79 100hp.V4 Please help!!!!

[lennygilbert]

ok this is kind of long but please read...<br />I took my boat to the mech to find out why i am only getting 3500rpms at wot.they found that my top left cyl is dead.The other three have over 100psi and are within 2psi of each other.The top left cyl has 0psi.<br />My questin is do you think this could be caused by gummed up rings?When at wot the engine would surge almost like the cyl was firing.Mech verified all spark is good and timing is good.I was going to run some seafoam through it this weekend then do another comp check.<br />Is it hard to replace a piston,is it posible to replace just one,How much is the avg cost for piston replacement.I only paid 1k for this boat and therefore do not want to sink a lot of money into it.I also considered just running the boat the way it is for this summer untill i get my new one.I mainly just use it to cruise around the lake in and fish with..any other thing i can do to raise the comp in that cyl without tearing it all apart?<br />any thoughts woud be appreciated..

 

[OBJ]

Re: 79 100hp.V4 Please help!!!!

Well Lenny, keep on using it the way it is and a cruise around the lake you may end up paddling back.<br /><br />With out seeing the innards, I would guess the cylinder is scuffed possibly from running too lean on the one cylinder.<br /><br />Yes you can just punch out one hole and hone the rest if they will still be in specs for bore size.<br /><br />Cost is decided by what you put back into the block.....and a carb overhaul along with new water pump and t-stats are and should be a must for any rebuild. Average cost.....hard to say. Varies with what area your from and who does the work. Get an estimate and compare it to the value of the motor.

 

[lennygilbert]

Re: 79 100hp.V4 Please help!!!!

The carbs were rebuilt last summer so that shouldnt need to be done again..Is there anyway to replace a piston/rings with the head still on the lower unit.I've never worked on a marine engine before i dont want to screw it up further.<br />how hard is it to replace a piston/rings on these motors?About how much time would i be looking at?

 

[OBJ]

Re: 79 100hp.V4 Please help!!!!

Gotta tear it down Lenny. With comprssion at zero on one hole, most likely will need bored. Pull the block off the midsection, clear a place on the work bench and take it apart.<br /><br />Why not just pull the head and take a look. See how bad the hole is.<br /><br />A service manual, OEM, would be a big help.

 

[lennygilbert]

Re: 79 100hp.V4 Please help!!!!

I've got the service manual,I just want to make sure its worth my time to do it.I dont want to put a lot of money into to it just to find out i did it wrong.Also afraid to pull power head off lower unit.Kinda like changing the tranny fluid in a used car.Almost every time you get big pblms.<br />Whats the avg time from removing power head to changing piston to puting it back on?

 

[lennygilbert]

Re: 79 100hp.V4 Please help!!!!

i have the clymer and seloc manuals for this engine.I think seloc does a better job..

 

[DHPMARINE]

Re: 79 100hp.V4 Please help!!!!

Len,when I find compression readings like yours,I call the customer for an okay to pull that cylinder head,and then call him back with a better explanation as to what happened.In your case I would doubt a blown head gasket,but I'd pull the head before I told you a piston was needed.Someone should pull that head and take a look.<br /><br />DHP

 

[Solittle]

Re: 79 100hp.V4 Please help!!!!

Pulling the head won't cost you a dime.

 

[lennygilbert]

Re: 79 100hp.V4 Please help!!!!

Im going to pick it up either tomorrow or monday and will pull that head of then and look around.Im just kinda guessing that a piston would be needed if something was wrong with the rings????<br />I've replaced the pistons in my dirtbikes before and always just bought a new piston when i got new rings.