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  1. #1
    Adam's Avatar
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    GP1200/1300/800 owners urgent memo

    Just read a message from Harry Klemm of Group K fame about a design flaw that has gone unnoticed for 20 yrs in the rear crankshaft seals . Any long time owner of any of these engines will have seen random rear cylinder melt downs / seizures and so forth . Many are attributed to a worn crank seal air leak . Harry had just built a new engine and was pressure testing it and found the new seals leaking badly , upon disassembly he looked and saw the oil cross over hole actually allows all the crankcase pressure to bear on the outer seal only ! The inner seal doesn’t work as intended and everything relying upon the integrity of one seal lip ! Some last a long time ,some leak and suck air causing a lean mixture that destroys pistons. Upon sealing this cross over hole / slot the inner seal now functions with the outer seal giving a true double seal . I will be pulling my engines ( 2 GP1200R’s) down to seal this slot / hole as a matter of some urgency as a leak will cause a blown engine ( rear piston) . I have seen this many times and had NO idea the crank seal was the culprit, assuming that a “ fuel pump “ failed again , I have a fuel pressure gauge that I have set in the lid of the glovebox that I can see any fluctuations in fuel pressure, I see a constant 6 psi at full throttle and if starts to drop off I back off and check out the fuel filter for any sediment. However I have only had one rear piston meltdown and that engine has Factory pipes fitted, and I assumed it was a low octane fuel issue at the time . I suspect it was the rear “seal “ sucking air under the dynamic pulses of the Factory pipes , it doesn’t appear to be leaking with the stock pipe fitted . Thanks Harry Klemm for passing on this knowledge.


  2. #2
    Team Bilford's Avatar
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    Harry has done my machine work since 1994. I enjoyed visiting his shop a few years ago. He is a top 2 stroke expert. We have all seen too many Yamaha 1200 engines blow up totally stock. I bought a new GP12 in 97 and sold it a month later. It was a total POS. Hopefully Harry's info will help folks save repeated failures. Funny, the cracking heads of the 1.8L in the GP1800s remind me too much of the 1200 triple nightmares.

  3. #3
    steve45's Avatar
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    Thanks for the info!

    I had an unexplained seizure on the rear cylinder of an 1100 in my Exciter boat. Never was able to figure out what caused it. I'm guess that this also applies to the 1100 engines, too, right?

  4. #4
    butterbean_29512's Avatar
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    If we block the oil passage hole to the rear seal won't that cause the seal to run completely dry and fail prematurely? Even seals need lubricant to last.

  5. #5
    I saw that article but I don’t understand why it’s there if it causes a problem. I mean, Yamaha put it in for a reason.

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  7. #6
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by butterbean_29512 View Post
    If we block the oil passage hole to the rear seal won't that cause the seal to run completely dry and fail prematurely? Even seals need lubricant to last.
    Double crank seals are not uncommon. On Polaris red engines the outer (and inner) rear crank seal is oiled (or greased) during engine assembly. When the engine is running the inner seal lip is exposed to engine crankcase oiling mist and spray. The outer seal relies upon the assembly lube along with whatever 2-stroke oil seeps past the inner seal over time.



    I presume the Klemm modification suggested here would result in similar operation of the outer crank oil seal.

  8. #7
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Adam View Post
    Just read a message from Harry Klemm of Group K fame about a design flaw that has gone unnoticed for 20 yrs in the rear crankshaft seals ... the oil cross over hole actually allows all the crankcase pressure to bear on the outer seal only ... The inner seal doesn’t work as intended and everything relying upon the integrity of one seal lip ...

    Upon sealing this cross over hole / slot the inner seal now functions with the outer seal giving a true double seal .

    ... Thanks Harry Klemm for passing on this knowledge.
    Link to the original Harry Klemm post about this?

  9. #8
    Team Bilford's Avatar
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    Quote Originally Posted by daz_ni View Post
    I saw that article but I don’t understand why it’s there if it causes a problem. I mean, Yamaha put it in for a reason.
    maybe to sell short blocks....

  10. #9

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    Where is this oil passage located?

  11. #10
    Quote Originally Posted by Adam View Post
    Just read a message from Harry Klemm of Group K fame about a design flaw that has gone unnoticed for 20 yrs in the rear crankshaft seals . Any long time owner of any of these engines will have seen random rear cylinder melt downs / seizures and so forth . Many are attributed to a worn crank seal air leak . Harry had just built a new engine and was pressure testing it and found the new seals leaking badly , upon disassembly he looked and saw the oil cross over hole actually allows all the crankcase pressure to bear on the outer seal only ! The inner seal doesn’t work as intended and everything relying upon the integrity of one seal lip ! Some last a long time ,some leak and suck air causing a lean mixture that destroys pistons. Upon sealing this cross over hole / slot the inner seal now functions with the outer seal giving a true double seal . I will be pulling my engines ( 2 GP1200R’s) down to seal this slot / hole as a matter of some urgency as a leak will cause a blown engine ( rear piston) . I have seen this many times and had NO idea the crank seal was the culprit, assuming that a “ fuel pump “ failed again , I have a fuel pressure gauge that I have set in the lid of the glovebox that I can see any fluctuations in fuel pressure, I see a constant 6 psi at full throttle and if starts to drop off I back off and check out the fuel filter for any sediment. However I have only had one rear piston meltdown and that engine has Factory pipes fitted, and I assumed it was a low octane fuel issue at the time . I suspect it was the rear “seal “ sucking air under the dynamic pulses of the Factory pipes , it doesn’t appear to be leaking with the stock pipe fitted . Thanks Harry Klemm for passing on this knowledge.

    Wow ! mostly seen center cylinder seizure's on the PV 12's gummed up carbs running lean I will need to check out !

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