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Discussion Starter · #1 ·
Quick and dirty:
'76 GL1000 w/44K miles comes to me making a noise in right valve area. Sounds a little like a misadjusted valve, but is quite noisy and not so much 'tapping' as a loose valve adjustment would make

Pull valve cover and crank engine...using stethoscope I hear what EXACTLY RESEMBLES an exhaust leak(BRRRRR) coming out of #3 Exhaust valve spring area. I pull the head, only to find that the exhaust guide on the #1 cylinder has broken off the 'nose' sticking down into the inlet port, and the broken piece is nowhere to be seen. After pulling the head, the dinks in the #1 piston tell me where it went, and stayed only briefly. It likely is now inside the exhaust system.

Inspection of exhaust valve on #3 cylinder tells nothing. Guide wear is minimal and is precisely the same as Cyl #1. Seal is hard but still intact. No cracks in metal. NOTHING OUT OF THE ORDINARY ON CYL #3.

I rebuild head number 2 using the valves/cams from head number 1 and viton valve seals. Check compression...145/150psi. Crank up bike and *voila* there is that noise again. Exactly the same... sounds like exhaust leak coming up from around the spring area, not heard on any of the other valves.

Possible causes:
Worn valve stem - measured stem, well within spec. Wobble when valve inserted is exactly the same on #3 as #1. No noise on cyl #1 exhaust at all.

Bad Valve Guide - in exactly the same cylinder? hard to believe

Tweaked cam or follower - this strikes me as possible, but improbable. Valves bend without damaging follower or cam frequently...but there was that missing valve guide chunk...

So... my friendly masters of techno-knowing... how and why?

I am off to swap a cam/follower set into the head for fun.....hate to pull that head again and burn a cyl gasket. All input is appreciated, guesses involving Cajun voodoo or Japanese gremlins will be laughed at
 

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Discussion Starter · #2 ·
for those looking for an easy answer...

not the timing belt... I installed about 20 sets last year, think I have that procedure down now
 

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Quick and dirty:
'76 GL1000 w/44K miles comes to me making a noise in right valve area. Sounds a little like a misadjusted valve, but is quite noisy and not so much 'tapping' as a loose valve adjustment would make

Pull valve cover and crank engine...using stethoscope I hear what EXACTLY RESEMBLES an exhaust leak(BRRRRR) coming out of #3 Exhaust valve spring area. I pull the head, only to find that the exhaust guide on the #1 cylinder has broken off the 'nose' sticking down into the inlet port, and the broken piece is nowhere to be seen. After pulling the head, the dinks in the #1 piston tell me where it went, and stayed only briefly. It likely is now inside the exhaust system.

Inspection of exhaust valve on #3 cylinder tells nothing. Guide wear is minimal and is precisely the same as Cyl #1. Seal is hard but still intact. No cracks in metal. NOTHING OUT OF THE ORDINARY ON CYL #3.

I rebuild head number 2 using the valves/cams from head number 1 and viton valve seals. Check compression...145/150psi. Crank up bike and *voila* there is that noise again. Exactly the same... sounds like exhaust leak coming up from around the spring area, not heard on any of the other valves.

Possible causes:
Worn valve stem - measured stem, well within spec. Wobble when valve inserted is exactly the same on #3 as #1. No noise on cyl #1 exhaust at all.

Bad Valve Guide - in exactly the same cylinder? hard to believe

Tweaked cam or follower - this strikes me as possible, but improbable. Valves bend without damaging follower or cam frequently...but there was that missing valve guide chunk...

So... my friendly masters of techno-knowing... how and why?

I am off to swap a cam/follower set into the head for fun.....hate to pull that head again and burn a cyl gasket. All input is appreciated, guesses involving Cajun voodoo or Japanese gremlins will be laughed at

exhaust guide has broken off the 'nose' sticking down into the inlet port
"Inlet port" on exhaust would be an exhaust port, wouldn't it?

As to the missing pieces maybe someone else has been in there to retrieve them???
So did you replace the valve guide?
I just went down to the garage and looked at a head I have down there to see what you were referring to a little better. :shock: EYES! (Boot camp thing)
If it's broken in the port, that is where the leak is from allowing passage instead of the guide to seal it to a closer tolerance to the valve stem base from the exhaust pressure. That is what I would be looking at anyhow.

