Author Topic: Leakdown -- air coming out of intake  (Read 634 times)

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Offline drumstyx

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Leakdown -- air coming out of intake
« on: October 24, 2017, 05:41:05 pm »
Testing out an engine I'm planning to swap into my 2002 (if it's good) and I found on at least one cylinder that the gauge read very little loss, but I could hear and slightly feel air coming from the intake. Cylinder is at TDC, and with the valve cover off I can feel the rocker is clear of the valves.

Do I have to find yet another good cylinder head?

EDIT: Sigh -- just checked the rest of the cylinders, and #2 was trouble. Even a cold engine should have at least even numbers across the board; #2 has a huge leak through the intake :(

Guess I'll be inspecting cylinder heads of both engines to see what I can make of it.
« Last Edit: October 24, 2017, 06:19:59 pm by drumstyx »

Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #1 on: October 24, 2017, 06:52:16 pm »
Any advice on what to try before I tear the cylinder head off this, essentially costing me $70-$150 for a new head gasket (bloody expensive, any advice there either?)?

Offline MAN OF BLUES

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Re: Leakdown -- air coming out of intake
« Reply #2 on: October 24, 2017, 06:56:20 pm »
That's a totally unreliable test on a engine sitting, that has not been run, and all the internals are dry...
Unless the piston, rings, cylinder, and valve seats are "wet" using a light weight oil, you will never see a positive result on an engine sitting on the floor.
How are you "pressurizing" the suspect cylinders? Thru the sparkplug hole? How much pressure? Are you checking that this pressure has not moved the piston, hence the timing on the valves, during this process?


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Offline MAN OF BLUES

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Re: Leakdown -- air coming out of intake
« Reply #3 on: October 24, 2017, 07:02:39 pm »
Spraying a copius amount of oil into the intake and exhaust ports, and rotating the engine to completely wet the valves, is about the only way you will see any pressure loss... pulling the head ain't gonna do it, you can't "see" anything, and will have rendered pressurizing the head impossible without a flow bench or plate clamped onto the head...

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Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #4 on: October 24, 2017, 07:36:41 pm »
Pressurising through the spark plugs hole, yes. What sort of oil would be best for this? I've seen ATF recommended?

Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #5 on: October 24, 2017, 08:05:30 pm »
Ok, used some 3 in 1 oil everywhere I could, and still getting 50% loss.

Only reason I was thinking I could see something with the head off is because the other cylinders (1,3,4) all check out pretty well perfect, but #2 shows 80 and 40 on my leakdown gauges (shop air and cylinder pressure, respectively). There's some air escaping through the intake on all of them, but dry I'm not surprised, just that #2 is a huge leak.

Offline MAN OF BLUES

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Re: Leakdown -- air coming out of intake
« Reply #6 on: October 24, 2017, 08:09:10 pm »
I'm not to fond of ATF, any super light, non drying oil, no silicone, no moly, no graphite etc., just a lightweight oil that stays "wet" and doesn't evaporate...
And which can easily be burned off in a normal combustion process later.. like 3 &1 oil, or even kerosene or diesel fuel...

Something tonwet, and keep wet, the parts that should seal...

Cheapo pump spray bottle from Dollar General, and some kerosene will work fine..

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Offline MAN OF BLUES

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Re: Leakdown -- air coming out of intake
« Reply #7 on: October 24, 2017, 08:15:13 pm »
Ok, used some 3 in 1 oil everywhere I could, and still getting 50% loss.

Only reason I was thinking I could see something with the head off is because the other cylinders (1,3,4) all check out pretty well perfect, but #2 shows 80 and 40 on my leakdown gauges (shop air and cylinder pressure, respectively). There's some air escaping through the intake on all of them, but dry I'm not surprised, just that #2 is a huge leak.

You really have to soak the complete area, so it may take a lot, like a couple spoonfulls, to soak those valve head sealing surfaces to a point they are wet... then you have to open and close the valves, and reapply,

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Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #8 on: October 24, 2017, 08:44:43 pm »
Ok, used some 3 in 1 oil everywhere I could, and still getting 50% loss.

Only reason I was thinking I could see something with the head off is because the other cylinders (1,3,4) all check out pretty well perfect, but #2 shows 80 and 40 on my leakdown gauges (shop air and cylinder pressure, respectively). There's some air escaping through the intake on all of them, but dry I'm not surprised, just that #2 is a huge leak.

