Leak down test on a 911...

[steve meltzer]

I've had such great success with tech issues, I decided to wade in again. This gets filed under "a day late and a dollar short", but here goes...I bought this car impulsively on BaT, but, so far, I don't have buyer's regret. The shop that's looking at the defective alternator offered to do a leak down on the engine (yeah, I know, this should have been done BEFORE I bought the car!). They want $375, which I think is high.

I've done leak down testing before, and have the proper gauges and, of course, a compressor. My question is, is the pulley or flywheel marked off in equal thirds, so that I can easily find TDC for each cylinder and do this myself at home?

Thanx for answering another newbie question. steve

[Rich76_911s]

I don’t know the specifics on each pulley, but my 1987 930 has marks to indicate TDC on each cylinder. I’d assume they all have those markings.

[rwest]

Hi Steve,

My '77 has the pulley marked in thirds- little hard to see, but there.

Just a tip to make getting help easier, put a signature line at the bottom of your post with car info so people can quickly see what year and model you have; makes getting advice specific to your car.

[Reiver]

Yeah, I think that is high compared to what I've had done.

[manbridge 74]

Takes about 2hr, sometimes 3 if problems or more interpretation is needed.

[proporsche]

Hi Steve..i do leak down test listening to my gauge .When you turn the engine it will whistle when you get to the point of measuring It is almost perfect every time i do it.

manbridge..why is it you think taking 2-3 hours to do??I do mine in 1 hour .remove the plugs insert the tool and spin the engine...by hand of course;-)

Ivan

[gomezoneill]

It depends it can be a pita to do depending on the year. Have to remove the a/c compressor, the booster fan (if installed), the smog pump can be a pain, removing the spark plugs etc...Most shops these day's are getting $100 per hour this can easily be a 3 hour job.

[proporsche]

hmm i guess you are right and the price went up these days....but Steve`s 911 is 1974 so easy to do.And 375 for a leak-down test is a little too overboard....

Ivan

[Peter Zimmermann]

$375 for a leak down test...on a '74 911? Are you kidding me? One hour labor - tops! Put the engine on TDC, #1, remove the plug and get after it.

BTW; DO NOT remove the plug for the cylinder you're testing until AFTER the engine has been placed on TDC for that cylinder. I have documented why, in other posts, for this comment. Briefly, it prevents carbon debris, that might be on the tip of a plug, from falling down, landing on the exhaust valve seat, and holding the exhaust valve open (after the engine is turned to that cylinder) a tiny amount. This false reading can cause panic, engine tear downs, and valve jobs, all for no reason!

[proporsche]

Good point Peter about the plugs..

Ivan

[steve meltzer]

I too, thought it was ridiculously high, especially with no AC, etc. to remove. thanx for the help. steve meltzer '74 Carrera (USA) new to me

[steve meltzer]

arggh...i've always pulled all the plugs to make it easier to turn the engine over by hand. steve

[proporsche]

Steve don`t beat your self too much..it most likely your leak down test is fine.
Only after you would see any problems, you would have to take off the valve covers and hit the possibly bad cylinder ,on the rocker arm, with a rubber hammer .To try to take away the possible carbon....but
that is not your case....
Ivan

[steve meltzer]

Thanx for the reassurance, Ivan. one could always do a compression test. probably not as good, but much easier. s

[gomezoneill]

I did not see that it was a 74 anywhere in his post. Easy 1 hr job.

[proporsche]

gome..Steve has opened another post regarding his 1974 911 alternator regulator;-)

Ivan

[proporsche]

Hi Steve..yup;-)

[steve meltzer]

I'll keep you guys busy with a million queries! steve

[Peter Zimmermann]

Originally Posted by proporsche

Only after you would see any problems, you would have to take off the valve covers and hit the possibly bad cylinder ,on the rocker arm, with a rubber hammer .To try to take away the possible carbon
Ivan

Or, if you end up with 30% leakage on a couple of cylinders, do the fun thing. Take the car for a drive, at least a few miles, let it cool down, and re-test the bad cylinders only! Driving is always more fun than removing rocker covers!

[proporsche]

That is correct Peter ,but i would be already pist , to know there is a problem,because if there is a problem i could hear it without the testing;-)so i would not even drive it..but idea is good for peps who would not know what to listen to...;-)

ivan