Cylinder #2 no compression

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LBC TITAN
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Cylinder #2 no compression

Post by LBC TITAN »

About 3 months ago I replaced all the rings and pistons and rod bearings because the left bank had little compression and cylinder number 2 had no compression.

The car drove perfectly after that repair and I thought my engine woes were over. Now I know you guys are gonna say I should have did a complete rebuild. This was only my backup motor while I rebuild my other 140 with 280 Isky cam and .040 over pistons.

I changed the break-in oil about two weeks ago with Chevron 10w-30 synthetic and its not being running good and now no compression on number 2.

Compression:
#2 @ 0
#4 @ 100
#6 @ 115

Why does this stuff keep happening?
Charles
Long Beach, CA
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terribleted
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Re: Cylinder #2 no compression

Post by terribleted »

All these numbers are quite low, you should see 130-160. Did you take these readings with all the plugs removed and the throttle held wide open? When you did the pistons, rings, and rod bearings what did you do to the cylinders, hone them or nothing? What was the piston to cylinder clearance? Since it changed when you changed oil I would try doing hot valve adjustment. Set the preload to 3/8 turn in from quiet and recheck compression. Your lifters may now be pumped up more and holding valves open too long losing compression.
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azdave
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Re: Cylinder #2 no compression

Post by azdave »

Don't worry about low compression numbers on a back-up engine when one cylinder has clearly signed off. Pull the valve cover on that side and check the rocker arms and pushrods. Could be a failure there and a relatively easy fix.
Dave W. from Gilbert, AZ
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Re: Cylinder #2 no compression

Post by bbodie52 »

The consistently low numbers on the functioning cylinders could conceivably be due to a faulty, uncalibrated compression tester. You might consider borrowing another compression tester for comparison purposes to verify the accuracy of the actual numbers.

As mentioned earlier, changing the oil may have triggered an issue with one of the hydraulic lifters supporting the cylinder that is now reading zero compression (assuming that it was functioning before the oil change). The old hydraulic lifter may have been gummed up and sticking,and the oil change might have triggered a change. Loosening and readjusting the rockers on that cylinder bank may improve readings and return compression to the faulty cylinder.
Image


A healthy engine would have compression readings close to 130 PSI with all cylinders within 20 lbs of each other. You might try a different compression test tool to see if it shows similar numbers, and make sure the carburetor throttles and chokes are wide open when performing the test to obtain the highest readings. If the average remains low, a cylinder leakdown test can tell you more about the nature of the worn components (bad piston and rings/cylinder barrel wear, bad cylinder head valve seal, etc.)

A cylinder leak down test is a more advanced diagnostic procedure, and little more difficult to perform, because it requires some fabricated plumbing or a special test instrument, and a large capacity air compressor. Each cylinder to be tested is set at Top Dead Center (TDC) on the compression stroke (both valves closed). External air pressure is applied through the spark plug hole, and the percentage of leakage is evaluated. The source of the leakage (intake valve, exhaust valve, cylinder head gasket, or piston/cylinder seal) can be determined using an automotive stethoscope to listen for the leakage path (intake manifold, exhaust manifold, or crankcase). This test is performed on each cylinder, to determine the mechanical seal and condition of each cylinder. A video demonstration of this process (in this case, using a Volkswagen engine) is shown below.



There are many leak down testers available on Amazon.com. An example is shown below...

Image

OTC 5609 Cylinder Leakage Tester Kit

4½ Stars out of 5 with 807 customer reviews | 75 answered questions

Price: Price: $73.31

:link: http://www.amazon.com/s/ref=sr_st_revie ... eview-rank

A decent mechanic's stethoscope can be had for about $15.00...

Image

Also helps to locate noisy idler bearings, blower bearings, etc.

OF COURSE, A PURCHASE OR A RENTAL WILL DO YOU NO GOOD IF YOU DON'T HAVE ACCESS TO A DECENT AIR COMPRESSOR WITH ADEQUATE CAPACITY.
Brad Bodie
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azdave
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Re: Cylinder #2 no compression

Post by azdave »

Could be a sticky or seized valve stem not allowing the valve to fully close. As I mentioned above, pulling the valve cover is a pretty easy way to check for cracked rockers, dislocated rockers, rocker nuts that have backed out, pushrods bent or popped out of position and also check for valve stem motion.
Dave W. from Gilbert, AZ
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LBC TITAN
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Re: Cylinder #2 no compression

Post by LBC TITAN »

Yes the readings with were taken with all the plugs out.
The cylinders were honed, standard size rings used.
I didn't measure the piston to cylinder clearance.

I'll check the lifter as recommended.

