Author Topic: leak down test? (Read 7075 times)

aberegg05 · « **on:** March 08, 2014, 07:14:35 PM »

Is it better to do a leak down test on a fresh motor or after the initial break in?

Morse250r · « **Reply #1 on:** March 08, 2014, 07:58:17 PM »

Fresh !

4WHLr · « **Reply #2 on:** March 08, 2014, 09:07:29 PM »

Yes, pressure test it before it comes off the work bench, for a fresh build

Langbolt · « **Reply #3 on:** March 09, 2014, 10:40:13 AM »

The reason you do a leak down test is to see if all the seals & gaskets are doing their job....if you have a leak and don't know it, you might not make it through the break-in! (too lean)

aberegg05 · « **Reply #4 on:** March 09, 2014, 01:06:43 PM »

I got ya. I thought if the motor got warm the seals and gaskets got hot they would seal better after the very first heat cycle. Thanks. Will wait to fire it up until I i to the leak down test. Ill have to yank it back out of the frame.

Jerry Hall · « **Reply #5 on:** March 10, 2014, 09:58:58 PM »

If you have an air leak that is severe enough to hurt your engine you will know it when it runs. Very small air leaks will cause the engine to have the Ring-Ding-Dings as the RPMs decelerate after blippng the throttle. If the air leak is more severe, the engine RPM may hang at a high RPM or the RPM may continue to climb even though the throttle is closed.

The above statement is only true if you carburetor's low speed jetting is in the ball park.

Jerry Hall · « **Reply #6 on:** March 11, 2014, 10:49:11 AM »

Quote from: aberegg05;28323

I got ya. I thought if the motor got warm the seals and gaskets got hot they would seal better after the very first heat cycle. Thanks. Will wait to fire it up until I i to the leak down test. Ill have to yank it back out of the frame.

I have seen crank seals that are worn on the "suction lip" of the crank seal leak when the engine is cold and seal when the engine is hot. I have not observed temperature affecting a gasket's ability to seal.

Rupp250 · « **Reply #7 on:** March 11, 2014, 11:37:49 AM »

You don't have to remove it from the frame to do a leak down.

aberegg05 · « **Reply #8 on:** March 11, 2014, 11:44:57 AM »

Well I just did my leak down. Started at 7 1/2 lbs and only went to 4 lbs in 8 mins. Good or bad???

Tbone07 · « **Reply #9 on:** March 11, 2014, 12:41:35 PM »

That's probably a little more of a loss than you want. Is this a PV cylinder?

Put some pressure in it and get some dish soap and warm water to find your leaks

F-Red · « **Reply #10 on:** March 11, 2014, 12:49:02 PM »

^^ Agreed. Too much of a loss. Right now, dish soap is your best friend.

rablack21 · « **Reply #11 on:** March 11, 2014, 01:30:29 PM »

Also make sure it is not leaking from your actual pressurizing device in the intake boot.

aberegg05 · « **Reply #12 on:** March 11, 2014, 01:58:00 PM »

I checked the Intake boot. Im leaking around the base gasket. Im gona use a little sealer and see what happens. Thanks everyone.

supernutt · « **Reply #13 on:** March 11, 2014, 06:42:52 PM »

Had a tough time with my base gaskets also. Also my spacer plate was not even close to flat. Used 3 bond 1211 on my base gaskets and the center crankcase gasket. Mine held 7psi for 3 days when I was done!!!

aberegg05 · « **Reply #14 on:** March 11, 2014, 09:09:31 PM »

Put some rtv blue on her. Will try another test tomorrow.