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Tunebug engine diagnosis, thoughts anyone?
- Thread starter AN5Sprite
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Hap Waldrop said:AN5Sprite said:
Hap,
Nice to see someone stand behind their work like that. Well done!
Hear! Hear!
D
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Usually when I do leakdowns on 4 pot LBC's I pull the rocker shaft assembly.
That way there is no way it will be partially open, like a cam ramp.
Coming back out the intake is NOT a head gasket......unless it's leaking to an adjacent cylinder that happens to have the intake open!
So, pull the rocker shaft and re-check.
Weak or broken spring, bent valve, seat adrift, burned valve or seat, cracked head will all either blow back up the intake or contribute to it.
Unless you or the esteemed previous owner had to loosen lash a whole bunch at one point, after 2K the chances of carbon are small, as that's what 3-angle cut seats do....break the carbon away.
Stray gasket jammed in a seat, but after 2K that would have burned away, too.
That way there is no way it will be partially open, like a cam ramp.
Coming back out the intake is NOT a head gasket......unless it's leaking to an adjacent cylinder that happens to have the intake open!
So, pull the rocker shaft and re-check.
Weak or broken spring, bent valve, seat adrift, burned valve or seat, cracked head will all either blow back up the intake or contribute to it.
Unless you or the esteemed previous owner had to loosen lash a whole bunch at one point, after 2K the chances of carbon are small, as that's what 3-angle cut seats do....break the carbon away.
Stray gasket jammed in a seat, but after 2K that would have burned away, too.
D
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I should probably add, with rockers off, to determine head gasket...if you get air out of an adjacent cylinder, open the throttle plates to make sure it's not going up and back (not likely), if you have air in adjacent cylinder with rockers off, head gasket (or crack between both cylinders...not likely).
G
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TulsaFred said:
If it wasn't, it'd be at BDC REAL quick. :wink:
Hap Waldrop
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kellysguy said:
Unless it was already there, I would suggest removing the valve cover, and making sure you are on TDC for the cylinder you are testing, meaning you have lash on both rocker arms, and you see the top of the piston thru spark plug hole. As mentioned if the cylinder is not on tdc, the engine will rotate under air pressure, and test would be invalid.
D
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You would not believe what you can find off TDC if creative. Many moons ago, we had this odd issue....low on power (a bit), higher than normal on blow-by. Did compression...good. Did leakdown, very good. So, after twiddling me thumbs a wee bit, I thought, geez, what does it look like on leakdown off TDC?
Got my biggest breaker bar, chunk of pipe, and applied pressure, and rolled it off TDC. Took a bit to hold it (and had adjusted air input lower), and oh, and inch or so down the stroke, suddenly the leakdown wasn't so "very good" any more.
Kept going, and it got better.
Seems #3 ring was all wobbled out (can't recall if broken or just badly keystoned), but it had worn the bore a bit, and with top rings at TDC, they were past this "spot". Took a bore and pistons to fix it, but we knew where to look before teardown.
Got my biggest breaker bar, chunk of pipe, and applied pressure, and rolled it off TDC. Took a bit to hold it (and had adjusted air input lower), and oh, and inch or so down the stroke, suddenly the leakdown wasn't so "very good" any more.
Kept going, and it got better.
Seems #3 ring was all wobbled out (can't recall if broken or just badly keystoned), but it had worn the bore a bit, and with top rings at TDC, they were past this "spot". Took a bore and pistons to fix it, but we knew where to look before teardown.
OP
AN5Sprite
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TOC, I took your suggestion to pull the rocker shaft and recheck. (even though, I admit I didn't see the point when I first read it, I figured it's wise to listen to the elders...) Here's what I found: Still get air out the intake, but now I also get air at the base of the head stud. (sorry for the bad video quality but I think you can see what's going on.) Can't bring myself to type what I think this means...
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OP
AN5Sprite
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Here was my vacuum test: between the scratched up gauge face and the 10 year old camera, the detail is missing, but you can see the flickering needle...
mMWlSTQ&feature=context&context=C29411ADOEgsToPDskKwWQyHPMNAB1W5GR3dTtua" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350"> </embed></object>
G
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What it means is you have only half of the head tightened down. The other half has no clamping force and the head is probably cocked allowing air to exit past the gasket.
I hope you didn't warp the head by only taking one side of the nuts loose, but you probably didn't.
Relax, it aint as bad as you think. The good news is you're already half way to the head being off. Pull that puppy and see what's up.
I hope you didn't warp the head by only taking one side of the nuts loose, but you probably didn't.
Relax, it aint as bad as you think. The good news is you're already half way to the head being off. Pull that puppy and see what's up.
D
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Yeah, you put a deep socket over each stud and the nuts/washers on it.
Or turn the rockets out of the way (I think you can do that...been a while) and put the shaft back.
Air still coming out the intake and not the next cylinder means pull the head, pop the intake valve out and look.
Or turn the rockets out of the way (I think you can do that...been a while) and put the shaft back.
Air still coming out the intake and not the next cylinder means pull the head, pop the intake valve out and look.
G
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AN5Sprite said:Comical. Not sure why that didn't occur to me...
Cause you gots too much sludge in yer nuggit right now.
I suggest you thin it out wit some nuggit flush.
Don't fergit, the higher the numbers, the quicker it flushes.
G
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I suggest you thin it out wit some nuggit flush. [/QUOTE]
I like the way you think my man, I'm having a WTF nuggit flusher night capper right now.
Heads off, To this untrained pair of naked eyes it looks good.
Hap, I'll call you this afternoon. [/quote]
Better make it two, you'll see better.
Ten if yer callin' Hap, that should make for an interesting conversation. :crazy:
[/QUOTE]I like the way you think my man, I'm having a WTF nuggit flusher night capper right now.
Heads off, To this untrained pair of naked eyes it looks good.
Hap, I'll call you this afternoon. [/quote]
Better make it two, you'll see better.
Ten if yer callin' Hap, that should make for an interesting conversation. :crazy: