entropy
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posted November 13, 2008 10:49 AM
 Edited By: entropy on 13 Nov 2008 18:51
leakdown on cold vs warm motor
I know i am "mic-ing the brick" here, but this morning i did a leakdown in prep for dyno on Sat.
The numbers were perhaps just a titsch higher than they were a few weeks ago.
Certainly nothing to worry about, but i got curious if anyone had experience doing leakdowns on a stone cold vs warm motor????
18oct - leakdown after dyno (??Temp motor)______#1=2.5%, #2=1.5-2%, #3=2.5%, #4=1.5-2%
13nov- leakdown after dyno (cold motor)__________#1=3.0%, #2=2.0%, #3=2.0%, #4=2.5-3%
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KZScott
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posted November 13, 2008 10:54 AM
interesting for sure, and makes sense imo. ring end gap decreases with heat. thats my guess as to why the numbers were less on a warm motor
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01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
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entropy
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posted November 13, 2008 11:12 AM
i don't even know if the difference is significant, but i betcha someone has experience. 
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KZScott
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posted November 13, 2008 11:37 AM
are you certain that the air compressor(s) were at the same psi each time? i think that makes a diff right?
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
|
entropy
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posted November 13, 2008 12:27 PM
quote:
are you certain that the air compressor(s) were at the same psi each time? i think that makes a diff right?
i am never 110% certain of anything, but i'd say i'm pretty sure. I find that if I tap-tap-tap the guages on the leakdown tester, i can get very, very reproducible results. Like i said above the differences i am seeing are miniscule, but it started me thinking.
hell it could be just a difference in atmospheric pressure?
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dougmeyer
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posted November 13, 2008 06:04 PM
Normal. Those numbers are great in either case.
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ninja12
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posted November 13, 2008 07:51 PM
Warm would have oil in the rings meaning less loss there. Ninja's .02
Who did the valve job?
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KZScott
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posted November 13, 2008 08:00 PM
Jim(y2k) @ competition cnc?
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01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
|
tcchin
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posted November 13, 2008 11:00 PM
Karl - I think those numbers are within the accuracy range of your gauges. The difference in coefficients of thermal expansion (cte) between pistons and cylinders should be minimal, although the profile of the piston may change with heat, which may affect sealing. I would think that the smaller cte of the ring material would mean that the ring gap would increase with cylinder temp.
Strange that my leakdown numbers are consistently in the 0.5% to 1% range (cold) and yours are consistently in the 1.5% to 3% range. While I agree that anything less than 5% is acceptable, it would be nice to know why there's a difference. It's not like my motor is particularly fresh any more...
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entropy
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posted November 14, 2008 02:46 AM
Tim,
does piston diameter make a difference?
Maybe big, robust & MANLY 87mm pistons generate big, robust & MANLY leakdown numbers?
While lil, cute & delicate 1000cc gixxer pistons generate lil, cute & delicate leakdown numbers?
if not,
Perhaps sheng fui plays a role?
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ZRXDean
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posted November 14, 2008 09:23 AM
You guys are using different gauges, right?
(both of you have fantastic leakdown % so STFU already)
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entropy
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posted November 14, 2008 12:58 PM
Edited By: entropy on 14 Nov 2008 21:03
quote:
Warm would have oil in the rings meaning less loss there. Ninja's .02
Who did the valve job?
Hey Gerard,
I am using the "Andy" head while i do the Chin-directed systematic search for my 20hp which went to Ft Lauderdale on Spring break early this year and never came back.
Girls gone wild/greased-up musta captured them???
I am dyin' to try my Y2K "Jim" head, but waiting till hp sheepishly returns and tells me some complicated story about County lockup or detox or something...
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entropy
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posted November 14, 2008 01:11 PM
Edited By: entropy on 14 Nov 2008 21:12
quote:
You guys are using different gauges, right?
(both of you have fantastic leakdown % so STFU already)
Chin is using Sheng fui (CA) guages...
(and I don't know how to STFU  , )
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KZScott
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posted November 14, 2008 01:15 PM
I love the humor that goes with the tech info on this board
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
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tcchin
Zone Head
Posts: 867
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posted November 14, 2008 01:49 PM
quote:
Chin is using Sheng fui (CA) guages...
(and I don't know how to STFU , )
How else can you locate the energy exchange point in the combustion chamber? Does a motor have a taint?
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dougmeyer
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posted November 14, 2008 07:54 PM
Other than the valves, the biggest factor is how round the cylinders are staying (they move a bit when cold, equalize out more when hot. On the real special Reynolds 390 Chevy engines we experimented with running hot water through the block with torque plates bolted on when we were final honing them. It made a difference but was more trouble than it was worth. Also you often can "fix" a leaky valve by smackinig it with a mallet and letting it slam shut. They tend to trap crap on the seat sometimes.
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Y2KZX12R
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posted November 15, 2008 05:57 PM
Edited By: Y2KZX12R on 16 Nov 2008 02:00
I agree anything under 5% is ok. It basically means that the engine doesnt have anything majorly wrong with it.
Leak down testing is not a very accurate way of measuring anything other than to show a major problem.
Example: We build about a dozen $30,000 + road racing SBF engines a year for this one particular customer. The parts are all the best of the best and no expense is spared. Anyway, they all use custom gas ported pistons with very trick very thin rings (much like these bike rings) that only will work with a dry sump, vacuum pump evacuated crank case setup. We dyno tune each one before it gets sent to the customer and then it gets raced hard. Now you would think that these engines would last a while with top notch parts. But the truth is that the rings dont last that long at all. Its not uncommon to see the engine loose 15 hp from worn rings after one race. However, heres the kicker, the leakdown test will show about the same % leak down as it did fresh, well under 5%. We put rings in it and the 15 hp comes right back.
Now granted gas ported pistons and an evacuated sump will wear out the rings faster due to faster ring reaction time and higher cylinder seating pressure. But the point is that a leak down test wont show the problem.
Just somthing to think about.
Doug, we actually use an infrared temp gun to monitor boring and honeing operations. It makes a difference when measuring bores etc. Like when resizing rods, you have to keep them from getting too warm so they can be accurately measured.
Interesting thou about the boring and honing at operating temp.....
Thankfully most of the modern race blocks are leaps and bounds better than the factory blocks with very thick decks etc.
Now the zx12r is a different thing. The bolts go thru the block and pull on the upper crankcase half. Thus eliminating any cylinder wall or deck distortion.
Unlike the zx14 that loads the deck because the bolts thread into the block close to the deck.
The GM gen III and gen IV engines actually "float" the heads. They allow them to move independently of the block during heat cycling. But thats a whole nother topic for another day.
But yes Karl, you can see slight differences in a cold vs just run engine in a leak down test. I think its a combination of fresh oil coating everything and clearances tightening up to running spec.
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