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Old 01-30-2015, 07:02 AM   #1
wiseblood OP
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Replacing valve stem seals: Anyone ever do it?

This is for my 2007 KTM 950 (SMR). My bike has always consumed oil, and it has been slowly increasing over time. In the past year, I've had spark plugs fail twice due to oil fouling.

In past service, I've been able to see a small bit of oil on the top of the valve (looking down the intake). I got what I believe is a confirmation of my leaky stem seals a couple months ago: Doing a bit of mixed-surface riding, a friend riding behind me noticed a big puff of blue smoke when I twisted the throttle after a long slow downhill section during which I was entirely engine braking.

My understanding is, engine braking will suck oil through the leaky valve stem seals. When I get back on the throttle, the accumulated oil burns, causing blue smoke for a moment, which is exactly what I got.

FYI, I already replaced the balancer shaft seal last year.

So, my questions:
  1. Can anyone think of any other reason, besides a leaky valve stem seal, that i would have these symptoms?
  2. Has anyone ever replaced their valve stem seals?
  3. Is there any realistic and safe way to replace these seals without removing the heads, and all the work related to that?
FYI, I'm just about to do my 20k miles valve check service. That's why I'm asking this now.

Thanks!
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Old 01-30-2015, 08:00 AM   #2
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You'll have to remove the heads and the valves to replace the seals if my memory serves correctly.
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Old 01-30-2015, 08:03 AM   #3
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I've done valve seals on a lot of engines but not the LC8. There is really no way to replace the seals without removing the heads. It's not hard though just take your time, snug the seals well and affix the springs correctly. Pay attention to your valve seats while you have the heads off. You can do a vacuum test OR...old school turn the heads upside down and pour some gas behind the valves to ensure your have proper seating. If gas leaks through you need to re-seat and lap (some modern engines don't allow for lapping), or grind the valves (take it to a respected machine shop). With your symptoms you need to pay attention to the seats since there may be some carbon build up around there.
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Old 01-30-2015, 08:03 AM   #4
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I had them replaced on the rear head by my dealer (who is a friend of me, so I was there during the operation, "helping"), and the head has to be removed - you can't remove the valves otherwise ofcourse, but IMO it's not a big deal to remove it.
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Old 01-30-2015, 08:05 AM   #5
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Originally Posted by TheMuffinMan View Post
You'll have to remove the heads and the valves to replace the seals if my memory serves correctly.
Yeah, that's the vibe I've been getting. Which makes me think: If I'm gonna do all that, seems like I might as well do a full top-end rebuild. (Which I've never personally done. )
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Old 01-30-2015, 08:06 AM   #6
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Quote:
Originally Posted by wiseblood View Post
Yeah, that's the vibe I've been getting. Which makes me think: If I'm gonna do all that, seems like I might as well do a full top-end rebuild. (Which I've never personally done. )
How many miles are on your bike?
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Old 01-30-2015, 08:08 AM   #7
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How many miles are on your bike?
Just about 21,000.
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Old 01-30-2015, 08:12 AM   #8
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Oh that's way too early for a top end in my opinion. I'd just do the valve seals and call it good unless you see something massively wrong with the piston or cylinder when you get the head(s) off.
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Old 01-30-2015, 08:14 AM   #9
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Originally Posted by themuffinman View Post
oh that's way too early for a top end in my opinion. I'd just do the valve seals and call it good unless you see something massively wrong with the piston or cylinder when you get the head(s) off.
+1
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Old 01-30-2015, 11:49 AM   #10
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Oh that's way too early for a top end in my opinion. I'd just do the valve seals and call it good unless you see something massively wrong with the piston or cylinder when you get the head(s) off.

Stupid question: I've been looking at the service manual as well as Pyndon's rebuild page in the HOW, and it is never explained how I might remove ONLY the valve head, and not the cylinder.

Is it possible? If not, sounds like I will have to remove the whole cylinder head in order to do this job!
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Old 01-30-2015, 12:34 PM   #11
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On some engines(not sure on 950-990) I have seen rope stuffed through spark plug hole(leaving enough rope sticking out to remove) into the combustion chamber just before TDC on compression stroke,bring up to TDC and lock in place,lever spring retainer down,rope will hold the valves in place,remove collets ,valve retainer top and valve spring exposing the seal,pry off and replace seal, reverse order to complete.not sure if there is adequate access space,cams removed as if doing valve shims,might be possible....smoking on over run due to valve seals,valve guides,dirt on valve seat would not cause oiling,just loss of compression on leak down test.Oiling all the time due to bad rings,worn bores,etc. 20,000 miles sounds awfully short in a modern engine with high tech valve,guide and seal materials,rings could wear from bad air cleaner in a very dusty environment but valve seals would be unaffected by this,only exposed part of valve stem when valve is open.Just stuff to think about!
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Old 01-30-2015, 12:46 PM   #12
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Originally Posted by Oldebonz View Post
On some engines(not sure on 950-990) I have seen rope stuffed through spark plug hole(leaving enough rope sticking out to remove) into the combustion chamber just before TDC on compression stroke,bring up to TDC and lock in place,lever spring retainer down,rope will hold the valves in place,remove collets ,valve retainer top and valve spring exposing the seal,pry off and replace seal, reverse order to complete.not sure if there is adequate access space,cams removed as if doing valve shims,might be possible....smoking on over run due to valve seals,valve guides,dirt on valve seat would not cause oiling,just loss of compression on leak down test.Oiling all the time due to bad rings,worn bores,etc. 20,000 miles sounds awfully short in a modern engine with high tech valve,guide and seal materials,rings could wear from bad air cleaner in a very dusty environment but valve seals would be unaffected by this,only exposed part of valve stem when valve is open.Just stuff to think about!

I've seen that process done (with the rope) on Youtube... crazy!

98% of my riding on this bike is paved street-only, so it's not dirt. (Plus, I checked the air filter, and it's good.) Smoking doesn't happen on overrun. It happens on throttle AFTER a period of overrun. As I understand it, the vacuum pulls oil past the valve stem oil seals, if they are not great.
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Old 01-30-2015, 02:26 PM   #13
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Are you sure it's not oil from the engine breather?
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Old 01-30-2015, 02:41 PM   #14
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Maybe reroute crankcase breather into a catch bottle for a while and see what comes out of it?

http://www.dirtyadv.com/balancer-sha...l-replacement/

/Johan
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Old 01-30-2015, 02:56 PM   #15
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Are you sure it's not oil from the engine breather?
Yes. Pretty sure. I replaced the balancer shaft seal just a few months ago, specifically to exclude that as a possibility.

I'll add: Prior to replacing that seal I did see a little oil in the brather, and on the carb intake stack. I've seen none since replacing that seal.
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