Hi all,

This question is maybe ignorant. When you use a hi gauge to measure
compression, could it be a false result - compression too high ? There is a
scale on the hi-gauge which indicates a green zone above 10 bar and below 15
bar, readings outside this zone are marked in red.

Can compression be low, but compensated by oil leakage past the piston rings
? When I had compression of another car checked, the mechanic said that if
compression improves when you inject some oil in the cylinder through the
plug hole, it is indicatieve of worn-out piston rings.

Anyone  who can help me understand ? Many thanks in advance !

Cheers,

Peter

peter wrote:
>    Hi all,
>
> This question is maybe ignorant. When you use a hi gauge to measure
> compression, could it be a false result - compression too high ?
> There is a scale on the hi-gauge which indicates a green zone above
> 10 bar and below 15 bar, readings outside this zone are marked in red.
>
> Can compression be low, but compensated by oil leakage past the
> piston rings ? When I had compression of another car checked, the
> mechanic said that if compression improves when you inject some oil
> in the cylinder through the plug hole, it is indicatieve of worn-out
> piston rings.
>
> Anyone  who can help me understand ? Many thanks in advance !
>
> Cheers,
>
> Peter

An engine with low compression will not be showing a falsely high reading 
because of piston rings letting oil past.  (unless we are talking of 
something esoteric like a radial engine)

You would only get a massively high reading if the combustion chamber is 
full of something (eg fluid or coke).  Oil leakage past the rings is 
irrelevant to the reading.  An improvement in reading by putting a SMALL 
amount of oil in the cylinder MAY show that the rings are worn.

A better test is to air pressurise the cylinders with the valves shut and 
find out where the air leaks out, this can show up blown head gasket or 
cracked head/liner, leaking valves, worn bores/rings etc etc.

What are you testing and why?

Mrcheerful

"Mrcheerful"  wrote in message 
news:WWvtk.49145$E41.34945@text.news.virginmedia.com...
> peter wrote:
>>    Hi all,
>>
>> This question is maybe ignorant. When you use a hi gauge to measure
>> compression, could it be a false result - compression too high ?
>> There is a scale on the hi-gauge which indicates a green zone above
>> 10 bar and below 15 bar, readings outside this zone are marked in red.
>>
>> Can compression be low, but compensated by oil leakage past the
>> piston rings ? When I had compression of another car checked, the
>> mechanic said that if compression improves when you inject some oil
>> in the cylinder through the plug hole, it is indicatieve of worn-out
>> piston rings.
>>
>> Anyone  who can help me understand ? Many thanks in advance !
>>
>> Cheers,
>>
>> Peter
>
> An engine with low compression will not be showing a falsely high reading 
> because of piston rings letting oil past.  (unless we are talking of 
> something esoteric like a radial engine)
>
> You would only get a massively high reading if the combustion chamber is 
> full of something (eg fluid or coke).  Oil leakage past the rings is 
> irrelevant to the reading.  An improvement in reading by putting a SMALL 
> amount of oil in the cylinder MAY show that the rings are worn.
>
> A better test is to air pressurise the cylinders with the valves shut and 
> find out where the air leaks out, this can show up blown head gasket or 
> cracked head/liner, leaking valves, worn bores/rings etc etc.
>
> What are you testing and why?
>
> Mrcheerful

His car with the silicon and glycol in the oil samples when he had them 
tested?

:-)

Mike P

"peter"  wrote in message 
news:gKvtk.123359$gM4.38628@newsfe25.ams2...
>    Hi all,
>
> This question is maybe ignorant. When you use a hi gauge to measure
> compression, could it be a false result - compression too high ? There is 
> a
> scale on the hi-gauge which indicates a green zone above 10 bar and below 
> 15
> bar, readings outside this zone are marked in red.
>
> Can compression be low, but compensated by oil leakage past the piston 
> rings
> ? When I had compression of another car checked, the mechanic said that if
> compression improves when you inject some oil in the cylinder through the
> plug hole, it is indicatieve of worn-out piston rings.
>
> Anyone  who can help me understand ? Many thanks in advance !
>
> Cheers,
>
> Peter
>
It'll could possibly show a small improvement with a very small amount of 
oil dribbled into the cylinder if the rings/bores are worn. I can't see how 
it would create a much too high reading unless you've got a hydraulic lock 
(cylinder full of water/oil/crap etc) going on. I had a Saab 900T16 with a 
blown head gasket, occasionally it would fail to turn the engine over 
because one of the cylinders was full of water..

Mike P

On Thu, 28 Aug 2008 12:12:52 +0100, peter  wrote:

>     Hi all,
>
> This question is maybe ignorant. When you use a hi gauge to measure
> compression, could it be a false result - compression too high ? There  
> is a
> scale on the hi-gauge which indicates a green zone above 10 bar and  
> below 15
> bar, readings outside this zone are marked in red.
>

Which isn't a helpfull indication anyway, it depends on the engine.


