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lost compression in cylinder
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Zero419
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PostPosted: Fri Sep 30, 2011 10:07 am    Post subject: lost compression in cylinder Reply with quote

This is a new thread from the running horrible in rain thread.

So I new I was down a cylinder, so I started digging.
I pulled the plug wire on the left front plug and nothing changed.
Then I tested the compression in that cylinder and got next to nothing.
Next I adjusted the valves on that side until they just touched. compression came back. I then turned them in one turn, put everything back together, pulled the wire, and found that it is still a dead cylinder. I have spark on that wire.

Guess I can't do a valve adjustment to save my life.

Is it OK to run it with the valves adjusted just a little past snug?

Haven't tried it yet...
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IdahoDoug
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PostPosted: Fri Sep 30, 2011 11:19 pm    Post subject: Reply with quote

pull injectors from that side, wrap half a paper towel around business end so you can see if they are putting out fuel. then hit starter and come back to see if dead cyl's injector is putting out squirts making towel wet.

DougM
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PostPosted: Fri Sep 30, 2011 11:33 pm    Post subject: Reply with quote

Did you do a compression test after turning the valves in 1 turn? If not it then please do. It seems like you may have one or both hydraulic lifters misbehaving and acting like solid lifters. Try running it without preload on those lifters. If it runs better then replace those lifters. We've seen this happen a few times at the shop, but mostly on the wbx 1.9

-Dan
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Wildthings
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PostPosted: Sat Oct 01, 2011 5:17 am    Post subject: Reply with quote

You will not have good compression immediately after tightening a hydraulic lifter. You will need to run the engine for a while first so the lifter can self adjust. Do the injector test mentioned above to make sure you are getting fuel into that cylinder or better yet a spray pattern test. You might want to change the plug and plug wire going to that cylinder as well, maybe followed by replacing the cap and rotor.

If your valve springs are weak the lifters can over pump, that is they do not bleed off enough oil to make up for what is entering. You could try replacing your lifter as mentioned above and you could check the valve stem heights to make sure you are not getting any recession. If you have AMC heads the valve, seats, springs, retainers, and keepers are all pretty low quality and they can cause a loss of valve spring tension for many reasons.
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Zero419
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PostPosted: Sat Oct 01, 2011 9:09 am    Post subject: Reply with quote

I do have AMC heads.
ran them stock for 20-30k miles.
during rebuild 10K ago, I had the head rebuilt.
Replaced the exhaust valves with quality valves suggested here (TWC? or something like that)

If it ever stops raining again, I'll look at it again.
hopefully I can get this figured out before winter sets in.

After I went in one turn I went for a mile ride, never got power back to that cylinder.

plugs are that 3 prong deal suggested here. all of them are dark and look like they are running rich.

Is a burnt valve a possibility?

If I burnt up a piston, I would see smoke, right?
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Zero419
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PostPosted: Sat Oct 01, 2011 9:12 am    Post subject: Reply with quote

molybdanum wrote:
Did you do a compression test after turning the valves in 1 turn? If not it then please do. It seems like you may have one or both hydraulic lifters misbehaving and acting like solid lifters. Try running it without preload on those lifters. If it runs better then replace those lifters. We've seen this happen a few times at the shop, but mostly on the wbx 1.9

-Dan


No, I didn't do a comp. test after the single turn.
I do have enough parts to replace those two. (collapsible tubes, seals and lifters.)

Ya know, that was the first wire a pulled and I stopped there. I should check the others. I wonder If I'm only running on two cylinders. It sure is weak.
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Wildthings
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PostPosted: Sat Oct 01, 2011 12:05 pm    Post subject: Reply with quote

hero419 wrote:
I do have AMC heads.
ran them stock for 20-30k miles.
during rebuild 10K ago, I had the head rebuilt.
Replaced the exhaust valves with quality valves suggested here (TWC? or something like that)?


One of the problems with AMC valve parts is keepers that don't fit the valve stem tightly and thus wear at the retainer. If your head rebuilder reused the AMC keepers that could be your problem. With the rockers removed or at least with the adjusting screws backed fully off, compare the deck height of the retainers.

If you were able to get good compression by backing off the adjusters then your valves, pistons, and rings should be okay.
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PostPosted: Sat Oct 01, 2011 1:19 pm    Post subject: Reply with quote

You're confusing lifters and pushrods. No need to replace pushrods. Just used those clever adj pushrod tubes from Van Cafe. Very nice product.
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Zero419
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PostPosted: Sat Oct 01, 2011 1:25 pm    Post subject: Reply with quote

IdahoDoug wrote:
You're confusing lifters and pushrods.


