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 1000 cc 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-times, I’m also going to have him inspect them. That way I learn more about what to look for when evaluating the condition of the valve train.
Bob Fleischer has an article on valves and the history of problems when no-lead gas was introduced that is in the first article below.
- Bob Fleischer: All About Valves
- Bob Fleischer: All About Rocker Arm Assemblies
- Bob Fleischer: Setting Valves
- Duane Auscherman: Setting and Adjusting Valves
- Duane Auscherman: Specifications for BMW motorcycle engines
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
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 his documents I linked to in the Resources section above.
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.
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. The catalytic material (platinum and palladium) can not be used with leaded fuel, as the lead will “poison” the catalyst rendering it useless.
The elimination of tetra-ethyl lead adversely impacted the valve train of all vehicles designed to assume its use in gasoline. BMW had to react to this change in gasoline additives and use new materials for the valves and 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 valves and 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 life of the valve to efficiently 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 deform it. This alloy allowed the valve temperature to get too high and the affect was to deform the valve (plastic valve deformation). That in turn allowed hot exhaust gas to leak past the valve and seat accelerating the deformation.
For an example of how bad that can be, see below.The 1000 cc motors produce more heat than the smaller bore engines, so the problem was particularly evident in them. And, in an attempt to reduce emissions, BMW introduced the “Pulse-air” system, but the side-effect of that was to increase the exhaust gas temperature near the exhaust valves which didn’t help things.
The pre-1980 bikes that had been designed for leaded gasoline also had valve problems, but the problems too several years to show up due to lead being retained in the valve and seat as well in the gas tank lining. Eventually, the seats of the pre-1980 models began to erode away and the earlier bikes joined the ranks of models with valve train failure.
By 1985, BMW changed the valve seat materials and the problems went away. But, it took four years for them to solve the problem caused by stainless seats, 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 but gets the job done.
Quick Tour of the Heads
Each head in the 1983 R100RS has a 40 mm exhaust valve and a 44 mm intake valve. For this reason, these heads are often referred to as “big valve” heads. 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 leaving the cylinder, so the cross-sectional area of the intake valve and its intake port has to be larger to flow the same volume of gas into the cylinder that is exhausted.
These 1983 heads are used with BMW’s Pulse-air system. This was designed to circulate fuel vapors from the crankcase back to the exhaust valve port so they would be burned. This helped BMW meet EPA hydrocarbon emission requirements. But, it also increased valve and valve seat temperature accelerating exhaust valve failure as discussed above.
I “updated” this system to reduce exhaust gas temperatures when I first got this bike. You can read about how I did that here.
As I removed the heads, 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. Note also on the left head, toward the left side of the fin is an “L10” marking and on the right head toward the right side of the fin is an “R10” marking. These indicate which head is the left and which is the right. It’s second nature to me to mark things and not rely on manufacturer marks to ensure I don’t mix things up. 🙂
I made a short video of the procedure in this write-up and show some of the inspections I made of the condition of the valve train.
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 be visible and proud of the seat. Mine are, 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 leaking and not sealing. That’s not what I want, but the result certainly 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 my valve spring compressor. There are many different designs, and 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 valve spring compressor and disassemble the valve train. The spring assembly has a top retainer that squeezes the collet halves together, a valve 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 more precisely 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. I noticed that one valve didn’t slide out of the seat easily. So something is amiss with the valve stem and/or the seat.
Valve Face and Seat Inspection
I can inspect the valve faces and valve seats. I clean the carbon off the valve face with a wire wheel and then measure the thickness of the edge, or lip, of the valve face as shown in the picture below. 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 prevented a tight seal. But, I didn’t see evidence of the right inlet valve seat being pitted. Nonetheless, it leaked, so it needs attention.
This is what I learned from Randy Long after he inspected the heads and valves.
- One valve guide was loose in the head. I noticed that one valve didn’t slide smoothly out of the valve stem, and this explains why. So it needs to be replaced. That said, I had him replace them all.
- The right intake seat had been cut wrong and had cut into the head. This explains why it leaked. The cut isn’t deep enough to rebuild the aluminum, but a new seat is needed.
- The seats had been replaced, but the pocket for them had been cut a too deep. Randy felt the new seats would work, but if after assembly the valve stem height was out of the acceptable range, he would build up the pockets in the heads and cut them to the correct depth.
- The valves are in good condition. We decided to reuse the intake valves. I opted to replace the exhaust valves since they are subject to harsh conditions and it made sense to refresh them along with new exhaust seats.
- I asked Randy to convert the heads to dual plugs and to weld up the outer plug face so both the top and bottom plugs can be the standard length. If you don’t do that, the bottom plugs have to have a shorter reach to avoid contact with the piston. This extra touch makes it “stupid proof” to replace spark plugs.
- He concluded that the exhaust valves and seats had been replaced previously, but the workmanship was not “top drawer”. I have every confidence they will be after Randy rebuilds them this time. So, they should be good for 100,000+ miles.
2019-06-24 Added Resources section. Minor editing.
2019-11-22 Edits, typos. Added Postscript section.
As always I greatly appreciate your sharing of knowledge and experience. Thanks for your efforts, I learn soooo much.
Great article,… I am considering purchasing a 81r 100 rs and the previous owner has had it for 15 years but knows nothing of valve issues- is it possible( for a amateur ) to see if the valve seats have been replaced by simply removing the heads ?
This has some information about how to identify the correct BMW replacements:
I hope that helps.
thanks ,lots of info to digest ! so the bottom line is that the correct valve seats have 2 scribes on the inside…..which I guess is only accessible before the seat is fitted.
The lines are visible on the outside of the seat so you don’t need to remove the seat to see them.
thanks for clarifying that !