R100 Mono Shock Airhead, Pros & Cons

Having now ridden the new-to-me 1995 R100RT about 2100 miles, I have noted several pros and cons in comparison with twin shock R100s. First the pros: no ping; accepts regular gas; electric fuel valve shut off solenoid (good backup, in case I forget to close the manuals); the infamous exhaust valve recession problem has been fixed, tubeless tires, better front brake (same pathetic rear), larger fork tubes; though slightly de-tuned, power is still comparable with earlier, "big valve", R100s.

Cons: possible slight drop in MPG; possible circlip missing in transmission (only time will tell); even worse OEM rear shock than the OEM twin shocks were.

Sure glad to be back on an Airhead, and thankful to have gotten to experience a mono shock model. Overall, looks like they saved the best for last.

Another plus maybe a minus

Mind you, I don't own a 85 and newer airhead, but one of the things improved over the 85 and newer bikes is they removed the wiring from the headlight shell.

I just put all new wiring harnesses in my 84 R80RT and can say, trying to stuff a jumping bundle of snakes back into the confines of the headlight shell is a three shot whisky job. Having the wiring on the frame as the newer bikes is a welcome change to a lot of people.

The only down side to this would possibly be less protection of stuff from the elements. Most owners won't have to worry about that point as they don't ride in the inclement weather I sometimes do. It took a long time and lot of miles riding in winter salted roads to wreck my wiring system resulting in the replacement.

As for pinging, I have never had a pinging problem with my 78 Euro spec R100RS, and with my R75/7, the only time I did have pinging problems was when the bloody points started to wear out. That problem with the RS was solved by going to a Boyer system and ditching the points.

Enjoy the bike, any airhead is a thing of beauty. St.

There was a thread on Mono shock vs Dual shock a couple of months back. if you can find it it probably covers what you want to know.

Anyname said:

There was a thread on Mono shock vs Dual shock a couple of months back. if you can find it it probably covers what you want to know.

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Don't, "...want to know" anything. Just posting observations based on recent experience with a mono shock, and prior experiences with twin shocks.

Rt

jhall said:

Having now ridden the new-to-me 1995 R100RT about 2100 miles, I have noted several pros and cons in comparison with twin shock R100s. First the pros: no ping; accepts regular gas; electric fuel valve shut off solenoid (good backup, in case I forget to close the manuals); the infamous exhaust valve recession problem has been fixed, tubeless tires, better front brake (same pathetic rear), larger fork tubes; though slightly de-tuned, power is still comparable with earlier, "big valve", R100s.

Cons: possible slight drop in MPG; possible circlip missing in transmission (only time will tell); even worse OEM rear shock than the OEM twin shocks were.

Sure glad to be back on an Airhead, and thankful to have gotten to experience a mono shock model. Overall, looks like they saved the best for last.

Click to expand...

I bought my '93 RT new when it came out and you did a good job in pros and cons.

I thought the Monolever chassis handled much better than the older twin shock frame. Having a '74 R90s, the handling was definitely better and the brakes were a huge improvement over the S equipped ATe's. A couple of issues I had with the bike was a failed output shaft bearing in the tranny (closest to the engine). I repaired that with an upgraded bearing. I also had a never ending issue that when the bike got warm, the clutch lever felt sticky. Found that the throw-out lever bearing assembly is more of a nylon material and expands at a different rate than aluminum. Had I kept the bike, (switched to an Oilhead RT), I would have probably taken a few thousandths diameter off on a lathe.

The motor always felt torquey but really didn't compare to my R90s in top end or roll on power. If I recall, the Monolever R100RT's had smaller valves, smaller intake tracts from an R80 and with the lower 8.5 compression, it's performance was quite a bit less than older R90's or R100's.

Just my opinion of course.

RPGR90s

Detune

The early R100RS and RT bikes were higher compression, and bigger valves, carbs. Not sure when BMW started to detune them Perhaps 81? First compression was lowered, then valves got smaller and carbs got smaller. If you put a 77, 78, or 79 up against a 95, there is a noticeable difference in HP and torque. St.

STEVENRANKIN said:

The early R100RS and RT bikes were higher compression, and bigger valves, carbs. Not sure when BMW started to detune them Perhaps 81? First compression was lowered, then valves got smaller and carbs got smaller. If you put a 77, 78, or 79 up against a 95, there is a noticeable difference in HP and torque. St.

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The 79-84, "big valve" (bigger intake) 1000cc Airheads maybe had a bit more power, but the PITA exhaust valve recession took all the fun out of them, at least for me. Small valve R100/7s did not have the recession problem, at least mine did not, nor did my R90/6 with same valves. I sent the 82R100RT's and 79 R100RT's heads off to Randy Long for valve upgrade, but still had to adjust the valves every 2500-3000 miles, even though setting the exhausts wide, to .010".

