So...I was all psyched to do my first leak down test......

[mike911996]

I read all about it...bought the proper test equipment....I enter the garage today eagerly and then after lifting the rear decklid and actually looking down at the crankshaft pulley my heart sinks....why?

there is absolutely no way to get a socket on the pulley nut...the bottom is completely blocked....there is not enough clearance to get at it from the top or side either....if the AC pulley wasn't mounted i think it would be possible....

am i missing something?? is it possible to rotate the crank with the engine mounted in the car (1984 carrera) with the AC pulley installed?

not one thing i have ever read addressed this issue...i was hoping to complete this test without having to do something like do a partial drop etc etc....

thank you for any advice you can give me!

[fastfredracing]

With all of the plugs out, the motor spins quite easily off the alternator bolt. You may have to use a little "thumb " pressure on the slack side of the belt , to keep it from spinning. Easy peasy. Good luck

[Grady Clay]

Mike,
First, welcome to Pelican
You will find a lot of help here.
Good for you having researched this subject.


I agree, use the fan belt.


There are situations where you need to turn the crankshaft.
One of the ‘tricks’ is to slip the proper length 6-point socket in/on the crankshaft bolt and then connect the ratchet wrench.
A 3/8” long-handle ratchet and proper length socket will fit.
You will find an array of socket lengths available.
One will fit your situation.

In an unusual case, you can always turn (machine) a socket to the best length.
I removed the detent ball from a long-handle wrench so it is easy to engage the 3/8” drive and (more important) remove it.
With a powerful detent ball, you must use a long screwdriver to get the ratchet wrench off the socket.
A long ‘magnet-on-a-stick’ is useful for retrieving the socket.


All the little silly details make a job easy (or possible).


Please post images of your tools and equipment.
Your step-by-step procedure, including failures, will be useful for the next Pelican.
This is how we all learn.

Best,
Grady

[James Brown]

With the plugs out, you can move the car forward in first to get to the proper cylinder for the check. So you need some room to maneuver the car forward. you can push it back out of gear.

[FrinkFrog]

Reading recently in P. Zimmerman's "The Used 911 Story" he discusses leak down testing and the importance for the technician to not remove all 6 plugs at once. The reasoning given is that by removing only the plug for the cylinder to be measured, there is less opportunity for dried engine crud to be sucked into a cylinder and perhaps find its way to a valve seat... thereby skewing the test results. I've never done a leak-down test myself, but this makes sense. I do not know how difficult a 3.2 turns over with a wrench on the pulley nut, but my 2.7 turned over quite easily with all 6 plugs in.

[James Brown]

Ether way is fine. you can turn it over with the fan pulley, just go slow and wait for the compression to leak out.

[Silveresrty911S]

Just did this today, it's easier if you turn it from the 17mm nut at the crank directly below the fan

[T77911S]

use the fan pulley nut. press on the right side of the belt to add tension so it will not slip.

[mike911996]

thank you all for your replies...they have been very helpful.....

i need to ask one more question.....when doing the leak down test when is the cylinder exactly at TDC?....when the crank pulley notch lines up with the case line? or when the distributor rotor lines up with the notch in the distributor housing?

the reason i ask is they dont line up simultaneously....it is my understanding that they should be 4 degrees off? is this correct?

when the rotor is lined up with the distributor notch, the crank pulley notch is about a centimeter passed the case line....

if you are indeed supposed to use the distributor rotor in line with the notch in the distributor housing....do you guys make a mark just passed the case line to help with the other cylinders after #1......ok....sorry...i am rambling...

thank you for any answers you can give me!

[DDD]

I'm not an expert, but if you're looking for a quick reply...You use the crank pulley. There are three notches on it. The Z" is TDC, assuming your distributor is pointing to #1. Distributor goes around once for every two cranks of the crankshaft.

I don't recall firiing order, but it bounces back and forth across the engine after #1. Do a search and you can find that. So, you will make six stops as you make tow turns with the crankshaft, using each mark twice. Make sense? --DDD

[donporfi]

Once I saw in a shop that they rised one of the rear tires, they put the car in gear and when they needed to move the engine they rotated by hand that tire. It seem to move very easily.

[mike911996]

i am having no problem turning the engine over with the fan pulley nut....what is bugging me is finding TDC....crank pulley notch or distributor notch....i went through each cylinder several times and honestly i dont think i got repeatable consistent data...i have to try again....plus i was using the harbor freight chinese tool.....eh..it is calibrated for 15 psi....i want a 100 psi tool...so i am going to upgrade and try again....

[euro911sc]

You can take a long socket extension/other stick like object and shove it down the spark plug hole. when it stops coming out as you rotate it its TDC

[mike911996]

did you try this?....if so when you found TDC how were your notches situated?

[DDD]

You want to use the three notches on the crank pulley. Just make sure distributor is pointing generally at #1 (not necessarily lined up with a specific notch) when you are on Z1 notch, and NOT at the opposite (#4 I think). If it is, you need to turn crank 360 degrees to be at #1. Then just do 120 degrees at a time. You want your CRANKSHAFT dictating what is going on here, not your distributor. Distributor is simply a general checkpoint to make sure you are on the right cylinder.

[mike911996]

i hear what you're saying DDD...thank you....when i get a better tester i will go off the crank.....

what is the deal with the intake valve opening 4 degrees before TDC?

[j911brick]

Originally Posted by mike911996

i hear what you're saying DDD...thank you....when i get a better tester i will go off the crank.....

what is the deal with the intake valve opening 4 degrees before TDC?

Its kinda complicated but the IV starts to open before TDC to give the intake charge a head start on the induction process; then it closes after BDC to suck in the most volume. The trick is to get the valve closed before the pressure from the rising piston gets back the the intake valve. The exhaust valve is actually still closing as the intake opens so the intake and exhaust are actually open at the same time. This is known as overlap. This isn't true of all motors, and the relationship of the valves opening and closing is what gives the motor its power characteristics. If you look at older Porsche tech spec books you can see the different specs for the cams and all the different relationships. A higher performance cam will usually have more overlap and low speed/performance have less, sometimes no overlap.

[euro911sc]

Originally Posted by mike911996

did you try this?....if so when you found TDC how were your notches situated?

Don't remember and probably didnt look past checking the dist. so I knew I was on a firing stroke. If you have a dial indicator and long rod for it then you can get TDC exactly, regardless of pulley marks. For leak down its not that critical. The idea here is to get both valves closed at the same time, not the piston at perfect TDC. So if you are off a few degrees no big deal.

Compression calculations and deck height are a different story

-Michael

[euro911sc]

FYI: You want to be sure to test leak down on the compression stroke. Its kinda useless on any other stroke as one or both valves may be open at the same time so you will have a really big leak... :P so your worry on IV opening before TDC is on the wrong stroke

[CCM911]

I put this reply on the RTR forum as well. Flame suit on for the screwdriver reference.

The way I do it is to first make sure that the rotor is aimed at the cylinder I want to work with. That tells me that we are at the ignition point for the cylinder. Then I put a screwdriver in the plug hole and move the pulley until I find the highest point. Most folks will tell you that you can only move in one direction, as reversing may foul the timing chains, but if you are only moving in small increments, it should not be a problem. But then again, maybe I am just lucky.

Now you may wonder why the piston is not already at the top when you align the hash mark. Have you ever seen the term BTDC? Before Top Dead Center. That is the degree measurement telling you when the ignition will fire. If it was Zero, then you would be at top dead center when the rotor points to the cylinder, and the hash mark(notch) on the pulley aligns.

Hope this helps.