Could you expand on the lifters being pumped up more.
Also since I didn't see any changes with the right bank and the same procedure was used to assemble both sides it could just be the head.
terribleted wrote:
Tue Jul 21, 2020 8:01 pm
All these numbers are quite low, you should see 130-160. Did you take these readings with all the plugs removed and the throttle held wide open? When you did the pistons, rings, and rod bearings what did you do to the cylinders, hone them or nothing? What was the piston to cylinder clearance? Since it changed when you changed oil I would try doing hot valve adjustment. Set the preload to 3/8 turn in from quiet and recheck compression. Your lifters may now be pumped up more and holding valves open too long losing compression.
Charles
Long Beach, CA
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Turbo 180
Hurst 4spd

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Re: Cylinder #2 no compression

Post by terribleted »

Particularly if you did not change the lifters it is very possible that one or more became un-gummed up and are now functioning better and therefore holding valves open some.
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azdave
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Re: Cylinder #2 no compression

Post by azdave »

LBC TITAN wrote:
Thu Jul 23, 2020 4:48 pm
Also since I didn't see any changes with the right bank and the same procedure was used to assemble both sides it could just be the head.
Probably the last thing I would suspect is the head being at fault. If the engine was running fine after you freshened it up and then you lost compression in #2 look for the easy stuff I mentioned under the valve cover. Have you pulled the valve cover and checked for anything we've been suggesting? Yes, maybe you could have blown a hole though the piston top but unlikely. Much more likely to be a valve train component or adjustment in my opinion.
Dave W. from Gilbert, AZ
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5

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flat6_musik
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Re: Cylinder #2 no compression

Post by flat6_musik »

I'd say that if it is zero compression, that will most likely point to the valve hanging open......or a broken valve spring. Hopefully not a valve seat that dislodged and cocked in place, keeping it hung open.

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LBC TITAN
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Re: Cylinder #2 no compression

Post by LBC TITAN »

Today I had time to do some more troubleshooting. I did a leak down test on on the number 2 cylinder by setting it to TDC, set to compressor to 100 psi and saw about a15psi loss. I listen through the exhaust no leaks, remove the oil filler cap no loud hissing, listened through the primary carb on the left bank and could hear a slight hissing.

I also readjusted the valves and tugged on the valves and springs to check if they were broken or loose, all were just fine.

See leak down test here. https://youtu.be/hO24sz3JNoc
Attachments
TDC #2
TDC #2
Charles
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Re: Cylinder #2 no compression

Post by terribleted »

How did you adjust the valves? Cold or hot? How much preload did you set?
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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LBC TITAN
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Re: Cylinder #2 no compression

Post by LBC TITAN »

I adjusted cold because I had the headers off, it's pretty hard to adjust with them on. I adjusted a quarter of a turn, I possible could readjust with a feeler gauge.
Charles
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Re: Cylinder #2 no compression

Post by terribleted »

Well 1/4 turn in from zero play is a little on the loose side perhaps, but, should be loose enough as long as you adjusted the valves when the were indeed fully closed that should be loose enough for them to maybe not be holding open. So you got compression of 100psi on number 2 now? If that's the case and it was zero I think you may have found that you have a valve adjustment problem as art least part of your issue. A major mechanical malfunction resulting in zero compression is not likely to improve from zero to 100 by only valve adjustment. I again suggest a running valve adjustment, just to see if more improvement is there. I would do only the bad side initially. If the number come up to be like the other side of the engine then I would do both sides. Headers make it hard but I have worked around header systems on these before. I have always found a way. Gloves and and old jacket to keep from getting immediately seared can be useful. Best way is to install a set of old dual exhausts hanging under the oil pan for doing adjustment. I have had a set laying around for this purpose on and off over the years.
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LBC TITAN
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Re: Cylinder #2 no compression

Post by LBC TITAN »

No, the compression on number 2 is still 0. I even put my finger over the hole while i used the remote start and no pressure at all. I'll see if I can pick up some used 140 exhaust system and adjust the valves while the engine is running.
Charles
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Re: Cylinder #2 no compression

Post by joelsplace »

Just back off the adjustment until you have extra clearance on that one cylinder. No preload at all. If the compression comes back your valve adjustment was the problem and you can fuss with making that right. If you still have zero compression then the engine has to come apart.
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Re: Cylinder #2 no compression

Post by terribleted »

joelsplace wrote:
Sun Jul 26, 2020 9:31 pm
Just back off the adjustment until you have extra clearance on that one cylinder. No preload at all. If the compression comes back your valve adjustment was the problem and you can fuss with making that right. If you still have zero compression then the engine has to come apart.
Yup. Indeed.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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