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stuck valve

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robert manbeck

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I have a 58 Austin Healey 100-6. I just did a compression check: all cylinders were 150psi except #1=30psi. If this is a stuck valve, how do I "unstick" it?

Thanks for any ideas.

Bob
 
If you have access to a compressor and an air regulator and can make an adapter to thread into the spark plug hole you can do a little troubleshooting before you disassemble anything. If you put the low cyl. piston at TDC on compression stroke and pressurize the cylinder with enough air pressure to hear leaking, you can listen at the carb air intake, the exhaust pipe exit and also take the oil filler cap off and essentially listen to ring blow by. If a valve is leaking you will likely hear it at either the carb (intake valve), exhaust (exhaust valve) or crankcase (rings). I'm not an expert on failure modes for our engines but I don't recall that sticking valves seems to be a common problem. If a valve stem is warped it needs to be replaced along with the guide. If there is carbon in the clearance between the stem and the guide, it needs to be reamed, finished and checked for clearances to avoid blow by. Either way if that is the problem you will need to remove the head and bad valve. If the valve is burned (more likely with exhaust valves) it needs to be replaced or at least reground and installed with a new or reground seat. It is possible that a valve may become stuck, be freed by removing the rocker arm assembly and whacking the valve stem with a mallet but that is not likely to be a permanent fix. Stuck valves are a sometimes problem for air cooled aircraft engines and since they have two spark plug holes you can fill a cylinder with rope, bring the piston up and compress the valve springs, remove the keepers and drop the valve into the cylinder and ream the guide, replace the valve and carry on. We can't do that so easily. You might see if you can look at the valves with a bore scope and might possibly see if there is a burnt seat if it is in fact valve leakage.
 
Bob,

Did you remove the rocker ("valve") cover and verify that a valve is stuck (very loose rocker clearance @ TDC compression-it should be obvious)? Also check there is indeed clearance (@ TDC compression) between the tops of the valve stems and rocker arm faces on the suspect cylinder. No clearance could cause the valve to stay open and leak badly - not good in many ways, and may be indicative of more problems, like a burned valve.

This would a simple first check, then move on to more troubleshooting GL, Jim
 
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Thanks for the instant response. A little history and update on today's findings. I drove the car every summer for 12 years. It always started instantly and ran smoothly. Four years ago I parked it (running great) and haven't run it since (mea culpa) I finally decided to resurrect the old girl (all brake cylinders frozen as well as master brake cylinder and clutch master/slave cylinder, etc...all repaired now). It's still not running, so I'm guessing not a burned valve or it would have manifested itself earlier. However, I removed the valve cover and found that there was no clearance between the rocker arm and the valve stem, in any position. The rocker arm is "opening and closing" the valve.

I'm guessing that if I remove the rocker arm and still getting no compression, the valve is stuck or the tappet is stuck?

You're impressions valued.

Bob
 
Sounds like a tappet is stuck . Take off the side access cover and watch the pushrods move . Maybe just needs some release agent to soak around the tappett and free it up .
 
Healey Nut said:
Sounds like a tappet is stuck . Take off the side access cover and watch the pushrods move . Maybe just needs some release agent to soak around the tappett and free it up .
Click to expand...

I like this suggestion. I prefer Kroil as a penetrating oil (we discussed this, ad nauseam, a couple of weeks ago :fatigue:smile:, but ATF or WD-40 or....

Good luck.
 
The Exhaust valve for #1 cylinder is closest to the front of the car. E-I-I-E, etc etc.
 
If the rocker arm is opening and closing the valve then a tappet is not stuck . With no valve lash the valve won't close when the engine warms up. Re-adjust the clearance . The engine will run on 5 cylinders so maybe something else is wrong also.
 
Jon, I tried your air compressor suggestion (by removing the gauge from my compression tester, I found the hose had a fitting for the compressor hose; I removed the valve stem from the other end of the hose, and so had perfect adaptor). I put the cylinder at TDC (well. about 10 degrees BTDC since I can't find a way to turn the engine). There did seem to be more movement between the exhaust valve stem and the rocker arm. When I pressurized the cylinder, there was some faint "hiss", but at the tailpipe air was flowing out so I could feel it with my hand...so that identifies the problem for sure...thanks.

Could you tell me more about your "rope trick"...seems only possibility before removing the head. The last time I ran the car it was running smoothly, I haven't run it since. If the valve was burned then, wouldn't there be rough running then?

Thanks again. Bob Manbeck
 
A six cylinder engine can run smoothly enough with a burned valve so that most wouldn't notice it . Just make sure you adjust the valves properly before you just assume its a burned valve.
 
Brinkerhoff said:
A six cylinder engine can run smoothly enough with a burned valve so that most wouldn't notice it . Just make sure you adjust the valves properly before you just assume its a burned valve.
Click to expand...
Oh, it's quite noticable. On initial startup after overhaul, I had a pushrod come loose.
 
Burnt out valve ! doesn't take a lot when the valve is weakened, to break through.

Happened to me whilst driving home one day - had to drive 6 miles on 5 cylinders - terrible sound but strangely exiting.

:cheers:

Bob
 
The rope trick I was referring to was for removing the valve keepers on aircraft engines. The whole procedure is doable, along with dropping the valve into the cylinder and then actually getting it back into the guide and re installing the keepers because the aircraft cylinders have two spark plug holes that are 180 degrees apart (top and bottom on horizontally opposed configuration). That plus the fact that the valves sit more or less horizontal (as opposed to the Healey head which has vertical valves) allowed one to fill the cylinder with soft rope with the piston down, then bring the piston up with enough pressure to keep the valve from moving while you compressed the springs and removed the keepers. You could then push the valve into the cylinder, ream the guide and thoroughly and with some "special tools" made from welding wire you could look into one spark plug hole while you used your wire crutch to re-position the valve back into the guide and repeat the rope part to put the keepers back in. I doubt you'd be able to get the valve back in if you tried this. I'll tell you what, the sound of the valve going "clink" into the cylinder is un-nerving but once you've done it a few times it is really pretty easy. It was done specifically to check the "wobble" of the valve stem in the event of a worn guide and also to remove carbon debris that on some engines would cause the valve to seize in the guide during running. You could use part of this trick if you wanted to replace a broken valve spring without pulling the head or wanted to let the valve much lower into the cylinder without letting it fall out of the guide, so you could get a good look at the valve seating contact areas.
 
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