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Kelvin - mystery illness? (lengthy)

A bit beyond the remit of this group, perhaps, but anyway.......
I was called out to look at a Kelvin T6 (1964, around 200 bhp @ 1000rpm AFAIR) this morning which the barge captain was a bit concerned about as it had started 'blowing' from somewhere yet to be identified. There was a definite 'chuffing' from the air intake which shouldn't have been there, apparently an inlet valve blowing somewhere. It turned out to be No.6 cylinder - this one had blown a head gasket last year, so I had had the valves refaced & lapped in while the head was off, as well as having the head face skimmed. This was the only substantial work the engine had had done to it since I did a 'medium overhaul' at least 15 years ago (new liners, pistons regrooved & new rings, heads overhauled & refaced etc). Of course my first thought was 'why that cylinder?' - had I done anything wrong, etc., though it's performed happily for the last six months. Watching the valvegear with the engine on tickover (~200 rpm) the inlet could be seen to apparently open slightly immediately after closing, for no obvious reason - plenty of tappet clearance etc. To cut a long story a bit shorter, the only rational explanation I could come up with was that the cams for that cylinder have slipped on the shaft. This assumes a built up camshaft, I haven't the manual at the moment so I don't know for sure yet. The valve reopening is,according to my theory, because it is being sucked open on the induction stroke. If that's the case, and *if* (also don't yet know, but it looks likely) there is major work to to to get access to the cams (maybe gearbox {3/4 ton} & flywheel off, etc), I intend to propose to the owners disabling that cylinder temporarily, by removing the valve rockers & diverting the fuel into a container, on the basis that 5 cylinders will give ample power for the time being. An unplanned lengthy period out of service for repairs could be disastrous, so this would enable them to keep running for a few weeks while something can be worked out. I would remove the valve rockers in case the cam slips again, to avoid the risk of valves & piston makeing contact. I'm looking at it again tomorrow, better prepared, and with the manual, and will check the valve events etc to establish whether I'm right or wrong. If wrong, it should just be a simple matter of taking the No.6 head off again :-(
Any comments, adverse or otherwise?
Cheers Tim
Tim Leech Dutton Dry-Dock
Traditional & Modern canal craft repairs
Reply to
timleech
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A bit beyond the remit of this group, perhaps, but anyway.......
I was called out to look at a Kelvin T6 (1964, around 200 bhp @
1000rpm AFAIR) this morning which the barge captain was a bit
concerned about as it had started 'blowing' from somewhere yet to be
identified.
There was a definite 'chuffing' from the air intake which shouldn't
have been there, apparently an inlet valve blowing somewhere.
It turned out to be No.6 cylinder - this one had blown a head gasket
last year, so I had had the valves refaced & lapped in while the head
was off, as well as having the head face skimmed. This was the only
substantial work the engine had had done to it since I did a 'medium
overhaul' at least 15 years ago (new liners, pistons regrooved & new
rings, heads overhauled & refaced etc). Of course my first thought was
'why that cylinder?' - had I done anything wrong, etc., though it's
performed happily for the last six months.
Watching the valvegear with the engine on tickover (~200 rpm) the
inlet could be seen to apparently open slightly immediately after
closing, for no obvious reason - plenty of tappet clearance etc.
To cut a long story a bit shorter, the only rational explanation I
could come up with was that the cams for that cylinder have slipped on
the shaft. This assumes a built up camshaft, I haven't the manual at
the moment so I don't know for sure yet.
The valve reopening is,according to my theory, because it is being
sucked open on the induction stroke.
If that's the case, and *if* (also don't yet know, but it looks
likely) there is major work to to to get access to the cams (maybe
gearbox {3/4 ton} & flywheel off, etc), I intend to propose to the
owners disabling that cylinder temporarily, by removing the valve
rockers & diverting the fuel into a container, on the basis that 5
cylinders will give ample power for the time being. An unplanned
lengthy period out of service for repairs could be disastrous, so this
would enable them to keep running for a few weeks while something can
be worked out.
I would remove the valve rockers in case the cam slips again, to avoid
the risk of valves & piston makeing contact.
I'm looking at it again tomorrow, better prepared, and with the
manual, and will check the valve events etc to establish whether I'm
right or wrong. If wrong, it should just be a simple matter of taking
the No.6 head off again :-(
Any comments, adverse or otherwise?
Cheers
Tim
Tim Leech
Dutton Dry-Dock
Traditional & Modern canal craft repairs
Reply to
timleech
Trying to visualise the cycle, it occurs to me that the piston is on its way back up the cylinder after the cam releases the valve. With the pressure rising, it couldn't be that the valve is being sucked open - unless the valve is closing before BDC
Is it possible that the cylinder head gasket has blown between 5 & 6?
Frankly, I'd be surprised if the springs had deteriorated to the extent that atmospheric pressure can open it. Automatic inlet springs are poor, whoosie things.
Best of luck with it Tim, I think this is going to be one of those "Well, bu**er me!" moments !
Don't leave us in suspenders, will you?
Regards,
Kim Siddorn.
