Dealer says compression test is good

[MURX]

Hello everyone, I'm new here names Don, getting ready to head down to texas to pick up a '91 searay laguna 20 with a 175 merc dealer says the compression test is good @ 100-95-110-100-100-100 this sounds too low to me, the boat is from a private party owner has no mechanical knowledge, boat has been sitting, the dealer has done an impeller and carb rebuild, they say the boat is in immaculate condition, I'm ready to back off do to the readings sounding low to me, I'm probally going to have to drain and possibly remove the tank, its had gas sitting in it for a year, that dosen't bother me as much as the low compression what do you guys think? thanks great site Don

 

[hondon]

Re: Dealer says compression test is good

All cylinders are about even and this thing sounds like it has been mothballed for awhile.I would ask that owner to give it a good run on a remote fuel source and then check comp. again ,or even better a leakdown test.You're right ,those comp. readings are not impressive but they can be misleading.

 

[grandx]

Re: Dealer says compression test is good

From what I'm reading here, I wouldn't let it scare me away from a good deal (I would be more concerned about the "95 and 110 psi" readings. I have a pair of freshly rebuilt Merc 150's, the cylinders all were at 100 psi when completed. I also thought this was a bit low, but the engines needed to be broken in and the engines were checked cold as well. Run the engine on a remote tank till it reaches operating temperature, then check the compression on each cylinder with all plugs removed and the throttle wide open. You might see the readings go up. These compression gauges are generally a "relative" type tool, showing that all cylinders are equal or close to each other, they are generally not "calibrated" instruments which give exact pressure readings. I've looked through my clymer and found only specs of +/- 15 psi between cylinders, no mention of minimum or maximum. I haven't checked mine since broken in and warm, but I will, and I expect them to be somewhat higher after 60 hours of running. I've seen others post minimum compression readings here, I would be pleased to find out where they find this information. By the way, mine run like a pair of scalded apes...

 

[MURX]

Re: Dealer says compression test is good

GrandX, The 95 and 110 would apperar to be within 15% of 100 so i'm not concerned about that I just thought compression should be like 120-125# if you had new rings on a rebuild and got 100 on all six jugs sounds like I'm good to go! the boat is from San Antonio of all places! It's over at Magnum trailer getting brakes and bearings as I type, The owner is bringing it up to El paso for me, I'm going to pick it up friday or sturday and turn around and head for home So Cal thanx for the tip appreciate it P.S. If you live by magnum trailer take a peek as I've only seen pics! be nice to get a second opinion Have ever done business with magnum trailers?