How to do a leak down test on small engines

Metal in Motion shows you how to perform a leak down test on a small engine...specifically a single cylinder Intek Briggs and Stratton. A leak down test will show you specifically what is leaking in your engine and how much its leaking. For this reason, I prefer the leak down test over the compression test, although I still do the compression test just because it's so easy.
**On some engines, you may be required to turn the engine 1/4 inch past top dead center on the compression stroke to bypass the compression release mechanism. Do this by using the rod you have rested against the piston. When it's at its max height, continue rotating the engine in the direction it normally turns, until the rod drops down 1/4 inch. Then lock the engine down and test**

[@bienhelado204]

Great video. I knew many small engines have a compression release mechanism. A leak-down test gets around that issue. I love the rubber glove finger trick. Takes care of the "are you top of compression stroke or exhaust stroke?" question. Very clever.

[@johnnellis3025]

It might be on exhaust stroke, but because he has removed push rods the ex.valve can't open.

[@mrhomefinder1]

Very good video, simple, informative, and creative. True technicians work.

[@chipembrey]

Great video. Probably the best one I've seen about how to diagnose a head gasket leak, valve or rings leak for the single cylinder B&S Intek engine. And I've seen a lot of videos lately.

[@wcjcnc]

You should have everything plugged in from the start. You don’t pressurize the tester then plug it in. Also, The fastest easiest way to find exact top dead center is with the leak down tester. You turn the reg up so you have 5 PSI in the cylinder. Then turn the engine. You will feel TDC. Very fast and easy.

[@somethingtrulyhorrifying]

Silly me replaced a head gasket and valve guide seals on a 21.5hp intek v-twin thinking it would fix the cheech and chong oil burner edition, naturally neither of those fixed the problem. So here I am after the fact kicking myself for not doing this effective test first. Prior to that I bolted on a new carb and installed an inline shutoff valve, then drained the oil thinking it was gas-fouled and put in the correct amount of oil. Mower was ran and cut grass for 40+ mins after each wrenching session so it's definitely not residual oil. So, at this point it's *gotta* be the piston rings as there's literally nothing left, and when I remove the dipstick while she's running...well let's just say next time I'm gonna put on a face shield first lol. Anywho, just finished building my leak down tester, gonna confirm my thoughts tomorrow, thanks to this video. Thanks for the awesome information, subbed.

[@somethingtrulyhorrifying]

EDIT: Dropped the muffler, removed carburetor and both valve covers, ran leak down test on both cylinders TDC on compression stroke per cylinder. Some dipstick leakage, HEAVY exhaust pipe leakage, confirmed by ear and putting my hand over the pipe during the test. It's like saying "aaaahhhh" while putting your hand on and off your mouth. Pulled the head, exhaust valve is more crispy and full of gunk than Val Kilmer's arteries, no way that it could've seated properly. Gonna get some compound and a lapping tool 5000(aka suction cup) and lap me some valves! Day 28374: Lapped both valves to a nice consistent grey ring, cleaned head with wire wheel and carb cleaner followed with compressed air, slapped on a new head gasket and threw it all back together. Leak down test still has air from exhaust pipe, but less than before lapping the valves. Lots of crankcase air from both cylinders. A very loud "wah" noise from crankcase breather tube during the test, removing dipstick relieves pressure and the wah noise goes away. Didn't bother calculating the percentage loss, small double tank air compressor was losing pressure too fast to read the gauges and the air leak was obnoxious enough to prove a point. Cut the grass, less smoke than usual, until I let it idle, and then the smoke comes rolling in like business as usual. Conclusion: *bad piston rings eventually caused a badly carbon fouled exhaust valve due to the excessive oil burning over time, causing avoidable problems with the exhaust valve/seat. Gonna need to rip her off the frame and tear into her upside down on a milk crate and replace the rings...It will be done with many drive and much motivation*

[@Slowpoke5055]

I have learned something today. Have seen many of your vids well done, looking forward fo more

[@hswing11]

Good explanation WELL DONE

[@mosfet500]

Good test. I think that when the engine is turning from the starter and reaches full starter cranking speed the compression release is no longer bleeding air to lower compression. The reason compression tests don't work on small engines is that the ratio of air in the compressed cylinder to the line from the compression gauge is too great. These compression testers are made for large diameter pistons where the ratio is negligible. On small engines especially trimmer size engines you just can't get a really accurate compression test without making a special adapter that puts the gauge right at the spark plug hole and has a very small orifice to the gauge itself. Leak down is a much better solution, you got it right!

