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Author Topic: Leaking Decompressor  (Read 2345 times)

Roger

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Leaking Decompressor
« on: December 12, 2007, 08:55:43 AM »
Hello All,

Has anyone experienced a leaking decompressor. I noticed a brown stain around the decompressor and when I put a spanner on it was just tight and that was all.

I removed the decompressor and lapped the valve into the body, blued the set to check that I had a complete lap which there appeared to be and generally cleaned the thing up.

I used a new decompressor washer kit when I reinstalled it however the it still leaks. What I am hearing is a faint hiss sound as the enging is running.

At this stage the bike has covered less then 1500 miles since new.

Any clues??

Roger

Leonard

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Re: Leaking Decompressor
« Reply #1 on: December 12, 2007, 02:35:15 PM »
Understand that this is just my idea and I haven't actually done it.
Assuming the decomp is adjusted correctly I would put a spark plug into the decomp hole and run the engine.  It there was no leakage I would suspect a faulty decomp.  If it leaked with the spark plug in I'm not sure what that would be telling you.

Hello All,

Has anyone experienced a leaking decompressor. I noticed a brown stain around the decompressor and when I put a spanner on it was just tight and that was all.

I removed the decompressor and lapped the valve into the body, blued the set to check that I had a complete lap which there appeared to be and generally cleaned the thing up.

I used a new decompressor washer kit when I reinstalled it however the it still leaks. What I am hearing is a faint hiss sound as the enging is running.

At this stage the bike has covered less then 1500 miles since new.

Any clues??

Roger
2009 Triumph Bonneville T100
2004 Royal Enfield Sixty-5 (RIP)
2001 Kawasaki W650 (going, going...gone)
http://www.romeoriders.com

mbevo1

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Re: Leaking Decompressor
« Reply #2 on: December 12, 2007, 04:29:39 PM »
Leonard -

Good suggestion about the spark plug - are the threads the same in the plug/decomp holes? 

I was (reluctanly) completing my storage preps after six weeks of no riding and wanted to start my bike to run stabilized fuel through everything and drain the carb.  When I did my starting drill, I had no compression to speak of and thought my decomp was leaking (though it worked well all season).  I ended up squirting some oil in the plug hole, and got my compression back after the rings got lubed up.  Might have saved some guessing if I had just "plugged" the decomp hole...

Mike and Stumpy in Michigan
'07 Classic - Stumpy
'10 C5 Military - Sherman

Leonard

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Re: Leaking Decompressor
« Reply #3 on: December 12, 2007, 09:28:19 PM »
Leonard -

Good suggestion about the spark plug - are the threads the same in the plug/decomp holes? 

That is my understanding, however I have never tried it myself.
2009 Triumph Bonneville T100
2004 Royal Enfield Sixty-5 (RIP)
2001 Kawasaki W650 (going, going...gone)
http://www.romeoriders.com

sewerman

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Re: Leaking Decompressor
« Reply #4 on: December 13, 2007, 04:08:45 PM »
When I had that problem the first thing I did was rebuild the valve assembly but it did the same thing.  Then I checked thehead where the valve seats and it was not flat enough for a good seal.  I put a small disc on a die grinder and "milled" the seating area flat and BAM no more leak. 

Roger

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Re: Leaking Decompressor
« Reply #5 on: December 15, 2007, 09:46:22 AM »
Thankyou everyone for your thoughts and suggestions. I had more of fiddle with the decompresser, this time I used some loc-tite gasket sealent and some Teflon tape on the thread. Still leaked... I did note however, that twisting the valve stem in the decompresser while the engine was running seemed to have a positive affect as the leaking stopped momentarily.

Once again I removed the decompresser and this time gave the valve seat a good lapping with both course and fine lapping compound. reassembled the valve and refitted it to the engine. Still no luck. I then sprayed some soapy water on the decompresser while the engine was running to see I could see any bubbles (The engine was just warm). I noted some very tiny bubbles coming from between the steel washer and the copper crush washer. I will investigate the actual sealing surfaces as mentioned by sewerman as this may well be the problem.

In regard to the lose of compression mentioned by Leonard, I have also experienced this phenomenon. I could actually hear air escaping through the inlet valve when kicking the through the compression stroke.

