Page 1 of 3 1 2 3 LastLast
Results 1 to 15 of 38

Thread: Loss of Compression-Bent valve

  1. #1
    James.A
    Guest

    Loss of Compression-Bent valve

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

  2. #2
    James.A
    Guest
    Then, I held the head up to the light and looked in the exhaust port and found this.
    Attached Images Attached Images

  3. #3
    James.A
    Guest
    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.

  4. #4
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    18,211
    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.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    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.

  6. #6
    Registered User
    Join Date
    Dec 2007
    Location
    Reno, NV
    Posts
    1,968
    Quote Originally Posted by crazydrummerdude View Post
    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.
    30 miles? That's it?
    Is Black Diamond not the way to go?

  7. #7
    #4869 DennisDarrow's Avatar
    Join Date
    Jan 2006
    Location
    Sugar Valley, Ga
    Posts
    1,780
    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

  8. #8
    Quote Originally Posted by jforgo View Post
    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.

  9. #9
    Registered User
    Join Date
    Dec 2007
    Location
    Reno, NV
    Posts
    1,968
    Quote Originally Posted by crazydrummerdude View Post
    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

  10. #10
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    18,211
    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.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  11. #11
    Registered User
    Join Date
    Dec 2007
    Location
    Reno, NV
    Posts
    1,968
    Quote Originally Posted by 20774 View Post
    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.

  12. #12
    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
    "Wow I didn't know BMW made motorcycles, Yeah I think Honda does too."

  13. #13
    Quote Originally Posted by 20774 View Post
    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.

  14. #14
    Bill Burke
    Guest
    Was it a sudden failure at WFO throttle?

  15. #15
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    18,211
    Quote Originally Posted by jforgo View Post
    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.
    Last edited by 20774; 03-09-2009 at 09:46 PM.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •