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Leakdown test
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Sun May 03, 2009 12:11 pm    Post subject: Leakdown test Reply with quote

So, I need a little elementary guidance here.

I have emabrked on the leakdown test full on today- Started the smoking POS, warmed it up, shut it down. Pulled the plugs, pulled the plenum, pulled the valve covers and backed off the rockers.

Now, turned #1 to TDC. Attahced lines, set inlet air @ 90 (for whatever reason trying to get 100 @ the inlet is a pain- garbage air regulator at compressor has a very small orifice) and got 78 psi on second gauge. so 78/90 = .867 so I have 13% loss in that cylinder. Ugh.

So then, I am under the impression that the marks on the balancer that are staggered around- one unmarked, then one marked 90 degrees, another unmarked, one marked 180 etc- making a total of 8 evenly spaced timing marks on it. I assumed these were used to tell where TDC is at on each cylinder.

Next to fire is 3, so I put the hose on 3, turn the crank clockwise to the next line (next of the evenly spaced Cool hook up the air and have the crank go spinning. What did I miss? How else would I know where TDC is without using a TDC checker and turning the crank back and forth 5 times per cylinder?

I am pretty frustrated with this whole thing- and really pissed off to learn later how LITTLE I was ever taught in tech school...

I am sure some of you have done this test a hundred times- clue me in here?!?!
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10sec.et
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Joined: 29 Mar 2006
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1969 Oldsmobile Cutlass

PostPosted: Sun May 03, 2009 12:44 pm    Post subject: Reply with quote

it really requires two people unless you have a camera that you can use to watch the top of the piston. if no camera, get a mirror and flashlight and have a buddy turn the engine over BY HAND untill the piston comes to TDC. it takes some time to get it exact. i usually end up going past TDC and have to back up several times to get a good feel of where the piston should be. if youre hooking up air and the crank is spinning, it wasnt at exactly TDC. if you hook it up and have 90% leakdown, you probably have the crank 180 out. just turn it 180 and try again.
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Sun May 03, 2009 2:35 pm    Post subject: Reply with quote

Well, I managed to get it by using a thin rod and feeling when it quit rising... took a couple rotations but got a feel for it...

The results-

Test Pressure: 90 PSI

Cylinder PSI Leakdown
1 76 15.6%
2 70 22.2%
3 64 28.9%
4 68 24.4%
5 62 31.1%
6 86 4.4%
7 82 8.9%
8 74 17.8%

Min 4.4%
Max 31.1%

Average % 19.2%
Variance 26.7%

Ouch. Definitely have some issues.

I am a bit confused as to why the numbers would be so drastically different? as in, cylinder 5 is so high then cylinder 6 is the best one...

All of these were done back-to-back so the block temp wouldnt have changed much...
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clay
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1972 Chevrolet Nova

PostPosted: Sun May 03, 2009 4:18 pm    Post subject: Reply with quote

I'll have to say I usually take the easy way out and do my tests at BDC. I know it isn't the best or most accurate way, but so far I have either gottten really good results or really bad results and it still showed where the problem was. You could use the 90* marks on the balancer and test the cylinders that are on the same rod journal. If you tested #1 at TDC on a Ford, then you should be able to turn the engine 90* clockwise and then #5 would be at TDC. Clay
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af2
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1933 Willys Coupe

PostPosted: Sun May 03, 2009 5:18 pm    Post subject: Reply with quote

So, where is it leaking? smoking
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Sun May 03, 2009 5:54 pm    Post subject: Reply with quote

I want to assume its the rings- the heads have maybe 1k miles on them.

But they are the Patriot Performance SBF heads, which as far as I can tell now are reworked Pro-Comps. I didnt know any better when I bought them, and they still try to claim they are 100% their own stuff.... But once youve bought something and installed it then its yours so I am trying to do what I can with them.

How exactly do I determine which it is? Its burning oil, which is what lead to me delving into the testing.

