Here's a way for a novice to think of it....

The explosion resulting from the burning of fuel is what drives the piston down, thus turning the crank. If you don't follow that statement, then we can't help at all. 😛 So at start and idle speeds the plugs are firing after the piston reaches the top of the stoke, and starts on its way down. What a technician would describe as "after piston top dead center" or simply "after TDC".

However, gasoline burns very, very slowly; slower in fact than the piston can move. So at high RPM we have to ignite the gasoline before the piston reaches TDC in order to get the explosion to occur after the piston reaches TDC. So we need a mechanism to make the exact moment of spark plug firing change as the engine runs. We have to "advance" the timing (fire sooner) with higher RPM. This feat is accomplished with a small centrifugal device beneath the points plate called the auto advance unit. At higher RPM, bob weights fly out and advance the ignition cam; at low RPM springs pull the weights back inward to retard the ignition.

Good images of the advance unit here

When that mechanism sees mechanical wear and/or those springs wear or stretch, the bob weights fly out too fast, therefore the ignition timing is no longer in sync with the engine RPM. That is, the ignition is far too advanced for the RPM and you get poor performance and possibly hear spark knock, aka pre-ignition, aka "pinging".

Since no springs last for 40 years, it's a good bet your advance springs are stretched.

Hope this helps.

Not sure I needed it that simple but it did make a lot of sense. I understand the basic functions of the engine and drivetrain train really well. Electronics have always seemed like such a puzzle to me I get flustered with just the idea of them. I'm wondering why I didn't just deal with that when I was gapping the points and setting the dwell anyways.

Mr Cullen -
Sincerely not trying to insult your intelligence, but did want to start where you were comfortable and hopefully move you to a place where you better understood 1) the importance of the auto advance, and 2) how a worn auto advance could cause issues even with the engine strobe timed correctly.

This has nothing to do with "electric-trickery" and everything to do with the result of the ignition system. What we're discussing is the timing of the spark [ when ], not the generation of the spark [ how ]. As such, topics like point gap and dwell are of little concern here.

All the best.

Oh, no worries man. I was not offended. Just felt the need to defend my pride a little. The truth is, I am a novice. I understand the functions of the engine but not entirely how to fix it yet and surely not all the vocabulary. lol I'm getting there. I really appreciate the help and simplified definitions. I will approach my cylinder heads and advance mechanism with some confidence, now. Then I have to figure out why she (yes the bike) started backfiring when she gets hot.

The R60/5 engine is notorious for engine knock. The slide carburetors produce a lean fuel:air mixture during acceleration. Dual plugging will reduce potential for knock.

I recall having this very problem on a R60/5 I owned in the early 70's ..... I went into Dunbar's in Brockton,MA complaining of pinging and knocking on acceleration. I remember they fixed it while I waited and watched [those were the days] by pulling the heads and installing new thicker cylinder base gaskets. At the time it was an inexpensive fix that worked.

I recall having this very problem on a R60/5 I owned in the early 70's ..... I went into Dunbar's in Brockton,MA complaining of pinging and knocking on acceleration. I remember they fixed it while I waited and watched [those were the days] by pulling the heads and installing new thicker cylinder base gaskets. At the time it was an inexpensive fix that worked.

Any Idea where to get that replacement gasket?

Any Idea where to get that replacement gasket?

► It's not a "gasket", but rather a metal shim that fits onto the cylinder base WITH the gasket. Several models came with metal cylinder base shims. These should be listed on the parts fiche.

► Another option that may be more appealing is to simply install an electronic ignition (EI). This is far more direct, much simpler to complete, within the range of your tools and knowledge base, and will mean you'll never have to service the points again... ever. Good quality EI units start about $140 (Mk3 Boyer), while a BMW piston ring set is going to be about $100 without the gaskets. So you can see it's going to be roughly the same price either way.

Even if you do the cylinder shim trick, you'll still have to service your auto advance unit. However, if you install an EI, then it deletes the auto advance unit entirely, and does the ignition advance in software. And the electronic advance curve is much better suited to today's anemic fuels.

