Learning the Hard Way that Fiona's BMW engine came from a California Motorcycle

Yep, another lesson learned the hard way, the Chang way.

Monday, Memorial Day, I took Fiona out for a test drive to evaluate how the recently refurbished shock absorbers affected the ride.  In regards to this, she felt fine.

However, perhaps 3 miles into the test ride, Fiona suddenly started making a sharp snapping/tapping noise that followed the RPMs.  Dammit.

I stopped, put her in Neutral gear to evaluate while leaving the engine running.  It sounded very much like a backfire or exhaust leak.  I just couldn't spot anything amiss by the side of the road.  I then rode Fiona slowly back towards home, making quite the amount of noise as I went.

Got Fiona home and took another look, since it sounded like an exhaust leak, I concentrated on the mufflers, header pipes and such.  Found no holes that might cause the noise, this being a tip from RichardM.

I removed the headers as I realized that I'd installed one of the two metal seals backwards and not achieving a good seal at the exhaust ports on the cylinder heads.  While the header pipes were off, I cranked up the engine to see if the popping noise persisted and it sure did.

Not only that, but I could see big flames/fire coming out of the right cylinder head when I revved the engine, with nothing like it from the left cylinder head.

While it's apparently not unusual to see flames if the fuel mixture is too rich, I decided to dismount the right cylinder's head to do a leak test on the exhaust valve based on advice by Brook Reams, local Airhead Guru whom I had also called.

I could have saved myself a lot of work had I taken an even closer look at the heads before I took the sidecar off and removed the head!  Dammit.

So off came the sidecar from the tug mounts, off came the right side valve cover, rocker assemblies, push rods and cylinder head.  While doing the leak test, I rotated the cylinder head to prepare to pour gasoline into the exhaust port (this to see if the gas leaked out at the valve in the combustion chamber) and lo and behold I spotted this opening:

Quite evident that a cap was missing, isn't it?

This smaller opening was my damn exhaust leak!

Now, it was obvious why the exhaust leak noises came on all of a sudden from the right cylinder's area!  It had fallen off, backed off from its thread over time, and of course created a large exhaust leak!

The opening is for the connection from the cylinder head/exhaust manifold to the air box for the Pulse Air System used by BMW back in the early 80's to meet EPA emissions standards.  The previous owner or someone before him had removed it and capped off the openings by cutting the pipe and bending it shut.

Here's a picture of the left cylinder's exhaust manifold cap to give you an idea of what fell off the right cylinder:

The header pipes obscure one's view of these exhaust manifold caps if one isn't used to looking/checking for them.  All this time, I had thought these strange caps were for a previous dual spark plug setup on this engine; boy was I wrong!

So, I got some more practice removing the cylinder head yesterday and reinstalling everything and associated hardware this morning.  I obtained oil drain plugs that were the right size: M16 x 1.5.  I got the size from both RichardM and Brook Reams (airhead guru whose tutorials I followed to take apart and re-assemble the engine cylinders in order to replace the pushrod tube seals).

Note: I got the plugs from O'Reilly's Auto Parts, they were for Subaru cars, 2011-2017.  $4 each.

The plugs came with a composite materials washer so we'll see how they stand up to the head generated by the heads during engine operation!

Here's views of the replacement plugs:

 Right Cylinder Head

Left Cylinder Head

I waited about five hours or so and after getting confirmation from Brook, started up the engine for just a minute or so and was gratified to NOT hear the exhaust leak noise that had caused me such stress yesterday!

So now I know how to ID cylinder heads which used to be equipped with the Pulse Air System to meet emissions standards.  Now I know what the sound will be if one of the replacement plugs comes off in the future.  I also confirmed that in the case of this engine and frame combination, you can replace the push rod seals without removing the cylinder, though it's much easier that way to apply sealant during re-assembly.

I'm also on the lookout for high temperature red Loctite to secure the plugs, I am unsure the Loctite will withstand the head generated by the heads but it's worth a shot anyways.

Now Fiona is ready to go camping!  I'll double-check the torque on the rocker assembly nuts tomorrow morning, re-check the valve clearances, then mount the valve cover back on for riding.  Luckily, I had a spare valve cover gasket since I tore the one on the head during disassembly.

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