Dropped Exhaust Valves

[Gordons_HQ]

I'm just wondering if anyone has had an exhaust valve drop or break it's head off. On another forum I was reading it quotes the finite life of these valves as between 40 and 50,000 miles.
As I'm now on 41,000 it's a bit worrying. I'm wondering if these may have been isolated incidents which then become a the norm the more they are talked about or whatever.
So I would be interested to know if this has happened to anyone here.

Cheers,
            Gordon

[Ed Miller]

Paging Joan and Melena!

I don't remember reading about one coming apart before 50,000 miles.  What year is your R65?  Do the valve clearances change in between checks, say every 5,000 miles?

[Rob Valdez 79 R65]

What year is your R65?Do the valve clearances change in between checks, say every 5,000 miles?

Yes - you need to measure your valve clearances BEFORE making any adjustments, so you can tell if you have lost clearance, and how much on a regular basis.

If you find yourself on a extended trip, and you pull in to a rest stop and the engine won't maintain an idle (or even run at below 1500-2000 rpm), more than likely one of your exhaust valves has no play, and is probably not even closing all the way!  That was my experience.

I have a right side head for a '78-'80 (small valves) that has been rebuilt by Bob Grauer (remember that name if you live in the U.S.) that I would sell for $250.  It probably only has 2000 miles on it.
The left head was destroyed in a crash.

[Bob_Roller]

I think it depends on the year of bike .

The years with the valve recession problem, may be more prone to failure, than the later bikes .

My '81 R65 had so much valve recession on the exhaust valves, the shop that did the overhaul on the heads said I had 5-10,000 miles before the valve would have been pulled into the cylinder head port area .

The bike had 45,000 miles on it at the time .

[nhmaf]

I think that Suecanada's R65LS was very close to the point of valve head loss - the edge on one valve was certainly knife-blade thin in appearance.   I think that her bike is in the 80+K mile range.    
There is no super hard and fast rule, except that if your bike is from the 81-84 time period, you're gonna need to deal with this at some point, depending on how hard you ride, how lean/rich you run, how wide you gap the valve lash to begin with, how well/poorly those original valve seats were installed and any variances in their metallurgy, the phase of the moon and the number of sunspots in any given astrological sign..
I'd just be sure to check the adjustments carefully with every valve adjustment check/adjustment - don't trust stuff to memory - write it down in your log book (you DO have a motorcycle maintenance log book, don't you?) and when it appears to be closing up a few thousand every couple thousand miles, start saving your nickels.  You usually DO get some amount of early warning if you are careful/methodical with your engine maintenance..

[Barry]

I have no experience with valve heads falling off but I understand the the valve fails at the welding joint on the valve stem. Surely the valve would stretch a little before hand increasing the valve clearance. How is this related to valve recession ?

So there are 2 confusing issues:

Valve recession which we know can reduce clearances

Valves stretch which would increase valve clearance before the head falls off.

How would you differentiate if both were happening at the same time and what chance is there of catching a valve that's stretching i.e. how much does it stretch before failing? Do they stretch and  fail because extreme valve recession jambs the valve in the head ?
  
To answer the original question the valve heads don't fall off very often or it would have already happened to someone here. I guess all you can do is monitor for any unusual change.

[nhmaf]

The failure mechanism in the 81-84 bikes is actually called 'valve plastic deformation', and is essentially, valve stretching, as you put it.  This does NOT increase valve clearance (As measured at the rocker arm end) it REDUCES it (since the valve is essentially growing longer (valve head becomes more tulip shaped).   This results in thinning of the edges of the valve head where it contacts the valve seats (can get almost knife edge-thin in extreme cases).   Since the majority of the heat dissipation for the valve is through metal mass & contact with the vavle seat, this causes the valve to heat more and deform more rapidly, and the excess heat often ends up causing the head to break off at the weld on the stem and end up holing your piston and scarring the cylinder.   What causes this is that the original OEM valve seats for this era of bikes were made of much harder steel with poorer heat conduction ability - BMW changed the seats to better cope with the unleaded fuel requirement, but ended up making things worse in the process.   By 1985-86 they had more or less figured it out and changed the seat material again.

