Confusing compression test results - a good mystery (1 Viewer)

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What OSS said. No harm in doing a compression test for fun other than it makes you start wondering if you should rebuild or swap. Had you not done the first test you would have likely driven around in blissful ignorance of the engine's impending doom - in another 200k miles. If the intake was open (air cleaner off, carb open to rain) when it was stored outside then Dallas Cruiser very well could be right - some rust on a cylinder wall and/or rings. This could lead to poor compression, increased blowby, burning oil, possibly even a plug fouling occasionally. It could also lead to nothing. I'd take the chance at this point and button it up and go. If it turns I'm wrong, which has been know to happen, and the worst case happens (engine needs a rebuild) you've only lost a day or two of work on what'll be a month plus project.
Of course, if you're looking for justification for an LS swap ("Look Honey, everyone on the forum said the engine's toast. I'll be money ahead to put a V8 in it.") then yeah, pull that boat anchor and start looking for a donor. ;)
 

kenavt

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Finally got around to doing the valve adjustment (most of the valves were oddly too tight), and then to running the leak-down tests with a borrowed HF unit that shows the pressure on either side of the gauge (not a percentage).

tempImagebGhrd5.png


Got everything buttoned up Wednesday and tested cylinder 1 - got 82/67 psi (19% leakage) which I'm pretty happy with.

Then today had a chance to pick things back up and here's what happened:
Cylinder 1 (first attempt) - 80/64 (20% leakage). Leaking through piston seals (confirmed by sound change through oil dipstick and oil filler cap). Pretty happy with that one.
Cylinder 2 - 82/9 (89% leakage). Leaking through carb manifold hole (intake valve).
Cylinder 3 - 80/24 (70% leakage). Leaking through carb manifold hole (intake valve), a little through piston seals (oil dipstick).
Cylinder 4 - 80/6 (92% leakage). Leaking through carb manifold hole (intake valve), manifold to downpipe (exhaust valve)
Cylinder 5 - 74/14 (81% leakage). Leaking through carb manifold hole (intake valve).
Cylinder 6 - 80/4 (95% leakage). Leaking through carb manifold hole (intake valve), manifold to downpipes (exhaust valve)

After this array of really terrible results after cylinder 1, I went back to cylinder 1 again and got 80/32 (60%), 78/32 (57%), 80/34 (58%), 41/90 (54%), 30/72 (58%).

My hunch is that I'm either doing something wrong (see below) or this engine's valve seals are complete toast, since it keeps on leaking through the intake. Unless someone can find a hole in my leak-down test procedure, I think my next moves are to either just say f*** it and try to fire up the engine (mount the carb and figure out minimum emissions hosing to get things to fire up), or just take the head off and look at these valve seals.

For my leak-down test procedure, I've been sticking a hose or screwdriver in through the spark plug hole to figure out when the least amount of space in the cylinder is around. Spin the crankshaft by the pulley nut until that space seems as tight as it'll be, then screw in the leak-down tester hose and run the test.

I was worried that I can't get to TDC for each cylinder accurately enough- my strategy has been to stick a hose or a screwdriver in through the spark plug hole. The repeated cylinder 1 results at the end are from me trying slightly different positions at or around TDC based on looking at the flywheel mark. How close do you have to be to TDC - is +/- 5 crank degrees enough?

I also tried measuring electrical shorts across the distributor (which didn't work and also in hindsight might not be TDC since that's ignition, might be a few crank degrees off).
 

Spook50

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With that much leakage across the board except for cylinder 1, I'll bet your intake valves weren't closed all the way. Did you make absolutely sure your valves are correctly adjusted and weren't set at the wrong point in rotation? How I adjust my valves is cold with an extra 0.002". This has them spot on when the engine is hot, and doing it this way gives you plenty of time to do the correct valves at the correct point in crank rotation. Were it only a couple cylinders I would suspect damaged valves or valve seats, or possibly buildup betwen the valves and seats.

Are your EGR and PCV systems still operating properly? I'm unfamiliar with the layout of the EGR system on the 2F, but I'm wondering if (assuming your valves are adjusted right) you have carbon buildup around your intake valves.
 

2mbb

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yeah, you have to be on the compression stroke for the leak down test to work. You start with #1 on TDC (the timing pointer on the scribed line) with the #1 cylinder on it's compression stroke. Then you can follow the firing order: 1, 5, 3, 6, 2, 4. Each is 120deg out of phase with the one before. With #1 at TDC on the compression stroke, the next one, #5, should be on it's way up to compression. After finishing with one, put the screwdriver or dowel into #5 and spin the engine in the direction of rotation until it reaches TDC. Then repeat for the next cylinder in sequence. It's more important to make sure you are on the cylinder's compression stroke than it is to be exactly at TDC. A few degrees off TDC either way won't matter.