> Can compression be low, but compensated by oil leakage past the piston  
> rings


Not to any relevant extent

> ? When I had compression of another car checked, the mechanic said that  
> if
> compression improves when you inject some oil in the cylinder through the
> plug hole, it is indicatieve of worn-out piston rings.
>

It nelps seal the scratches. If you've got enough oil going past the  
piston rings to manage that normally then you wouldn't need a compression  
test.


> Anyone  who can help me understand ? Many thanks in advance !
>
> Cheers,
>
> Peter
>
>

Mike P wrote:
> "Mrcheerful"  wrote in message
> news:WWvtk.49145$E41.34945@text.news.virginmedia.com...
>> peter wrote:
>>>    Hi all,
>>>
>>> This question is maybe ignorant. When you use a hi gauge to measure
>>> compression, could it be a false result - compression too high ?
>>> There is a scale on the hi-gauge which indicates a green zone above
>>> 10 bar and below 15 bar, readings outside this zone are marked in
>>> red. Can compression be low, but compensated by oil leakage past the
>>> piston rings ? When I had compression of another car checked, the
>>> mechanic said that if compression improves when you inject some oil
>>> in the cylinder through the plug hole, it is indicatieve of worn-out
>>> piston rings.
>>>
>>> Anyone  who can help me understand ? Many thanks in advance !
>>>
>>> Cheers,
>>>
>>> Peter
>>
>> An engine with low compression will not be showing a falsely high
>> reading because of piston rings letting oil past.  (unless we are
>> talking of something esoteric like a radial engine)
>>
>> You would only get a massively high reading if the combustion
>> chamber is full of something (eg fluid or coke).  Oil leakage past
>> the rings is irrelevant to the reading.  An improvement in reading
>> by putting a SMALL amount of oil in the cylinder MAY show that the
>> rings are worn. A better test is to air pressurise the cylinders with the 
>> valves
>> shut and find out where the air leaks out, this can show up blown
>> head gasket or cracked head/liner, leaking valves, worn bores/rings
>> etc etc. What are you testing and why?
>>
>> Mrcheerful
>
> His car with the silicon and glycol in the oil samples when he had
> them tested?
>
> :-)
>
> Mike P

Dang, I didn't notice the originator,
Mind you it could introduce a raft of new queries about compression, such as 
the height above sea level, air density, phase of the moon, sun spot 
activity etc.

Mrcheerful

peter wrote:
> This question is maybe ignorant. When you use a hi gauge to measure
> compression, could it be a false result - compression too high ?
> There is a scale on the hi-gauge which indicates a green zone above
> 10 bar and below 15 bar, readings outside this zone are marked in red.

What is your altitude above sea-level?

Or, on a more serious note, is this a petrol or diesel engine?

Andrew

"Andrew Morton" <akm@in-press.co.uk.invalid> schreef in bericht
news:6hnnofFmi72hU1@mid.individual.net...
> peter wrote:
> > This question is maybe ignorant. When you use a hi gauge to measure
> > compression, could it be a false result - compression too high ?
> > There is a scale on the hi-gauge which indicates a green zone above
> > 10 bar and below 15 bar, readings outside this zone are marked in red.
>
> What is your altitude above sea-level?
>
> Or, on a more serious note, is this a petrol or diesel engine?
>
> Andrew
>
Hello,

A lot of replies, and I'm glad to see some interest. Yes, it is the same
engine as with the oil analysis, namely a Mitsubishi/hyundai (or daihatsu)
1,3 16v petrol engine. It's just that I should feel happy about high
compression readings, but are they realistic ?  I had the hi-gauge compared
to a professional tester and readings corresponded very well.

As I said, readings are 16 kgs of compression rotating the engine for some 4
seconds, which should only be 13 kgs or so. How come they are high ? I don't
imagine too much coolant entering through the head gasket or so. The car is
handling badly when accelerating, slightly shaking and not revving up
smoothly. Only when I run it in fourth gear it is performing well, it
accelerates smoothly. I can't describe the engine performance this easily in
text, sorry.

