Home Made Leakdown tester

[Morris]

Check out my ugly but functional leakdown tester. Total cost: roughly $30.00.

According to my tests, I have a bad intake valve on #1 and bad rings on #s 1, 2 and 4.

Number #3 was strong. A drop of only 2-3 pounds. The rest dropped 20-30 pounds. Would being off true TDC cause these results?

 

[healeyboz]

Fantastic rig Morris..

 

[jlaird]

For the mentaly impared how about a few details on that rig?

 

[drooartz]

I'm at a loss too (my fault) as all I see is an air hose with a spark plug welded on, and a pressure gauge. Of course, I haven't the faintest idea of how a leak down test works. Always nice to start off the year feeling a bit lost. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

 

[jlaird]

He must have a Y or a T on that gage.

 

[Bugeye58]

Here's a quick primer on leakdown testers.

https://www.xs11.com/tips/misc/misc3.shtml

Jeff

 

[Morris]

That's the article I based my rig on. The air compressor I used already had a pressure reg and line gauge, so I was able to eliminate those parts (though they had them at Lowe's for @ $13). I did not go the grease hose route because it would have necessitated buying a pipe thread tap. And also, welding is a lot more fun than tapping thread.

 

[Bugeye58]

Morris, if your compression tester has a removable hose, you can use that to thread into the sparkplug hole.
Jeff

 

[drooartz]

Thanks for that link, Jeff. I think I understand now...

 

[Bugeye58]

Glad it helped, Drew. it's a simple concept, and much more precise than a simple compression test.
I'll get the hub puller in the mail tomorrow, by the way.
Jeff

 

[drooartz]

Can you do such a test on an engine that's been pulled and is missing carbs/exhaust? Might be nice to test the 1275 I've got sitting on my floor if it was possible.

Thanks again for sending out the puller.

 

[Bugeye58]

Sure you can test an engine like that. It's actually a bit easier to do with the carbs and exhaust off. It makes it easier to listen at the ports. Also easier to rotate the engine with the crank nut accessible.
As always, make sure the piston for whichever cylinder you are testing is at TDC on a compression stroke. If it's a little off, the air pressure may force it back down in the cylinder. I usually leave the breaker bar on the crank bolt, or otherwise lock the crank to prevent that from happening.
Jeff

 

[Taz]

Each cylinder needs to be at TDC and stay there or your readings will be incorrect.

Taz

 

[Dave Russell]

Glad it helped, Drew. it's a simple concept, and much more precise than a simple compression test.
Jeff

Hi Jeff,
Good stuff. As you likely know, recip aircraft engines are rigorously tested in this manner. For aircraft engines, there are prescribed calibrated restrictor orifices to match the cylinder displacement. This gives an actual calibrated leakage reading that can be compared to the particular engine specs. The .040" diameter restrictor mentioned is a pretty good compromise for most engines. Sometimes, more elaborate testers use two pressure gages, but the single gage is usually more than adequate.

For folks who don't wish to be confused by a reverse reading pressure gage, or go to the trouble to make a new reversed dial face, the Moroso gage can be had for a bit more money.
https://www.pegasusautoracing.com/productdetails.asp?RecId=844

You are correct, the sparkplug end of a higher end (screw in type) compression tester works very well. It has a quick disconnect & numerous plug adapters. With the quick disconnect, it's very easy to set the pressure regulator to exactly full scale on the gage & then connect to the cylinder adapter hose.

I also agree, problems further down the cylinder can be checked, but as you say, once the piston is off TDC, the crankshaft must be securely held in position against air pressure.

I have also found the part about a speck of carbon under a valve causing leakage more than once.

Good thread, all of it. It gives far more information about engine condition & the location of problems which can not be done with the engine disassembled.
D

 

[GB1]

Nice Improv Tool. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[Hap Waldrop]

Here's what I have, it cost 89.95, probably about 10 years ago, if it blew apart today, I got my money's worth.

 

[JerryB]

""""", it cost 89.95, probably about 10 years ago"""

What happend...blew apart....did a gage blow?

Matco stuff of the truck is a lot pricier now.

Tavia (tavia.com) makes a very nice dual gage piece. They have moved to Florida about 4 years ago as Tom got tired of sunny So Cal.

He also makes a really nice bolt stretch gage that is priced rite and reads to .0001"

They have an engine builder deal.....

 

[Bugeye58]

Jerry, I can't remember if my leakdown tester is a Tavia or a Longacre, but it's essentially the same as Haps. I think around 85 bucks, or so, about the same time frame as Hap.
I've also got a Tavia bolt stretch gauge, and a valve spring rate tester that have served me well.
Jeff