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Old 05-10-2007, 08:49 AM   #1
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compression on a merc 2.4 200

Hi guys

I went to test a merc 2.4 200hp 1988/89, its a black max package on a fletcher 199 called Nice touch i am looking at to buy.

It was run up for 5 minutes to temperture, Ok port side bottom cylinder took time to warm up as the cold water first enters chambers around there,

Compression, I got a reading starting from the top port side at 110psi, middle at 118 and bottom at 110psi, then starboard bank top at 125, middle 114, and bottom at 110psi,

Ive known it should be 120/130.

what got me was after test and restarting her for another 8 minutes or so to see if the portside bottom cylinder runs up to temperature i then checked the compression again for a double check, the engine was alot warmer and all cylinders showed a balanced between 55, 65 to 70 psi! why is this?

I know its old and the boat is said to of lived on fresh water in scotland for 15years of its life and shows it is in very ggod condition but i am douting the condition of the motor, I feel its time for a short rebuild, but at that age it could start costing more than the engines worth.

I normally ask Chris Lewis to look at engines for me but i phoned his workshop to find he has sold up, is he working with ice marine? i dont know so thats why i am asking for advice here!

I should of check the gear oil which i missed! to see if has any water mixed in it! But I went along thinking it had been changed recently. Tom Stone was recently saying it had bike oil in it! the owner said Tom thought it had motorbike oil in it but didnt change it as he said it didnt after all.

Tom has seen the boat and worked on the engine! Tom if you read this i am trusting you word. I'd just like others thoughts too with the compression readings.

So guys! Whats your thoughts with the compression, any ideas why the compression went down on second test! any help would be much apreciated.

Its all way the way! nice boat shame theres no good feelings with the motor.

Cheers,

Steve.
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Old 05-10-2007, 08:55 AM   #2
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I normally ask Chris Lewis to look at engines for me but i phoned his workshop to find he has sold up, is he working with ice marine?
He's retired, but occassionally seen at Dorset Yacht doing a few odd jobs!
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Old 05-10-2007, 09:01 AM   #3
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but occassionally seen at Dorset Yacht doing a few odd jobs!
Gardening, cleaning the gutters, drains etc?
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Old 05-10-2007, 09:12 AM   #4
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Lol Very good! ill give him call when i need my wheelbarrow fixed.
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Old 05-10-2007, 07:21 PM   #5
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You're first set of readings show a difference of more than 10psi which should be concidered too much... It seems this engine isn't "dead" yet, but it's getting "ill" if you know what I mean...

It's logical that compression readings drop on a warm engine...
However dropping to 50-70psi sounds very abnormal !!! Are you sure about the readings ? always do a compression test on cold engine + warm engine to double check. remove all spark plugs, measure while giving full throttle, use trustable equipment. Inspect sparkplugs, inspect cyls through the spark plug holes... These simple inspections can learn you usefull things.
But I guess you did all that...


Sorry I couldn't really help, but I'm sure others on this site can, mate...
Best of luck,
T.
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Old 05-10-2007, 10:49 PM   #6
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Lol Very good! ill give him call when i need my wheelbarrow fixed.
I don't think he ever sat the wheelbarrow exam!
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Old 06-10-2007, 08:12 AM   #7
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I had a same engine only older (1981 don't know if it hase the same reeds...) it was overhauld 6years ago and now has a cold compression of 136psi on all 6 cilinders .
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Old 06-10-2007, 08:43 AM   #8
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Quote:
Originally Posted by Toffy View Post
You're first set of readings show a difference of more than 10psi which should be concidered too much... It seems this engine isn't "dead" yet, but it's getting "ill" if you know what I mean...

It's logical that compression readings drop on a warm engine...
However dropping to 50-70psi sounds very abnormal !!! Are you sure about the readings ? always do a compression test on cold engine + warm engine to double check. remove all spark plugs, measure while giving full throttle, use trustable equipment. Inspect sparkplugs, inspect cyls through the spark plug holes... These simple inspections can learn you usefull things.
But I guess you did all that...


Sorry I couldn't really help, but I'm sure others on this site can, mate...
Best of luck,
T.

Thank you Toffy, I didntcheck it with WOT what differents would it make? so people say do it that way to some say No!

Doesnt it give a better reading!

