Compression test
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09-13-2008, 10:53 PM
Post: #1
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Compression test
I just fitted a pair of 266 degree 9.5mm lift cams, new head gasket, skimmed head. (4AGE blue top)
After having problems getting the engine started I decided to do a cold (could'nt get it going ) compression test. All were around 150psi. Previously with standard cams it shows aound 175psi (warm) is this right ? I'm guessing there is some overlap but this would'nt be on the compression stroke should it ? My guess is that the cam timing is out, probably why it won't start and the reason for the low pressure readings. Thanks for any help with this. TC An analogue brain in a digital World |
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09-14-2008, 12:28 AM
Post: #2
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Compression test
If you increase the duration, the inlet valves will be closing later.
This will lead to some loss of compression at cranking speed due to some of the intake charge being pushed back out the open valve at the start of the compression stroke (charge reversion ??). Check your ignition timing, and make sure you connected up that multiple earth on the head that is hidden under the injector wiring Cheers... jondee86 |
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09-14-2008, 07:57 AM
Post: #3
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Compression test
sorry mate, but what do you mean "skimmed head"?
**COROLLA EE80 - 4AGE 124HP** |
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09-14-2008, 10:26 AM
Post: #4
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Compression test
Skimmed head = to take a thin cut off the surface of the head, just
enough to make sure it is flat and in perfect condition for the gasket to seal. Cheers... jondee86 |
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09-14-2008, 12:10 PM
Post: #5
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Compression test
but you can do it with a headgasket, i think.
**COROLLA EE80 - 4AGE 124HP** |
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09-14-2008, 08:25 PM
Post: #6
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Compression test
Pretty sure it's a cam timing problem, just set the cams with correct lift at TDC and the standard timing marks were 2.5 teeth out on the exhaust and 2 on the inlet
It will be running tomorrow... I hope ! An analogue brain in a digital World |
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09-15-2008, 10:09 AM
Post: #7
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Compression test
Cam timing is ok, the engine will fire once and that's it (won't start)
Can anyone confirm how to set the distributor ? I have it set with the rotor arm pointing at no 1 plug lead at TDC on the compression stroke. My suspicion is that it is flooding as there is quite a strong smell of petrol. The injectors are not a very tight fit in either the fuel rail or the head. Plenty to go by then... please help An analogue brain in a digital World |
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09-15-2008, 10:48 AM
Post: #8
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Compression test
The "snout" of the distributor will have a groove, dimple or similar
mark on top, when the dist is the right way up for fitting. The driven gear will also have a dimple or similar mark. These two marks should be lined up before you fit the dist to the head. When fitting the dist line it up so that the "ears" are at the mid-point in their adjustment range, and push the dist in without twisting. The rotor will turn a bit as the gears engage. Try fitting a new set of plugs (if you haven't already). Old plugs can be almost impossible to fire once they have been wet down with fuel. Cheers... jondee86 |
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09-16-2008, 02:51 PM
Post: #9
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Compression test
It lives
Thankyou to everyone, I disconnected the cold start device and it started straight away. I fear getting it started was the easy bit Warm compressions are all 180 psi give or take the thickness of the needle on the gauge. Ignition timing next, anyone give me a guide as to what to set it at given the cams installed ? An analogue brain in a digital World |
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