Putting to bed the R65 Dropping Valve myth

[steve hawkins]

So the concensus is that most of these occurances are caused by valve seat issues and not the valves themselves.

Once the valve has been undermined by the recession of the seat - it is only then that we are seeing failures or potential failures.

I feel it is a good idea to pull your heads at a certain mileage to be sure.  But where do we draw the line? 60, 70, 80, 90 thousand?

Or do we just say - watch out for closing up of the exhaust valve and leave it at that?

What do you think?

[nhmaf]

I think that more frequent/rapid closing up of the valve lash is a pretty good indicator - either of valve seat wear and/or wear at the keeper end and/or plastic deformation of the valve itself.   I don't think that the engine would just drop a valve without some indicators appearing first.  They key thing is to do regular maintenance checks so that it can be detected in time.   I also think running the valve lash at or a bit above BMW spec is best for longevity.   Running the clearances as low as some of the guys on B-works I personally think is a recipe for a repair bill.   I've gotten too tired of wading through all the BS on B-works lately to even bother posting there anymore.
 

[Ed Miller]

I wouldn't have pulled my heads if not for the valve clearances changing.  (The leaking push rod seals weren't sufficient motivation by themselves!)  The right intake actually kept opening up, don't know what that was about.  Like nhmaf, I think watching the clearances is a good diagnostic tool.  I wish Joan would let us know how recently she had checked Blueberry's valve clearances, and if they were giving any hint.

Unfortunately something like what happened to Rob (throwing a rod) probably doesn't give any warning.  

[Justin B.]

I seem to remember reading somewhere that the valves are actually "two-piece" with the head and stem being different metallurgies.   Although this is apparently common practice it seemed there was something about the thinner valve stems on the R65 engine that possibly made them more prone to failure at the mating point.

This is what snowbum has to say about BMW exhaust valves in general, he makes no mention of R65 valves:

"The BMW exhaust  valve is a TWO-piece, inertia welded, and pricey, but VERY good quality and performance.  It is VERY rare for a BMW two-piece exhaust valve to come apart in service...contrary to rumors pushed by other makers of valves."

[steve hawkins]

That is the point Justin - the R65 has what I feel is an undeserved reputation for dropping valves and the explanation often given was 7mm stem.  When it seems not to be that common - or at least no worse than other boxers of a similar age/mileage.

As with all other boxers, only when some other malady, like valve seat recession or excessive wear of the valve guides or keepers, is a factor on some high mileage machines does there seem to be a problem.  And we all must remember that the mileages we are talking about, most other bike manufacturers of aircoooled engines could only dream about.

It is an explanation put forward in the early days - that could easily be a 'damage limitation brush off' from the manufacturer.  Which, at the time, was replacing 19 inch cast front wheels at a significant cost.  This is purely conjecture of course.

It 'weak valve theory' also only affected a certain time period of early production - but the whole range from 1979 onwards is often implicated.  It also affected R80's and R100s as well.

It could be an RPM thing also - an R100 will be doing less RPM for a given speed than an R65 on the open road - a worn R100 engine might get away with it for longer as it is not being worked as hard.  

It could be that most R65's are not used in the same way as R100s anyway which will also fog the issue.  Although there is plenty of overlap - i.e there are plenty of long disance tourers/comuters on R65s as well as those R80/100s?

It has to be said I get really peeved when I hear this from someone who has had little or no experience of the model(R65) and is just repeating, inaccurately in most cases, what he/she has heard or read about weak valves - implying that the R65 is a model to avoid and that any R80/100 would be a better choice - when it is obviously not the case.

I have both.  I find the chassis of the R65 are far more competent package that that on the larger models - it handles better - or at least my R65 does!  Is it the forks?  The swb?  lower ride height? Or all three?  I find the R65 engine more than adequate for my purposes.

Cheers

Steve H

[Ed Miller]

YOUR R65 is considerably lighter than an R100, from the looks of it.  Do you have any way to weigh it?  I bet it's a blast to ride.  I think lighter bikes are more fun, unless it's really windy.  I don't remember what the weight difference is between a stock R65 and R100.  My R65 is all the touring/commuting bike I need.  

[steve hawkins]

I doubt if there is a lot in it.  It is essentially the same drive train for an R65 or an R100.

At least when comparing like for like agewise.  The big lumps will be similar weights - the only difference being the wieght of the longer barrels and bigger pistons.

And the battery and fuel tank.  A post 81 bike will be lighter that a pre 81 though.  That much is for sure.

The rest of it is detail.  Forks might be lighter?  I do not even know if the spoked wheeels are lighter than the cast ones!

Cheers

Steve H

[Semper Gumby]

So the concensus is that most of these occurances are caused by valve seat issues and not the valves themselves.

Once the valve has been undermined by the recession of the seat - it is only then that we are seeing failures or potential failures.

I feel it is a good idea to pull your heads at a certain mileage to be sure.  But where do we draw the line? 60, 70, 80, 90 thousand?

Or do we just say - watch out for closing up of the exhaust valve and leave it at that?

What do you think?

The exhaust valve was wearing thin.  The seats were just cut to fit the new valves when they were installed.

Yes!  Watch for closing valve clearences.  Your mileage may vary.