Just saying. 🙂

Well, I'll probably go with the spacer, replacing piston rings, and cleaning the pistons for now. I'll order those springs for the advance units and new jets and needles. I'll also be ordering a new accelerator pump. What model bikes have the cylinder base shim?
I assume you get the dual plugging done at a machine shop. Any recommendations in California around the Bay Area?
I'll keep the electronic ignition in mind as I continue to update parts on the bike.
Thanks,
Cullen

I assume you get the dual plugging done at a machine shop. Any recommendations in California around the Bay Area?

In my reading on the subject, dual-plugging is a thing of the past. It is effective, but has simply been eclipsed on the street (as opposed to track racing) by the technology of better ignitions. And too, consider that for the same or lower price of the machine shop, adding extra ignition coils, finding suitable plugs, et al, you could simply bolt on used R75 cylinders and be done with it.

Remember, the root cause is environmental. You are trying to use an under-powered 600cc machine in CA traffic, not any kind of wear on, or age of, the machine itself. That is to say, if you moved to a small country town in Alabama, the symptoms would most likely disappear !! In that light, increased displacement is the most effective solution.

🙂

I just re-read the topic and I am quoting Wobbly here from post #1337 on the first page of this thread.

" Although the 600 will putter around at low RPM very nicely, it cannot be done under any type load (2 riders, heavy luggage, heading up hill, etc). IMHO, all serious road work should be attempted with engine speeds in excess of 3000 RPM."

This is an important idea to keep in mind. The 3000 RPM+ number is where we want to run these motors. We have to train ourselves to operate these machines the way the Germans intended. When riding my R75/5, I select a gear for any given speed that I want to travel. For example; 2nd gear for 35mph, 3rd gear for 45 to 55mph, ect.

My buddy who owns the R60/6 with the Mikuni carbs doesn't have any pinging issues at all, but he weighs 140lbs soaking wet and always rides solo. I have ridden that bike. It runs very well, and your bike should be able to do the same.

If I switched to 75/5 cylinders wouldn't I then have the issue of replacing carburetors, final drive, piston, etc? If larger displacement would fix this for me then I may try to swap an entire 75/5 engine and drivetrain from a wrecked bike an acquaintance has. But would that solve my pinging problem? The 75/5 is ok with modern fuel even with me (180lbs) my girlfriend (120) lbs and luggage? I live in the East Bay and have to navigate steep hills and traffic constantly. Maybe 75/5 is the only way to go and the 60/5 engine would make a really nice go-cart.

Keep in mind I do plan to drive this bike all over the country at some point. My biggest passion above fixing bikes is riding them. I'll be seeing lots of miles on my bike one of these days.

I'm not the one to answer that question, but that's never stopped me before !! 😛

► My impression is that the engine block is the same, so the cylinders and pistons will slip right on. You can use your heads and carbs. The small bore carbs will limit acceleration somewhat, but give you added fuel mileage while touring.

► From what Haynes is telling me, the final drive only differs by a tiny ratio. It's the equivalent on a chain drive of about 1-2 rear sprocket teeth. The R60 final will give you more "get up and go" up and down those Frisco hills, and make your clutch last longer. If you feel the need to swap the rear end for touring, swap the whole final drive unit without disassembly; four bolts and it's done.

► Of course, you won't want your engine plates (emblems) lying about your new displacement. They sell a plastic set on Ebay for $39 that simply says "BMW". Swapping those might be the hardest part of the whole deal. 🙂

Others who really know will follow...

The cam timing on R75/5 has valve overlap. There is no overlap on the R60/5. The Bing slide carbs on the R60 produce leaner fuel:air mixture during acceleration. This increases potential for detonation. Reducing R60 compression to eliminate detonation is a poor trade-off of engine power. If you don't dual-plug then find a R75/5 power train or a R75/6 power train if you have a long wheelbase frame. Otherwise, run your engine in lower gear/higher RPM or otherwise don't whack open the throttle when riding.

Yeah I've been practicing keeping the bike in higher rpms. I have to guesstimate the 3000 range since my tach is broken. I keep hearing people mention the lean air fuel mixture of the Bing carburetors. Is there any way to re jet them to have a richer fuel mixture?