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Compression Check???


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Ok, so I've been talking about buying this 06' Vride for about a week now. I've got all the paperwork sitting beside me to close the deal. I have one quick question and would love to get some feedback on this.

It has the 340 Monsoon with 322 hrs, I rode in the boat, excellent hole shot with a top end of 48mph on semi choppy water. Does that tell me if the engine has good compression? I'm not sure if it had been repropped, I would assume no. The dealer is not a Malibu dealer but he thought that when they checked the engine it had a compression of around 180psi and all cylinders were close to that.

Please tell me what you take from all this information.

Thanks.

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180 psi seems a bit high. Usually the compression on Engines is between 140-160 psi.

If you are getting a relatively similar compression in all cylinder in the 140-160 range all is good. From my understanding, there should not be any one cylinder that is different by more than 5-10%.

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That is why I'm questioning it. I've heard numbers on compression for that motor from 120 to 160 psi. Does any one know what it should be if it's running in tip top shape? Does the performance I mentioned tell me anything?

Thanks

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Get the compression numbers for each cylinder from him. "I think" wouldn't do it for me, I wouldn't believe him, sorry. If they did a comp. test, they should provide the numbers.

I agree. If they did a comp check once, they can do another one in 15 minutes or so. Have him write down the numbers, or better yet watch them do it. His figure of 180 may prove to me a mistake. Just make sure they are all within 10% of each other.

Shouldn't be a problem getting him to do this, especially if your otherwise satisfied with the boat and are ready to close the deal.

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for 4 years, my monsoon compression on each cylinder has been 170-175. My local dealer said that is really good.

Edited by hawaiianstyln
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if it runs great, dont worry about compression too much. Years ago GM engine plant forgot to install piston rings on 144 350 chevy engines they all tested great compression on a gauge. Could not keep oil in them though.

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You can pick up a compression gauge for less than forty $$$, pull four random plugs in about 15 mins and test them in about 1 hr for a good peace of mind, and at the same time you can look at the plugs and make sure that none are burning any oil. That is what I would do, you buy at own on risk as "IS" unless you can get something in writing Thumbup.gif

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Sounds like the engine is ok. I'm not sure about 180 psi but, the "proper" way to do a cylinder compression test is...

1) Stone cold engine, remove all plugs, hold throttle wide open, connect compression gauge to a cylinder, crank engine approx. 4 times, take reading. Go to next cylinder and crank engine again, etc. etc.

2) Run engine to oper. temp. and perform step 1 again.

Edited by Pistol Pete
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Sounds like the engine is ok. I'm not sure about 180 psi but, the "proper" way to do a cylinder compression test is...

1) Stone cold engine, remove all plugs, hold throttle wide open, connect compression gauge to a cylinder, crank engine approx. 4 times, take reading. Go to next cylinder and crank engine again, etc. etc.

2) Run engine to oper. temp. and perform step 1 again.

That sounds like fun, I'll buy a gauge and it will be the first thing I do when I get her, thanks PP.

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Removing the lanyard will disable the EFI relay, thereby leaving the injectors and fuel pump without power.

edit; the ignition system too.

Edited by electricjohn
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Good to know but I would still like to verify that........I am remembering a few weeks ago when my boat would not start at the ramp. After some cranking I could smell the fuel. Of course the problem was the lanyard or what I like to call the dead man switch Whistling.gif

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Sounds like the engine is ok. I'm not sure about 180 psi but, the "proper" way to do a cylinder compression test is...

1) Stone cold engine, remove all plugs, hold throttle wide open, connect compression gauge to a cylinder, crank engine approx. 4 times, take reading. Go to next cylinder and crank engine again, etc. etc.

2) Run engine to oper. temp. and perform step 1 again.

Pete, your getting way too technical now. Just run the engine up to operating temp. let it cool a but to pull plugs and run the test. He isn't buying a super sport bike :)

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Pete, your getting way too technical now. Just run the engine up to operating temp. let it cool a but to pull plugs and run the test. He isn't buying a super sport bike :)

Tone,

Back in the day when I was working on Volvos we had a serious problem with valves sticking in the guides. The engine would spin and sound like there was no compression as if the T-belt was broken. Doing the compression test hot and cold was part of a long list of things we had to check to make warranty happy before we could rip the head off and fix the problem. Glad those days are over. Yahoo.gif I haven't had to do a compression test on a motorcycle yet. When in doubt, just add new engine. Whistling.gif

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If you are really serious about determining the condition of the engine, I would suggest a leak down test. It is pretty easy to cover up some leakage in a compression test, but a leak down test will show exactly where any issue might be. It does not sound like this case there is any major concern as it sounds like the boat runs just fine and the hours are really not very high.

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Pete, your getting way too technical now. Just run the engine up to operating temp. let it cool a but to pull plugs and run the test. He isn't buying a super sport bike :)

Tone,

Back in the day when I was working on Volvos we had a serious problem with valves sticking in the guides. The engine would spin and sound like there was no compression as if the T-belt was broken. Doing the compression test hot and cold was part of a long list of things we had to check to make warranty happy before we could rip the head off and fix the problem. Glad those days are over. Yahoo.gif I haven't had to do a compression test on a motorcycle yet. When in doubt, just add new engine. Whistling.gif

Gotcha, There was a similar problem with GM at one point, they used positive valve guide seals and the valves didn't get enough lubrication. But in this case they just stuck, never really had the hot cold problem and I'm glad those days are over also but I learned a lot :)

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