Rgds,

Peter

"peter"  wrote in message 
news:5Uytk.50861$_M4.14748@newsfe18.ams2...
>
> "Andrew Morton" <akm@in-press.co.uk.invalid> schreef in bericht
> news:6hnnofFmi72hU1@mid.individual.net...
>> peter wrote:
>> > This question is maybe ignorant. When you use a hi gauge to measure
>> > compression, could it be a false result - compression too high ?
>> > There is a scale on the hi-gauge which indicates a green zone above
>> > 10 bar and below 15 bar, readings outside this zone are marked in red.
>>
>> What is your altitude above sea-level?
>>
>> Or, on a more serious note, is this a petrol or diesel engine?
>>
>> Andrew
>>
> Hello,
>
> A lot of replies, and I'm glad to see some interest. Yes, it is the same
> engine as with the oil analysis, namely a Mitsubishi/hyundai (or daihatsu)
> 1,3 16v petrol engine. It's just that I should feel happy about high
> compression readings, but are they realistic ?  I had the hi-gauge 
> compared
> to a professional tester and readings corresponded very well.
>
> As I said, readings are 16 kgs of compression rotating the engine for some 
> 4
> seconds, which should only be 13 kgs or so. How come they are high ? I 
> don't
> imagine too much coolant entering through the head gasket or so. The car 
> is
> handling badly when accelerating, slightly shaking and not revving up
> smoothly. Only when I run it in fourth gear it is performing well, it
> accelerates smoothly. I can't describe the engine performance this easily 
> in
> text, sorry.
>
> Rgds,
>
> Peter
>
Sounds like a misfire under load to me. Do you have any of those mobile 
mechanic type people over there (you're in Belgium right?) who have all the 
diagnostic equipment - here in the UK we have (or had) Computa-Tune. They've 
sorted out similar problems for me in the past - might just be a dead plug 
or lead. Here , at least a few years ago, they usually had far better 
diagnostic equipment than garages and could find strange problems easily.

Mike P

> Sounds like a misfire under load to me. Do you have any of those mobile 
> mechanic type people over there (you're in Belgium right?) who have all the 
> diagnostic equipment - here in the UK we have (or had) Computa-Tune. They've 
> sorted out similar problems for me in the past - might just be a dead plug 
> or lead. Here , at least a few years ago, they usually had far better 
> diagnostic equipment than garages and could find strange problems easily.
> 

Sounds to me like an almost terminal failure of your engine block.  
Symptoms include silicon and aluminium particles in the oil, and usually 
acompanied by pinking. If I were you I would take the car to the nearest 
scrap yards and leave it. Hope this helps.

pb wrote:

> 
>> Sounds like a misfire under load to me. Do you have any of those mobile
>> mechanic type people over there (you're in Belgium right?) who have all
>> the diagnostic equipment - here in the UK we have (or had) Computa-Tune.
>> They've sorted out similar problems for me in the past - might just be a
>> dead plug or lead. Here , at least a few years ago, they usually had far
>> better diagnostic equipment than garages and could find strange problems
>> easily.
>> 
> 
> Sounds to me like an almost terminal failure of your engine block.
> Symptoms include silicon and aluminium particles in the oil, and usually
> acompanied by pinking. If I were you I would take the car to the nearest
> scrap yards and leave it. Hope this helps.

He'd only buy another one...

Chris

-- 
Remove prejudice to reply.

on 28/08/2008, peter supposed :
> Can compression be low, but compensated by oil leakage past the piston rings

No, that will be quickly burned off.

> ? When I had compression of another car checked, the mechanic said that if
> compression improves when you inject some oil in the cylinder through the
> plug hole, it is indicatieve of worn-out piston rings.

Oil deliberately injected into the bores and not burned off will help 
seal around the wear in the pistons, thus improving compression for the 
test. The idea is to prove it is worn pistons, rather than wear in the 
valves and their seatings in the head. If the compression doesn't 
improve with the addition of the oil, obviously the engine has (or also 
has) valve leakage problems.

-- 
Regards,
        Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Harry Bloomfield"  schreef in bericht
news:mn.e5207d8891773332.86812@NOSPAM.tiscali.co.uk...
> on 28/08/2008, peter supposed :
> > Can compression be low, but compensated by oil leakage past the piston
rings
>
> No, that will be quickly burned off.
>
> > ? When I had compression of another car checked, the mechanic said that
if
> > compression improves when you inject some oil in the cylinder through
the
> > plug hole, it is indicatieve of worn-out piston rings.
>
> Oil deliberately injected into the bores and not burned off will help
> seal around the wear in the pistons, thus improving compression for the
> test. The idea is to prove it is worn pistons, rather than wear in the
> valves and their seatings in the head. If the compression doesn't
> improve with the addition of the oil, obviously the engine has (or also
> has) valve leakage problems.
>
> --
Thanks, Harry.

This is - with all the other posts and comments, the engine which was
probably overheated  when  someone changed my coolant liquid, and got the
engine to run for half an hour without sufficient coolant in the engine ( he
had the engine run stationary and filled up the radiator slowly, he added at
least half the volume of coolant this way. While there was a bolt meant to
let the air out when filling the engine with new coolant, without having to
run the engine at all while filling. It shows that engineers make good
designs, but they were ignored by this garage. )

Peter