engine noise=lifter or piston slap??
04-30-2011, 05:43 PM
#11
Originally Posted by AKlowriderZ71
Backwards Billy. Camshaft speed is 1/2 of crankshaft speed. Faster noise would be crankshaft speed, slower noise would be cam/valvetrain noise.
)...I knew what I meant lol. Twice, half, what's the difference But yep, crank turns twice for every one full turn of the cam which can be seen by the larger cam gear and smaller crank gear duh. Edited my post so's not to cause any confusion 
Thanks fellas 
And yes, Roger explained why shorting the cylinder will reveal a rod knock, since there is no explosion to push down on the piston and rod, they're just along for the ride
04-30-2011, 05:48 PM
#12
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No. That doesn't make any sense at all.
If you take away the spark, the air/fuel mixture does not ignite. It just goes thru the cylinder. There is no explosion to force the piston back down, there is no load on that cylinder.
And, only one cylinder fires at a time.
Trust me, this does work. I've been doing this stuff for a long time.
If you take away the spark, the air/fuel mixture does not ignite. It just goes thru the cylinder. There is no explosion to force the piston back down, there is no load on that cylinder.
And, only one cylinder fires at a time.
Trust me, this does work. I've been doing this stuff for a long time.
04-30-2011, 06:05 PM
#15
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Like I said before, I didn't say you were wrong, but I understand why he's asking the question. There will still be a bit of load on the nonfiring cylinder due to compression, and maybe it would be enough to still allow for the piston or rod to make the noise. Perhaps a more thorough way of testing each cylinder would be to actually pull a plug and relieve all the compression pressure, instead of just pulling a wire. Just a thought. Hopefully no one is offended by my useless advice or thoughts. Sounds like good theory to me, if used in conjunction with the process you already outlined
05-01-2011, 10:38 AM
#16
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its the same exact sound it made on cold startup,in the past. but that would quickly go away, ive heard this same sound on several motors just like mine, on startup atleast. but they go away eventually. it seems like its going half the speed of the rpms, which would be a lifter ,right? its definately on bank 2- drivers side.
05-01-2011, 11:35 AM
#17
its the same exact sound it made on cold startup,in the past. but that would quickly go away, ive heard this same sound on several motors just like mine, on startup atleast. but they go away eventually. it seems like its going half the speed of the rpms, which would be a lifter ,right? its definately on bank 2- drivers side.
05-01-2011, 12:32 PM
#18
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Not doubting what your saying, just trying to understand it a little better as I also have been doing this a long time and have never used this method of diagnosis? What im trying to understand is this, If you have a bottom end problem ie, rod bearing, wrist pin etc... how would removing combustion change anything since the affected cylinder would still be moving on the force generated by the other cylinders? Every time combustion occurs it puts force on not only the cylinder it occurs in but also on the cylinder its opposite of on the crankshaft. Like I said, just trying to understand a little better by asking?
05-01-2011, 01:19 PM
#19
Not doubting what your saying, just trying to understand it a little better as I also have been doing this a long time and have never used this method of diagnosis? What im trying to understand is this, If you have a bottom end problem ie, rod bearing, wrist pin etc... how would removing combustion change anything since the affected cylinder would still be moving on the force generated by the other cylinders? Every time combustion occurs it puts force on not only the cylinder it occurs in but also on the cylinder its opposite of on the crankshaft. Like I said, just trying to understand a little better by asking?
Now on a piston slap, which is the piston rocking in the cylinder, it will make noise no matter what, like you're thinking about with the rod knock. We recently had an older IS300 with a piston slap that was confusing the tech that was working on it. Once we determined it was bottom end, I had the tech disconnect the coils one at a time and the noise remained. I told him "piston slap" and he was skeptical (not a common Lexus problem). We sent the shortblock to the machine shop who freshened it up, replaced the piston and pin, and now all is well.
We've been using this method in the shops that I've worked in since day 1, it's common practice, and may even be a question on the A1 ASE test IIRC...I know that it has been outlined in the Engine Repair Study Guides.
Know somebody with a rod knock? Try it out for yourself