Troubleshooting Camshafts and Valve Gear BMW’s M10 and M30 Engine

“We discover how to keep the camshafts and valve gear happy in your BMW’s M10 and M30 engine..” 

Troubleshooting Camshafts and Valve Gear BMWs M10 and M30 EngineIt’s just over 57 years since the four cylinder BMW MIO engine went into production, and 51 years since we first saw the six-cylinder version, the M30. Both are good engines even if the cam lubrication set up was a bit flawed. When it worked it was fine, but often it didn’t due to inadequate maintenance – in some eyes these engines are not quite the bulletproof gems they’re often made out to be…

How it works

The cam is of course chain driven, duplex on engines up to September 1980 and simplex thereafter – there is nothing wrong with the later set up and because a simplex chain is lighter, it places less load on the sprockets. MIO chain rattle is always a worn-out cam sprocket though, and new ones are available from BMW.
The camshaft is lubricated by a steel tubular spray bar with four oil holes (MIO) or six (M30) and these spray oil between the cam lobes with enough oil to lubricate both. Oil comes up the head to the camshaft bearings and on most cars, two are slotted to allow oil past and up to the spray bar. The bar is secured by hollow banjo bolts with alloy crush washers – oil comes up the head oilways, into the banjo bolts and then along the spray bar, exiting via the oil holes. This great in theory but two things go wrong; the small oil holes block easily leading to rapid lobe wear and the banjo bolts work loose and eventually fall out with the same consequences. The service schedule says you need to remove the cam cover every 12,000 miles to do the tappets and check the banjos but if using standard bolts, I’d be doing it every six months or 3000 miles.

BMW do make a new type of bolt. This has a circular groove machined into the top and it is both pre- thread locked with dry thread lock compound and it has a slightly different thread pitch so that it grips into the head better. Two of these and new washers are about $20 from BMW and they are essential. It’s also essential to twist the spray bar around by 180-degrees with the banjo bolts removed, and run a tiny drill through the oil holes, both cleaning them out and making the holes bigger to avoid future blocking. The banjo bolt holes must be cleaned out with aerosol brake cleaner and allowed to dry before fitting the new banjos, torquing them to 10-15 nm. Once they are torqued, do not undo them again as this breaks the thread lock seal and allows them to work loose. Also, do not use regular threadlock on the old banjos – this will congeal in the oil hole and cause oil starvation. There is a mod that involves crushing the centre of the spray bar flat. This is supposed to increase bar pressure but you need to be very sure you have the cam with both journals slotted for oil to come up – some do not. The standard set up is perfectly okay when in working condition.

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If you remove the spray bar or are fitting a new one during a head rebuild , make very sure you fit it with the tiny arrow pointing forwards. This is so the oil holes are in the right place. If you fit it back to front, only six lobes will get oil and the other six will run dry.

Valve clearances should be checked and adjusted every 12,000- miles but if you do few miles, yearly is fine to check everything including the banjo bolts. There are two camps for doing the tappets. Some say do them hot, BMW say do them cold. The 12 thou cold clearance will reduce slightly as the engine gets hot and that’s the idea as the M30 top end is slightly ‘busy’. The trouble with doing them hot is that the engine is always cooling and if it takes you 30 minutes or more, the engine will cool quite a lot in that time

1. Start by removing the bits above the cam cover such as the airflow meter on fuel injection cars and the complete airbox if it’s going to get in the way. This takes a couple of minutes with a 10mm spanner and screwdriver on a E34-era car. …

2. Now remove the two retaining nuts for the spark plug lead plastic tube, disconnect the king lead from the coil and move it out of the way. On cars with a separate distributor you can unclip the distributor cap to remove the whole lot.

3. Undo the jubilee-type hose clip from the crankcase breather tube and remove it from the cam cover. The rubber tube can often be in a rough old state and some have an oil catching gauze inside that needs cleaning out

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4. Undo the eight 10mm nuts and one 10mm bolt, and remove the cam cover. The gasket was pretty knackered on this one and although it wasn’t leaking, it was last off in 2011 so it was now ripe for replacement.

5. The old gasket had stuck in places to the head, so I used an old Stanley blade to carefully clean if off, taking care not to mark the soft alloy of the cylinder head. Make sure none of the stuff gets inside the head though…

6. These later-style banjos were fitted in 2011 but they were starting to loosen when the tightness was checked. I ordered two new ones along with the alloy washers from BMW and they arrived just the following day.

7. Two new banjo bolts showing the circular groove machined in the top, and the baked on blue threadlock. Some owners have drilled tiny holes in the bolt heads and used locking wire to secure them, not a from BMW and they are essential. It’s also essential to twist the spray bad idea but these are fine. bar around by 180-degrees with the banjo bolts removed, and run a

8. Before fitting the new banjos, the hole in the alloy head must be completely clean and dr/. Use aerosol brake cleaner to wash the oil out and leave it five minutes to dry out. Then you can fit the new banjos and alloy washers.

9. Twist the spray bar around, and run a small drill through the oil holes to clean and slightly enlarge them. As standard they are a touch on the small side and can block easily – enlarging the oil holes does not affect oil pressure

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10. This is the tiny arrow on the front of the spray bar. Many new camshafts have been ruined because the owner or engine builder did not know that the spray bar is handed. The arrow must point to the front – you have been warned!

11. Torque the banjo bolts to between 10nm and 15nm – 13nm is the optimal torque. Overdo it and you’ll damage the thread in the head (bad news), under tighten and they’ll come loose. I use a small Halfords torque wrench for this.

12. Now we can do the tappets. Do each one with the cam lobe at 180-degrees from the rocker and aim for a tight 12 thou sliding fit- you should be able to get it in fairly easily. Crank the engine on the key bit by bit to do each one. Do the tappets with the engine stone cold.

13. Always fit a new cam cover gasket – they are only  $9-$20 so there’s no excuse. Clean the head and cover faces thoroughly and you can smear Castrol LM grease on the gasket to give a better seal. Do not use a silicon sealer.

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