 On pre-1981 bikes with high mileage engines, the valves can eventually wear (Recede) into the valve seats - these eariler bikes had different valve seat materials and different valves- and this wear also causes reduced valve clearance and subsequent problems.

There are (2) different problems, but if left undiagnosed, can result in similar poor running and engine damage.   We've had a few members who've been unfortunate enough to experience valve head separation and subsequent engine damage in the past couple years, and one or two members who have narrowly avoided it!

Incidentally, these (2) issues afflict ALL BMW airheads of the same vintage/model years.   The 81-84 valve seat issue is what actually caused BMW to stop shipping R100 bikes (which produced the most heat and thus suffered the worst) for this issue.

Many people don't know the difference between these issues, or they don't care to quibble over the technicalities, so they just generically call it valve recession.   The actual recession into the seats issue over the older, pre-81 bikes will generally just give one worse and worse running and failure to idle and a frequent closing up of the valve clearance.   The valve plastic deformation of the 81-84 bikes will also do these same things, but if either is  left unresolved can result in the valve head separation - this is especially true with the 81-84 valves&seats.

[Barry]

nhmaf,  I wasn't thinking through the effects of valve stretch clearly.

I see now that both effects close up the valve clearance.

Interesting to hear that one or two members narrowly avoided valve head separation. Did they catch it in time by monitoring the clearances closing up rapidly.

[Bob_Roller]

Suecanada, narrowly avoided having a valve issue with LRB, the valve clearances were closing up at a fairly fast rate .

The report that she got when she sent the heads in for 'overhaul', was that the heads had been previously worked on and were done poorly, also the ridges at the top of the valve where the split keeper sits were worn to knife edges and were ready to fail, would have resulted in a 'dropped' valve .

Maybe she'll see this thread and repost the pictures of the parts .

[Ed Miller]

Joan almost never posts on here anymore, but something like that happened to her Blueberry, an early 80s R65.  And didn't it happen to Melena too?  Where's she been lately?

[Bob_Roller]

Melena had it happen within the last six months .

[Julio A.]

How could you tell if the valves are perished without opening the engine?
are there tell tale signs in performance?

[Rob Valdez 79 R65]

How could you tell if the valves are perished without opening the engine?
are there tell tale signs in performance?

You can pull the exhaust headers and get a pretty good view of the exhaust valves (I think).
I'm not sure if they are visible from the spark plug opening, or not.

Typically, the intake valve does not suffer quite so badly.

Performance wise - only if it no longer idles (see above).  Do you check your valve clearance on a regular basis?

[Barry]

You can get something of a view through the spark plug hole with the right illumination. I have a very small LED light on the end of a slim flexible wand which is USB powered and that works well.

I guess the exhaust port would be far better but removing the headers is a much bigger job.

[suecanada]

Yup, I caught my valve clearance issues just in time and avoided a major disaster by simply checking and checking and checking the exhaust valve clearances. Checking for closing up clearances
(much less than < 5000 miles and they were closed up again))and how fast they are closing up is a 'diagnostic' exercise that is easy and very worth the effort!!!! You don't even have to be suspicious of upcoming problems...just do it as a matter of course.

Here is a link to my pics of the valves from LRB which got all fixed up by Ted Porters Beemershop. Even though I am in Canada, I sent my head to the best mechanic....Bob Grauer is too right Rob???

http://my.fotopic.net/collection/01459975/

The collettes that hold the valve in place were knife edged and the other 'head' end of the valve looked ok....not knife-edged. And yes, I could see the head end through the sparkplug hole with a small flexible flashlight. If I had relied on that view, the valves looked OK and I would not have caught the disaster about to happen in short order.