As for mono shock 1000s being detuned, not sure I agree. It's been over 20 years since my last 1000cc (79 R100RT), but I do not recall it being any faster than the current 95 R100RT. Someone used the word, torquey above, and that's how I'd describe the mono. Also, I definitely agree with others who say the mono shock handles better.

Ping is another PITA I had to live with, on the 78 and 79, 1000cc Airheads. It all but disappeared in 1981 when BMW installed nikasil cylinders. To me, the ultimate dog was the 1980, last year of iron cylinders. They were reduced to 8:2 CR, if I recall, in effort to reduce ping; they still pinged, but MPG and performance suffered. The smaller valve R100/7 also pinged. I dual plugged my 78 R10/7, and later my 79 R100RT; they both still pinged, but not as badly. If I recall, with dual plugs the advice was to reduce ignition timing by setting it on the OT mark at 3000 RPM and up. Many claimed dual plugs eliminate their bikes' ping, but it did not for mine. It did allow for slightly leaner carb jetting, which got a bit better MPG, but not enough to justify the cost fo dual plugging.

Ping

I read about people having such problems with pinging in their bikes from the 70's and I must say, I never had a problem then or now. I had a 77 R75/7 that would only ping when the points started getting out of adjustment. When they were adjusted, I never had a problem. When I bought my 78RS, I put in a Boyer unit, and have never had a pinging problem ever and I do ride the bike briskly. I have friends with bikes from that age who also have no pinging problems.

My 84, R80RT suffered valve seat recession and the first head rebuild solved the problem. I adjust valves now in the recommended range of 15k miles. On the RS, the heads lasted 140k miles before needing rebuilt.

I bumped the compression up when I rebuilt the R80RT to 9,5 to 1 from 8.5 and noticed a difference in the performance. I get no pinging with this bike.

Sadly when you detune a bike, you loose performance. I have not done a lot of riding on the 85 and newer machines but, when I compare my 77RS and my friend's 79 RT against the detuned 85 and newer bikes, hands down there is a difference. The earlier bikes will smoke the newer ones.

I don't know, maybe where people lived who had the pinging problems the gas was or is different. I just know I have never had a problem with pinging, except for when my points got out of adjustment. St.

As for pinging, I've not had any issues at all with my '78 R100/7 except whenever I got bad gas. I've always run the highest octane I could get and have continued to do that with the Siebenrock top end kit. I included a base gasket to knock the compression back from the 9.5:1 to closer to stock...I was just fine with the 9.0:1 or so that it came with. Pinging was a noticeable thing with the '70s 600 cc models...they had a mild cam which resulted in the tendency to ping. My Dad had an R60/6 that we could never get to stop pining. This was back in the early 80s before the internet and the wide range of options. For that bike/model, the issue was likely the advance curve, getting too much advance too early. A "fix" for that might have been an electronic ignition such as a Boyer where different advance curves could have been used...they might have slowed the rate of advance, thus creating less tendency to ping.

I read above about valve recession and wanted to include here a little more of a nuanced discussion of recession. I think people use this term to describe the symptom of valve clearances closing up as a result of valve recession...that's a little broad in the reasoning. Oak Okleshen discussed this extensively in several ABC Airmail articles. I'm sure Snowbum also mentions this on his site as well. Basically, the Airheads had three periods of valves/seats grouped as up to 1980, 1981-1984, 1985-on. Except for the 1985-on, the other two periods saw valve clearances close up over short periods of time. The problem seemed to be worse on the 1000cc models and especially the fully faired models as more heat was generated...heat just exacerbated the problem.

For the 1970-1980 models (and I suppose by extension all conventional valve/seat heads that came before), the issue was the classic valve seat recession. With the loss of lead additives through the 1970s, the cushioning effect of the lead deposits on the valve seats began to be eliminated. What began to happen was transfer of material between the valve face and the seat began to take place. Since the valves rotate in the head (due to the influence of the lifter surface offset to the cam lobe), this material transfer and loss of material would result in the valve face sinking deeper into the head and the resulting clearance at the tappet diminished. So just about any classic iron cylinder valve/seat interface would eventually suffer from this. There were lots of factors, as mentioned heat, the precise angles cut into the valve seat, how the bike was ridden, and others I'm sure. Maybe some bikes built on Friday suffered more!

