A pumping or groaning sound could be the crankcase breather, or worse yet, air working past the rear main seal. If the internal engine pressures are building up, the air has to go somewhere. If the pressures are building, then it is likely ring blow-by which you could check as part of a leakdown test.
Vech sold a type of rear main seal that eliminated this chirping sound. I'm sure it available somewhere currently. But that won't help you much without removing the trans again. That may very well be your noise.
If you just did the test with the dipstick out/loose, and the noise was still there, then I don't see how a leakdown test will tell you anything? Even if the rings are leaking (which is not wholly unexpected until the rings are fully seated/worn-in), the dipstick-out test demonstrates that it is not excess pressure in the case that is causing the noise. Same with the rear seal and the engine breather--if the noise still occurs during the dipstick-out test, then neither the seal nor the breather is the likely cause (as neither is under an excess pressure condition). Am I understanding this incorrectly?
Have you run the engine long enough to see if you are getting any oil on the rear shelf? That would be a positive indication of a rear seal leak, in my mind.
Good luck--I am sure you will figure it out.
I very much admire your "it's just me out here" stick-to-it-tive-ness".
Ken Walker
Scottsdale, AZ, USA 1960 R60 (currently), 1974 R75/6 (past), 1981 R100CS (currently), 1984 R100RS (past), 1989 K100RS (past)
When the engine is running, you should put your finger over the end of the vent tube, and feel air coming out in a more or less continuous stream. If you don't feel air coming out, something is very wrong.
Just so all the readers understand how the crankcase ventilation works, when the pistons move down the bores, to bottom dead center, the air is compressed in the crankcase. At the pistons bottom travel, the window of the timed breather lines up with the vent passageway in the front gear cover, and the engine exhales. As it continues to rotate, and the pistons move up, the window in the breather closes, and a vacuum is created in the crankcase. How does air get in? The engine sucks air in through the rear main seal. That is why any weird nose at idle, that you might hear, disappears if you unscrew the dip stick. What you hear, is the lip of the rear main seal vibrating, as the air is pulled through it! /5 and /6 bikes, while using a reed valve, many times develop a weird squeal at idle that disappears if you unscrew the dipstick, to allow air to get pulled in, and the squeal will disappear.
Also, there are differences in the timed breather plates. There was an early, single locating pin type, a later twin pin type, and last, there was two cast "feet" that went into the screw access holes for the cam screws, in the gear. You see, the window of the timed breather plate must line up with the vent hole of the front cover, when the engine is at BOTTOM dead center. I have seen people mix up timed breathers and cam gears, and end up with a mistimed vent hole in the timed breather.
Likewise, the early engines used a coil spring to put tension on the timed breather to push it up against the timing cover.
Later engines, (with the last version of the timed breather use a shim washer with a spring WAVE washer to push the the plate against the timing cover. You cannot use the coil spring behind the later plate, it can completely bottom out the coil spring and cause excessive pressure in the face of the timing gear cover that the timed breather runs on. And it will chew up the surface of the timing gear cover.
And this may sound weird, but I once was brought a bike that was forcing oil out of all the seals, that had never done so previously. Here in the USA, we have a wasp like insect referred to as mud dabbers. They build tubular nests out of mud on buildings. You would not think that they would build their mud nest inside an oily vent tube, but they will! And their nest plugged the passageway completely up. Once I cleaned/dug out the mud nest, the engine returned to running normally.
Vech
Technical Adviser, Former owner, Bench Mark Works
662 312 2838 cell 9 am to 4pm CST PLEASE!
This may be a silly question, but, when you had the push rods out, did you roll each one on a piece of glass, to check to see if they were absolutely straight? Once a push rod gets bend in it, (they are only strong when perfectly straight) it will continue to flex and bend. This will make an audible ticking nose.
Hi Vetch
Well I had four slightly bent push rods - Maybe there are other glitches but I have replaced the pushrods - so I will continue the process to make sure I have everything running smoothly now.
Thank you for your invaluable advice. Very much appreciated.
I purchased one of those stethoscopes and ran it over the engine at idle. It would seem, and yet it is still to be confirmed, that the slight croaking sound is strongest on the crankcase between the pushrod tubes.
Maybe the 2nd oversized cam followers bedding in or maybe pushrods interfering with the hole in the crankcase.
I will do some more investigation and see what observations are forth coming.
Thank you to everyone who has contributed. This forum is just terrific.
When the engine is running, you should put your finger over the end of the vent tube, and feel air coming out in a more or less continuous stream. If you don't feel air coming out, something is very wrong.
When the engine is running there is a more or less continuous stream of air from the crankcase vent tube.
New timing gears? Does it have a tight fitting set with minimal toothplay? I have read about a growling sound in freshly build engines with tight fitting gears. I haven't ever heard it myself so I don't know if it sounds like this. According to this source (the book Boxer im Detail, Band 6, Thomas Welzel) it is not a problem and will disapear over time.
New timing gears? Does it have a tight fitting set with minimal toothplay? I have read about a growling sound in freshly build engines with tight fitting gears. I haven't ever heard it myself so I don't know if it sounds like this. According to this source (the book Boxer im Detail, Band 6, Thomas Welzel) it is not a problem and will disapear over time.
I guess I just found this sound a bit disconcerting. A chap who knows a lot about these engines sent me this short extract from an early BMW manual. "Humming" seemed pretty tame buy "growling" seems a better description.
