002 ti the block is STD but I'm going to rectify 0.20.

the engine compression rate at around 12/14.

The car is ready to racing but i would like to know what the best pistons to compete..

waitting your opinions and some alternatives.

my e-mail :Pedro.pacodascortes@gmail.com

Best regards

P.Rosado

[Adhvanit]

Is there any chance you still have the photos from this build floating around somewhere so I can see them?

 

When I finally do purchase an '02 I want to rebuild the engine so seeing the process would be very helpful.

 

Thanks

-Adh