I checked the plugs just a bit oily and used a torch through the plugs hole and only saw pistons coated in coke! As if it could do with a decoke! Maybe the ring are sticking?
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Old 06-10-2007, 08:45 AM   #9
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Originally Posted by Ph@ntastic View Post
I had a same engine only older (1981 don't know if it hase the same reeds...) it was overhauld 6years ago and now has a cold compression of 136psi on all 6 cilinders .
Thats interesting, Psi is above the normal reading, How much did the overhaul cost!
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Old 06-10-2007, 09:20 AM   #10
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when you measure @ WOT there's no limit on airflow into the cils. Airvalve on the carbs are wide open. I'm not sure how this influences the readings, but I was always told to measure this way!

What's more important is the fact that you should measure all cils in the same way. Pressure difference between the cils shouldn't exceed 10psi.

Decarbonizing the engine can be a solution : your readings will go up. Some people say upto 30-40psi, but I personally think this is bit optimistic. There indeed is the possibility of a blocked piston ring. If so, there could be damage on that cylinder-wall.

All in all, you 're right to have doubts about this engine. It sure isn't new anymore and it's bound to have smaller or bigger damage. Fact is, you won't really know untill you open it up. Think you'll need an overhaul sooner or later, and that's a decision you'll have to make. Ph@ntastic is the right man to advize you since he did an overhaul on the same type of motor. Runs it on a P18 and I've always heard good things about this combo

Good luck!
T.
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Old 06-10-2007, 09:44 AM   #11
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Quote:
Originally Posted by Toffy View Post
when you measure @ WOT there's no limit on airflow into the cils. Airvalve on the carbs are wide open. I'm not sure how this influences the readings, but I was always told to measure this way!

What's more important is the fact that you should measure all cils in the same way. Pressure difference between the cils shouldn't exceed 10psi.

Decarbonizing the engine can be a solution : your readings will go up. Some people say upto 30-40psi, but I personally think this is bit optimistic. There indeed is the possibility of a blocked piston ring. If so, there could be damage on that cylinder-wall.

All in all, you 're right to have doubts about this engine. It sure isn't new anymore and it's bound to have smaller or bigger damage. Fact is, you won't really know untill you open it up. Think you'll need an overhaul sooner or later, and that's a decision you'll have to make. Ph@ntastic is the right man to advize you since he did an overhaul on the same type of motor. Runs it on a P18 and I've always heard good things about this combo

Good luck!
T.
Thanks T

Yes! i will look into a overhaul for it before using now!
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Old 06-10-2007, 11:11 AM   #12
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200 2.4 Mercs have chrome lined bores, check the chroming has'nt lifted,
I had your problem, had all bores stripped rechromed through my work, i cannot say i was'nt tempted to put a little 2 stroke down each bore and sell, allways lifts the compession check when selling an engine.
I think that what the seller did to me when i arrived compression tester in hand.I should'nt av told him my intentions on the phone before arrving.

And before anyone asks i never sold Shelby steve that motor!!
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Old 06-10-2007, 05:38 PM   #13
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Quote:
Originally Posted by Toffy View Post
when you measure @ WOT there's no limit on airflow into the cils. Airvalve on the carbs are wide open. I'm not sure how this influences the readings, but I was always told to measure this way!
What's more important is the fact that you should measure all cils in the same way. Pressure difference between the cils shouldn't exceed 10psi.
In general the compression wil be higher at WOT.
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Old 06-10-2007, 06:44 PM   #14
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When i compression tested our engine from cold it had 155 psi -159 psi on all cylinders,
one thing you have to take into account, is that the lasy cylinder u test will normally be lower on the gauge due to you draining the batterey,
you can try to put a t spoon of oil into the combustion chamber which would would fill the gaps around the rings got a little while, if its warn, if there isnt a noticble difference in the compression then should worry about it as much as its not warn pistons/rings, and may be warn reeds on that side, or just due to the rotation of the engine, just like right bank runs hotter than left until max rpm.
if one bank isnt warming up this may be a thermostat stuck open so that bank may have run colder for a long time hents the drop in compression on that side.
Good luck mate
Ross.
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Old 07-10-2007, 05:45 PM   #15
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Thanks Guys!

Interesting opinion's

I am hoping to look in to it more this week! yes i may get a new thermastat for it, So i know from the work go things like that are working!
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