I mentioned to one of the guys at work (A Mopar man) and he suggested that is was most likely some soft carbon under the inlet valve seat and to spray a fine mist of water into the mouth of the carburettor while the engine was running at high revs (just enough to cause the engine to die and then recover) as this will dislodge and carbon around the valve seat. I did this a few times and all well again.

I'll keep you all posted regarding my adventure with the decompresser.

Thanks guys,

Roger

LotusSevenMan

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Re: Leaking Decompressor
« Reply #6 on: December 15, 2007, 05:36:07 PM »
Thanks for that last tip Roger!
Sounds like a workable (and very cheap!) fix.  ;D
If it ain't broke-------------------------- fix it 'till it is!

Royal Enfield Miltary 500cc  (2003)
Honda VTR FireStorm (SuperHawk) 996cc 'V' twin
Kawasaki KR1 250cc twin 'stroker
Ducati 916 'L' twin

Roger

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Re: Leaking Decompressor
« Reply #7 on: December 16, 2007, 06:02:49 AM »
Hi All,

I think I have cured the leaking decompresser...

First of all I examined the crush washer seating surfaces as Sewerman mentioned in his earlier post and yes they are very ordinary. Mine looks at though the tool used to cut the seats was either blunt or clogged with swarf. To repair this properly the head needs to be removed and the seats re-cut.

Now for the cure... I reassembled the decompresser less the cable and FITTED NEW CRUSH WASHERS OVER THE USED ONES, TWO BIG AND TWO SMALL. I installed it into the head tightening it firmly. I then started the engine and sure enough "Pht Pht Pht" it was still leaking. I then rotated the valve, nothing, I then tightened the decompresser, leak stopped, tightened a little more leak started again, DAMN!! backed it off still leaking, tightened a little more leak stopped. Time to leave sleeping dogs lie...

All I can do now is monitor the situation and see if the leak redevelops finger crossed it won't.

Roger


LotusSevenMan

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Re: Leaking Decompressor
« Reply #8 on: December 16, 2007, 10:27:32 AM »
Bit too hit 'n' miss for my liking. You'll spend lots of riding time stopping and just listening etc.
I'm afraid I'd have to take it down and fix it correctly. That's the trouble with ex aircraft engineers; It has to be right!  ::)
If it ain't broke-------------------------- fix it 'till it is!

Royal Enfield Miltary 500cc  (2003)
Honda VTR FireStorm (SuperHawk) 996cc 'V' twin
Kawasaki KR1 250cc twin 'stroker
Ducati 916 'L' twin

Roger

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Re: Leaking Decompressor
« Reply #9 on: December 16, 2007, 08:35:40 PM »
Lotus7,

I agree with your comment and have seriously considering removing the head and fixing it properly, however in the mean time I will keep an eye on it.

There is something that has occurred to me and that is the leak may not be coming form the combustion chamber but the result of the exhaust gas pressure wave.

The decompression chamber is linked to the exhaust port by way of a drilled passage connecting the two, it may be that a pressure wave is being set up in this chamber as the exhaust gas exits the on the exhausts stroke and this pressure wave is the sound that I hear as it escapes under the copper washer.

Roger

LotusSevenMan

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Re: Leaking Decompressor
« Reply #10 on: December 18, 2007, 09:24:00 AM »
All getting far too complicated I feel.
What you need to know "Is the decomp valve 1) Leaking or 2) Not leaking!
From a cold start can you put a bit of little diluted washing up liquid around the decomp area to see if it blows bubbles? You'll have to be quick before it warms up (otherwise it'll boil the liquid off as bubbles!!) but might help to diagnose the leakage/supposed leakage area eh?
If it ain't broke-------------------------- fix it 'till it is!

Royal Enfield Miltary 500cc  (2003)
Honda VTR FireStorm (SuperHawk) 996cc 'V' twin
Kawasaki KR1 250cc twin 'stroker
Ducati 916 'L' twin

Roger

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Re: Leaking Decompressor
« Reply #11 on: December 18, 2007, 10:23:37 AM »
Lotus7,

I did exactily that. I use as spray bottle containg detergent and I did detect very fine bubbles coming from one area of the copper washer. Since the leak appears to have stopped I have not yet used the detergent to confirm whether or not I have been successful.

The engine was quite hot at the time the leak appeard to be sealed and I have not had a chance to get back to it. I have some carburettor parts arriving any day now and one they are installed I will check for leaks again.

Roger