Techniques - Compression testing - Revision history

HarryMann at 22:00, 8 October 2008

2008-10-08T22:00:22Z

← Older revision		Revision as of 22:00, 8 October 2008
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	~~Compression testing is one of the easiest and most revealing tests that can be done on an engine.~~

	==When, why?==		==What, When and why?==

			Compression testing is one of the easiest and most revealing tests that can be done on an engine.

	It can be used to discover whether there is piston-ring/bore wear/damage; either exhaust or inlet valve leakage; and possibly a leaky head gasket or warped/cracked cylinder head (in combination with other tests).		It can be used to discover whether there is piston-ring/bore wear/damage; either exhaust or inlet valve leakage; and possibly a leaky head gasket or warped/cracked cylinder head (in combination with other tests).

HarryMann: /* Diesel engine compression testing */

2008-10-08T15:04:52Z

Diesel engine compression testing

← Older revision		Revision as of 15:04, 8 October 2008
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	==Diesel engine compression testing ==		==Diesel engine compression testing ==
	This requires a different gauge, that cost quite a bit more than petrol ones. These usually screw into the fuel-injector hole and go to a lot higher pressures, circa ~~450~~~550 psi.		This requires a different gauge, that cost quite a bit more than petrol ones. These usually screw into the fuel-injector hole and go to a lot higher pressures, circa 400~550 psi.

	Method is basically the same, but due to the cost its usual to ask a garage to do these tests		Method is basically the same, but due to the cost its usual to ask a garage to do these tests

			Engine oil temp > 30°C; disconnect fuel solenoid & return bleed hoses; remove injectors; replace olf heat shield in inhector hole (to checkit); screw adapter of tester into injector hole; neutral gear;

			Do tests; re-check any that are low with new heat-shield

			Re-install injectors with all new heat-shields.

	==Forum extract - walk thru==		==Forum extract - walk thru==

HarryMann: /* Analysing Results */

2008-10-08T15:00:27Z

Analysing Results

← Older revision		Revision as of 15:00, 8 October 2008
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	\| '''Engine''' \|\| '''Min''' \|\| '''Typical''' \|\| '''Max diff'''		\| '''Engine''' \|\| '''Min''' \|\| '''Typical''' \|\| '''Max diff'''
	\|-		\|-
	\|WBX 1.9\|\|8 (116)\|\|10 (147)~ 13 (189)\|\| 2 (29)*		\|WBX 1.9\|\|8 (116)\|\|10 (147)~ 13 (189)\|\| 2.5 (37)*
	\|-		\|-
	\|WBX 2.1\|\|8 (116)\|\|10 (147)~ 13 (189)\|\| 2 (29)*		\|WBX 2.1\|\|8 (116)\|\|10 (147)~ 13 (189)\|\| 2.5 (37)*
	\|-		\|-
	\|Air Cooled 2.0\|\|5 (73)\|\|6 (87) ~ 9 (131)\|\|3 (44)		\|Air Cooled 2.0\|\|5 (73)\|\|6 (87) ~ 9 (131)\|\|3 (44)
	\|-		\|-
	\|Diesel 1.6 NA\|\|11\|\|28 (406) ~ 34 (493)\|\|5 (73)		\|Diesel 1.6 NA\|\|11\|\|28 (406) ~ 34 (493)\|\|5 (73)
			\|}

	\|}		<nowiki>*</nowiki> Not quoted, so estimated

	~~<nowiki>*[/nowiki> Not quoted~~

	==Interpreting poor compressions==		==Interpreting poor compressions==

HarryMann: /* Analysing Results */

2008-10-08T14:58:40Z

Analysing Results

← Older revision		Revision as of 14:58, 8 October 2008
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	\| '''Engine''' \|\| '''Min''' \|\| '''Typical''' \|\| '''Max diff'''		\| '''Engine''' \|\| '''Min''' \|\| '''Typical''' \|\| '''Max diff'''
	\|-		\|-
	\|WBX 1.9\|\|8 (116)\|\|10 (147)~ 13 (189)\|\|		\|WBX 1.9\|\|8 (116)\|\|10 (147)~ 13 (189)\|\| 2 (29)*
	\|-		\|-
	\|WBX 2.1\|\|8 (116)\|\|10 (147)~ 13 (189)\|\|		\|WBX 2.1\|\|8 (116)\|\|10 (147)~ 13 (189)\|\| 2 (29)*
	\|-		\|-
	\|Air Cooled 2.0\|\|5 (73)\|\|6 (87) ~ 9 (131)\|\|3 (44)		\|Air Cooled 2.0\|\|5 (73)\|\|6 (87) ~ 9 (131)\|\|3 (44)
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	\|}		\|}

