Mercury 135 Powerhead Help Please!

[Viper89]

2 part question. I have a 1989 Mercury 135 v6. It has low compression on 1 cylinder (top right). The motor runs very well though. Idle and WOT no problem. Getting around 110 on 5 cylinders and around 80 on the top right cylinder. Boat still goes around 55mph (Checkmate) as always. What are the potential troubles ahead i was wondering?? If I was to change the power head could a larger power head fit my v6 (eg 200hp) lower unit?? Thanks again all...newbie :)

[Robert Meyer]

Any merc v6 2.0,2.4or 2.5 will fit on there all these blocks bolt op the same. So you could put up to a 280 on it if you want.

[Raceman]

Depending on which powerhead you go to you may have to change the two plates on top of the mid section. The bolt patterns are the same, but the exhaust openings in the powerheads vary. Your gearcase would be fine.

If you were asking of potential problems to keep running your powerhead as is, it depends on why the compression is low. If it's from ring coking you may get by with it for a while, but if it's from partially seizing it'll most likely go ahead and fail.

[j_martin]

I'd decarbon it, and check again. might just be a stuck ring. If it were partially seized and you kept hammering it, I'd think it'd go to zero pretty quick.

I mix a can of SeaFoam into about a gallon and a half of fuel mix in a pony tank, idle it through (nursing it, it won't like it any more than a kid likes his medicine). Let is sit for an hour or so, then go run it. Watch the wind direction, it's hard on neighbors. It will clean the cit out'n yer motor, though.

hope it helps
John

[Viper89]

Thanks all for the quick

[Viper89]

sorry hit the wrong key....thanks again for the quick response to my question.....I was reading about seafoam in the forum.....(alot to read).....

[kingsbiship]

Top rite is number one cylinder... the one most susceptible to lack of water
and overheat! Farthest from the pump! I'm not saying that's it... Just
tellin' the facts

[j_martin]

Top rite is number one cylinder... the one most susceptible to lack of water
and overheat! Farthest from the pump! I'm not saying that's it... Just
tellin' the facts
Also would run warmer and tend to stick a ring quicker. :D more facts.

Pull the plug and take a peek into the hole. Piston spalling should be pretty evident.

hope it helps

John

[Viper89]

Hey all thanks for the quick response. I want to add a previous problem that occured a few weeks back. While out running the boat the lower hose of 2 hoses (short one) connected after the fuel line in series with the o/inJ into the side of the powerhead had cracked and was leaking causeing the motor to loose power and die at increased throttle, but would run ok 5 mph to get back to the dock..( 5 minutes runtime tops). When i returned home i replaced the hose and checked all the rest and all seemed fine. 1 week later when starting the engine cold it sounded different so i did a compression check and discovered the low cylinder.

[kingsbiship]

THAT don't sound good!

[j_martin]

Shoot, they don't like to go lean.