[@MowerMike]

Great video, I really enjoyed the corrections. Makes me feel better about my goofy videos.

[@thedobermangang3503]

Very good video my brother you would be a excellent instructor.. let me know when your class starts I'll be there..

[@peterlabiak1051]

Great guide, excellent all around guide, many thanks

[@rv6864]

Do you have a video on putting the tester together?

[@philliphall5198]

Remove fan cover and use socket and break over to hold engine on tdc

[@jeffhahn01]

Very good video. Thanks!

[@joecorrie1]

Nice video thanks

[@Sipho-Msayi]

Great video, learned something today

[@jimmypopp2695]

Thank you for the information my friend!!

[@abbaskhan3888]

Thanks a lot.great and informative video

[@mikealvarado4338]

Hi, Have you ever done a leak down test on a briggs and Stratton l head engine? I was wondering when you check the number one cyl does the number two cyl also end up at top dead center with both valves closed?

[@johnaverick7468]

Does a 22 hp Briggs Intek V twin even have a compression release ? Or do only the big singles have them ?

[@The_Dastardly_Dan]

I would love a parts list on your leak down tester please? thanks for the video too, gonna diag my dead Deere this week and this has been helpful. Also, that glove trick was cool advice 🤯

[@bobsoft]

Leak down tester how to make: kzbin.info/www/bejne/jaavinevZd-entk I don't see the point of the glove when you put something in the cylinder to see where the piston is at and you check that both rockers are loose indicating both valves are closed (TDC). The glove seems redundant.

[@circlepfarm9729]

How do you test if the head is warped?

[@daviddrum8877]

that briggs engine has had an issue with blowing the head gasket could not tell you how many i replaces but use a good thick heavy duty one when you replace it and you wont have issue again

[@AdamC5013]

Great video boss!

[@tankabbot22]

Great video! Leak down is the way to go. I love the conformation with the smoke test. What's your go to compression test for two stroke?

[@metalinmotionshop]

Usually just using the compression tester and looking for a minimum of 90psi for trimmers and blowers and such......however I usually dont like to work on many if they are below 110psi. Though I have seen several run around 95 psi often times they don’t idle well and are hard starting. If I suspect an air leak, then I’ll do a leak down test on the engine to make sure it holds psi and vacuum of about 10psi / in hg

[@mrih1586]

Liked. Very good video. I don't have acess to the leak down tool or compressed air. So I can't do this test. But I have a question for you or anyone willing to share info. Since the OHV Engines. Briggs & Stratton Intek in my case. Have a compression release valve for easier starting. What's the minimum amont of compression I can have and the engine still start fairly easy? Thanks in advance.

[@donens9310]

Couple of questions. How did you get the smoke to show the intake head gasket leak? Also, are the symptoms same that would result in no vacuum that operates the fuel pump?

[@johnaverick7468]

Loved the glove trick myself too. I have a question, I have a newer 22 hp V twin Briggs on a rider. The drivers side if you will , cylinder has like 140 + psi compression ( cold btw ) . But the passenger side cylinder has very little compression. I'm thinking " that " cylinder has the compression release mechanism in it. If I were to start the engine on one cylinder the good one btw. With the spark plug out of the weak cylinder ( with that spark plug wire grounded ) would the RPM be high enough at that rate to deactivate the compression release so I could just momentarily stick the rubber seal end of a compression gauge up against the spark plug hole just for a second to get a rough compression number for that weak cylinder ? Hell, that cylinder might be actually fine. No ?

[@Dave-jc6ky]

Hi, I appreciate this video! Though I have A husqvarna tiller with a briggs engine. So the setup with the pulley on crankshaft doesn't make it easy to lock the crank in place. Also my engine I understand says 1/4" past TDC on compression stroke. In any case if you have the rockers off like in your example what would be the effect of the crank moving when air is applied as it did in my attempted test? I had rockers off, crank moved and I had air coming out of the exhaust push rod valve guide. Does that suggest a blown gasket too? Or erroneous test since crank moved?

