924Board.org

scottc · Posted: Thu Apr 05, 2007 6:09 am Post subject: No compression

So I bought a non running 924 on Ebay

Having spent a number of days trying to get it to run, I finally bought a compression tester and .....

1. 70
2. 68
3. 71
4. 85 PSI

after some oil down the plug holes

1. 90
2. 72
3. 71
4. 90 PSI

so I'm guessing that Cylinder 1 has broken rings. and 2/3 are blowing through the gasket.
Though even number 4 seems very low. So do I strip it down, or just forget it and buy another engine, thats 300 miles away and £40 ($80) ?

Scott.

Smoothie · Posted: Thu Apr 05, 2007 6:17 am Post subject:

Check your valve timing (timing belt installation) before disassembling it.
-And remember to hold the throttle open while compression testing.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

scottc · Posted: Thu Apr 05, 2007 6:37 am Post subject:

Thanks smoothie, I did have the throttle open.

I've checked the valve timing about 3 times lol. and its spot on. I used the mark on the flywheel and the one on the back of the camshaft pulley.

Ozzie · Posted: Thu Apr 05, 2007 7:06 am Post subject:

buy the other lump, quicker to replace and then you have a spare to rebuild at your leisure.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

scottc · Posted: Thu Apr 05, 2007 7:13 am Post subject:

Cheers Ozzie. Notice you're car of the day! It's looking good.

Ozzie · Posted: Thu Apr 05, 2007 11:58 am Post subject:

Ta mate, got a midnight blue metallic respray coming soon.
Should be the bees knees after.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

20v924 · Joined: 24 Jan 2007 Posts: 205 Location: Phoenix,AZ

Do a leakdown first! you may just have crap between the valve seats and the valves. With the cam cover off, you can fill the cylinder with pressure and tap on the top of the valve lifter with a rubber mallet and a brass drift punch. The pop that you will hear should be loud and crisp. This should clear the seats off. Pop away!! You will need a headgasket for sure though.
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A person is smart. People are stupid

scottc · Posted: Fri Apr 06, 2007 5:42 pm Post subject:

thanks 20v924, how do I do a leakdown test, I've got an aircompressor, but no way of connecting it to the cylinder, I could probably bodge something with a tyre inflator and the Compression tester.

Might be disasterous though. And where should the piston be when I fill the cylinder or doesn't it matter?

Thanks.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Take a look at this article on how to build your own Leak Down Tester:
http://www.xs11.com/tips/misc/misc3.shtml

I'm going out today to pick up the parts so I can build my own. If successful, I'll post pics and a how-to.
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erstwhile owner of just about every 924 variant ever made

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Is it really that much cheaper than just buying a real one to begin with?

http://www.amazon.com/Astro-Pneumatic-7751-Engine-Cylinder/dp/B000GBNDT8
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Don't know...that's what I intend to find out...besides, if I build it today, I can use it today, instead of having to wait a week for it to get here...
_________________
erstwhile owner of just about every 924 variant ever made

scottc · Posted: Sat Apr 07, 2007 5:28 am Post subject:

I pulled the head today, and noticed a little wear on the 2nd cylinders bore, weird shape, kind of round ish.

However, the camshaft doesn't turn smoothly. At points its easy to turn, then it sort of jumps forward, obviously opening and closing valves as it does.

So....I assume the cam should turn smoothly, should each valve spring, kindof cancel out the other and make it smooth? As you can guess, I don't have much experience of this. Last time I participated in a head removal job was 14 years ago. LOL.

Scott.

20v924 · Joined: 24 Jan 2007 Posts: 205 Location: Phoenix,AZ

The cam should not spin in the head smoothly. That would indicate weak or dead springs. The lobes forcing down on the strong valve springs is why it feels this way. No problem there. Look closely at each lobe of the cam for excessive wear.
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A person is smart. People are stupid

scottc · Posted: Sat Apr 07, 2007 7:07 am Post subject:

Theres no noticable wear on the cam, but it does kindof jump forward from it current location. if that makes sense.
As you turn the camshaft it will jump clockwise an 1/8th or so of a turn. jut doen't seem right.

scottc · Posted: Sat Apr 07, 2007 7:09 am Post subject:

when I say smooth I really mean consistent, rather than hard to turn at some points and easy at others.