Do you think this exhaust valve is deforming?

[nhmaf]

Pulling my cylinders because of leaking push rod tube seals - now that I've pulled the worst offender I discover that my 1978/79 R100/7 has the non-brazed push rod tubes... so maybe I could have fixed things with some small hose clamps and enough pounding.

Anyhow, I noted that the valve lash seemed to have closed up to .004" on the exhaust and .002" on the intake in the past 800 miles - I thought that I had set it to .004" and .006" previously, but maybe I had made a mistake.   I was planning to keep the head and the cylinder together, but decided to take them apart to look at the valve heads.   The pics are prior to cleaning, but the tiny dimple in the middle of the exhaust valve (on the left) seems a bit odd to me...
Could it be starting to deform?  Maybe the closure is due to all the carbon - I'm still trying to get it running better - way too rich these days.

[Tony Smith]

How many miles?

Even R100s will drop a valve eventually, if you do not know the miles and do not know the bike's history I'd be having new exhaust valves fitted anyway, and frankly, for the money involved, I'd do the inlets as well.

I'd be more concerned with the apparent gas leak past the sealing edge of the head gasket in the short term.

[nhmaf]

No idea of the mileage - the speedometer that was fitted to the bike showed 70K miles, but it wasn't even the correct ratio for the stock rear end.  I found a replacement (used of course) with the proper ratio and have only put about 800 miles on the bike thus far.

The PO claimed it had been serviced at a very reputable dealer, but the things I've discovered so far tend to indicate to me it wasn't likely true.

[Bob_Roller]

You need to see the sealing surfaces of the valves to tell whether you have recession or not .

[nhmaf]

I'm going to look at this more closely - at initial glance, the edge of the valves seem normal thickness - not getting thin/sharp, but the odd looking dimple in the middle had me start thinking about possible head/stem separation.   I have no idea if the seats are originals from 78, or if they'd been replaced with the non-conducting early 80s seats, or what...

[Tony Smith]

I'm going to look at this more closely - at initial glance, the edge of the valves seem normal thickness - not getting thin/sharp, but the odd looking dimple in the middle had me start thinking about possible head/stem separation.   I have no idea if the seats are originals from 78, or if they'd been replaced with the non-conducting early 80s seats, or what...

Save your money on new seats, in the case of 999 out of every 1000 airheads they aren't needed. and guess what, 1 our of every 1000 airheads with the later supposedly better "lead free" seats will suffer valve recession anyway.

New valve seats is money you spend only if your old ones are worn, or if you actually do suffer recession.


You should however get the valves done and unless the head to barrel mating surface cleans up perfectly, look at getting that face machined (you can buy spacing rings from BMW to restore the correct combustion chamber volume).

[Tony Smith]

I'm tempted too start a thread elsewhere entitled "Lies Previous owners tell".

[Barry]

I thought Valve plastic deformation was caused by the new valve seats introduced to combat valve seat recession being poor heat conductors and didn't those valve seats come later than your model year.  I suppose it might already have had a head job.

[nhmaf]

The "hardened" lead-free seats were introduced in the 1981 or 1982 model years, and yes, they did not conduct heat worth a damn -> resulting in valve plastic deformation.   At first it was thought it was an R100-only problem, but it was eventually learned that it would happen on other smaller displacement machines, depending on how lean they were run, RPM/loading conditions, etc.   By the 1986 model year, BMW figured it out with the valve seat metallurgy.

Some folks in the US got their heads redone with these new valve seats right away, as they wanted to be prepared for the lead free fuel.   However, that was a false path, as those early seats caused more problems than they solved, and needed to be changed again, or at least closely monitored.    The engine and frame numbers on this bike match, but otherwise it shows various signs of mucking about by POs.

I have no idea about these seats/heads.   I don't think that the heads were properly torqued when I bought the bike, as my initial valve lash check and head torque resulted in finding loose nuts.   I don't know how long it was run that way.     When I went to check out the bike at the seller's home, he was changing the oil&filter, and wasnt using any metal shim in the oil filter canister - and it definitely needed one.  Aieeee!

[montmil]

Mike, Your comments about discovering loose nuts during a head torquing session are quite possibly the cause of any loss of compression and/or blow by on that jug. Might also explain the valve lash differences. Loose nuts, by themselves, rarely get tighter. On the other hand, looser and looser'er they be.

Does the other head look fair to middlin'? The dimple in the valve may indicate a non-BMW valve. Opposite head have the same dimple? Photos do not show signs of a thinning valve edge.

When my '81 R65 began puffing an inordinate amount of smoke out of the left side, that motivated me to do a ring job during the weepy pushrod tube seal replacement. Left head didn't look too good so I dropped off a spare pair of complete heads, scored off eBay several years ago, at an indie shop operated by a Butler & Smith-trained wrench. He disassembled and cleaned the heads, checked valves, valve guide dimensions and had to take a "kiss cut" on one seat. I got really lucky on the $60.00 I paid for the pair of heads.

My suggestion would be to take both heads to a trusted shop for disassembly, inspection and service as needed. If your bike was mine, I'd also consider new rings... since you was in there. Plus those new p'rod seals you have on hand.

Happy wrench twistin'. And there ain't a trace of snow... yet.  [smiley=thumbsup.gif]

[nhmaf]

At the moment, I don't have the other head off yet - my garage is kind of a disaster with my wife's teaching supplies and fair face painting paraphenalia, so to make sure I don't lose something or get parts swapped incorrectly I'm only doing one side at a time.

I *did* discover the reason the push rod tubes seals were leaking - the stop rings are basically "floating and can be easily moved 5mm - 6mm further up the tube. than they should be.  There is no evidence of a spot weld or brazed metal on the tube - so I don't think it's been broken - probably always was that way and just has gotten 'tired'.  

I was going to do the ghetto-garage fix of putting a couple hose clamps against them, but now I am thinking I may clean them up a bit more, lightly sand the tubes where the stoprings should and try a bit of JB Weld instead - would look better than hose clamps anyway.  Or I may also put the hose clamps after the JBWeld has cured as and added backup.

Have you tried JB Weld in this sort of situation?  Seems like it should work, I think...

[mrclubike]

I would think the JB weld would work good for that.
I keep forgetting how well that stuff works
I just used it last week to reattach the turn signal light stem that had broken off  
Thought I was going to have to weld it back on and burn up the paint and then remembered the old JB trick.  

[montmil]

JB Weld is a Texas-produced product outta Sulphur Springs so you know it's a good thing. I always keep it in the shop.

Another option might be to clean up the tubes and rings, position them correctly, then use a propane torch to silver-solder the rings in position. I've never liked the hose clamp ghetto fix.

[Tony Smith]

Or possibly a further approach. Buyer a set of stainless steel pushrod tubes, they are cheap so buying the recommended 6 is not too big a pain.

The rear axle makes a perfect mandrel for driving the new tubes in. and the marks left by teh old tubes show you exactly where to stop.

The final prep involved either good relations with your wife, or her absence - put the heads in the domestic oven for 30 minutes at 300 degrees Celcius and the pushrod tubes and axle in the freezer (and prepare a bucket of ice water to keep the tubes and axle cool.

I suspect that you will discover quickly why it is recommended to buy 6 tubes, the first three I did went as smooth as silk, the last tube proved more difficult and I ruined two tubes before (mercifully) the last one seated perfectly.

[nhmaf]

LOL!   Tony - - that is exactly why I'm looking for an easier approach too try first - if this fails, I will go the route of new stainless tubes.. but for the moment I am hoping to not end up in the dog house with a kitchen stove that smells like my garage does now!

I may try silver soldering them if the JB Weld doesn't seem like it will work.