Alfa Pages

BigAl · P4 Joined: 06 May 2003 Posts: 2995 Location: U.K Surrey

hey guys, i am about to do a compresson test later today, i have never done one before and have looked at some old threads
http://www.alfa-pages.co.uk/viewtopic.php?t=2603&highlight=compression
http://www.alfa-pages.co.uk/viewtopic.php?t=2558&highlight=compression
http://www.alfa-pages.co.uk/viewtopic.php?t=2470&highlight=compression
http://www.alfa-pages.co.uk/viewtopic.php?t=2130&highlight=compression
I have been advised to do when at running temp, something im not looking forward to, as the 16v spark plugs are hard to get to and i will end up burning my hand.
I have the correct alfa spark plug tool, i bought off paul.h
What should i expect; 165 psi, 150psi, 140 psi, (>8bar)??
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

lee16v · Posted: Mon Sep 07, 2009 10:49 am Post subject:

Pretty sure when I did mine I was told to expect a reading of around 160-165 psi. I can see the logic in doing it at running temp but unless you have asbestos hands it's out of the question really. Have you ever tried working with oven gloves on? Laughing

john 33_16v · Posted: Mon Sep 07, 2009 12:03 pm Post subject:

Al,

I wouldn't worry about the temp too much.

I've only done this with the lump out and it was cold.

Is your gague screw in? You can get press on ones which I think will be impossible to do, and never seal properly.

Good luck.

John
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If it aint broke, fiddle with it until it is!
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93 33 16v Mirtle Met
08 Fiat Grande Punto Exotica Red
90 Yamaha FZR600 Genesis- Silky white/red/blue

BigAl · P4 Joined: 06 May 2003 Posts: 2995 Location: U.K Surrey

Thanks guys,
I have just walked 5 miles round trip to borrow the gauge and can now tell you it’s a snap-on screw in type, I’m all hot and sweaty before I’ve even started. Hope I can get it in there.
I was advised to take out all spark plugs, jam open the throttle, so butterflies are wide open and the engine can breathe easier, remove the CAS sensor and disconnect the power leads to the coil. I think I will remove the ecu and fuel pump and injector relay as well. Let’s hope my battery doesn’t go flat.
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

john 33_16v · Posted: Mon Sep 07, 2009 1:46 pm Post subject:

Hi Al,

I'd just remove the coil LT wires so it can't fire on any plugs in.

I'd also probably do one plug at a time leaving the others in- but maybe that's just me. It doesn't take much cranking to get the compression up to max on the gauge.

John
_________________
If it aint broke, fiddle with it until it is!
- - - - - - - - - - - - - -
93 33 16v Mirtle Met
08 Fiat Grande Punto Exotica Red
90 Yamaha FZR600 Genesis- Silky white/red/blue

BigAl · P4 Joined: 06 May 2003 Posts: 2995 Location: U.K Surrey

Hey John,
I was in the middle of the job and only read your post afterwards.
I ended up just removing the ECU and wiring up a push to start button between the + on the battery and the exciter wire on the starter wire. I was flying solo today and didn’t have anyone to turn the key, so I didn’t even have to turn on the ignition Laughing

.
I removed all the spark plugs, leaving the favourite one until last and removed the chassis brace for easy "whatever" access. I had the plenum chamber off and whilst cranking I held open the butterflies.
I had the plenum off as I had to plumb in a T piece to do a fuel test.

I triple tested, as I was getting erroneous figures, due to me not screwing the tester in home fully and again left the favourite cylinder until last, I got the following.

I think I have the cylinders labelled correctly, 1 front right, 3 rear right, 2 front left and 4 rear left

No1
168

No 3
200

No 2
165

No 4
210

WTF is going on here??
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

Oggie · Posted: Mon Sep 07, 2009 8:17 pm Post subject:

It looks like a lottery draw al, sorry couldn't resist Rolling Eyes

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PHAT 33

john 33_16v · Posted: Mon Sep 07, 2009 9:04 pm Post subject:

Hi Al,

Well at least the compression looks respectable on all cylinders. No idea why you would get higher figs on the rear cylinders.

Compression loss can only realy be rings/bores, valve/seat problems, or plug thread damage. Compression gain- not sure really, build up of carbon effectively reducing capacity??

What's the official recommended fig? Can't really remember as mine was almost 8 years ago- Lee's fig sounds ok.

Why are you testing compression anyway? Down on power or still having emissions problem?

John
_________________
If it aint broke, fiddle with it until it is!
- - - - - - - - - - - - - -
93 33 16v Mirtle Met
08 Fiat Grande Punto Exotica Red
90 Yamaha FZR600 Genesis- Silky white/red/blue

BigAl · P4 Joined: 06 May 2003 Posts: 2995 Location: U.K Surrey

Hey john,
Power is ok, fuel economy is ok, emissions are still a little high, 2 qualified mot testers, who are mechanics have both ruled out the cat and say the car is slightly over fuelling. They said not to bother replacing the cat when I suggested fitting one. I was told to check fuel pressure, I’ll do that on Wednesday, correctly this time and to test the compression.

When i was doing the compression test, i was expecting to find the N/S to be different to the O/S, as the N/S belt snapped and bent 2 valves. I had all the valves reground whilst the head was off and replaced the 2 bent ones with second hand ones, as I didn’t want to upset the balance of the engine too much. To have both sides doing the same front compared to rear is confusing.

Iain, lol
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

JeremyC · Posted: Mon Sep 07, 2009 11:13 pm Post subject:

Doing dry then wet tests (squirting some oil in the bores) can help establish whether it's a bore wear problem.

Harder on a flat four than a conventional engine though.
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'93 Black 33 1.7 16v

BigAl · P4 Joined: 06 May 2003 Posts: 2995 Location: U.K Surrey

Hey J.C
I walked another 5 mile round trip and returned the compression tester, so cant do it again.
What i dont get is that the rear 2 cylinders are higher than the front 2 which are at expected levels, i think.
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

JeremyC · Posted: Tue Sep 08, 2009 10:11 am Post subject:

Most people I've spoken to say the absolute values are not really that important and are very depdendant on the tester you use and the number of times you crank. More important are the relative values so it could be that the front are low and the rears are normal.

Neither sound disasterously low and at least the sides are consistent.

My guess for the front rear discrepancy would bore wear due to slightly less efficient lubrication.

How many miles has the engine done?
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'93 Black 33 1.7 16v

BigAl · P4 Joined: 06 May 2003 Posts: 2995 Location: U.K Surrey

I don’t know what the expected figures are but the consensus is around the 160 mark, given that, the rears are higher than should be and the fronts are normal. I cranked until the needle stopped moving.
Engine has done about 65k, I’ve owned the car for 3 years and look after it very well.
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203