Where did I do that?
I do have some new lifters and collapsible tubes. I ordered them last time I had a tick. Did a full adjustment (didn't use any parts) and everything was great for 50-100 miles and then this happened.
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Last edited by Zero419 on Sat Oct 01, 2011 1:28 pm; edited 1 time in total
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Zero419
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PostPosted: Sat Oct 01, 2011 1:26 pm    Post subject: Reply with quote

Wildthings wrote:
hero419 wrote:
I do have AMC heads.
ran them stock for 20-30k miles.
during rebuild 10K ago, I had the head rebuilt.
Replaced the exhaust valves with quality valves suggested here (TWC? or something like that)?


One of the problems with AMC valve parts is keepers that don't fit the valve stem tightly and thus wear at the retainer. If your head rebuilder reused the AMC keepers that could be your problem. With the rockers removed or at least with the adjusting screws backed fully off, compare the deck height of the retainers.

If you were able to get good compression by backing off the adjusters then your valves, pistons, and rings should be okay.


I will look at that too.
Thanks.
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PostPosted: Sat Oct 01, 2011 1:45 pm    Post subject: Reply with quote

Wups - my bad. So you have spare lifters. Bring the engine to TDC for the dead cylinder and see what the lifters feel like as to spongy or hard. I was able to slowly learn what passes for a normal feel after several rounds of valve adjustment (including one round where I was adjusting them at wrong TDC on each). I can't imagine how they might be too hard, but a very soft one would be an issue.

I would: Yank the valve cover. Use a chunk of wood to push that %^&* coolant pipe up a quarter inch so you can see into the pushrod tube (between exhaust pipe and tube with a wedge or big screwdriver) hole. That is the toughest one to see. Use a small bright light to confirm the pushrod is centered. Then see how firm the lifter feels simply by pushing on the rocker arm. If it's rock hard you may have adjuster cranked in so far the valves aren't closing. If so, loosen adjuster while pressing with a lb or two of pressure on the rocker to keep the pushrod from falling out of position. When it is not touching, turn with a very delicate feel until you feel the slightest adjuster resistance indicating its in contact. Then 1.5 turns. Repeat on the other valve.

I feel like this issue will be resolved in the valve adjustment. Let us know what happens with the injector spray also though I feel like that's not it.

DougM
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PostPosted: Sat Oct 01, 2011 1:45 pm    Post subject: Reply with quote

Stop raining yet? Heh...
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PostPosted: Sat Oct 01, 2011 2:42 pm    Post subject: Reply with quote

Hey Hero419:

Regarding your comment:

"plugs are that 3 prong deal suggested here. all of them are dark and look like they are running rich.

Is a burnt valve a possibility?

If I burnt up a piston, I would see smoke, right?"

When you have a misfiring cylinder, there is plenty of unburnt oxygen from that misfring cylinder getting to the oxygen sensor. Remember, it is not a "rich or lean" sensor - - it's an oxygen sensor. The whole lambda system depends on there being no misfires.

So with the unburnt oxygen being sensed, the Lamba system compensates for a perceived lean condition by adding fuel. That results in your black, sooty plugs. This will ruin your catalytic converter and your oxygen sensor if you continue like this for long.

The remedy, while you are trying to find the reason for the misfire, is to disconnect the oxygen sensor. If the basic settings (ie: Co adjustment) is in spec, this will result in a mixture of about 13:1, which is a lot leaner than the overfueled mess you have now. The lambda system maintains a 14.7:1 Air Fuel Ratio (AFR) when there are no misfires.

As for what is causing your loss of compression, all the comments above about valves not fully closing are right except I would point out that the Bentley, at 15.24, mentions that "hydraulic lifters have been known to become air bound." The Bentley recommends using 0.006" clearance (meaning NO pre-load) which will allow the air to be cleared out of the affected lifter(s). I strongly suggest you try this, along with some Marvel Mystery Oil, which really helps these hydraulic lifters.

The AMC keepers might also be the source of your problem. Here's how:

When they wear, they allow the retainer to back away from the head further and thus increase the valve-spring height. That height has to be within tolerance to provide enough spring pressure to overcome the oil pressure in the hydraulic lifters. This can be tested by shimming up the valve springs. However, the proper fix is to replace the keepers IF the grooves on the valve stems are not already destroyed.

You can do this without disassembing the engine. Set the piston in the affected cylinder to TDC on the compression stroke. Check the valve spring installed height and compare too other cylinders.