You really have to soak the complete area, so it may take a lot, like a couple spoonfulls, to soak those valve head sealing surfaces to a point they are wet... then you have to open and close the valves, and reapply,

Alright, loaded up the valves (closed) with oil, then spun in round a few times, then did it again. First reading: 70/70. Not bad, still leaking through the intake, as indicated by the lovely 3-in-1 mist coming from it, but I guess it also sealed up the rings to deliver a better looking result.

I spun it a few more times and took another reading, and the pressure is backing down, and I read something like 75/60.

Like I said before, the others seem just absolutely perfect -- as the engine has sat for a few years, maybe that one cylinder's intake valves/seats caught some corrosion?

EDIT: I filled the ports with 3-in-1 and I'll leave em soaking for a couple hours.
« Last Edit: October 24, 2017, 09:00:04 pm by drumstyx »

Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #9 on: October 24, 2017, 11:43:15 pm »
Update: I think I'm happy enough with it that I'll try installing and running it.

After a couple hours of it soaking, I turned it over a few times, and tested again, only to find it had gotten worse! Then I remembered a little trick someone had mentioned to me before about something like this -- tapping on the valves with the leakdown tester attached.

I figured if the engine was going to 'clean itself up' once running, the best way to simulate that is probably having the valves hit the seat much harder than simply turning over the engine would allow. So I took a piece of softwood (some mutilated old (relatively clean) piece of 2x4 I had laying around), balanced it evenly between both tappets on the rocker, and gave it a couple taps. Lo and behold, leakage dropped immediately to acceptable levels!

Now, I'm sure a block of wood and a hammer is not usually internal-engine-parts tooling, but hey, desperate times! I'm now pretty confident that it'll run at least reasonably well.

Now to just work up the nerve to git er done.

Offline Steve in Sunny Fla

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Re: Leakdown -- air coming out of intake
« Reply #10 on: October 25, 2017, 12:05:31 am »
Update: I think I'm happy enough with it that I'll try installing and running it.

After a couple hours of it soaking, I turned it over a few times, and tested again, only to find it had gotten worse! Then I remembered a little trick someone had mentioned to me before about something like this -- tapping on the valves with the leakdown tester attached.

I figured if the engine was going to 'clean itself up' once running, the best way to simulate that is probably having the valves hit the seat much harder than simply turning over the engine would allow. So I took a piece of softwood (some mutilated old (relatively clean) piece of 2x4 I had laying around), balanced it evenly between both tappets on the rocker, and gave it a couple taps. Lo and behold, leakage dropped immediately to acceptable levels!

Now, I'm sure a block of wood and a hammer is not usually internal-engine-parts tooling, but hey, desperate times! I'm now pretty confident that it'll run at least reasonably well.

Now to just work up the nerve to git er done.

yeah, I posted that a while ago. It was immediately obvious to me that the valves needed adjusting and /or there is carbon on the seats. Remember that when spun at starting speeds, the cams lower the valves verrry lightly to the seats. Not enough force to clean carbon off the seats. HTH, steve
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Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #11 on: October 25, 2017, 12:19:50 am »
Update: I think I'm happy enough with it that I'll try installing and running it.

After a couple hours of it soaking, I turned it over a few times, and tested again, only to find it had gotten worse! Then I remembered a little trick someone had mentioned to me before about something like this -- tapping on the valves with the leakdown tester attached.

I figured if the engine was going to 'clean itself up' once running, the best way to simulate that is probably having the valves hit the seat much harder than simply turning over the engine would allow. So I took a piece of softwood (some mutilated old (relatively clean) piece of 2x4 I had laying around), balanced it evenly between both tappets on the rocker, and gave it a couple taps. Lo and behold, leakage dropped immediately to acceptable levels!

Now, I'm sure a block of wood and a hammer is not usually internal-engine-parts tooling, but hey, desperate times! I'm now pretty confident that it'll run at least reasonably well.

