| Author |
Message |
    
Floyd Hauffe
Member
Username: floydh
Post Number: 6
Registered: 06-2009
| | Posted on Friday, June 19, 2009 - 11:53 am: | 
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Can anyone tell me the proper way to perform a compression test on a single cylinder P6?
Thanks,
Floyd |
George Martin
Visitor
| | Posted on Saturday, June 20, 2009 - 08:35 am: |
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I just used a normal car compression test guage and crnked the engine over as fast as possible, only needs a couple of turns. I got about 100lb/psi. I also have a vac/pressure guage which could probably be utilised to measure crankcase vac/press, but not tried that yet, cos I put new seals etc in it. |
Miah Gregory
Member
Username: mace
Post Number: 8
Registered: 05-2008
| | Posted on Saturday, June 20, 2009 - 08:23 pm: |
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I have been having some trouble with my P5 lately, and happened to do a compression test today, getting around 100 PSI, which feels about right.
However upon replacing the spark plug, i noted that there is some loss of compression from around the plug itself - does anyone have any ideas as to how to work around this?
Thanks. |
George Martin
Visitor
| | Posted on Sunday, June 21, 2009 - 04:53 am: |
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Surely it must be the plug gasket. unless its a new plug badly machined. |
Miah Gregory
Member
Username: mace
Post Number: 9
Registered: 05-2008
| | Posted on Sunday, June 21, 2009 - 07:44 am: |
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Seemed to have the same problem with a number of plugs; I had some limited success borrowing a rubber O ring from my compression tester and using that as a gasket but obviously not for very long as its not designed to handle heat.
Thanks. |
herbert alfaro
Visitor
| | Posted on Saturday, October 09, 2010 - 01:02 pm: |
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I have twin 454 cid mercruiser marine engines that show low compression on a number of cylinders in both engines when tested both hot and cold.Does this indicate a need for a major overhaul of both engines.The engines have approx. 1700+ hours of run time.They are original installation ala 1986.Comments would be welcomed. |
Andrew Menkart
Moderator
Username: andrew
Post Number: 1079
Registered: 11-2001
| | Posted on Saturday, October 09, 2010 - 02:51 pm: |
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Herbert,
That 454 mercruiser is a bit too new for this board. We are focused on antique style marine engines, mainly pre 1940's.
You should post that question in the board.Mercruiser category of the MarineEngine.com Forum |
Andrew Munns
Member
Username: johnoxley
Post Number: 11
Registered: 04-2010
| | Posted on Saturday, October 09, 2010 - 06:43 pm: |
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Hi - despite the Mercruiser being "modern", one day it will be an antique.
The priciples are the same for old or new engines - do a compression test and check manufacturers specs (if they exist). Remove all plugs + throttle should be kept wide open + remove coil lead to prevent sparks --> shocks/fires.
Low pressures indicates leaky valves/piston rings/head gasket. Adjoining low pressures suspect head gaskets between cylinders. If you can get a teaspoon of oil onto the top of the pistons* and retest pressures go up, the valves and head gasket are OK, but you will need big overhaul anyway! If the pressures stay low, suspect valves/head gasket --> top end overhaul.
* Getting oil onto piston will be difficult if you are testing a side valve engine or have bowl type piston (eg. Gardner diesel). |