			<nowiki>*[/nowiki> Not quoted

	==Interpreting poor compressions==		==Interpreting poor compressions==

HarryMann: /* Analysing Results */

2008-10-08T14:56:33Z

Analysing Results

← Older revision		Revision as of 14:56, 8 October 2008
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	On an in-line 4-cyl engine, often No.3 (3rd from the front, pulley) runs hotetst and is often the first to succumb to cylinder or burnt-valve trouble. With Subaru boxers, the front left overheats easiest.		On an in-line 4-cyl engine, often No.3 (3rd from the front, pulley) runs hotetst and is often the first to succumb to cylinder or burnt-valve trouble. With Subaru boxers, the front left overheats easiest.


			On VW WBX flat-fours, No. 1 is said to run hottest and thus usually have lowest compressions.

			Compression pressures: throttle fully open; all plugs removed (earth central HT lead); oil temp > 30°C;


			{\| border="1" cellpadding="2"
			\|+'''Compression pressures - Bar (psi)'''

			\| '''Engine''' \|\| '''Min''' \|\| '''Typical''' \|\| '''Max diff'''
			\|-
			\|WBX 1.9\|\|8 (116)\|\|10 (147)~ 13 (189)\|\|
			\|-
			\|WBX 2.1\|\|8 (116)\|\|10 (147)~ 13 (189)\|\|
			\|-
			\|Air Cooled 2.0\|\|5 (73)\|\|6 (87) ~ 9 (131)\|\|3 (44)
			\|-
			\|Diesel 1.6 NA\|\|11\|\|28 (406) ~ 34 (493)\|\|5 (73)

			\|}

	==Interpreting poor compressions==		==Interpreting poor compressions==

HarryMann: /* Forum extract - walk thru */

2008-10-08T13:07:32Z

Forum extract - walk thru

← Older revision		Revision as of 13:07, 8 October 2008
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	With a ring problem on right front (121 > 160)		With a ring problem on right front (121 > 160)

	'''Morganman:''' ~~SMokes~~ on overrun, is this valves/guides or bore wear		'''Morganman:''' Smokes on overrun, is this valves/guides or bore wear

			1= 9.9, 10.1 (+2%)

	~~1=9.9, 10.1 (+2%)~~
	2= 10.5, 12.0 (+14%)		2= 10.5, 12.0 (+14%)

	3= 10.2, 11.2 (+10%)		3= 10.2, 11.2 (+10%)

	4= 10.4, 11.9 (+14%)		4= 10.4, 11.9 (+14%)

HarryMann: /* Forum extract - walk thru */

2008-10-08T13:05:48Z

Forum extract - walk thru

← Older revision		Revision as of 13:05, 8 October 2008
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	On mine the instructions were to put a cap (''NB. cap, not cup!'') full of engine oil down the cylinder bore through the spark plug hole and then do the compression test. One cylinder at a time!		On mine the instructions were to put a cap (''NB. cap, not cup!'') full of engine oil down the cylinder bore through the spark plug hole and then do the compression test. One cylinder at a time!

	So, do the dry test first and then the wet test. It's supposed to give an indication of how worn the bores are, depending on the difference between the 2 readings. On my old CU the differences on 3 cylinders were ok, but on the 4th the compression readings wet and dry were both the same, and low, which confirmed what I thought and that is it was down on one cylinder. The readings on my Aircooled CU were ~~138,140,121 and 110 dry, and 152,152,160 and 110 wet, going from left rear to left front, right front and right rear.~~		So, do the dry test first and then the wet test. It's supposed to give an indication of how worn the bores are, depending on the difference between the 2 readings. On my old CU the differences on 3 cylinders were ok, but on the 4th the compression readings wet and dry were both the same, and low, which confirmed what I thought and that is it was down on one cylinder. The readings on my Aircooled CU were:

	'''HarryMann:''' Then that's a burrnt valve problem on right rear, as they didn't change with oil..		138, 140, 121 & 110 dry

			152, 152, 160 & 110 wet,

			+ 10%, 9%, 32% & 0% from dry to wet

			going from left rear to left front, right front and right rear.

