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homemade leakdown OK?

 
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240Z8
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1972 Datsun 240Z

PostPosted: Thu Mar 05, 2009 2:07 pm    Post subject: homemade leakdown OK? Reply with quote


I'm trying to confirm my 7+ year old engine is up to taking a power adder, 8-10 psi. I've been running zero gap rings, oil breathers always look new and dry. Plugging off breathers, putting gauge on dipstick tube with engine running 1500-2000 rpm will eventually raise pressure 1psi or a little more after 20-30 seconds.
Looking for advice on proper way of running a leakdown test.
I built tester with a .040 restrictor between guages...crummy gauges, but read the same in either flow direction.
Engine running temp. Piston at TDC, (I locked in place with long breaker bar) regulate wimpy old compressor to read 100 psi on pressure side, limit flow to achieve steady needle, read difference between guages.

Is that it??

Doing this indicates 6 cyls at 98 psi, two at 97psi. Doesn't explain my oil consuption since new, but enough talk throughout the internet on early afr castings. Will address that with new or reworking heads.

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Paul P
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PostPosted: Thu Mar 05, 2009 2:19 pm    Post subject: Reply with quote

Not ok should be a regulator in there not a restrictor. It might give you an idea but also be misleading.
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clay
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PostPosted: Thu Mar 05, 2009 2:30 pm    Post subject: Reply with quote

I agree with Paul P, not having a regulator is the only thing I see wrong with your setup. There is a 0.040" or 1mm restrictor between the gauges to allow a pressure drop to occur if there is any leakage. What you have might be working, but I'm not sure how the method you are using to regulate pressure might affect the results - it might not, but I'd put a regualtor in. The only other thing I did when I made mine was plug the hose going to the cylinder to simulate 0% leakage and set the regulator gauge at 100 p.s.i. and see what the cylinder side gauge reads. They should be the same but mine were about 2 p.s.i. different so I set the regulator gauge at 98 p.s.i. as my reference to compensate. 86GN fought the AFR casting flaws with oil drainback on here a few years ago. I'll search around an look for the thread. Clay
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240Z8
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1972 Datsun 240Z

PostPosted: Thu Mar 05, 2009 2:40 pm    Post subject: Reply with quote

Paul P wrote:
Not ok should be a regulator in there not a restrictor. It might give you an idea but also be misleading.

I'm not sure what you mean. A regulator between the guages?



I have one on the compressor set to 100 psi. Plugging the cylinder end results in both gauges reading steady 100. I also have a butterfly valve coming into the guages, but only to limit compressor pulsations gauge fluttering.
Tell me more...

clay wrote:
86GN fought the AFR casting flaws with oil drainback on here a few years ago. I'll search around an look for the thread. Clay
Thanks! I hate that they denied this years ago, yet now claim they've fixed the oil problem on the old design. Lots of hard earned $$ went their way. My head guy claims he can cut channel in head and rework drain backs. Will depend on future $$
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Last edited by 240Z8 on Thu Mar 05, 2009 2:50 pm; edited 1 time in total
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clay
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PostPosted: Thu Mar 05, 2009 2:48 pm    Post subject: Reply with quote

I think what Paul P and I were thinking is you were using the valve you have at the end of the red hose to try to regulate pressure. If you have a regualtor at the tank you use to set the 100 p.s.i., that should be fine. Clay
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TSHACK
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PostPosted: Thu Mar 05, 2009 4:45 pm    Post subject: Reply with quote

Okay I'll ran 100's of leak down test on aircraft. 240's set up is close to right. My tester also has a valve after the second gauge(to shut off air to engine & set the primary gauge to 80)..I'm not sure of the restricter size. I'll have to look it up. In aircraft, We set the incoming air at 80 psi (It's better to keep the incoming air pressure constant). More than 10% loss & or More than 10% difference between cylinders, Was the cut off they tough at school, Not real world be any means. But the continentals where allowed more. Your readings look fine. let me know if you want the restricter sizes. The Hard part is holding the piston at tdc on the compression stroke on a car. Aircraft you have a big handle A prop, but if your a little off TDC the air pushes the piston down pretty fast,& spinning handles can hurt.. Shocked
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af2
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PostPosted: Thu Mar 05, 2009 6:49 pm    Post subject: Reply with quote

