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Old 20-02-2016, 08:54 PM   #1
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Country: UK
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Boat name: Insane
Boat make: Phantom 21 1990
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225 Compression test

Just Hand some one look at my boat, they did a compression test and said that the cylinders where out of they service limits.
Please help. This is a 26 year old yamaha 225hp V6 and has run perfect for me for the last 3years. The buyer said that the cylinder should all be equal or there about.
The top two are 125psi the bottom two are 125psi but the middle two are at 140psi, have checked the Yamaha manual and the service limit is 10-15%, stating if more than 20% service work is required. This was done after warming the engine.

The last time i used this engine it run 70mph at 5800 on a trophy 24 plus for more than 30miles without a hitch, can't understand why i am being told it needs the heads off to check for wear.
I trying not to be one of those scum bags, sell a boat with loads of problems that cost a load of money to fix.

please let me know
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Old 21-02-2016, 08:27 AM   #2
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Country: Uk
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Talking Compression check

Hi as to your question it is always best if you can get them equal but I have seen this before I'm sure there will be nothing wrong with these compressions I always spec all my engines to be with you in 15 PSI of each other and no more I would perform a leak down test if you was that worried you might find it has been re-board over the years and this is why the compressions R different hope this helps many thanks Keith at K H marine
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Old 21-02-2016, 09:49 AM   #3
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Country: UK
Location: Bromley
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Interests: Boating jet ski and Scuba diving
Boat name: Insane
Boat make: Phantom 21 1990
Engines: Evinrude 250 HO
Cruising area: Isle of Sheppey

Join Date: Feb 2013
Location: Bromley
Posts: 67
Hi Keith

Many thanks for your reply, just looked at the work shop manual and your right 15PSI is within limits, it also goes on to say that the difference between cylinders should be no greater than 25% (lowest reading and highest reading). The manual then states that the cylinder head design on V6 models was modified to enable better cooling and should be measured between pairs of cylinders which share the same crankshaft throw. The readings should be top 1/2 same, middle 3/4 same, bottom 5/6 same, it then goes on that the middle two 3/4 should be the highest as to cool the head the most.
This is exactly where my 26 year old engine is at and why when i asked Power Products Marine to fully check the engine out last year, and i know they did a compression test, nether Richard or Andy said they was a problem, just saying it was good for its age.
I was alway told and read that the compression across the cylinders should be equal, just 10 minutes reading a Yamaha work shop manual goes to prove that a little knowledge is a dangerous thing.

Kevin
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Old 22-02-2016, 04:26 PM   #4
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Boat make: Hydrostream V-king, 650SS OCR ,Ring 21, Ring 18, Phantom 18.
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Yamahas have staggered compression..
It sounds fine to me!
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