tennjed

folks

Just got leakdown and compression check results for a ppi. Results are as follows:

Compression- all cylinders except cylinder two were either 150 or 155. Cylinder 2 was 145.

Leakdown- all cylinders except one were at 10% or 15%. Cylinder one was at 25%.

This is a 1983 SC with 136,000 miles on the clock.

How do these results sound?

Thanks for any comments.

Wayne

Peter Zimmermann

Your numbers sound like the leakdown test wasn't done correctly, or the car has been in storage with little or no recent use. As my PPI guide states, a compression check can be flawed by its nature, so I won't comment on those numbers. My advice, drive the car once until it reaches full operating temperature, park it and let it cool down. Perform the leakdown test again, I'm pretty sure that you'll be pleasantly surprised.
Pete

tennjed

Thanks for the tip Peter. I have done compression tests on several BMW motorcycles. In those instances it was pretty much go or no go. I would make sure the engine was cold, open the throttle, and crank the engine. I am not familiar with how it should be done on a 911 engine. If the test is done properly, what sort of compression figures should one get?

Is there anywhere on the web where accurate, detailed info on leakdown tests for 911 engines can be found. I ask because it would seem, judging from your helpful comments, that there is a possibility that the individual performing the ppi may not be fully aware of how a compression or leakdown test is to be accomplished. Problem is, I would not know how to determine if he does or does not.

Thanks again

Wayne

Peter Zimmermann

Wayne:
1. Compression test. Due to the configuration of a 911 cylinder head (the exhaust valve is at the bottom) compression test results are often flawed. A compression test requires removal of all 6 plugs prior to doing the test, so the engine can crank evenly. During plug removal crud breaks off the ends of the plugs, falls down and lands on the valve seats of exhaust valves that are open (because of valve timing some valves will always be open, while others are closed). When the test is performed exhaust valves can close against dirty valve seats, the carbon can be just enough to skew the result.
2. Leakdown test. To insure that you don't get flawed leakdown numbers, for the same reason compression numbers can be wrong, the engine must be cranked by hand until it's on TDC cylinder #1, only then can cyl #1 plug be removed. Of course, on TDC both valves of that cylinder are closed, which keeps the exhaust valve seat nice and tidy. After testing #1, the engine must be turned clockwise to cyl #6 (firing order = 1,6,2,4,3,5), BEFORE removing #6 plug. When the engine is on #6 the plug can be removed and the cylinder tested. Proceed through the firing order until you're done. Never shortcut the process and you will always have accurate numbers.
The reason that I suggested driving the car until it's at full temp, then, after cool down, doing a retest, is that the drive will "clean" any dirty valve seats that may have skewed your numbers. A proper engine will have leakdown numbers in the 3-6% range; over 10% is usually considered unacceptable. Good luck with it!
Pete

tennjed

Pete

Thanks for the additional info. It will be a big help when I go in tomorrow to discuss the entire ppi with the mechanic. I want this car but have quite a bit of aprehension about waltzing into a nightmare.

Thanks again

Wayne

Slotcar

Who's performing the PPI....? Is this a local car? Make sure the PO provides you with as many records as possible. Has there been any engine work...ie; chain-tensioner upgrade, valve work etc.... I looked at a few S's and SC's before I found my Carerra. Like anything, it all depends on how they were taken care of...especially the preventitive maintenance (inluding proper major services for valve adjustement/guides, tranny etc... ). Best of luck to you...I've had a great time learning as I go...

tennjed

Actually the ppi is being performed buy a mechanic who works for the dealer. Before you laugh, it has turned out that he has been pretty straight forward and honest. Today, during my first lenghty discussion with him, he pointed out that the transmission is excessively noisy and will need a rebuild in the not to distant future. I, in my ignorance, did not catch this during my test drive. He may not be the best Porsche mechanic in the area but I am pretty comfortable that he is competent and honest. Now all I have to do decide if I want the car. It does run well and the tensioner upgrades have been completed. No problems noted related to the engine. Suspension and brakes in good shape. Targa top alignment pins are all loose and will need to be repaired at some time in the future. Body is in near excellent condition with original red paint in very good shape and no signs of past damage. No tool kit. No jack.

The only major consideration is the transmission. It does rumble in 3rd and 4th under hard load. When oil was drained from the transmission there were no significant metal particles on the drain plug. However, there was a small amount of silver deposit of a pastelike consistency.

Price is $12,800. I like the car. From searching the web it appears to me that the transmission is not so expensive an item to rebuild as the transmission.

Thanks for the past help.

Wayne

Slotcar

Is the mechanic a Porsche mechanic? If not, I would take his info...and then get a second opinion. In addition (even though you say he is honest)....I would never let the dealer (who's trying to sell the car)...perform the PPI...there's a potential conflict of interest (even if they are honest). Unfortunately, many of the potential issues will only be found by someone who knows exactly what to look for...Nothing against the guy you've been working with, but I'd take it to someone like Ken Farler (Farler Performance) or Mark Grimey at Beechmont Porsche (P-car master mechanic...25 yrs of experience).
On the topic of the transmission... Unfortunateluy, there's a lot of companies that advertise "cheap" rebuilds on P-car engines and transmissions...at the end of the day....there is no cheap rebuild (and you always get what you paid for). American cars have affordable transmissions...T-5's/Tremec are $1500 (new)....a rebuilt 915 (unless you can do it yourself and have the special tools/jigs required)...are heck of lot more. I'm not trying to rain on your parade....just want you to know what could be in store. Most of P-car books recommend having at least $2,500 set aside for immediate fixes after you purchase the car...this amount doesn't cover major items like a transmission. This SC might be an excellent car...so I'm not trying to discourage you. However, there will be many other cars that hit the market as Spring draws closer...Have you checked the local PCA website for any cars...? Rennlist classifieds...Pelican's classifieds etc... Here's the local PCA site... http://www.pca.org/ovr/mart_main.html

Lot's of places to look and research...have fun.

Peter Zimmermann

Wayne: Noisy 915 transmissions are really rare. Be careful with that one, it might have mismatched gear sets from a previous hack-level repair. Rather than "rebuild" that one a rebuilt exchange might be the better option. Slot is right about a second opinion, the newest 915 gearbox is about 20 years old, so another experienced opinion is well advised.
Pete

tennjed

Thanks again

I have decided to hold off for now.

Pete, I could not find your book at the bookstore today. I will order it I guess. I did by Gold Plated Porshe by Wilkinson. It looks like an entertaining and informative read.

Thanks again for the great advise. I have budget of $12,500 for initial purchase price. I fully expect to have some issues to resolve no matter what car I wind up with. I would like to get one with sound motor and transmission.

I will check the PCA sites as you suggest.

Wayne

Slotcar

Keep us posted...best of luck in your search.

Peter Zimmermann

Wayne: Call my publisher, RPM Auto Books, in Stillwater, MN. I'm sure that they can get one out to you next day. Their number is (888) 237-4359. I'm pretty sure the 8th edition is back in stock at Amazon, com (the book has only been available about a month). Seriously, don't give up on the car that you've found, if everything else checks out you can always attempt to negotiate with the seller regarding the trans. Thank you for looking for the book!
Pete