I’m going to have the heads on this bike dual-plugged. It improves mileage (I went from the mid-forty MPG to the low 50 MPG on one of my bikes) and I like the redundancy (engine still runs on both cylinders if a coil fails).
I use, Randy Long, at Long’s Mechanical Services in Honey Brook, PA, to do head work. He is well respected and used by many shops for many motorcycle brands for valve and head work.
This bike has 83,000+ miles on it, and is the year range where BMW had known problems with rapid valve wear, (aka, valve recession or valve plastic deformation), particularly on the 1000cc engines. Based on the history of this problem, it’s very unlikely this bike has the original valves and seats. So I’m going to remove the valves and inspect them and the seats before I send the heads to Randy. Since Randy has seen more heads than I could in two life-timnes, I’m also going to have him inspect them.
Short History of Airhead Valve Problems
The following is based in part on a summary of what Bob Fleischer has written on this subject in the following document I linked to in the Resources section above.
The biological damage to all life forms from lead in the environment lead to it being banded in US and eventually the rest of the world. Starting in 1975, the EPA required lead in gasoline to be phased-out (the final complete ban from motor vehicles was in 1996) and mandated use of catalytic converters in automobile exhaust systems which could not be used with leaded fuel.
Tetra-ethyl lead was used for decades as an octane booster to eliminate pinging in engines. And it acts as a lubricant between the valve face and valve seat and reduces wear. So its elimination impacted the valve train of all vehicles.
BMW had to react to this change in gasoline additives and use new materials for the valve seats so they would survive the lack of lead lubrication and keep the valve seat from failing. Starting in 1980, BMW installed the first generation of new valve seats. They went from a cast-iron seat to stainless steel with a nickel-chrome alloy. Unfortunately, this design had poor heat transfer capabilities. It is important to the valve to be able to conduct heat to the seat for the brief time it is closed so the valve temperature is kept low enough that the constant pounding on the valve face doesn’t damage it. This alloy allowed the valve temperature to get high and the effect was to deform the valve and eat away at the valve face where it pounded against the seat. For an example of how bad that can be, see below.The 1000cc motors produce more heat than the smaller bore engines, so the problem was particularly evident in them. And, BMW introduced the “Pulse-air” system to reduce emissions, but the side-effect of that was to increase the exhaust gas temperature near the exhaust valves which didn’t help things.
By 1985, BMW changed the valve seat materials and the problem finally went away. But, it took four years for them to solve it, in part because Europe wasn’t as aggressive in removing lead as the US was, BMW didn’t do much analysis of this problem until it became common in all their markets.
I use a valve spring compressor to remove the valves from the heads. This particular one I used on British twins. It’s fiddly to adjust to the valve, but gets the job done.
Bob Fleischer has an article on valves and the history of problems when no-lead gas was introduced.
- Noisy valves; leaded fuels; valve seats; sick valves; valve guides; valve springs; valve seals; aftermarket valves; bead-blasting
Randy Long does any kind or work you might need for heads including installing new seats. Randy does not have a web site. Here is his contact information:
Long’s Mechanical Services
74 Risbon Rd
Honey Brook, PA 19344-1754
Quick Tour of the Heads
Each head in the 1983 R100RS has a 40 mm exhaust valve and a 44 mm intake valve. The intake valve is larger because the velocity of the air-fuel mixture coming into the cylinder is lower than the velocity of the burned exhaust gases, so the cross-sectional area of the intake port has to be larger to flow the same volume of gas that is exhausted.
These heads are used with BMW’s Pulse-air system. This was designed to circulate fuel vapors from the crankcase to the exhaust valve port so they would be burned. This helped BMW meet EPA hydrocarbon emission requirements.
I “updated” this system to help reduce exhaust gas temperatures. You can read about how I did that here.
I marked each head with the side it was on so I would not get the valve train components confused as to which side they came from. Note each head is “sided” as shown by the different casting numbers for the left and right head.
I made a short video of the procedure and some of the inspections.
Visual Inspection Of Valve Height
The valves ought to be proud of the seat unless valve recession has advanced. So a quick visual inspection can show if this problem is in it’s advanced stage. In particular, the exhaust valve face edges are visible and proud, so that’s a positive sign.
Test Valve Sealing Ability
Before I remove the valves from the heads, I want to test how well they are sealing. I put some gasoline (or you can use kerosene which is safer) into the inlet and exhaust ports.
Then I look at the valve face inside the head to see if it leaks. I found three of the valves were not sealing. That’s not what I want, but justifies taking the heads apart and sending them to Randy Long to address this.
Remove Valve Train
Before I remove the valve train components, I mark baggies for each valve train so the parts don’t get mixed up.
I install the valve spring compressor. There are many different designs. This one has a cup that fits on the top of the spring and pin that fits on the center of the valve face. The cup and pin have stems with screw threads. It’s easiest to tighten the pin side to compress the valves.
I compress the spring until the collet is exposed. The collet has two halves that fit into grooves on the top of the valve stem and hold the stem onto the spring assembly.
I use a magnet to remove the collet halves.
Then I slacken the springs, remove the compressor and disassemble the valve train. The spring assembly has a top retainer that squeezes the collet halves together, the spring and a bottom cup that centers the spring around the valve stem.
Inspect Valve Stem Height.
Before I remove the valve from the valve guide, I measure the height of the valve stem above the aluminum base of the head with my vernier caliper. The length should be 1.600 inches if the valve and seat have not worn.
My rough measurement is 41 mm which is a bit more than 1.600 inches. Randy will do this measurement when he gets the heads, but I wanted to see what I could learn. It’s not easy to take this measurement since the valve guide is secured with a cir-clip and I have to avoid that to get the measurement.
Then I pull the valve out of the bottom of the head.
Valve Face and Seat Inspection
I can inspect the valve faces and valve seats. I clean the carbon off the valve face and then measure the thickness of the edge, or lip, of the valve face. The minimum thickness is 1.0 mm. Less than that indicates the valve needs to be replaced.
I find the exhaust valve face lips are both about 1.3+ mm thick while the inlet valve face lips are about 1.6+ mm thick. So they are all serviceable.
The seat inspection doesn’t show any problem with the inlet valve seats, but both exhaust valve seats have pits in them likely caused by hard carbon deposits being pounded into them. These may be shallow enough that regrinding the seats will remove them. If they are too deep then the seats will have to be replaced. I will let Randy make that call.
I can see why the exhaust valves leaked as the pits allow leakage. But, I didn’t see evidence of why the right inlet valve seat being pitted. Nonetheless, it leaked, so it needs attention.
2019-06-24 Added Resources section. Minor editing.