Leak down test, short block
Thread Starter
Safety Car
Joined: Jan 2008
Posts: 3,795
Likes: 435
From: Aarhus, Denmark
Keep in mind that with the piston at TDC that is is going to want to turn the crank very quickly to BDC. So you need a way to secure the piston at TDC.
From most leakdown test documentation that I can find it is usually much higher pressure than 12psi.
!00 psi is common as with the one gauge method it makes math easy. IE, If the gauge shows 100 psi before connected and 90 psi after connected it's 10% leakage.
Here is a page with various recommendations on how to do a leak down test.
http://www.gress.org/Home/Cars/Track...down%20DIY.htm
From most leakdown test documentation that I can find it is usually much higher pressure than 12psi.
!00 psi is common as with the one gauge method it makes math easy. IE, If the gauge shows 100 psi before connected and 90 psi after connected it's 10% leakage.
Here is a page with various recommendations on how to do a leak down test.
http://www.gress.org/Home/Cars/Track...down%20DIY.htm
Maybe I bought the wrong leak down tester ??
Former Vendor
Joined: Mar 2011
Posts: 6,215
Likes: 152
From: spring branch Texas
TDC is only necessary with an assembled engine (to insure that both intake and exhaust valves are closed).
With assembled engine, your ears tell where the leak(s) are-----
1) rings---- heard through the PVC system
2) intake valve---heard through the carb.
3) exhaust valve--heard through the tail pipe
Higher (100) PSI is needed.
G.
With assembled engine, your ears tell where the leak(s) are-----
1) rings---- heard through the PVC system
2) intake valve---heard through the carb.
3) exhaust valve--heard through the tail pipe
Higher (100) PSI is needed.
G.
Instructor
Joined: Jun 2009
Posts: 157
Likes: 1
From: Sebring florida
Doing a aircraft eng we use two gauge tester, base pressure is 80psi and the differential pressure is anywhere from 0 to 78. This is done at TDC and at 80psi it takes a good grip on the prop or you can be seriously hurt. Most aircraft engs have 4 rings and even a newly broken in eng wont give you 80 over 80 on both gauges. A good cylinder will give you approx 70 to 78.
Be careful trying to hold the crank at TDC, if not dead on TDC the piston will be pushed down with grate force. Hang on.
Be careful trying to hold the crank at TDC, if not dead on TDC the piston will be pushed down with grate force. Hang on.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Oh a Rotax 912S or 912SU will. A Rotax 912 will give u 80psi over 80psi after a 1000 hrs. I just did one in October. 912 Rotax is a high quality engine - modern tech also. And your correct u need to hang onto the prop or it can become a butchers axe. But finding TDC is much easier as u can feel the air stop blowing on compression by turning that prop - something u cant do very well with an auto engine in the car.
c3_dk u need to use a leakdown tester sized for your engine. Each leakdown tester has an orifice between the source press gauge and the leakdown gauge. That orifice is sized to give u the correct fill rate for your cyl. If the orifice is to big u will never see any leakdown on the measure gauge as the cyl air is replaced too fast. And yes i used the correct tester for the rotax.
c3_dk u need to use a leakdown tester sized for your engine. Each leakdown tester has an orifice between the source press gauge and the leakdown gauge. That orifice is sized to give u the correct fill rate for your cyl. If the orifice is to big u will never see any leakdown on the measure gauge as the cyl air is replaced too fast. And yes i used the correct tester for the rotax.
Thread Starter
Safety Car
Joined: Jan 2008
Posts: 3,795
Likes: 435
From: Aarhus, Denmark
Thx everyone.
Can anyone send me a link for leak tester, if I've bought the wrong, then I would like to buy a new.
As I see it, I can't use the leak tester I have differently??
Can anyone send me a link for leak tester, if I've bought the wrong, then I would like to buy a new.
As I see it, I can't use the leak tester I have differently??
Thread Starter
Safety Car
Joined: Jan 2008
Posts: 3,795
Likes: 435
From: Aarhus, Denmark
Oh a Rotax 912S or 912SU will. A Rotax 912 will give u 80psi over 80psi after a 1000 hrs. I just did one in October. 912 Rotax is a high quality engine - modern tech also. And your correct u need to hang onto the prop or it can become a butchers axe. But finding TDC is much easier as u can feel the air stop blowing on compression by turning that prop - something u cant do very well with an auto engine in the car.
c3_dk u need to use a leakdown tester sized for your engine. Each leakdown tester has an orifice between the source press gauge and the leakdown gauge. That orifice is sized to give u the correct fill rate for your cyl. If the orifice is to big u will never see any leakdown on the measure gauge as the cyl air is replaced too fast. And yes i used the correct tester for the rotax.
c3_dk u need to use a leakdown tester sized for your engine. Each leakdown tester has an orifice between the source press gauge and the leakdown gauge. That orifice is sized to give u the correct fill rate for your cyl. If the orifice is to big u will never see any leakdown on the measure gauge as the cyl air is replaced too fast. And yes i used the correct tester for the rotax.
But how big a hole for a v8??
Instructor
Joined: Jun 2009
Posts: 157
Likes: 1
From: Sebring florida
No you don't want a home built unit, you wont get the proper orifice to get the proper differential.
www.chiefaircraft.com
click on aircraft then on tools.
Run the piston up to TDC to seat the rings in the bottom of the ring land not on the down stroke.
And once again, HANG on to the braker bar your using to turn the crank.
www.chiefaircraft.com
click on aircraft then on tools.
Run the piston up to TDC to seat the rings in the bottom of the ring land not on the down stroke.
And once again, HANG on to the braker bar your using to turn the crank.
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Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
I use this l/d tester for my corvette and it worked great: http://www.summitracing.com/parts/sum-900010/overview/. But for the Rotax aircraft engine i used the Rotax mfr tester.
I wouldnt bother with that home made l/d tester in your video as a dedicated manufacture made l/d tester would be verified with test equipment and that home made tester is not - just an amateur attempt. Funny what u can find on U-twit. And an orifice has some specific dimensions that are not just a hole in JB weld. An orifice has a design length and bevel and bevel depth for a design flow rate at a design press - again it is tested/verified before/after manufacture.
Aircraft have a variety of chamber volumes and nowadays autos do to as displacements continue to decrease. If u want the correct orifice size for the correct fill rate for the sbc u have to contact the mfr or sometimes u can find it in the instruction sheet.
Hope this helps ya c3_dk.
I wouldnt bother with that home made l/d tester in your video as a dedicated manufacture made l/d tester would be verified with test equipment and that home made tester is not - just an amateur attempt. Funny what u can find on U-twit. And an orifice has some specific dimensions that are not just a hole in JB weld. An orifice has a design length and bevel and bevel depth for a design flow rate at a design press - again it is tested/verified before/after manufacture.
Aircraft have a variety of chamber volumes and nowadays autos do to as displacements continue to decrease. If u want the correct orifice size for the correct fill rate for the sbc u have to contact the mfr or sometimes u can find it in the instruction sheet.
Hope this helps ya c3_dk.