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Compression tester


Greenie

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Hello,

I'm thinking of buying a compression tester but wouldn't use it very often, are the cheapy ones any good for a skinflint infrequent user?

Something like this...

http://www.ebay.co.uk/itm/PETROL-ENGINE-AUTOMOTIVE-COMPRESSION-TESTER-TOOL-KIT-/400303386303?pt=UK_Diagnostic_Tools_Equipment&hash=item5d33f0eebf

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That should be fine; in fact, I have one very similar to it, and it seems to work very well. Understand that you don't really need anything with accuracy down to 6-7 decimal points. Relative readings are fine, so if the gauge is actually off by several psi, it doesn't matter, as you're really comparing amongst all cylinders. In other words, that gauge might show readings of 130-125-128-130, while someone else's might show 135-130-133-135. No problem, unless you're dead-set on knowing the absolute correct number.  ;)

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I use the Gunson Tester, available from Machine Mart etc.

However, the thing to remember is to basically ignore the actual readings, OK it may well read in the ballpark area but these devices are not accurate!! For accuracy you pay a LOT more, and have to faff around calibrating the darn thing everytime you use it.

What these testers are good for (and this is what most of us use them for) is showing variations between cylinders, and also showing dramatic loss of pressure in any/all cylinders.

So when you look at it like that, basically all your tester needs is to have an easy to read dial, the correct fittings for your engine and be able to cope with the expected pressures (in particular hose fittings etc, the last you want is a cheap tool where the hose pings off in your face as you try to read guage!! 150-200 PSI will hurt!!)

Cheers,

Phil

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Simon,

Like the others say, that one should be good for what the average d.i.y'er needs.

I have one similar that I had from a tenneager, and it's fine, I also have a top notch one, from an old company I worked for that folded.
I once tested an engine with both gauges, and there was not a lot between them.

Also, when you have her read the gauge for your safety, tell her it's because you can't read it and turn the motor over at same time!  ;D

Good luck
Shaun

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1936 wrote:
Hello,

I'm thinking of buying a compression tester but wouldn't use it very often, are the cheapy ones any good for a skinflint infrequent user?

Something like this...

http://www.ebay.co.uk/itm/PETROL-ENGINE-AUTOMOTIVE-COMPRESSION-TESTER-TOOL-KIT-/400303386303?pt=UK_Diagnostic_Tools_Equipment&hash=item5d33f0eebf



I have the same one as that. Works a treat. I also found it fairly accurate when testing a motorbike with a known compression.

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Thanks Dannyb and everyone, I've just ordered one - saw the same one even cheaper at £9.49, and I need to save all my pennies for Beaulieu this weekend

Shaun, I don't know if I'll get away with spinning her that line - I was all brave until the reality sank in of what would happen to me if she got a high pressure hose on the nose.

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its not just the figures you need to look at, but how the figures are got

look at how far it jumps up in first strokes,
a lang way, is good, then slightly less on other pumps,till its gone no further, generaly about 6-8 pumps
but ,if its only very slow build up,and not much on first pump, then some thing amis.

also try a running test, it shows just how well your engine is working at tick over.
will be alot less than cranking test, by about  60-100 depending on cam.

M

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Wide open throttle, turn over on the starter. Turn over a few times and write down each compression. If something odd, add a teaspoon or 2 of oil to each cylinder in turn, and measure again. That will give a basic diagnostic of piston or valve leaks.

Best to take all the plugs out first! (and label the plug leads)

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cliftyhanger wrote:
Wide open throttle, turn over on the starter. Turn over a few times and write down each compression. If something odd, add a teaspoon or 2 of oil to each cylinder in turn, and measure again. That will give a basic diagnostic of piston or valve leaks.

Best to take all the plugs out first! (and label the plug leads)


Clive is correct, but just to add to it, disconect the H.T. Lead from the coil also.
And I would turn over the engine, until the needle stops increasing on the gauge, (may be more than a few times) make sure your battery is charged!  :)
Some testers have a pressure release button on them, don't forget to release pressure before testing the next cylinder.
Then write down your results comparing figures to manufacturers specs, and to the other cylinders.

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Hi,
One thing I do to make a more complete check of the readings is to repeat the first cylinder test after testing all other cylinders. This gives a second reading to show how much, if any, has been lost from the battery during the test. Occasionally it will show enough loss that when added to the last cylinder it is within a safe range of the highest cylinder where without this allowance it would indicate the need for more serious engine work.
                                                                           Cheers,
                                                                           Paul

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1317 wrote:
Hi,
One thing I do to make a more complete check of the readings is to repeat the first cylinder test after testing all other cylinders. This gives a second reading to show how much, if any, has been lost from the battery during the test. Occasionally it will show enough loss that when added to the last cylinder it is within a safe range of the highest cylinder where without this allowance it would indicate the need for more serious engine work.
                                                                           Cheers,
                                                                           Paul


Crikey, I shall keep this tip in mind from now on!! A dull battery could make quite a difference when you think about it.

Cheers for that Paul :)

Phil

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