How about some snake oil?
:waving:
 

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Maybe someone tagged that valve earlier and it bent or busted off the valve in the cylinder, and replaced just that valve?
That would explain the "dinks in the piston" Except I've seen the results of high rpm broken valve putting a hole in the piston, not just "dinks"
 

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Discussion Starter · #5 ·
Ok...lets get the picture clear...

the #3 cyl (right rear, adjacent to the fuel pump) had the noise... when stethoscope was pointed directly at exhaust valve spring while engine was running (and oil falling out like a waterfall) noise was clearly heard

the #1 cylinder had a broken valve guide... the guide sticks out 3/8in into the cam area and 3/8in into the port above cylinder inlet. The inlet guide broke off flush with the surface directly above where fuel enters the cylinder. It may have immediately cracked and fallen into the cylinder, or it may have bounced up and down on the valve stem till it broke, but it was gone and MINOR signs that it fell to the bottom of the cylinder were evident.

When any foreign object falls into the cylinder it will cause stresses somewhere... keep a valve open, bang between the piston and cylinder head, etc. If your engine swallows a valve the damage is widespread.... trust me on this. This pea dinked the piston/cyl head a couple dozen times and fell out...and engine kept running.

I replaced the head with the broken valve guide with another used head. Can't guarantee it did not have problems, but I gave it a good inspection, lapped the valves, and checked compression - all good.

So I have a carefully inspected head with carefully lapped valves and new seals all around using some valves (like the exhaust valve from original cyl#3) and cam/followers from the original. New cyl head has good compression, lets bike idle fine. But noise is still there, detected again in exactly same spot. Valve guide problem goes to bottom of list... that leaves:
- Valve
- cam
-follower
- valve seat (I'll try anything here)
- Houdini happenings?
 

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Houdini happenings? Naw

A ventriloquist gremlin hiding on the other side!
 

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Cam bent? Damage to the fuel pump drive? Piston is cracked where you can't see it? Are you sure there's not excessive bearing journal wear on your cam?
 

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Those used doubble springs. damedged inner spring binding in outer spring?:?
 

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This is my four penny worth.

Is it at all possible that the guides were replaced but not reamed at all. There are also wire loops round the guides that may well not have been present when installed. The guide then is loose.

The last thing is something that happened to me.

The PO did some head work and left a collet in the double spring basket. The guide was very badly damaged as you can imagine. It leaked passed the guide in a similar way.

Guides wear much quicker in the exhaust valves as they are hotter. Inlets are cooled by the fuel.
 

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One last thing. Check the springs are installed the right way up. refer to the manual but there is a right way and wrong way. Very easy done.
 

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Its wery unlikely that the exhaust would leak around valve stem unless the exhaust system is WERY clocked.
I would try running the engine with the fuelpump removed and listen for change .
 

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Discussion Starter · #13 ·
update...
pulled cam/followers/cam tower... compared to two others... the installed one looked great. Measured bearings, examined wear surfaces... all match up very nicely. In other words, unless I have 3 very goofed up cams/followers/etc the ones installed were okay...

the last thing installed is the valve. As stated, compression check upon assembly showed 145psi... very good in my book. Cyl #1 was 150. That lead me to believe I had it all working just fine... *sound of the Gods laughing in the background*

So...next step is to pull the head. Not sure if I will swap out the entire head or just the exhaust valve... maybe a bit more comparison is in order. My spare head is filthy, hate to spend the time to clean it up but I sure as hell hate to install another bad head.

OH.... one last thing occurred to me.... if pressure was pushing exhaust up through the valve, maybe it had nothing to do with the head... maybe the exhaust was blocked! So I pulled down the pipes and ripped 'em apart (literally cause the mounting flange for the header broke right off). Looked inside all I could this side of a proctoscope and no problems apparent. I was hoping to find that gremlin living inside the header of cyl #3 but no go.