Then came 1981 and BMW thought they had the solution. They started using a new tool steel valve seat and changes to the valve. Turns out the valve seat material was not a good conductor of heat, so the heat generated would stay in the valve face. Over time, the valve face began to warp or tulip since it was relatively thin. Once that started to happened, the valve clearances again began to close up. It's hard to realize this (for me I guess) that with the engine running along at 4000 RPM and the valves going in and out, resting on the valve seat for fractions of sections, that some heat transfer is supposed to happen. Oak also mentioned that sometimes the new valve seat had one of the angles cut so thin, the angle that the valve actually sits on, that coupled with the poor heat transfer of the seat and the reduced surface area, the problem was worse. This situation Oak called Valve Face Plastic Deformation...basically describes physically nature what was going on.

BMW noticed the problem, I'm sure there were plenty of complaints maybe even warranty claims...I don't recall. So for the 1985 models, they changed all the valve seats and valves and the problem has tended to drift into the background. I'm sure though that some attention still has to be paid to this situation and to check valve clearances on a routine basis. Stuff still happens!! So when someone goes for a top end overhaul, getting quality (IMO BMW) sourced valves and seats done by someone who know how BMW heads/valves are supposed to be set up is the way to go.

So just for the record: through 1980 models --- valve seat recession; 1981-1984 --- valve face plastic deformation. Same problems with valve clearances, it just results from a different process.

20774 said:

So just for the record: through 1980 models --- valve seat recession; 1981-1984 --- valve face plastic deformation. Same problems with valve clearances, it just results from a different process.

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1000cc, Bg Valve Unique Problems

In mentioning valve recession (or whatever you wanna call it), I was careful to distinguish between big valve, 1000cc and all other. I did not have the problem with the R100/7 or R90/6, and both had smaller intake valves. They'd go 9000-10,000 miles between adjustments. On all models, it was the exhaust valves that closed, never the intakes. I had read the problem also stemmed from the larger intake valves and not enough space between intakes and exhausts, and agree it may have been at least a contributing factor. The 1979 R100RT and 1982 R100RTs I had were the only Airheads to have the problem, and both had big intake valves. The suggested fix, back then was to have the valves & seats upgraded. I had the 82 RT's upgraded in early 1990s, and the 79 RT's in late 90s. Both were improved, but still fell way short of the 5000 mile valve adjustment intervals the factory called for; before upgrade, maybe 2000 miles at most, after upgrade maybe 3000. I think, back then, BMW gurus were still learning about the problem. I recall the first set of heads, RL said I'd have to run a short reach plug on the bottom, which I did. The second set, he included a bottom spacer to allow running same long reach plugs as on top.

I followed Oak's guidance in dual plugging, as written in BMWMOA News; retarded timing and leaned the carbs a bit. It reduced ping maybe 50 percent, but did not eliminate. Biggest advantage was the ignition booster made the points last indefinitely. The contacts no longer burned away, only need to change points when the wear block was excessively worn. Oak said the R60 was most prone to ping, but I was never attracted to much below 1000cc. My R65 quickly became boring so I sold it. To me, it was kinda like a Harley Sportster, a.k.a., "baby Harley". My R90/6 had minimal ping. In all iron jug Airheads, I used premium gas, and usually octane boost. I'd buy booster pellets about the size of a 20 gauge shotgun shell, in packs of 3. I'd break them in half, and keep them handy. Each gas fill up, I'd drop in 1/2 pellet. The pellets, again, helped, but did not eliminate ping. I rode Airheads when living in NY State, California, and Kentucky. Also rode them coast to coast a few times, so I doubt it was a local gas problem.

So far, this 95 R100RT seems to have conquered both of those PITA problems of ping and valve recession. That alone, puts it head and shoulders above the 84 and earlier, 1000cc Airheads. I don't mind slightly reduced MPG or power, as long as no ping and no valve adjustments at ridiculous intervals.

Sorry you had so many bouts with pinging. From my limited experience and reading things, your situation seems to be fairly rare.

I feel bad

JHall, I feel bad you had such problems with your bikes and feel the way you do. I don't know why it happened to you to have problems when I and a lot of people I know did not.

BMW made and still makes a lot of mistakes add things out of their control like the elimination of leaded gas or tightening EPA standards and they do the best they can.

It is nice you have an airhead you are happy with. St.

Common Problems

Not sure if archive editions of BMWMOA News are available from the early 1980s but, as I recall, they document that the problems I experienced were more common than not. Ping was mainly why dual plugging instantly became popular in the early 1980s, as a way to reduce ping on earlier Airheads. It's just the way it was, with existing technology. As mentioned earlier, the real fix for ping was the intro of nikasil jugs in 1981.

