plopping noise @ idle...crankcase vent?

[scottnichols]

Hi, Anyone know about the noise caused by the original crankcase vent on a 1979 r65? I read in the manual that there is an updated version available that doesn't make noise. I was wondering if anyone had experienced this. The "plopping noise" is only at idle, almost sounds like something is loose, but nothing is.

Thanks for any replies.

[Barry]

What you have there Scott is the "Turkey Gobble" noise. It can indicate an air leak at the oil filler plug or rear main seal or a damaged engine breather disk.

Yes there is the later reed valve replacement but if your disk is not damaged there is a no cost solution you can try first.

Be very careful not to drop any of those small bits down into the sump.
 
Drill a very small hole (approx 1 to 1.5 mm) in the disc about half way in from the edge. My theory is that this reduces the crankcase vacuum very slightly which is just enough to stop air from being sucked in past a less than perfect rear main seal. I think air passing the seal is where the noise is comes from not the breather valve itself. If it doesn't work then you've lost nothing by trying. It did substantially cure mine. Instead of a continuous noise I only get an occasional gobble on engine shutdown now.

To fit a reed valve You will need to contrive some sort of slide hammer arrangement to get the old valve body out of the crankcase. Here's a link to an excellent write up on changing to the new breather http://www.bmwscotter.com/procedures/oil_breather_service/oil_breather_service.htm

[Bengt_Phorqs]

The permanent fix is to replace the rear main seal.

[Barry]

The permanent fix is to replace the rear main seal.  

Probably true but if the bike has been stood some time which is not uncommon with a change of owner ship and given it's not exactly the easiest job on an airhead it might be worth waiting to see if  the seal improves with use which can happen. Also if the rings are little gummed up piston blow by may reduce with use too.  Mine had very little use for years before it came to me so perhaps it's hard to know what has cured the gobble noise. It was without question instantly quietened by drilling the disc valve and may have improved further since. I don't think any engine breather can be silent in operation so I don't suppose mine is but the noise it made before the mod was truly horrendous and the improvement so enormous that I do think of it as cured.

I get the impression this could be a problem from new or nearly new hence the small hole mod was suggested and then the change of breather valve design came along with the later model.

[scottnichols]

Thanks so much Barry. The link will be very helpful, I have not had time to look into it, and thought it would be less involved. I have less than 500 miles on the bike since I've owned it, and it was sitting for two years before that, so these things may be factoring into the problem. For now I will try drilling the disc and see what I get. I'll save the main seal job for the dead of winter.

Thanks again