To retain the valves in place, remove the spark plug on the affected cylinder, turn the engine to BDC on the compression stroke, and then feed 1/4 inch diameter nylon rope through the spark plug hole into the cylinder until no more will fit. Then turn the engine clockwise to compress the rope against the valves. Now you can remove the retainers from the valves using a "claw" style valve spring compressor like the one in this link:

http://diytoolsca.com/index.php?main_page=product_...5put88g211

Then you can inspect the valve stems, replace the keepers if necessary, retainers if necessary, and shim the valve springs to the proper installed height.

But before you do any of this, try the 0.006" valve lash setting first.
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Zero419
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PostPosted: Sun Oct 02, 2011 6:24 am    Post subject: Reply with quote

Wow, lots of good stuff here.

Do I ground the O2 sensor.

I hope the keepers are fine.

All the lifters have been rock hard these last few times. I have pushed in on them and felt spongy in the past, but lately, every time I try it, they a hard, and if they are going it, it's so slow I cant detect it.

I may get a shot at it today if my wife doesn't get ticked that I'm not hanging out with the family. rained all night, I'll be laying in mud. Wish I had a garage.
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PostPosted: Sun Oct 02, 2011 10:12 am    Post subject: Reply with quote

Got some time, here is a little update.

pulled all plug wires one by one and found only one (same) offending cylinder.

pulled valve cover. Noticed on compression stroke that the screw for the intake was turned in much farther then the other 4 on that side.
also noticed that the rod was sticking out the least.
I figure a fully collapsed lifter.
I pull the rocker assy.
pull the intake push rod.
yank the tube.
stick the magnet in the hole and cant get the sucker out.
futzed with it for an hour.
tried inserting the new lifter to loosen any debris. still no go.
I can move it an inch or so depending on the position of the cam lobe, but cant get it past that one point.
Tried running the starter for a bit hoping oil pressure would spit it out.

guess I'm on hold until I find a stronger magnet.
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PostPosted: Sun Oct 02, 2011 12:37 pm    Post subject: Reply with quote

Not very likely, but if it had been running very loose for a while the face of the lifter could have mushroomed. Hope not.

Go back and set that lifter so that it has a little lash .001-.006" and run it a bit to see if it will pump up. If it does then a quart of ATF or MMO added to your oil may make things right. Don't run it for too long with lash before going back and setting the preload, just a few hours or at most a few days.
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Zero419
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PostPosted: Sun Oct 02, 2011 1:02 pm    Post subject: Reply with quote

sprayed some carb cleaner and got in there with a tooth brush.
got a hook in the lip of the lifter and 20lbs of force or so wouldn't pull it free.

It must be stuck on the other side being that I can push the new lifter in the hole 'till it touches the old lifter.

I'm going to let it sit with that carp cleaner and give it a tug tomorrow, if that doesn't do it, I'll try the lash.
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PostPosted: Sun Oct 02, 2011 1:14 pm    Post subject: Reply with quote

I can yank it to a point that it gets stuck and needs a good amount of force (10lbs?) to push it back in inch or so.

Not sure if that helps.
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PostPosted: Sun Oct 02, 2011 1:56 pm    Post subject: Reply with quote

Since that lifter gets stuck when trying to pull it out, it does sound as though it might be mushroomed. They don't have to be mushroomed very much at all to get stuck since the clearances in the lifter bores are quite tight. I don't recall if those lifters are old or recent or how recently you engine was rebuilt. If very old, then it is possible that varnish in the untravelled portion of the lifter bore is causing the friction. If that lifter or the rebuild is fairly recent, then not so likely.

You might only have slight mushrooming or you might have major mushrooming. Only a teardown will tell. If it is major mushrooming, then lifter wear will be serious and so, eventually, will cam lobe wear.

Assuming the mushrooming is minor, then getting that lifter to pump up and function as intended will solve your problem and as Wildthings pointed out, the MMO is the way to go on that.

I suspect that the lifter collapsed and an over-zealous valve adjustment followed that to produce an open valve.

You need to check that the lifter will return to the base circle area of the cam without much friction. You need your helper to turn over the engine while you apply finger pressure to the pushrod. If the lifter is sticky - - it's time to remove the engine and investigate. If not, count your blessings, set the lash at 0.006", and run the engine with the MMO to try to remedy the lifter problem.

This could take a few tries if the lifter was fully collapsed. That is, after you run the engine for a while and the lifter pumps up again, you need to adjust the valves again to 0.006" lash until the lifter is fully pumped up at which time you can go back to the zero lash setting.
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Zero419
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PostPosted: Sun Oct 02, 2011 2:11 pm    Post subject: Reply with quote

Thanks.
lifters are 10-20k miles old.
Looks like it's stuck good.
I'll try again to pull it tomorrow, and if that fails, I'll do the partner test and continue with the lash path.
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