860GT valve seal confusion

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rjk40
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860GT valve seal confusion

Post by rjk40 » Thu Jun 01, 2017 12:22 pm

Hi All,

I know that this topic has been visited many times, and after reading the Forums and after getting into the top end of my bike, engine s/n 851539, I have found that the valves have the cap type seals , not o-ring seals; this cap type seal matches my parts manual, but not some postings elsewhere. I have ordered the cap-type replacements, even though they are sometimes described as seals for Desmo engines (mine is non-Desmo, a "springer"). The seals are quite stiff (42 years old), and did not come out undamaged due to that stiffness, even when using care with the hook tool.

Anybody want to tell me that I'm crazy, or is this just the "mystique" of the engine? I would guess that it is prudent to replace the seals with ones of the same type.

Thanks in advance.

Regards,
Richard
Malabar, Florida USA

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BevHevSteve
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Re: 860GT valve seal confusion

Post by BevHevSteve » Thu Jun 01, 2017 1:13 pm

Hi Richard, not crazy. What is crazy is that SOME valves have both o-rings AND cap type seals on them........... Anyways, you are correct, replace with the same type you removed and, since you got them from me, use the green ones for exhaust, black for intake.
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wdietz186
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Re: 860GT valve seal confusion

Post by wdietz186 » Thu Jun 01, 2017 4:57 pm

If my memory serves, I think the springers all had the cap type seals and the desmos o ring type was superseded by the cap type in '74 ish. I used to have some Ducati service bulletins that mentioned the change along with the recommended relieving of the bottom of the closing rocker to clear the seal. The engines having one or both types of seal are probably the result of Ducati using what they had lying in their inventory at the time or maybe a mix up from one of their suppliers.

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abmartin
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Re: 860GT valve seal confusion

Post by abmartin » Sat Jun 03, 2017 3:05 pm

My early '79 SS has the o-ring valve seals. I've read that the guides with both top hat and o-ring seals were fitted beginning in 1981. Contrary to some things I've read the valve stems have tapered heads so they slide more easily into the guides without cutting the o-rings. Not really all that difficult to replace the o-rings when required.

Bruce
1979 900SS
Fredericton, NB
Canada

ducadini
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Re: 860GT valve seal confusion

Post by ducadini » Sun Jun 04, 2017 12:44 am

abmartin wrote:
Sat Jun 03, 2017 3:05 pm
Contrary to some things I've read the valve stems have tapered heads so they slide more easily into the guides without cutting the o-rings. Not really all that difficult to replace the o-rings when required.
When those o-rings were old and hard, had to fabricate a tool to get them out (although a dentist tool would've made that easier)
Even with the tapered stem, the groove that holds the two 'wire' halve rings is machined and doesn't have that tapering and after inserting the valve I found a very tiny piece of rubber that was cut off the o-ring, something that could happen every time You take the valve out or put it in.
Putting some kind of paste in that groove could've prevented this, but the seals were changed every year so no problem.
I changed to later valve guides with the outer seals :-D

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ducadini
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abmartin
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Re: 860GT valve seal confusion

Post by abmartin » Sun Jun 04, 2017 3:59 am

I use a dentist tool to pick out the old o-rings which I changed after my SS had been in use for more than 30 years. I greased the valves so they slid in quite easily without cutting the seals. Result, no more exhaust smoke which formerly was quite apparent at idle.

Bruce
1979 900SS
Fredericton, NB
Canada

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