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Compression Test...Can someone tell me what's next...

I did a compression test on my 914 2.0 D-Jet. I received the following readings:

Cylinder #1: 145
Cylinder #2: 145
Cylinder #3: 100
Cylinder #4: 160

I did the test with all spark plugs pulled, coil wire pulled and at full throttle. I would appreciate any advice on what to do next. I know #3 is pretty low. Should I start getting ready for a rebuild and what should I rebuild? Again any advice is greatly appreciated.

Thanks,
Rod

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1974 914 2.0 D-Jet

Last edited by 415pb; 09-06-2003 at 03:47 PM..
Old 09-04-2003, 07:33 PM
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The Haynes manual says that the maximum permissible difference between cylinders is 21 lb/in^2 so you do seem to have a problem. A leak-down test will give you a much better idea of what the problem is. You can find more info here .
Old 09-04-2003, 07:53 PM
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Try adjusting the valves and re test first. Sounds like a tight valve to me.

Geoff
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Old 09-04-2003, 08:31 PM
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You can diagnose valves vs rings by re doing the test "wet". To do a wet test you add a few drops of oil and retest.

if they come up much it is rings, if not valves.
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Old 09-05-2003, 04:23 AM
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I adjusted all the valves to spec before the test. If I did have a tight valve, would it be cylinder 3 or 4? I will also try to re-test with oil. Thanks again for the help...
Old 09-05-2003, 05:05 AM
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It would be #3 since that's the low cylinder.
Try the wet test to eliminate the possiblity of a cracked ring or scoring of the cylinder wall. My guess is a valve that is burnt from being too tight.
Geoff
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Old 09-05-2003, 07:34 AM
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Geoff, what am I looking for when I do the wet test. When I put a teaspoon of oil through the spark plug hole, what do I do next...Sorry but I am new to this. Again thanks...

Rod
Old 09-05-2003, 09:10 AM
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You should make sure the engine has warmed up fully if possible before you do the compression test too. Do a "before adding oil" compression test and be sure to count the jumps the gauge takes to top out. Then add the shot of oil and test each cylinder again. If the low one has jumped up then it is probably the rings that are worn and the oil has sealed them some. I agree with the previious post about making sure the valve adjustment is right on spec before you do the testing and insure the batt is fully charged. Good luck
Old 09-05-2003, 09:18 AM
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Okay, just did the test wet. After doing a dry test, cylinder #3 was still at 100. I then squirted some oil into the cylinder and at first it jumped up to 105. I then tried the test again and squirted some oil into #3 again and it jumped up to 125 and held there. Is this bad? Is it time to rebuild? Thanks for the help guys, I really appreciate it.


Rod
Old 09-05-2003, 04:34 PM
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I'd say that is a ring problem.

It is harder to do a wet test on a flat type of engine, it probably took the second shot and a few spins to distribute the oil fairly evenly. It's still a bit low thhough.

If it runs well otherwise, you could probably just replace the P/C's and inspect / grind the valves. You might even get away with just rings / gaskets.

I have this bad habit of letting stuff snowball though, so I'd go through the whole thing.
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Old 09-05-2003, 05:26 PM
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What does the plug look like? If its all oily and black then maybe I would say the rings are bad in that cylinder. Maybe the cylinder walls are scored?

Hmmm, worth taking a look at before something really bad happens.
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Old 09-05-2003, 06:32 PM
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I changed the plugs about three months ago and they look fine.............I know the pics are probably overkill, but I'm trying to explain this stuff as best I can. Thanks for all your help..



Thanks again
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Old 09-05-2003, 06:53 PM
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re-ring. check end play on teh crank to determine condition of bottom end.
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Old 09-05-2003, 07:41 PM
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Leakdown test anyone?
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Old 09-06-2003, 03:44 AM
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Next thing, junk the platinums! Use the regular plugs or copper cores instead of those things.
I'd go the leakdown test next.

Geoff
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Old 09-06-2003, 05:57 AM
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Sounds like I'll be doing the leak down test next. Can you guys let me know how. I've heard you can put together your own, is this true? Thanks again............

Oh, I forgot, I'll trash the platinums...Your like the third person to tell me that, so out they go.....
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Last edited by 415pb; 09-06-2003 at 06:41 AM..
Old 09-06-2003, 06:19 AM
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I'll be the 4th............get rid of the platinum plugs,they don't work well in our engines............get the Super Bosch they work better!
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Old 09-06-2003, 07:17 AM
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Set that piston at TDC, put it in 5th gear with the parking brake on and wheels chocked.
Pull the valve cover off of that side.
Hook up a pressurized air source through the spark plug hole and put air pressure on that cylinder.
Listen for the air leak. If it is going out the exhaust pipe you have a bad exhaust valve. If it leaks out the intake, bad intake valve. if it blows out from the crankcase breather, bad rings. If it blows out the head where the valve cover normally is, it's leaking valve guides.
A little leakage into the crankcase is normal, but a lot is not normal.
Old 09-06-2003, 08:14 AM
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DIY Leak Down tester

I bought one from these guys:

https://www.carshopinc.com/

But the site seems to be down right this second.

$53

James
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Old 09-06-2003, 08:16 AM
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You guys are great, thanks for the help and I'll give it a try...

Rod
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Old 09-06-2003, 10:25 AM
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