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PostPosted: Wed Nov 06, 2019 9:39 am 
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D'oh - remembered last night that I have a leak down tester somewhere in the big tool box. When I find it, I can run some tests.

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PostPosted: Wed Nov 06, 2019 6:43 pm 
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Falcon67 wrote:
D'oh - remembered last night that I have a leak down tester somewhere in the big tool box. When I find it, I can run some tests.


Be sure Chris to run those tests with pistons at TDC and BDC. We used to test each cylinder long ago at mainly TDC until a nitro racer taught us to do both....as a crack in a wall down in the hole may be 'covered' when the rings&pistons are at TDC.


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PostPosted: Thu Nov 07, 2019 5:55 pm 
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LOL, when I put 100 PSI to it, that cylinder tends to go to BDC right away.

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PostPosted: Thu Nov 07, 2019 7:14 pm 
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Falcon67 wrote:
LOL, when I put 100 PSI to it, that cylinder tends to go to BDC right away.


LOL! 2nd time I used a leakdown tester I almost broke my finger when the high pressure kicked the long handled bar I was using on the crank bolt around! Ouch!


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PostPosted: Thu Nov 07, 2019 7:21 pm 
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Falcon67 wrote:
LOL, when I put 100 PSI to it, that cylinder tends to go to BDC right away.



Yep!
For me, I have found it generally doesnt matter where the piston is when I start the test, cuz unless something is seriously broke, it always ends up at BDC anyways.


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PostPosted: Sun Nov 10, 2019 12:21 am 
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Ha, BDC doesn't work because the intake valve opens. I finally got one test done on #5 and the reading was 6%. I need to do #1 and mark the balancer at 90 degrees around to make ringing TDC easier.

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PostPosted: Sun Nov 10, 2019 1:45 pm 
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Always back the rockers clear off on whatever cylinder I am checking.

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PostPosted: Tue Nov 12, 2019 10:20 am 
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Results -
Cyl - Comp Test - Leak Down
1 - 175 - 8%
2 - 180 - 16%
3 - 175 - 14%
4 - 185 - 10%
5 - 170 - 6%
6 - 170 - 10%
7 - 170 - 6 %
8 - 170 - 6%

Obvious whats going on with the left bank. Both heads are coming off anyway. I'll check again tonight but I noted that (after backing off all rockers) that most cylinders leaked 100% if the piston rotated down from TDC during leak down testing. Only one I really tested was #8 and it was 6% top and bottom. Not sure what makes #2 and #4 so happy on the comp PSI, all deck and chambers are same size, may be a sealing thing.

All I could get done in a couple of hours, not a lot of free time some days.

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PostPosted: Tue Nov 12, 2019 4:44 pm 
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If you believe that static "leakage" numbers mean much of anything (I do not). The test should always be done with the engine warmed up and the piston at TDC. Leakage tests are meaningless unless you're trying to find a big problem.


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PostPosted: Tue Nov 12, 2019 11:38 pm 
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DaveMcLain wrote:
If you believe that static "leakage" numbers mean much of anything (I do not). The test should always be done with the engine warmed up and the piston at TDC. Leakage tests are meaningless unless you're trying to find a big problem.


While I agree that warm-to-hot is ideal, it ain't always that easy with a dragster engine w/o a cooling system. I also agree that a TDC check is best as a first option but....when dealing with a potential cracked cylinder wall (in a block that still carries coolant, i.e., not hard-blocked all the way up) that crack can be hidden at TDC. And as mentioned, rockers backed off AND when doing TDC checks, some effort to lock the crank/flywheel in place to keep it there!

Yes, the pass. side bank #'s look odd for sure. Surprised you didn't hear escaping air sounds on that bank from the ports or cooling system passageways.


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