At the same time, being "new" or just having a few hundred miles on the heads doesnt mean they are right either, ya know?
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af2
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PostPosted: Sun May 03, 2009 6:41 pm    Post subject: Reply with quote

On a leak down you should be listening to: exhaust for leakage, intake for leakage and crank case so you have an idea where to go from there.
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Knarley Darley
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PostPosted: Sun May 03, 2009 7:10 pm    Post subject: Reply with quote

The only reason for finding exact TDC on the compression stroke is for testing with the rockers still on. Since you backed them off just put the pressure to it and dont worry about the piston moving to BDC as Clay stated. As beers stated all you need to do is screw a fixture into the spark plug hole and hook your air hose to it. Then just listen to where the air is leaking from. If it is rings you will hear it in the crank case. Otherwise listen at the tail pipe, or the intake for valve leak. Did you do a cranking compression test? I have seen engines with no or very low compression that were fine mechanically and had the rings so stuck in the pistons that they would no longer seal the cylinder from carbon and sludge build up. How old is your bottom end? If it is old, I would dump a bottle of STP oil treatment in and see what happens. This stuff removes build up from the ring lands. I have had V-8 engines with 30 pounds of compression come back to 150 pounds with in 30 minutes of driving. Its worth a try. BTW it is STP in the Blue bottle. Good luck
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Sun May 03, 2009 7:19 pm    Post subject: Reply with quote

Short-block is the original 1995 production unit, with somewhere between 108k and infinity on it. My brother bought this thing with 108k on an odometer that doesnt turn...

I guess I need to continue by redoing this and chasing further where the air is going... I am 99% certain its going to the crankcase...

As far as rings sticking goes- its sat a lot, and it was running pretty bad when first assembled, so its possible the rings are sticking. I kinda lean towards that also as the 2 cylinders are strong and that makes me wonder some...

Again, far from an expert over here but willing to try whatever it takes to learn and sort this all out...

Did I mention how much I love this forum? Very Happy

I think I may try putting something in the oil to clean it out- really nothing to be hurt by it??? I used to be a fan of Marvel Mystery oil, but could try the STP also...
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Knarley Darley
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PostPosted: Sun May 03, 2009 7:27 pm    Post subject: Reply with quote

My dad was a mechanical engineer for Rocketdyne for 42 years, and he finished his career as the systems auditor on the space shuttle for 8 years. He loved old cars and he swears by the STP, and frankly I have had good results with it on older engines in my 23 years in the auto repair industry. It wont however do a bit of good if the rings are broken, but it will unstick them.
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clay
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PostPosted: Sun May 03, 2009 8:35 pm    Post subject: Reply with quote

Yours sounds like the bottom end on my wifes Mustang. I had to replace a retainer when I fixed a bunch of leaks it had and that cylinder showed about 25%. It doesn't have excessively high mileage but I think mine has to do with my buddy that owned it before me though. Do a search for AutoRx. I have never used it, but it sounds good. Clay
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sun May 03, 2009 9:00 pm    Post subject: Re: Leakdown test Reply with quote

MufflerBearings69 wrote:

I have emabrked on the leakdown test full on today- Started the smoking POS, warmed it up, shut it down. Pulled the plugs, pulled the plenum, pulled the valve covers and backed off the rockers.



didnt catch that "backed off the rockers" part when i read it the first time. as others stated, you can just stick an air hose on it at that point and see (hear) where the air is coming from.

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It seems we can look at our magical Balls and come up with a fix?

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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Sun May 03, 2009 9:01 pm    Post subject: Reply with quote

Some people on BITOG seem to like it, they also seem to attack the marvel mystery oil users... weird.

This car was poorly kept mechanically before my brother bought it... I know a lot of its issues have come from its long hard life. If i remember right we are the 6th or 7th owners- had been repoed 4 times... So probably every one of those fools beat on it too...

Oh well, ive spent so much time on it now that there is no turning back! Plus that would be admitting defeat! Shocked
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Mon May 04, 2009 10:05 am    Post subject: Reply with quote

Walked back out this morning with a clear mind and looked at something else I need to figure out-



left plug is plug #6 and is typical of all of the plugs I pulled out besides plug #7 on the right. I am going to think its an ignition problem to cause this?

Cyl #7 had a good leakdown test- but did this oil being in there skew that number? Or rather, could it?
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Mon May 04, 2009 1:21 pm    Post subject: Reply with quote

are you sure thats oil and not fuel ? i dont see oil deposits on the plug from it burning. every plug that i have seen that was that wet with oil had a serious problem that would definitely show up on a compression or leakdown test.
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