Leak Down Test

[L84THSKY]

I've already explained the results of a Leak Down Test performed by a BMW dealership. I'm gonna do my own test soon, I just won a tester on Ebay. Here are a few questions;

1. Is there a marker on any of the pulleys denoting TDC? If not, how do I easily find TDC?
2. If I were on TDC of Cylinder #1, what other cylinder is also on TDC?
3. This test is performed with the piston TDC, and all valves closed. Can someone explain how the Piston is TDC and both the intake and exhaust valves are both closed? Seems the exhaust would be closed, and the intake open. But then I wouldn't have a sealed chamber.

Here is the tester I bought.

http://cgi.ebay.com/ebaymotors/ws/eB...0470943&rd=1,1

[316i compact]

the moment all valves are closed is when spark plag ignites, and the "explosion" is happening.

[L84THSKY]

I knew that was true. What I forgot to realize was that the air is sucked in, then the intake valves close, then the gas is injected and the spark ingnites.

Any idea how to set TDC for my test?

Originally Posted by 316i compact

the moment all valves are closed is when spark plag ignites, and the "explosion" is happening.

[DustenT]

Originally Posted by L84THSKY

I knew that was true. What I forgot to realize was that the air is sucked in, then the intake valves close, then the gas is injected and the spark ingnites.

Any idea how to set TDC for my test?

Take a long screw driver and stick in down the spark plug hole. Remove all your spark plugs. With a large breaker bar turn the crank pulley until the screw driver is pushed up as high as it will go. It will peak and then fall. Stop it at the peak.

[campaiar]

How do you know your at TDC or one full crank rotation away with a screw driver?

You could be finding the peak after the exhaust cycle and before the intake cycle instead of the peak before the power stoke. Wouldn't you need to take the valve cover off to determine where you are in the cycle?

For those that are completely lost, www.howstuffworks.com has a great animated diagram on the internal combustion engine. Your BMW has a four-stroke engine.

[DustenT]

Originally Posted by campaiar

How do you know your at TDC or one full crank rotation away with a screw driver?

You could be finding the peak after the exhaust cycle and before the intake cycle instead of the peak before the power stoke. Wouldn't you need to take the valve cover off to determine where you are in the cycle?

For those that are completely lost, www.howstuffworks.com has a great animated diagram on the internal combustion engine. Your BMW has a four-stroke engine.

Trial and error. If you get a super high reading, turn the crank one more cycle. There should be a dramatic difference between "all valves closed" and "exhaust valves open".

EDIT: There is also a whistle on the market that tells you when you are on the correct stroke.

[campaiar]

I miss working on cars with distributors.. No guess work involved.

[L84THSKY]

There is no marking on a pulley or anywhere that tells you TDC?

Originally Posted by DustenT

Trial and error. If you get a super high reading, turn the crank one more cycle. There should be a dramatic difference between "all valves closed" and "exhaust valves open".

EDIT: There is also a whistle on the market that tells you when you are on the correct stroke.

[DustenT]

Originally Posted by L84THSKY

There is no marking on a pulley or anywhere that tells you TDC?

Might be. The screw driver method is pretty simple though.

[mohaughn]

You seem to like tools. This should do it for you.

http://www.atoolcrib.com/catalog/pro...ducts_id=14817

[L84THSKY]

Great, I'm gonna get one.

Originally Posted by mohaughn

You seem to like tools. This should do it for you.

http://www.atoolcrib.com/catalog/pro...ducts_id=14817

[DustenT]

Let us know how it goes. I'd like to do a leakdown test on both the 318ti and the m3, just for giggles. Maybe I can borrow your tool when you're done, in trade for a case of tasty Wisconsin brew?

[L84THSKY]

I gotta go my brother's place and borrow his compressor. Not sure what compression level I will pump into the cylinder for best results. I can lend you the tools when I am done.

After my initial measurements, I'm gonna put some seafoam in the intake, and recheck my results.

Originally Posted by DustenT

Let us know how it goes. I'd like to do a leakdown test on both the 318ti and the m3, just for giggles. Maybe I can borrow your tool when you're done, in trade for a case of tasty Wisconsin brew?

[DustenT]

Originally Posted by L84THSKY

I gotta go my brother's place and borrow his compressor. Not sure what compression level I will pump into the cylinder for best results. I can lend you the tools when I am done.

After my initial measurements, I'm gonna put some seafoam in the intake, and recheck my results.

I'd recommend doing an oil change prior to doing a leak down test too.

[aceyx]

Might be a better place to ask:

http://tech.bentleypublishers.com/ca...tegoryName=bmw

I can't imagine the germans forgetting something in the timing gears to mark TDC, but it's entirely possible.