getting engine at TDC

04superzillaSTi · 02-07-2008, 02:03 PM

im going to atempt to do a leak-down test on my engine. how do i get each cylinder at TDC.

hellomyles · 02-07-2008, 06:47 PM

-First, take all of your plugs out. -Then you need to screw the little whip hose with the o-ring seal into one of the spark plug holes.
-Next you need to put your finger over the hole from the end of the whip hose.( It's the little air fitting that you plug into the guage part of the leakdown testing tool.)
-Now, have someone get in the car and make sure to set the park brake and put the vehicle in neutral. Have the person "bump the starter" one little bump at a time until you start to feel pressure coming from the hole that your finger is over.
-This means you are getting close to top dead center (TDC).
You may have to do this a bit to get the 'Feel of it". The pressure only happens as you are coming up on TDC because the valves are closing and it is building compression/pressure.
-When you think you can't bump the engine anymore or it will open the valves and spin over you connect your gauge to the whip hose and shop air. Make sure you zero/calibrate your guages.
-If you are just before or at TDC the engine may move just a touch because it is getting to the true TDC and will stop and give you your leakage reading. If you went just a bit past TDC and when you hook up your gauge the engine spins over quite a bit and shows you have A LOT of leakage you need to disconnect the gauge and try to bump the engine till TDC is found again.
-If a reading seems odd or shows more leakage than most other cyl. try it again just to make sure. They also sell a little adapter that fits on your whip hose that is a whissle so when the engine is building the pressure it whissles to let you know when you hit TDC. It is very easy to find TDC so don't get frustrated, just keep trying.

gosu · 02-12-2008, 05:47 PM

The way I did it once was,

- take all the plugs out.
- Stuck a telescoping magnet in the cylinder you want to test.
- Put the car in gear and move the car forward or backwards til the magnet rod is at the tallest point. (or in our case, sideways. I did this on an inline motor so id imagine its probably 87x's easier)
- If that cylinder is doing horrible, your probably on the exhaust stroke! You need to be on the compression stroke (all the valves are closed)

04superzillaSTi · 02-13-2008, 04:52 AM

ah! thats a great idea. thanks

will12345 · 02-13-2008, 07:55 AM

well you have to remember, on boxer motors, top dead center the pistons are halfway in the stroke and all 4 are even with each other..it may be more work, but take off your belts and the stock crank pulley and you should be able to see the timing marks

02-07-2008, 02:03 PM	#1
04superzillaSTi Junior STI Driver Car: WRB 04 STi Posts: 97 Join Date: Aug 2006 Trader Rating: (1)	getting engine at TDC im going to atempt to do a leak-down test on my engine. how do i get each cylinder at TDC. This ad is not endorsed by this member. Please register or login to hide this ad.

02-07-2008, 06:47 PM	#2
hellomyles Amateur STI Driver Car: Black 04 STi Fav Mod: Coming Soon Location: Chattaroy Wa Posts: 17 Join Date: Oct 2007 Trader Rating: (0)	Re: getting engine at TDC -First, take all of your plugs out. -Then you need to screw the little whip hose with the o-ring seal into one of the spark plug holes. -Next you need to put your finger over the hole from the end of the whip hose.( It's the little air fitting that you plug into the guage part of the leakdown testing tool.) -Now, have someone get in the car and make sure to set the park brake and put the vehicle in neutral. Have the person "bump the starter" one little bump at a time until you start to feel pressure coming from the hole that your finger is over. -This means you are getting close to top dead center (TDC). You may have to do this a bit to get the 'Feel of it". The pressure only happens as you are coming up on TDC because the valves are closing and it is building compression/pressure. -When you think you can't bump the engine anymore or it will open the valves and spin over you connect your gauge to the whip hose and shop air. Make sure you zero/calibrate your guages. -If you are just before or at TDC the engine may move just a touch because it is getting to the true TDC and will stop and give you your leakage reading. If you went just a bit past TDC and when you hook up your gauge the engine spins over quite a bit and shows you have A LOT of leakage you need to disconnect the gauge and try to bump the engine till TDC is found again. -If a reading seems odd or shows more leakage than most other cyl. try it again just to make sure. They also sell a little adapter that fits on your whip hose that is a whissle so when the engine is building the pressure it whissles to let you know when you hit TDC. It is very easy to find TDC so don't get frustrated, just keep trying.

02-12-2008, 05:47 PM	#3
gosu STI Driver Car: 07 WRX STi Fav Mod: Tires and Brakes! Location: AZ Posts: 200 Join Date: Dec 2005 Trader Rating: (1)	Re: getting engine at TDC The way I did it once was, - take all the plugs out. - Stuck a telescoping magnet in the cylinder you want to test. - Put the car in gear and move the car forward or backwards til the magnet rod is at the tallest point. (or in our case, sideways. I did this on an inline motor so id imagine its probably 87x's easier) - If that cylinder is doing horrible, your probably on the exhaust stroke! You need to be on the compression stroke (all the valves are closed)

02-13-2008, 04:52 AM	#4
04superzillaSTi Junior STI Driver Car: WRB 04 STi Posts: 97 Join Date: Aug 2006 Trader Rating: (1)	Re: getting engine at TDC ah! thats a great idea. thanks

02-13-2008, 07:55 AM	#5
will12345 Senior STI Driver Car: 04 subaru sti Fav Mod: 35r turbo kit Location: sunny san diego Posts: 315 Join Date: Apr 2007 Trader Rating: (1)	Re: getting engine at TDC well you have to remember, on boxer motors, top dead center the pistons are halfway in the stroke and all 4 are even with each other..it may be more work, but take off your belts and the stock crank pulley and you should be able to see the timing marks This ad is not endorsed by this member. Please register or login to hide this ad.