Upper end knock

[wagon-r]

I don't think he is getting a hiss "at the cap". It's just that the hiss is being generated at the rings and so the sound is loudest inside the crankcase, so if the cap is taken off and you listen at the filler orifice it will be louder.

I don't think the 'wet' readings are reflective of real compression or ring problems, but 'operator error'...

He said he heard a hiss when he listened at the oil cap. I'm just going by what he said.

The combustion chamber still has over 60 cc even at TDC. That's about 2 ounces. Also, any excess oil is going to go out the exhaust after the first crank. Unless he is pouring the oil in with a funnel, its not going to artificially increase the compression readings to any significant degree.

[johnl]

..........Also, any excess oil is going to go out the exhaust after the first crank...........

When cranking for the compression test, if the first upward stroke is a full compression stroke then it's this that will see the high compression and be what is recorded on the tester. Excess oil will only be expelled on the upward exhaust stroke, on either of the downward strokes or the upward compression stroke it won't be. There's a very good chance that excess oil won't be expelled before the tester records a high reading, and not all the excess oil will necessarily be expelled on the exhaust stroke.

It would perhaps be good practice to crank the engine over a few times with the plugs removed before attaching the pressure tester, in order to expel excessive oil...? This might also help ensure that oil is fully distributed around the rings.

The combustion chamber still has over 60 cc even at TDC. That's about 2 ounces. ........... Unless he is pouring the oil in with a funnel, its not going to artificially increase the compression readings to any significant degree.

Well, my first experience of 'wet' testing involved a young novice (me) putting in too much oil resulting in a massive over-pressurisation in the cylinder. I just poured some in (it didn't seem like a huge amount...). The engine however was a very modified 1020cc A series BMC engine with a nominal 11/1 compression ratio, so X oil quantity in the relatively small / high compression cylinder would be more significant than in a larger / lower compression cylinder.

All I'm suggesting is that an unmeasured oil quantity may result in significantly different quantities of oil in each cylinder, and my be enough of a difference to artificially give higher readings in some cylinders than in others.

If we assume a 60cc combustion chamber at TDC, then if we put say 5cc of oil in one cylinder and say 10cc in another, then this would be enough to make a significant difference in the compression readings. 5cc of oil represents 3% of the combustion chamber volume, 10cc represents 6%. If we assume a starting compression of 180psi (and ignoring any ring seal improvement caused by the oil, which will occur to some degree even with good rings, let alone bad ones) adding 5cc of oil should displace 3% of the chamber volume, theoretically giving 185.4psi (assuming my maths isn't as bad as it sometimes is...) and 10cc oil should displace 6%, giving 190.8psi (again assuming...).

If a good slug of oil was poured in, then the difference will be larger again. A jump from 180 psi (dry) to 240psi (wet) seems a very large increase to me, especially as 180psi already seems a healthy number. I can't account for such a huge difference other than displacement of compressible air with incompressible fluid...

[BreckAConner]

Okay, I'm still trouble shooting. The knock hasn't gotten worst, and I don't see any metal shavings at all when I pull the dip. With my car bogging and in correct timing, the car hiccups at 1700 RPM most the time when it passes that range. I with weather motor will run differently depending on if it's cold/hot whatever. I kind of wonder if my intake has a problem, and maybe it's causing issues or what not. My car doesn't not run hot when I look at the tempature gauge, but when I got to pull the throttle by hand at the intake it's extremely hot. Could this be causing my hiccups, and possibly my knock say if it's not recieving the air correctly or it's too hot of air? I know this all may sound stupid, but I try to observe every little detail. I'm an IT guy, and basically that's what I do all day to figure out what's wrong with computers.

[F20A CB7]

I hear it on start up only when cool or cold out. For like 3 seconds and goes away... for the rest of the day I drive it and start it up I don't hear it.. only 1st time in the morning

[johnl]

Okay, I'm still trouble shooting. The knock hasn't gotten worst, and I don't see any metal shavings at all when I pull the dip.

If there any "shavings" in the oil your very unlikely to see any on the dipstick because they will be sitting on the floor of the sump.

With my car bogging and in correct timing, the car hiccups at 1700 RPM most the time when it passes that range. I with weather motor will run differently depending on if it's cold/hot whatever. I kind of wonder if my intake has a problem, and maybe it's causing issues or what not.

"Hiccups" are misfires. Either there is a fuelling problem, or an ignition problem. A fuelling problem would include incorrect AFR caused by air leaks in the intake. It could be a lot of things...

My car doesn't not run hot when I look at the tempature gauge, but when I got to pull the throttle by hand at the intake it's extremely hot. Could this be causing my hiccups, and possibly my knock say if it's not recieving the air correctly or it's too hot of air?

Overheating can cause 'pinging' (detonation), which sounds like a metallic rattling. Your gauge may be reading cooler than it actually is, but it's impossible to say for sure from vague descriptions.

I'm starting to think you might need to seek professional help (for the car, but a lot of frustration can lead to needing the other kind too...). An experienced mechanic should be able to tell what's going on from examining the car in person.