Custom leak down test |
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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Posted: May-03-2016 at 10:59am |
I work for a manufacturing company that has a lot of air/plumbing fittings in stock, so it was pretty easy to scrape together a DIY leak down tester. I took the schrader valve out my compression tester line with the spark plug thread end and plugged it inline with a regulator and needle valve. The needle valve basically let's me adjust the orifice size to the point where the engine leakage takes over as the bottleneck.
My #4 cylinder couldn't hold any pressure compared to the others, but I couldn't feel it blowing passed the valves. After pulling the head I wanted to be 100% certain the rings were the problem. So I made a steel plate with a welded an npt coupling to bolt to the block over the individual cylinder. We had some cork gasket sheet lying around so I used that to seal to the block surface. Still no pressure, even after I opened up the needle valve. Air was rushing out of the oil passage holes by the lifters. I added a decent amount of oil to the cylinder and tried again, but no luck. Looks like it's a full rebuild unfortunately :( Setup Picture GOOD PRESSURE in #3 LOW PRESSURE in #4 |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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It leaked into the oil passages???????????????
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Keep it as original as YOU want it
1978 Mustang (modified) |
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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It was leaking out of this hole a decent amount. But when I tested the other cylinders with good compression, air would come out of these holes as well, just not as much as this bad one.
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6157 |
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That's not an oil passage. Duane is thinking "oil pressure supply passages". Those are just windows in the valley to drain excess oil back into the crankcase. Crankcase pressure could escape there if the pan and all are still assembled and the slugs are in all the holes I guess.
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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Yes, sorry I couldn't think of the correct name for it. My oil pan is still on and sealed, so this would be the easiest way for air to escape
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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That makes more sense. That is merely an oil return hole to the crankcase. Probably going past the rings and back up and out the closest escape route ie: return hole.
If your lucky it may just need a set of rings and a quick ball hone job. Pull that piston and have a look. Good luck edit: You beat me to it Zach!!! |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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JoeinNY
Grand Poobah Joined: October-19-2005 Location: United States Status: Offline Points: 5698 |
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Yep its got no where else to go, normal behavior. ... sounds like a broken or stuck ring anyhow. If you are looking to be cheap definitely pop that piston out and take a look before getting too crazy.
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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Thanks guys, that's what the plan is right now. Although since I'll already have it torn down this far, wouldn't it be better to just get new rings/hone on all 8?
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Autopsy first.
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Keep it as original as YOU want it
1978 Mustang (modified) |
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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yeah good idea, I'll post an update once I get in there
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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MARK YOUR LIFTERS . They need to go back in the same holes!!
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Keep it as original as YOU want it
1978 Mustang (modified) |
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JoeinNY
Grand Poobah Joined: October-19-2005 Location: United States Status: Offline Points: 5698 |
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Possibly, depends on hours, usage, local machine shop availability, need for speed, etc. But if it is very clean and everything looks good and you find a stuck ring there is something to be said for not letting an engine out of your hands and into a machine shop this close to ski season. |
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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Thanks Joe, that's what I'm worried about is opening up this can of worms right before ski season
The boat has 2100+ hours on the meter. I remember talking with the previous owner about there may have been a rebuild done on the engine a long time ago but I'd be willing to bet the engine hasn't been torn apart this far in its lifetime. |
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6157 |
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Hmmmm 2100 hours. I would do a quick refresh but that's just me. I assemble my own stuff and I had about 750 in a completely fresh rotating assembly/head job/.030 over bore and Pistons.
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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I have the engine sitting on a pallet in it's upright position. Is it possible to remove the connecting rod and push a piston out without flipping the engine upside down?
I should have about 10" of clearance between the engine block bottom and the pallet to get tools in to. |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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If you are able to get the pan off and take the rod cap off then you will be able to shove it out the top. DON'T let the rod bolts hit the crank. Take some air hose type tubing and put over the rod bolts to insure that you don't nick the crank. Also make sure you mark the cap so it goes back the same way.
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Keep it as original as YOU want it
1978 Mustang (modified) |
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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ok great thanks Duane!
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shierh
Gold Member Joined: April-29-2015 Location: Florida Status: Offline Points: 605 |
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nice test. One question though, why the test when you have it torn down to this level already? Bare minimum would be hone with new rings if engine is out and down to this level.
On side note, i did a bore inspection with a new bore scope i got from Harbor Freight, got the good one with bigger screen and all the toys. It was pretty good for cylinder inspection. New engine but had base plate gasket leak and wanted to make sure didnt burn up a piston head,,, all ok though. |
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mbshaw88
Senior Member Joined: April-28-2013 Location: Chicago Status: Offline Points: 244 |
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I did the plate test just to be 100% sure it was leaking passed the rings. If I found out the rings were sealing at its was a valve I wouldn't go through the trouble of tearing down the engine passed the heads. Now I have to at a minimum pop the bad piston out, then determine if I just want to fix that one or all 8 while I'm in. |
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shierh
Gold Member Joined: April-29-2015 Location: Florida Status: Offline Points: 605 |
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Im one of those who does while you are in there, bearings, rings hone etc. not expensive and then you can trust it. also opportunity to upgrade etc.
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6157 |
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Good tip Duane. I always put some clear tube on my rod bolts (especially when sticking the Pistons back in the holes on a fresh motor)
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