			'''HarryMann:''' Then that's probably a burrnt valve problem on right rear, as they didn't change with oil..

	With a ring problem on right front (121 > 160)		With a ring problem on right front (121 > 160)

			'''Morganman:''' SMokes on overrun, is this valves/guides or bore wear

			1=9.9, 10.1 (+2%)
			2= 10.5, 12.0 (+14%)
			3= 10.2, 11.2 (+10%)
			4= 10.4, 11.9 (+14%)

			AV. of 150 psi (10.25 bar), yes more like it

	----		----

HarryMann: /* Forum talk -walk thru */

2008-10-04T23:37:36Z

Forum talk -walk thru

← Older revision		Revision as of 23:37, 4 October 2008
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	==Forum ~~talk~~ -walk thru==		==Forum extract - walk thru==

	'''Aidan:'''		'''Aidan:'''
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	Write them down as you go...		Write them down as you go...

	and make ~~any~~ notes		and make notes

	Then do the oil test if you need to... (low pressure on some or all cylinders)		Then do the oil test if you need to... (low pressure on some or all cylinders)
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	''Always'' remove all plugs before starting so that cranking speed will be consistent and battery not become drained, speed can make a difference to a bad cylinder..		''Always'' remove all plugs before starting so that cranking speed will be consistent and battery not become drained, speed can make a difference to a bad cylinder..

	A good cylinder will also pump up almost immediately (within 2 or 3 compressions)... so ~~as Aidan says,~~ 'watch' the gauge as you crank the engine (use a helper or remote solenoid switch)		A good cylinder will also pump up almost immediately (within 2 or 3 compressions)... so 'watch' the gauge as you crank the engine (use a helper or remote solenoid switch)


	==Leak-down test==		==Leak-down test==

	Then there's the leak-down test... checking rate at which they leak back from compression, comparing them, and listening in exhaust or inlet for valve seat leaks...		Then there's the leak-down test... checking rate at which they leak back from compression, comparing them, and listening in exhaust or inlet for valve seat leaks...

HarryMann: /* Deducing the problem area when an engine shows poor compressions */

2008-10-04T23:35:49Z

Deducing the problem area when an engine shows poor compressions

← Older revision		Revision as of 23:35, 4 October 2008
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	On an in-line 4-cyl engine, often No.3 (3rd from the front, pulley) runs hotetst and is often the first to succumb to cylinder or burnt-valve trouble. With Subaru boxers, the front left overheats easiest.		On an in-line 4-cyl engine, often No.3 (3rd from the front, pulley) runs hotetst and is often the first to succumb to cylinder or burnt-valve trouble. With Subaru boxers, the front left overheats easiest.

	==~~Deducing the problem area when an engine shows~~ poor compressions==		==Interpreting poor compressions==
	~~Later~~

			See forum discussion below

	==Diesel engine compression testing ==		==Diesel engine compression testing ==

HarryMann at 23:13, 4 October 2008

2008-10-04T23:13:56Z

← Older revision		Revision as of 23:13, 4 October 2008
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	and make any notes		and make any notes

	Then do the oil test if you need to... (low pressure on some or all cylinders) ~~Then there's the leak-down test... checking rate at which they leak back from compression, comparing them, and listening in exhaust or inlet for valve seat leaks...~~		Then do the oil test if you need to... (low pressure on some or all cylinders)

	Always remove all plugs before starting so that cranking speed will be consistent and battery not become drained, speed can make a difference to a bad cylinder..		''Always'' remove all plugs before starting so that cranking speed will be consistent and battery not become drained, speed can make a difference to a bad cylinder..

	A good cylinder will also pump up almost immediately (within 2 or 3 compressions)... so as Aidan says, 'watch' the gauge as you crank the engine (use a helper or remote solenoid switch)		A good cylinder will also pump up almost immediately (within 2 or 3 compressions)... so as Aidan says, 'watch' the gauge as you crank the engine (use a helper or remote solenoid switch)


			==Leak-down test==

			Then there's the leak-down test... checking rate at which they leak back from compression, comparing them, and listening in exhaust or inlet for valve seat leaks...