Your suggestions:
- cam bent? not apparent from any damage to cam bearings/followers
- damage to fuel pump drive? none visible
- piston cracked? probably more likely on cyl #1...trust me I looked very close and none visible
- Excessive bearing journal wear? zero visible difference ...need special tools to measure inside diameter which I do not have, but all looked the same - good!
- damaged inner spring? taken apart and examined briefly, but nothing jumped out
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guides were replaced but not reamed at all? possible, but on replacement head it was all OEM stuff. Replacing guides is a bitch of a job.... much easier to just buy a replacement head
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guide then is loose? positioning clips all in place and flush at head
- springs are installed the right way up? have to get back to you on this one...hard to see that making a huge difference
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running the engine with the fuelpump removed and listen for change? will do that after head work. Fuel pump is spitting and about to be replaced. Hard to imagine how the fuel pump causes air to come out around the exhaust valve spring. The fuel pump spring is fairly weak compared to the valve springs... and is cantilevered outside the cam area. If there was significant wear on cam bearings it would be different story

Bless you guys for shooting the "why doncha try..." thoughts my way....every one helps
 

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My thought is, no way it is going to blow air out the valve guide.
On the valve spring installation, if it has a tighter wound end it would only matter at high enough RPM to float the valve.
 

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The valve spring warning I remember from my install of the two heads came from the Haynes manual I was using. It did not mention what would happen if you got it wrong just how to determine which way up was correct. I did get it wrong on one and had to undo the collets again.

Exhaust valves as said before are normally a bit looser in the guides than the inlet due to heat and faster wear. Would gas from the power stroke get passed? I'm not a scientist but the law of sod is bound to come into play.
 

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If your valve timing is off, it could cause one valve to open/close at at the wrong time. Cylinder #3 exhaust is set with timing at T1, cylinder 1 at tdc. You should have quadruple checked that by now. Are you using 1000 cam gear?
 

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Discussion Starter · #18 ·
As for the valve springs, I did check their position versus an original (never disassembled) head. They appear to be perfect

yes sodium filled valves are sometimes used, but I am pretty sure this bike did not get a set

I agree about wear on the exhaust guide... but the valve did not appear to be ANY looser than the intake when inserted upside down and wiggled. Yes there was play in both guides, but no different front to back or compared to another head(used)

Yes, timing is set when timing mark is at "T" for cyl #1, but correct timing for the right cam gear is set when the cam gear is 180deg away from original timing mark... this is done to relieve the pull on the belt and allow the tensioner to properly set belt tension. This is not stated in the manual but should be done or else you ALWAYS will either overtighten/undertighten the belt tension.

In either case the timing marks lined up perfectly after installation

I hope to swap this head with an entirely different one tomorrow... maybe I can write back with good news
 

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Ive seen casting flaws not show up for maney years. especially in sand castings.
 

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Discussion Starter · #20 ·
Problem solved

Finally found the Answer!!! yaaaaay

Removed head #2 after inspecting the bejeesus out of the cam, timing gear, everything I could on the outside, etc. Thought I had found an answer when it occurred to me the timing gear could slip and cause a mis-timed exhaust opening... but no.

Upon pulling the exhaust valve on the #3 cylinder, first thing I noticed is that the seal seemed to move as I wriggled the valve out... then I realized it was attached to the upper portion of the valve guide...which had broken off

Seems I failed to closely inspect the valve, and put a valve with a slightly bent stem back into the head. Used the same valve from head #1 in exhaust port #3... bent valve leaked through the guide same as before

One reason for the flaw is that two(at least) valves got dinged when the original valve guide broke off and jumped into the cylinder. It is possible the bending occurred from a previous timing belt break... but previous owner never mentioned replacing the valves/head.

The thing that put me off-track was the fact that the head had excellent compression... approx 150psi. The valve would seat perfectly, but the stem would bend slightly when depressed...thus opening up a gap through which exhaust could leak. It likely also occurred in the intake, leaking directly through the guide, but that did not make a noise.

In my experience when valves bend it always occurs around the seat...thus the valve will never seal the head again. I would guess something high speed occurred where the cam lobe swung around as the valve was popping up and whacked the top sideways. Valve stems were bent like my Craftsman screwdriver when I attempt to use it as a substitute kickstarter lever :)

Gettin' smarter every day I swear

Moral of the story: When a cylinder head suffers any kind of severe trauma, take time to inspect the valves(and other components) carefully... just because they seat does not make them a good valve

Thanks again amigos!
 
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