Still, coming off Harley pan and shovel heads, those old Airheads were much better. With the pan head's total loss front chain oiler system, per the manual, oil mileage was 250-500 MPQ, and that was optimistic. The 1965 and laters, with aluminum primary and recirculating chain oil, got close to 1000 MPQ. But they had other problems, I once got only 12,000 miles out of a valve job on a 1972 Shovel, before the rear exhaust valve began to stick. So it was ride awhile then fix awhile, with most any MC back then, but much less so with Airheads.

Not complaining about Airheads, but contend the mono shock version of the 1000cc was as good as it got. So far, I've had nothing but good experiences with the current 1995 version.

You mention that Nikasil was the answer. I'm curious...how was that a magic bullet? Is the elimination of the iron cylinder as sort of a blanket around the combustion what you're getting at? I do understand that the Nikasil bikes...as well as the Siebenrock top end kit I installed on my /7...should run a bit cooler. But there were other things going on with the 1981 models besides just the change in cylinders.

In the June 1998 Owners News, there was an index of articles. I checked that index and I don't find very much about pinging. I did find this entry:

Engine detonation 7.74.11, 1.76.15, 6.79.20, 7.79.13, 11.82.14, 1.83.12.18, 2.83.8

where x.yy.zz is x=month, yy=year, and zz=page. I only go back to the 1980s and haven't had the chance to look at those articles. But detonation and pinging are not the same, so I'm not sure what to say about the pinging issues you mention. My /7 must have been small valves...but that was never an issue. My Dad had a 1981 R100RT and I don't recall him mentioning pinging issues with his bike.

Here's the index listing for dual plugging:

Dual plugs 11.80.18, 12.80.20, 3.81.18, 5.81.28, 10.85.20, 6.87.71, 4.94.55 (hotter plug on bottom), 6.94.68.69

Nikasail

The introduction of Nikasil or however its spelled was for the same reason BMW just announced a diamond chain for the chain drive bikes. It was supposed to last longer and yes cool a bit better than the cast iron cylinders.

Funny, I myself found the claim for longer lasting to be false as I had to rebuild my nikasil cylinders at 160K miles. The cast iron bores I replace the nickasil with have lasted just about as long and upon most recent inspection, were in very good condition.

I myself have seen no great advantage of nikasil over cast iron other than the BMW parts when I had to rebuild my engine were Bite My Wallet expensive. Nickasil could not be bored out and new rings and pistons installed. The only option available was to buy new BMW only parts or do like I did, bore out the nickasil and have cast liners inserted which worked out perfectly well. At that time, I increased the compression of the bike from the anemic 8.5 to 9.5, with no problems of pinging.

Now of course there are OM kits available from Seibenrock and others who use Nikasail cylinders and are reasonable for price. Also I believe there are a handful of shops which will refurbish the OM cylinders with a new nickasail coating. Funny thing the kits use the higher 9.5 compression pistons. I know one person who bumped his R80 up to 1000cc using one of the kits and has no problem with pinging.

Yes, the archives will show a large bunch of postings regarding pinging problems, but it won't show the greater number of people like me who had/have no problems. Of the hundred of bikes my friends worked on it their shop, only a few were ever dual plugged. The years of bikes involved cover the 50's to 95.

So despite all written in all the forums and expert articles, I never had pinging and I still don't and the people I know never did nor have it now. Any rebuild I do in the future will be to bring the bikes to or keep them at 77 or 78 European specifications. Ie, the biggest valve heads, highest compression, biggest carbs, works for me and the riding I do. St.

OK, No Ping Then

Well I guess that settles it. If y'all say the pre-1981, 1000cc Airheads never pinged, then I guess they didn't. LOL

I have not

I have never said the early bikes NEVER pinged. Nor has some of the other posters. We told you OUR bikes never pinged and haven't! BIG difference.

Like I said I feel bad you had the problem and and other have not. I am happy you love your 95 RT.

BMW made some good improvements over the years but none have made me run out to change my bikes.

If I had the problems you had, then yes, I would have gotten rid of the bikes or dual plugged. There is a good chance if the pinging problem, if it existed, was not solved, I would be writing in another forum.

I love my two bikes but after 84, they turned me off on any of their new bikes. St.

The one key variable I have not seen mentioned (or maybe I missed it) is the build up of carbon in the combustion chambers. This will not only slightly increase compression, it can also result in glowing "hot spot" carbon bits that cause pre-detonation. Riders who ride hard much of the time, or who live and ride in hilly areas typically have fewer issues with carbon buildup than do some more casual riders.

If I had an Airhead that had pinging issues for no real apparent reason I would manually decarbonize the combustion chambers.