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Loss of Compression-Bent valve

J

James.A

Guest
Suffered a loss of compression on one cylinder of one of my R75/5's. I pulled the head and saw this.
 

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Then, I held the head up to the light and looked in the exhaust port and found this.
 

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The piston does not show any cracks or damage. Would you run the old piston, or replace it. The bike has 85K miles and around 3000 on a lead free re-build with Black Diamond valves.
 
Hard to tell what the damage is to the piston crown. What does the combustion chamber look like? Did the bike run for any time period with the broken valve? Seems like that would really chew up a piston face and or combustion chamber surface.
 
With only 3k after the rebuild, what do you think caused this?

My R90's got about 30 miles after a lead-free rebuild with Black Diamond valves, too.
 
For me, I would have a lot of concern for cracks around the wrist pin (whats the name of that spray on stuff to check for cracked pistons?) and every bearing for all the way down to the crank.
If the piston is just kinda skuffed a bit perhaps I am a bit too concerned; but if the valve notched it pretty good, that force/hammering had to be transfered someplace, like the bearings................Dennis
 
30 miles? That's it?
Is Black Diamond not the way to go?

No no no.. I don't want to start any rumors.

I mean, I just rebuilt my heads, and I was wondering if the same thing might happen to me, given _________. I was wondering if someone could fill in the blank.
 
No no no.. I don't want to start any rumors.

I mean, I just rebuilt my heads, and I was wondering if the same thing might happen to me, given _________. I was wondering if someone could fill in the blank.

Oh, OK.
I woudl not expect what we see on pix at 80K with unleaded job
 
I've not heard much good regarding after market valves. BMW valves should be the first consideration if you really want to get the life out of them. This was hashed quite a bit over on the Airheads listserve.
 
I've not heard much good regarding after market valves. BMW valves should be the first consideration if you really want to get the life out of them. This was hashed quite a bit over on the Airheads listserve.

Bob's BMW literature claims the Black Diamond is better than BMW factory.
 
So was the guide to tight or what do you think happened? Pistons are pretty stout but I would at least pull it, maybe have it magnafluxed or what ever they do to alumium to check for cracks and stuff. Had one that had a noise and I never figured it our till I had it knurled and the crack showed up
 
I've not heard much good regarding after market valves. BMW valves should be the first consideration if you really want to get the life out of them. This was hashed quite a bit over on the Airheads listserve.

Snowbum and the "local" airhead mechanic both use and recommend Black Diamond.. so I went with.
 
Bob's BMW literature claims the Black Diamond is better than BMW factory.

Would they say any different? But I've heard different from other people who also work on Airhead engines.

Edit:

OK, I'll back off of that after reading some of what Ted Porter wrote on the Airheads list back in October 2005. Prior to going into business for himself, he did a lot of his work with Bob's BMW. RE: Bob's BMW literature saying the Black Diamond is better, here's what Ted said in 2005: "In fact the quote they use in their advertising about Black Diamond Valves being superior, came from my mouth to their ad guy." Ted based that upon all of the experimentation he was doing in the mid '80s trying to "fix" the problem with early '80s engine valves cratering.

He goes on to say in that same post:

"The Black Diamond valve is a well made one piece stainless valve that has
been through a hardening process which hardens the keeper slots. It has a
fully machined tulip with a polish swirl finish that may improve flow. It
has a stellite tip, and works well with the Martin and Wells seats
(Kibblewhite now supplies their own seats too). Because of the hardening
process it is black in color and it does not have a steel chrome stem. As a
result it does not wear as well in the guide as a steel chrome stem does.
Sometimes when you take apart a head with Black Diamond valves installed you
will see some guide material imbedded in the stem of the valve. Kibblewhite
says there is a dry film lubricant impregnated into the stem of the valve to
counter this problem, but you can still see evidence of material
transferrence. Opening up the valve to guide clearance seems to help some,
but the issue is still there and now you're running wider clearances than
preferable. I have never had a failure related to this issue, and at the
retail price of about $40.00 for an exhaust valve it is a good deal, but the
material transferrence concerns me and guide wear occurs faster."

So, not too bad, I guess, however it does create a problem that maybe you can work around. If money is your hurdle, them maybe the B.D. valve is a suitable alternative. But when the proper solution is there, albeit not guaranteed, I'd prefer BMW parts. My engine...my wallet...I don't really want to compromise.
 
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I had the valve materials / construction discussion some years ago, with a client of mine who is a professional race / high performance engine builder. At the time, I was having my '82 RS engine completely rebuilt and modded.

My client told me that valve stems and tulips were made of different materials and then hammer welded together; an expensive process. This, to withstand different conditions at different parts of the valve. The cost is not a problem in the automotive scene, where millions are needed, but possibly a problem in an aftermarket where small quantities are made and sold. So the compromise would be to make the valve out of a single alloy, to keep that cost down.

My own tech would only use BMW valves in my motor, after I asked him about putting in aftermarket "high flow" mono alloy stainless steel valves. There was also one report in the News a few years ago, of an engine grenading after stainless steel valves were installed, but these may have been Luftmeister crap.

Just to be clear, I am not commenting on the Black Diamond valves specifically, as I know nothing about them.
 
My comment as a metallurgist--embeded material on the valve stem from the guide is not a good thing. Suggests either the guide to stem clearance was wrong or the choice of materials for guide and stem was not compatible.
 
My comment as a metallurgist--embeded material on the valve stem from the guide is not a good thing. Suggests either the guide to stem clearance was wrong or the choice of materials for guide and stem was not compatible.

I do not like this. It seems as though the stainless is "galling", or somehow is lacking in a lubricity property of some sort.

Stainless in other applications seems to be britttle, or not to hold an edge , or to have galling surface-to-surface tendencies, or not withstand torque.

Are automotive valves made from stainless?
 
re: 20774

Thanks for the post. Maybe I am missing something, but I am not seeing in it where the BD are judged superior - they seem more of an also-ran, pretty OK for the $ part. Bob's affirmatively says they are better, as well as cheaper. I am not seeibng what is better.
 
Mine looks a tad worse than yours. A valve seat let go,and the piston jammed a piece of the seat into the head,makin'it useable as a window prop.I picked up a set of heads from a guy in Calif., am in the process of gettin'it together now.
 

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