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Topic-icon Pre-ignition on R60/5

  • cullenr
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2 years 7 months ago #1331 by cullenr
Pre-ignition on R60/5 was created by cullenr
Hey guys,
I have a 1972 R60/5 that is experience some pre-ignition. I have retarded the timing, put sea foam in the gas, done my valves, and tuned my carbs. Nothing seems to be working. I'm looking now into either getting a seibenrock 1000cc kit, swapping for a 75/5 engine, or just replacing pistons and getting cylinders bored. I am on a very tight budget and need this bike running but I want to do it right. Any recommendations or solutions? Good sources for parts?
Thanks,
Cullen

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2 years 7 months ago - 2 years 7 months ago #1332 by 8053
Replied by 8053 on topic Pre-ignition on R60/5
I know of one owner who had a good result by swapping out for Mikuni carbs. Rocky Point Cycle used to sell a conversion kit. (this was on an R60/6) I'm not sure that your trouble is with the carburetors necessarily, but the Mikunis are arguably an improvement over the Type 53 Bings. What do the spark plugs look like? Golden brown is good, sooty is rich, whitish is lean. Before spending serious money while guessing about a solution, I might try a tank of premium, non-alcohol gasoline and/or different spark plug heat ranges. Maybe try changing the air fuel mixture by raising or dropping the needle setting by 1 notch. Y'know, small alterations that do not involve serious expense. If you want to open up the motor, look for carbon build-up on the pistons and cylinder heads. This might hold heat in the combustion chamber and contribute to a tendency to explode the fuel too early or make it burn out too fast. I would also recommend that you carefully read (Snowbum) Bob Fleischer's excellent web site for insight into this issue. bmwmotorcycletech.info/technical-articles-list.htm

James Strickland, IL. Airmarshal
Last edit: 2 years 7 months ago by 8053.

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2 years 7 months ago #1333 by cullenr
Replied by cullenr on topic Pre-ignition on R60/5
Thanks for the comment. I always run chevron premium in the tank. I may try an octane booster. As for the spark plugs, I would have to check again since I last tuned the carbs. In the past they had been pretty sooty. Maybe it was leaning up the mixture that caused the preignition to start. I know from looking down the spark plug holes that the pistons have a considerable amounts of carbon build up and small white specks marring the surface which I was advised could actually be small pin holes in the piston.

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2 years 7 months ago - 2 years 7 months ago #1334 by 8053
Replied by 8053 on topic Pre-ignition on R60/5
I think pin holes in a piston would result in a serious loss of compression. If it were my bike, I would try a cooler plug next. For example, I normally run NGK, BP6ES spark plugs. BP7ES would be one range cooler for an Airhead. Check out this web page www.ngk.com.au/spark-plugs/technical-inf...at-range-explanation

James Strickland, IL. Airmarshal
Last edit: 2 years 7 months ago by 8053.

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2 years 7 months ago #1336 by 8166
Replied by 8166 on topic Pre-ignition on R60/5
If you can see carbon build up through the spark plug hole, chances are that's what's causing the detonation. The added material on the piston crown and head will decrease the volume of the combustion chamber, effectively increasing the compression ratio, possibly to the point that the engine pings. The uneven texture of the deposits also provide hot spots for pre-ignitoin to start. First thing I'd do, then, is pull the heads and barrels and give everything a good cleaning.

Bob "Snowbum" Fleischer covers this on his web site; Google is your friend.

8166 Scot Marburger, This email address is being protected from spambots. You need JavaScript enabled to view it.
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2 years 7 months ago - 2 years 7 months ago #1337 by Wobbly
Replied by Wobbly on topic Pre-ignition on R60/5
I would not advise any major engine changes until you sort out your present issues. Your issues are most likely NOT tied to being 600cc displacement. Therefore, any "updates" will leave you with the daunting task of sorting out this issue and sorting out the needs of the new big bore kit simultaneously. That would be like getting a divorce because you have colon cancer. The original issue remains while you pile on more headaches, expense, and complications.

Pre-ignition has several causes, some of which have been touched on above. In no particular order they are...
► Fuel octane too low for the compression
► Ignition timing too far advanced OR ignition timing advancing too fast
► Fuel mixture too lean
► Running the engine RPM too slow for the load

1) You already told us about your fuel. Chevron high test should be high enough, unless you buy it at a station that does not sell a lot of high test fuel. The problem is the ethanol separates out during storage. You could be getting mostly ethanol, which has a very low octane. Try fuel from another, more popular gas station.

2) It is always best to strobe time a BMW at high RPM using the "F" mark. Your issue could be a slack timing chain that allows more ignition timing leeway when you static time on the "S" mark. Or, your advance mechanism may need new springs to restrain the advance curve. Weak or missing springs would allow the ignition cam to advance too fast for the engine RPM. You'll be able to see both these errors by using a strobe timing lamp.

3) It is quite common for ethanol fuels to clog the smaller jet(s) and coat the needle with mung that will effectively lean out the mid-range. Lots of people think that the pilot jet only controls the idle, but a clogged pilot will tend to lean out the entire running range. So you need to remove both carbs, and without intermixing parts, compare them side-by-side. Then set the idle and cable adjustments using a manometer to insure perfect balance.

4) 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.

Hope this helps. :)

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Last edit: 2 years 7 months ago by Wobbly.

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