leak down test procedure please

I was going to do a leak down and compression test over the weekend but all I could do was the compression test. The results came out better than when I had it done a few months back by a shop. All cylinders were between 182-205psi on a warm engine and later cylinders were cooler given the time that went by. I'm not sure how much cooling affects the results but the last 4 cylinders were all around 190.

I had trouble trying to perform the leakdown test, however. I was unable to figure out a good way to turn the crank to get each cylinder to TDC. Bumping the starter proved difficult and it took a lot of retries. I wouldn't want to do this for several cylinders and wear out the starter solenoid. I also tried turing the flywheel by accessing it through the bottom opening and wedging a screw driver in there to turn it but that didn't seem like a smart idea so I stopped.

What would be the procedure to turn the crank for this? I would do it during the upcoming engine out but then I can't warm it up and I think keeping it warm is more critical during this test.

 

The numbers will actually be better (e.g., lower #s and less leakage) when the engine is warm, so doing it cold will show the most leakage. The numbers produced after doing it warm, however, will probably be more relevant.

Otherwise I cannot answer your question.

 

You have stumbled onto the "tricky part" of a leakdown test on a mid-engine car. It's difficult to get it done at all before things cool off and finding a precise TDC for each cylinder is a problem with no easy solution. This is one reason I am reluctant to trust other people's numbers for this, there are just too many variables.

One way of rotating the engine slowly is by removing the spark plugs, putting it in the highest gear and rolling it forward (you should rotate the engine in it's forward direction only). If you have a little room and a helper this isn't too hard.

 

How is it done at the F-dealer?

Is the motor turned by the crank pulley thereby necessitating the removal of the under panels?

 

I would think after removing the spark plugs...... turning it by the crank pulley nut would be the way to go.

 

Standard procedure it will be.

One thing of note: I did try to put it in gear and move the car but I wasn't thinking and I put it in 1st. DUH

I'll try it again and if the procedure isn't feasible I'll go ahead and take apart the shielding underneath - it's about to come off anyway.

 

Finding TDC eight times before the engine cools too much without any timing marks is the fun part.

 

Good point. That brings up another question.

I'm assuming because this is a 180 degree crank two pistons will be at TDC and two will be at BDC on one side then 90 degrees later the same thing will happen on the other side (please correct me if I'm wrong). Of those TDC pistons one will be on the end of the exhaust stroke transitioning to the the intake stroke the other will be at the end of the compression stroke and transitioning to the ignition stroke (I think that's what it's called). Can I do the leak down on both cylinders or will I run into the situation where both valves are slightly open transitioning from exhaust to intake? I'm almost certain this will foil my plan.

Another idea; if the above won't work, what about determining which ones are in the compression stroke and doing it that way, then turning 90 degrees, doing the next two, repeat, repeat? I'm under the assumption that the piston doesn't have to be at TDC - just that the valves have to be closed. I could have someone hold the crank bolt (at the pulley) in place if the crank has a tendancy to turn under the air pressure.

The theory of all this being I'd only have to move the crank one rotation 90 degrees at a time.

Also, I found the firing order. But I didn't find a chart with the cylinders numbered. I only have the labeled ignition pack on each side to go on. Based on this I believe 1-4 were on the USA passenger side, 1 being at the rear of the car, and 5-8 were on the driver side, 5 being at the rear. Was I correct?

 

OK. Got the leak down done. Admitedly, I'm a DIY'er so keep that in mind. Also, I did this with the engine cold.

I pulled down the sheilding underneath and checked out how much room I had to get to the crank bolt -laughably small so I resorted to another tactic. Going on the advise of putting it in 6th gear and untilitizing the fact that the rear was in the air, I decided to put it in 6th and have a friend hold one wheel while I turned the other. A third friend would tell us when the cylinder was at TDC. We zero'd the gauge at the begining of each cyinder test.

I believe my results came out pretty well. I don't have my notes with me on wheich cylinder did what but I remember the numbers:
two at 3%
one at 10% (I'll discount this since there could have been some debri on a valve or maybe it wasn't quite at TDC)
one at 7%
four at 5%

Now I can get on with the 30k. Has anyone here ever done it with the engine in the car? As you all know it's "supposedly" possible.

 

Can be done with fuel tank removal and some "mucking around".

I have not done it personally.....

 

I believe on a 355 there is a cross member that is in the way for removing the bottom pulley, this means the engine has to be put on a large angle to make removal of this pulley possible so the cam belts can be changed.

I would pull the motor, easier and also give access to be able to clean up the engine, this would be the feel good part of the major service for me.

 

Hi James, I still don't see how anyone can get the pulley off even trying to tilt the engine. I've done 3 belt changes on 355s and each time I have looked at that concept and leave it scratching my head. And as you said it really is easy to drop the engine cradle on the 348 and the 355 and also agree on the feel good part of doing the service with the engine out.

 

Just curious...why discount the 10% figure? maybe it's accurate. If so it is only between 3%-7% of your other cylinders. You will feel absolutely no difference in performance. Your leakdown and compression #'s are fine. Now drop your engine and do the service the "right way" and clean that puppy up then enjoy her for 5-6 more years before you do it again.

 

If you saw how it was done, it would probably make you cry!

From what I have heard, a BIG long pipe is needed to tilt the engine down etc...