Reply to
J K Siddorn
Hmmm I don't know enough about this type of engine to be able to give any direct advice, but here's my bit. It sounds like the valve is behaving wrongly. However, the cam shape would not cause it to lift slightly no matter how the timing had altered. The cam opens the valve to full, then closes it. That cycle has to take place in it's entirety. You cannot have only a bit of the cycle. Also, as Kim says, I doubt that atmospheric pressure would be enough to open it during the induction stroke. Are you sure that the valve is actually opening for a second time? I have come across sticking valves. A build up of carbon means that the valve doesn't fully close. The piston starts on compression stroke increasing the pressure in the cylinder. That leaks past the valve at first until it reaches a point where it closes the valve. What you may be seeing is the last sudden closing of the valve without the opening bit. If the engine is rotated slowly, there may be enough time for the valve to close as you check the clearances. Can you remove the valve springs without taking the head off? If so, move the valve by hand and feel for tightness. Make sure the piston is near TDC so the valve won't disappear if you drop it though. If that fails, or the valve is actually closing and opening again, I would look for something causing the valve to re-open. First step is to rotate the engine slowly and see if the valve behaves in the same way. Then check the valve timing. A protractor on the crank and a dial gauge (or feelers on the valve clearance) will do. In the absence of a manual, check all the valves and see if one is wildly astray. After that I loose ideas. Disconnecting the cylinder should be OK as you suggest but remove the pushrods as well.
Good luck
John
Reply to
John Manders
My suggestion was that the cam had slipped on the shaft, so the valve timing was way out. That I've now proved to myself is not true, by checking the valve events against the makers' diagram. In any case, the camshaft construction probably wouldn't allow it. I had envisaged the Gardner type, with individual pairs of cams dogged onto a plain shaft. The Kelvin camshaft is made up of individual cyliner sections, welded together.
No, the heads & gaskets are all separate for each cylinder.
So would I, but I was getting stuck for ways to explain it. Of course, automatic springs designed for the job are intended to allow full opening, this is only a fractional movement. The springs are not strong, but I've ruled that particular theory out anyway.
Very likely!
Not for ever
Cheers Tim
Tim Leech Dutton Dry-Dock
Traditional & Modern canal craft repairs
Reply to
timleech
No, the camshaft isn't causing the valve to reopen. Something within the cylinder is.
It is definitely reopening very slightly after closing.
Bear in mind this head was off & thoroughly sorted last year. The others have been untouched for at least 14 years. This is the least likely to have sticking valves, though admittedly a dodgy injector could soot one up fairly quickly. This valve moves perfectly freely when pushed by hand. My experience has been that it's always exhaust valves which stick.
The inlet port is reasonably visible with the manifold off, I've just come back from playing around with torches & inspection mirrors to try to ascertain a bit more, but couldn't find anything definite. Using a screwdriver as a lever to hold the valve more tightly closed when running on tickover does reduce the blowing somewhat. Rotating the valve while running also found a slight variation depending on valve position.
My latest theory is that either a foreign body has been drawn into the air intake, or a piston ring has collapsed & broken out to the top of the piston, & the valve stem has been bent slightly when the body has come betwwen piston & valve. My only current idea for the valve reopening is that the 'body' is now welded to the valve face, & gets 'caught' in a hole in the piston at the top of each stroke & pulled down. There does seem to be a slight mechanical 'tic' at TDC on that cylinder.
Well, as I said, I was going to remove the rockers. The pushrods are guided top & bottom, so should come to no harm.
Thanks!
It is still firing on 6 cylinders when working (not on tickover), so he's doing one more 'trip'over the weekend & I'll have the head off on Tuesday. I hope that any loose bits inside the cylinder have already done whatever damage they were going to!
Times like this, an endoscope would be really handy!!
Cheers Tim
Tim Leech Dutton Dry-Dock
Traditional & Modern canal craft repairs
Reply to
timleech
I think I have the beginnings of an idea.
If there is/has been debris in the cylinder, it might have slightly bent the valve and although inertia will close the valve, the spring pressure is now insufficient to hold it closed. As the revs pick up, the valve does not have time to slide open before the rising compression holds it against the seat.
This would explain why it will not tick over on that cylinder but fires as the revs rise.
With breath a'bated, I exit for an event. (We are at the multi-period show at Whittington barracks on the A51 outside Lichfield, Staffs.)
Regards,
Kim Siddorn.
Reply to
J K Siddorn
To look down the plug'ole??
Brian L Dominic
NB Rumpus
Web Sites: NB Rumpus:
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Friends of the Cromford Canal:
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Mid-Derbyshire Light Railway:
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I may work for British Waterways, but my opinions are my own.
Reply to
Brian Dominic
Some of the larger engines here are not fully running yet but we can turn them over on air. On shutting off the air the inlet valves will suck open as the revs drop off.
If the valve has something on the seat that would stop the cylinder firing and release compression pressure it could well suck open slightly on the firing stroke. The 9H Ruston inlet valve you cannot move by hand yet that happily sucks open.
Paul
-- ____________________________________
Internal Fire, Museum of Power, Wales
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(under construction)
Reply to
Paul Evans

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