With the restrictor. How are you going to know the real #?
That is the same as I use less restrictor.
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240Z8
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PostPosted: Thu Mar 05, 2009 8:15 pm    Post subject: Reply with quote

af2 wrote:
With the restrictor. How are you going to know the real #?
That is the same as I use less restrictor.


With out a restrictor both gauges will read the same, the compressor overcomes any engine leakdown. The airflow through the area of a .040 restrictor, I guess, is smaller than the allowed clearances on the engine.

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af2
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PostPosted: Thu Mar 05, 2009 8:30 pm    Post subject: Reply with quote

240Z8 wrote:
af2 wrote:
With the restrictor. How are you going to know the real #?
That is the same as I use less restrictor.


With out a restrictor both gauges will read the same, the compressor overcomes any engine leakdown. The airflow through the area of a .040 restrictor, I guess, is smaller than the allowed clearances on the engine.


Ok, I understand and looking at a leakdown tester You are correct!
The stuff I learn every day is amazing!!!
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TSHACK
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PostPosted: Thu Mar 05, 2009 8:53 pm    Post subject: Reply with quote

here is the FAA requirements.
AC 43.13-1B specifications say that engines up to 1,000 cubic inch displacement require a 0.040-inch orifice diameter, 0.250 inch long, 60-degree approach angle.

Engines in excess of 1,000 cubic inch displacement require a 0.060-inch orifice diameter, 0.250 inch long, 60-degree approach angle.

for what it's worth. they are good priced at aircraft spruce.

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Paul P
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PostPosted: Fri Mar 06, 2009 11:25 am    Post subject: Reply with quote

It sounds like it will work it is just easier with a regulator like on a regular automotive leak down tester.
This one is cheap on E-Bay less than 20 bucks with 13 hours left.

http://cgi.ebay.com/CYLINDER-LEAK-DOWN-TESTER-QUICKLY-DIAGNOSE-PROBLEMS_W0QQitemZ270353158915QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item270353158915&_trksid=p3286.c0.m14&_trkparms=72%3A1171|

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10.97@121 MPH 1/4mi
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clay
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PostPosted: Fri Mar 06, 2009 12:19 pm    Post subject: Reply with quote

When we built a couple of homemade units, we borrowed either a Matco or Snap-on and measured the restrictor it had. 0.040" was it. Clay
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PostPosted: Fri Mar 06, 2009 12:39 pm    Post subject: Reply with quote

240Z8 wrote:

clay wrote:
86GN fought the AFR casting flaws with oil drainback on here a few years ago. I'll search around an look for the thread. Clay
Thanks! I hate that they denied this years ago, yet now claim they've fixed the oil problem on the old design. Lots of hard earned $$ went their way. My head guy claims he can cut channel in head and rework drain backs. Will depend on future $$

I posted a sticky in the Gen I small block section with pictures of the machine done to correct the problem.

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TSHACK
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PostPosted: Fri Mar 06, 2009 2:37 pm    Post subject: Reply with quote

Paul P wrote:
It sounds like it will work it is just easier with a regulator like on a regular automotive leak down tester.
This one is cheap on E-Bay less than 20 bucks with 13 hours left.

http://cgi.ebay.com/CYLINDER-LEAK-DOWN-TESTER-QUICKLY-DIAGNOSE-PROBLEMS_W0QQitemZ270353158915QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item270353158915&_trksid=p3286.c0.m14&_trkparms=72%3A1171|


WOW if any one needs one they should grab it, each part would cost you more than the current bid. That one is pretty much like mine. the orifice is in between the gauge in the block.

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