1991 Yamaha 90 HP cylinder compression

Just took my boat to the dealer for complete motor tuneup, etc. This motor has less than 40 running hours but has been sitting for about four years. It ran fine last time I used it. Dealer called and said "compression is 70/50/125 so the motor is basically shot". Now I'm definitely not a boat motor mechanic or expert but just to tell me the motor is shot seems a bit careless. I asked if they had pulled the head to check the gasket and they said "well we wondered if you wanted us to do that". (not gettin a good feeling here). Now my question, what are some of the more common possibilities for this problem ? (head gasket, rings ? who knows what else?) Any input will definitely be appreciated.....

How long have you owned it ??-------------I agree , not a good feeling about that dealer.----------I would look for a " second opinion " here.-----If it ran fine the last time you used it , then what happened here ?

I've owned it since 1992. You're probably wondering "what's this guy doin with a boat he's had that long with only 40 hours anyway?" The dealer was goin to take off the head and check the gasket yesterday but I haven't heard from him yet. It has sat the last time without being run for maybe five years. I'm wondering about bad gasket, rings stuck/broke, or (what I'm really asking) what other maladies might cause this ?

Not uncommon for a boat to have few hrs.---------If it ran properly 5 years ago , then it should run properly today !-------Head gaskets do not go bad sitting, nor do rings break !

Assuming that the compression number actually are 50/75/125 and the dealer was shootin straight, what else could cause the odd numbers ?

With those compression numbers there is no way that the motor " ran fine " the last time you used it.---------Time to take your boat somewhere else in my opinion.

Well "ran fine" is my opinion of it's condition. of course since I didn't use it all that often maybe I just didn't notice if it had less power but it didn't cut out or stall or have any problems starting. Dealer was gonna take head off and look some more. I'll call them this afternoon and see what they say and get back with you. Hopefully it wont be "yep she's shot, but we'll haul it off for ya for only 100 bucks"

Just spoke with the boat repair guy. He took the head off and the bottom two cylinders had quite a bit of rust in em. His plan now is to clean em up with penetrating oil, etc, put on a new head gasket, and give it a shot. Sound reasonable ? Kinda makes sense after sittin that some moisture might be in the cylinders (ethanol crap gas?).