For the valve adjustment search this forum for key words "valve adjustment" and posts by me. I have provided detailed instructions several times.
 

kenavt

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With that much leakage across the board except for cylinder 1, I'll bet your intake valves weren't closed all the way. Did you make absolutely sure your valves are correctly adjusted and weren't set at the wrong point in rotation? How I adjust my valves is cold with an extra 0.002". This has them spot on when the engine is hot, and doing it this way gives you plenty of time to do the correct valves at the correct point in crank rotation. Were it only a couple cylinders I would suspect damaged valves or valve seats, or possibly buildup betwen the valves and seats.

Are your EGR and PCV systems still operating properly? I'm unfamiliar with the layout of the EGR system on the 2F, but I'm wondering if (assuming your valves are adjusted right) you have carbon buildup around your intake valves.

I was pretty sure that I adjusted my valves properly (doing 0.014" for both intake and exhaust per engine builder's cam notes) until reading your post more thoroughly.

I did both intake and exhaust valves for each cylinder, and I did them on a random point somewhere in the middle when the valves appeared to be most closed for half of the crankshaft rotation - the compression and power strokes. Do they need to be done near TDC between compression and power or anywhere along those strokes? I figure it wouldn't matter too much as long as its somewhere along those strokes. From @2mbb's previous osts it seems like it doesn't matter too much where in the compression/power strokes you do the adjustment for each cylinder as long as you're firmly in those strokes.

This block didn't have an EGR system installed on it, I've mounted my old one on. I don't know if the PCV system was installed and working well, it isn't installed right now.

yeah, you have to be on the compression stroke for the leak down test to work. You start with #1 on TDC (the timing pointer on the scribed line) with the #1 cylinder on it's compression stroke. Then you can follow the firing order: 1, 5, 3, 6, 2, 4. Each is 120deg out of phase with the one before. With #1 at TDC on the compression stroke, the next one, #5, should be on it's way up to compression. After finishing with one, put the screwdriver or dowel into #5 and spin the engine in the direction of rotation until it reaches TDC. Then repeat for the next cylinder in sequence. It's more important to make sure you are on the cylinder's compression stroke than it is to be exactly at TDC. A few degrees off TDC either way won't matter.

For the valve adjustment search this forum for key words "valve adjustment" and posts by me. I have provided detailed instructions several times.

Being more on the compression stroke versus power stroke makes sense. I'll do it in cylinder order next time too, to make it easier when hunting around and finding them.

Thanks for mentioning your previous posts @2mbb - these will be really useful (particularly right way to do it wrong - https://forum.ih8mud.com/threads/right-way-to-do-it-wrong.276106/#post-4300965). I wish I had stepped feeler gauges, those look sweet too (noob on first time valve adjustment - https://forum.ih8mud.com/threads/noob-on-first-time-valve-adjustment.215227/#post-3213929).

At this point. I want to try doing another round of adjustment and leak-downs if I need to. But trying to fire up the engine seems like a quick way to give this a shot, and if that doesn't work then take the head off and look at these valve seals (possibly for corrosion... pretty worried about corrosion at them at this point).
 

2mbb

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Also, please note the valve lash (clearance) is different for intake (0.008" hot) and exhaust (0.014" hot). As Spook mentions you can add 0.002" to each and adjust with the engine cold and you will get real close.

Using the procedure detailed in your links above, you can adjust all valves with the engine at TDC. half get done TDC compression and the other half get done TDC exhaust. This does work for the stock cam. I don't know how different your aftermarket cam is, but since these are not race engines, I think the procedure should be OK.
 

kenavt

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Clearly, the problem with the engine is your fingernails are yellow.

That's because I can't stop chewing my fingernails... the only way I've been able to stop (temporarily) is to borrow some of my GF's nail polish, and the visual reminder (and weird texture) gets me to stop until it wears off. Not even the toxic tasting clear stuff was able to stop me. 😬 So I typically go with yellow and blue colors (Go Blue!)
 

Spook50

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That's because I can't stop chewing my fingernails... the only way I've been able to stop (temporarily) is to borrow some of my GF's nail polish, and the visual reminder (and weird texture) gets me to stop until it wears off. Not even the toxic tasting clear stuff was able to stop me. 😬 So I typically go with yellow and blue colors (Go Blue!)
If it looks stupid, but works....
 

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