[@donens9310]

Is the leak down different process for twins? If so, how? Since TDC is different on each cylinder.

[@Dave-jc6ky]

Ok, so I finally got a leak test done and while I did not try to get 100 lbs of pressure on left gauge, I will relay the following: With the left gauge at 50 lbs the right gauge showed 23 lbs and held that steady. Now I know you took the 100 lbs and subtracted the 20 lbs and came up with 80 % leakage. though in this case with the initial pressure at 50 if you multiply the 23 lbs x 2 you get 46% leakage. If you mulitply the 50 lbs x .46 you get 23 lbs. You could hear the leakage out of the muffler. So it appears to be an exhaust valve issue and perhaps head gasket. Is this correct?

[@pattygq]

Did you do a video on how to make this?

[@mikedevita5558]

What about a smaller 5hp engine that has oil fill ports/oil checks near the base of the engine block, how would you determine leaky rings?

[@metalinmotionshop]

Anything in the crankcase is getting in there from around the pistons rings. Listen for air out of those ports you mentioned and then determine your leakage using the gauge. A certain amount of air is acceptable.

[@joehaynes2717]

If I don't have a Compression tester tube with the ball removed to use with the glove...could I just put my finger over the spark plug hole to feel pressure?

[@metalinmotionshop]

Yes, if you partially cover the spark plug hole with your finger, and spin the over engine over by hand you can usually hear the air hissing out on the compression stroke.

[@wags9777]

It burns oil when on a hill. Sounds like an oil level issue to me

[@d_ward4871]

Great video, one of the best I’ve seen discussing this. I’m dealing with this right now with one of my walk behind mowers w/ a kohler command. Getting a head gasket tomorrow hoping it’ll fix it. It backfired and now won’t start and I can pull the cord and there’s no resistance, no compression stroke detectable. I hope to god head gasket fix’s it. 🙏🤞 what’d u think?

[@metalinmotionshop]

Were you able to do a leak down test? I’ve seen a backfire bend pushrods and mess up valves. It might be a head gasket but it’s hard to say without a test.

[@d_ward4871]

@@metalinmotionshop I put a new head gasket on and during reassembly noticed one of the valves (exhaust I think) was open just half a hair. After lots of head/beard scratching I tried using a clamp and a socket to force the valve closed. With a very small “click” it seemed to shut. Reassembled and it easily started. Fingers now crossed. Thanks

[@d_ward4871]

@@metalinmotionshop I didn’t have a leak down tool. Pushrods still straight too , few ,

[@Dave-jc6ky]

Ok I finally got a leak down test on a Briggs small engine. It appears there was high leakage percent of 46%. At first as per last comment, I thought the sound of air was coming out the muffler but on closer examination I discovered it was coming from two holes in the OHV assembly. Also when I took out the oil filler plug the sound of the air escape changed and I noticed a difference with my thumb on and or off of the oil filler opening. So based on what little I know it appears there is a head gasket issue and perhaps cylinder rings if air is getting into the crankcase. Does this sound correct? Prior symptoms were smoke in the exhaust. One kind of weird thing was at one point there was only around 40-45 lbs on leakage side of tester gauges and then the gauge jumped up to around 50 lbs at least briefly.

[@metalinmotionshop]

So...my experience is if you pull the valve cover off a head gasket leak is louder just below the intake cast into the head. If it leaking past the rings it will be louder coming out the dipstick. Theres obviously oil passages to get oil to the cylinder head, so you are going to have some air noise down where the pushrod sit on the tappets but it’s usually not as loud. Also there a minimum standard for doing a leakdown test and thats 60psi. Not that you wouldnt be able to diagnose it by listening but it might throw off the leakage ratio if the pressure is to low.

[@diablonunez6211]

If you take out racker arms you dont need top dead center

[@d_ward4871]

Stick the hose up into one of the fingers 6:00 Sounds backwards

[@mikeadler434]

👍👍

[@arnoldaltjr.2099]

Engaging the electric pto clutch will most often hold the engine.

[@metalinmotionshop]

I hadn’t thought of that. Good idea.

[@trappn]

Anything but placing vice grips on crankshaft if I understood him correctly. Some day you may need to replace the bottom seal.

[@billsimpson109]

First! Nice job bro