E21 316: More manifold gaskets for M10...

Stuck the new and much better quality exhaust-manifold gaskets on today from Euro Car Parts. They're thicker than the eBay ones and have steel rings round the inner rim like a head-gasket, should make a better seal. It's got rid of the cracking noise from that dodgy one on cyl. 4 [this post] and the engine sounds sweeter than ever.

Surprisingly the manifold nuts all came off as they should this time and left all eight studs in the head... weird, but it certainly made fitting the gaskets a lot easier.

E21 316: M10 Engine cured! - Culprit: manifold gasket...

After repeatedly timing the ignition perfectly to Z on the flywheel, [see this post], we decided there had to be something deftly wrong to be causing the loud noise and backfiring [in the vid below], rather than just the distributor being out of line.

The first hunch was the exhaust had broken while being twisted to get the cylinder-head out and was blowing like mad, but my initial inspections revealed no damage to the down-pipe or manifold and the four manifold gaskets looked all to be in position.

That is to say they LOOKED in position... Today, in the pouring rain, I got the car up on ramps to see what it was I'd missed and as soon as the torch flicked on I could see the answer at last - one of the exhaust-manifold gaskets had slipped off the stud and was only covering half the hole! Nightmare... Right at the back of the engine where we couldn't see and, ironically, the one for cylinder 4 that started all the trouble.

As you can see the gasket has been totally blown apart by the hot exhaust and has separated quite badly in the middle leaving only the metal. I checked the rest of the gaskets in my set for a spare, but can only find the same shape gasket with an oblong hole, perhaps for the E28, so tentatively decided to re-use the blasted one, correctly seated this time and caked in Holt's FireGum.

As soon as the engine fired up again it sounded like it used to. It's amazing the difference that gap in one single exhaust port made to the noise level. It was still idling low though and revving badly, so I grabbed the timing-light again to have another go, turning the distributor to line up Z on the flywheel - 25 degrees before TDC. Now the 30 year old M10 has really begun to purr once more. Awesome! Still some fettling to do on the carb. tuning, throttle/choke cables and checking to see if my damaged manifold-gasket is holding up, but at least she's back on the road after a tense month!

M10 Engine: Weber Carb. Rebuild [Twin DMTL]

As mentioned in this post [], rebuilding my Weber DMTL carburettor was one of the first things on my list of curing my misfire problems, which turned out to be a more serious blown head-gasket. Still, restoring the carb. is one of the first things the previous owner told me I should do and gave me a brand new Weber rebuild-kit with the car, so I guess it can't hurt the old girl.

This job isn't for the faint hearted though, so if you have a disposition towards botching fiddly things as I generally do, then it's probably best left to a pro - I messed up my throttle-cable and had to replace it, and fettling the throttle-spring arrangement was all but impossible to get back to how it was. It's still not right, throttle springs etc. a bit loose, but at least its running ok again.

Here's a great guide for tuning the carb. once it's rebuilt: http://www.carburetion.com/Weber/adjust.htm

**CAUTION: If you're running a Weber on an E21 then your 'Bowden' throttle-cable will likely have been cut to fit through the cable-eye on the throttle linkage. Cutting the metal end off the cable causes it to lose its tension and the strands begin to unravel immediately so be very careful when removing and fitting the cable to the carb. [especially if you need to do it more than once which broke mine], as once the cable has begun to expand inside the sheath it binds very easily and you will need a new one. These aren't in production anymore either and I got the last one from BMW Classic in Park Lane, though I'm sure plenty are still out there, but still save yourself the worry!

Does an early '80s E21 316 with an M10 run on unleaded fuel?

The answers before I bought the car pointed to yes but it turns out that the four-cylinders might not after all. Ignition timing is fine, apparently, down to as little as 92-octane unleaded fuel, but valve wearing is still a problem and an additive is recommended. It's about £8 a per tank so could be expensive over time. I don't reckon the previous owner had been putting any in regularly or they would have given me half a bottle with the car, so I think I'll be taking my chances.

The other thing is regular 95-octane unleaded or 98-octane super. The engines are designed for 100-octane leaded petrol so regular unleaded might be a fair drop performance wise, but does it make a difference to the valve wear?

As we parted company the previous owner said to fill it with super to get the best out of the engine, but said it would run fine on regular and that was all that was available to me at the filling station so it had to do. The car charged home without a grumble from the engine and feels very lively indeed, though I'll be filling it with super next and see if it makes any difference.

UPDATE: It turns out my engine has had the hardened valve treatment so it can run any unleaded without excessive top-end wear, so I haven't needed any costly, annoying additives and that's a relief. The engine seems happier starting up and a bit livelier running on 97/98-octane petrol, which is what I've been using for the infrequent use the car gets. Obviously the power gain isn't vast on a 100bhp engine and super-unleaded is dear stuff, so now I'm starting to use the car a lot more I'll be switching back to 95 RON for the sake of economy.

Fuel Consumption:

I've worked out from averages that my late 316 M10 1.8L engine, running a Weber DMTL carb. and the 5-speed 'sport' gearbox is giving me ~26mpg, which isn't bad at all really. Using the lower octane 95 RON fuel may give better mileage, or may make it worse, either way I would imagine the difference will be negligible given the amount I drive the car.