Now to just work up the nerve to git er done.

yeah, I posted that a while ago. It was immediately obvious to me that the valves needed adjusting and /or there is carbon on the seats. Remember that when spun at starting speeds, the cams lower the valves verrry lightly to the seats. Not enough force to clean carbon off the seats. HTH, steve

Yes! That was you! This is a different engine, as the other one, while running fine, still does have the issue of a bent rod. On the previous engine, I tried your suggestion of running those valves ~10 thou over spec and still hasn't completely removed the popping. Figured I'd look into it when I rebuild it for the rod issue :)

Offline MAN OF BLUES

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Re: Leakdown -- air coming out of intake
« Reply #12 on: October 25, 2017, 06:59:49 pm »
So now you see where I was coming from on my first comments made, on the reliability of a leakdown test on an engine that has sat, un running, and dry...

Carry on.... :great: :great:
Best of luck on your assembly.

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Offline Nosmo

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Re: Leakdown -- air coming out of intake
« Reply #13 on: October 26, 2017, 03:14:52 am »
That's an old A&P trick, called "staking the valves".  It will do just what you said, and cause small pieces of carbon or crap (if any) to get knocked loose and blown free of the valve/seat, and cause the valve to rotate slightly and sometimes get a better seal.

Go out and ride the piss out of it.
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Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #14 on: October 26, 2017, 03:52:14 pm »
That's an old A&P trick, called "staking the valves".  It will do just what you said, and cause small pieces of carbon or crap (if any) to get knocked loose and blown free of the valve/seat, and cause the valve to rotate slightly and sometimes get a better seal.

Go out and ride the piss out of it.

 Haha that's the plan! The old Italian tune up!

Offline RWulf

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Re: Leakdown -- air coming out of intake
« Reply #15 on: October 26, 2017, 06:52:52 pm »
You got me on this one A&P ???

Offline Ranger Jim

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Re: Leakdown -- air coming out of intake
« Reply #16 on: October 26, 2017, 07:40:21 pm »
A&P - Airframe and Powerplant. Also known as an airplane mechanic.
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Offline GKreamer

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Re: Leakdown -- air coming out of intake
« Reply #17 on: October 27, 2017, 01:19:06 am »
Thanks Jim, I was wondering too!  When I was a kid there were A&P grocery stores...

Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #18 on: October 27, 2017, 01:31:20 am »
Thanks Jim, I was wondering too!  When I was a kid there were A&P grocery stores...

Oh wow, I completely forgot about them! Dominion and Master Choice are just completely forgotten now

Offline frenche

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Re: Leakdown -- air coming out of intake
« Reply #19 on: November 06, 2017, 06:58:35 am »
"I could hear and slightly feel air coming from the intake"
Drumstyx,
        You may have this problem completely solved.
        I got a 2005 C-10, 10,000- milee.
        Several years storage time.
        I had a very similar problem with #3 cylinder. Stumbled across the likely fix. Carb boots are rubber & fit between carbs and head. They have a slight angle and.must be properly aligned.
        SISF did my carbs. In  carb removal for shipping, I found #3 carb boot clamp canted on the carb end causing air to leak into flow from carb. I did not know why it was canted until I reinstalled the carbs.
        On first few attempts at reinstall, carbs would not fit into boots 2&3. On inspection, I found a torn lip on #3 carb side boot. Why was it torn?
        Further inspection showed 12 o'clock noon alignment marks on the block for the carb boots. There is also a tit on each boot. The tit is supposed to align with each cylinder's alignment mark on the head.
        The problem turned out to be something unexpected. The #2 carb boot was inorrectly installed. It was off it's alignment mark by 20-30ยบ, a lot. The #2 carb boot caused the whole carb rack to skew to the downside. I could fit #4 in place, but then #3 would not go.
        Pulled carb rack out. Replaced torn #3 boot. Carefully checked and reset position of each boot to correct alignment. Carb rack fit well after that.
        So, you may want to check that your carb boot clamps are seated properly and tightened, carb side and head side for each cylinder.

frenche

Offline WillyP

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Re: Leakdown -- air coming out of intake
« Reply #20 on: November 06, 2017, 06:24:38 pm »
Carb boots will have no effect on leakdown.

 Unless maybe a small piece tore off and is lodged between the valve and valve seat, which I would think is highly unlikely.
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Offline drumstyx

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Re: Leakdown -- air coming out of intake
« Reply #21 on: November 07, 2017, 12:23:33 am »
Yeah, this was on an engine out of the bike -- no carbs, no exhaust.

I've since installed the engine, and she purrs great.

Of course, now I've got some other issues, as we always do when we least want them...