Vintage BMW Motorcycle Owners

I hope this information will help all people in the future.
I learned this the hard way, it turns out others did too viewtopic.php?f=7&t=18309.
When I brought my engine heads to the workshop, with all the assemblies shiny new (valves, springs, guides, etc.), I didn't have to ask him to do a good job. He is considered a leading workshop in the field and the whole country works with him. That's why I felt confident when I installed the rebuilt heads on my engine. After about 100 km I got stuck and needed a tow. Back home, lifting the RH engine head, I saw that the intake valve rocker arm was broken: the valve was stuck inside its guide. Oil reached the head and the push rod was full of it. To be on the safe side, I also pulled the LH cover, to find the following pictures. After consulting with the friends here and with Jan in the Netherlands, Salis BMW, I came to the conclusion that nowadays the workshops automatically ream the guides according to the tolerances accepted today, in the age of modern engines, but - it is important to ask them to give an oversize of 0.10 mm and to make sure that the valve stem does have a slight lateral play inside its guide. Mainly in a hot environment, which nowadays due to global climate change, most places on our globe, even in the relatively cold areas, already get there in one period or another, for a few days or weeks.

Can you find out what they used for clearance?

Sorry no.
Too late for that and the workshop guy does not remember.

This is a standard problem with the new guides and under-oiling. One of my machinist friends think it has to do with the specs being created for leaded fuel versus unleaded and the lubricity differences. Not sure if he is correct.

Anyway, I bring them to spec and then loosen them up a bit. I forget the exact numbers but I think I went .001” on the intakes and a bit more on the exhaust. Mine run perfect!

Hi, this happened to me too bought a replacement cylinder head for my R67 and after about 10 miles the valve [exhaust ]started to squeak so I stopped the engine and got brought home, my mechanic friend said that because the engine runs at very low oil pressure you need a greater valve guide tolerance to allow splash from oil to lubricate the valve stem!

I think a lot of valve guides are replaced when they do not need to be.

Dave

Hello all

I just have this kind of fail last Sunday on my way to Distinguished Gentleman's Ride, after less than 20 milles after a full rebuilt of mine R60/2.

While stopping at red light engine start to sound like a type writer machine and stops..

Post mortem autopsia shows a stuck exhaust valve on right cylinder head.

I said it was a lucky strike, found some dirty sludge on oil pan, maybe was some Sodium carbonate that stays inside block after cleaning.

In short, many engine builders do not understand the needs for the BMW's. Most rebuilders are used to V-twins which get far more oil in the head than ours do. The BMW is also cooled at a different rate than other air-cooled motorcycles because the heads are hanging out in the air.

If you are using a rebuilder that your not sure of, ask that they do two things:

1) Use high-quality valve guides! Even if you source them from a known reseller they may still be of lesser quality. I use KPMI guides.

2) Set the clearance appropriately for our needs. i.e. Loosen them up a bit and measure with thin oil.