no compression on cylinder, to build or not to build

[quicdsm]

I purchased a 90 javelin with a 200 rude xp last week and prior to purchasing i completed a compression check on all cylinders. They were all 80 psi. I ran it this morning attempting to adjust the idle . I then ran about 10 min or so and during a WOT at 53 i lost power and speed dropped to 43-45. When i returned i pulled plugs to view and check for a bad coil pack . One had no gap(plug). I replaced plugs over weekend and i m sure i gapped them. I rechecked compression to find i had no compression on that cylinder. zero. I assume rings came apart. Im concerned as to what banged the end of the plug to close the gap and how bad i have scored the walls. I need opinions here. Im more so familiar to turning a wrench than most as ive been a jet mechanic for 15 years but ive never rebuilt the powerhead on an outboard. I believe with the manual i could overhaul this. Am i correct? Should i look for another? I have even thought of removing phead and taking to shop then re assembling. I hate buying a used motor for 5 to 1500 dollars for i may inherit the same problems that i already have. What kind of money should i expect with the different options available.

Thanks for any advice.

 

[Gary H NC]

Re: no compression on cylinder, to build or not to build

Welcome to Iboats!

Very possible a piece of a ring took out the tip of the spark plug.
I would pull the head and have a look.

Those complete rebuild kits are expensive.

 

[wilde1j]

Re: no compression on cylinder, to build or not to build

I would do the same. Plus , if you think you want to rebuild, get an OEM shop manual (not A THIRD PARTY ONE ... THEY ARE JUNK imho). Use the manual to decide whether you want to have at it.

If you decide to rebuild, use a marine machine shop only, such as MarFab, a very good one.

Here's a link to one of the less expensive parts packages, depending on the damage:

http://www.powerheadkit.com/Looper 6 cyl.htm

These kits are very complete, but you may not need the whole deal. BTW, it's acceptable practice to just rebuild the bad hole, but measure all the bores and check for roundness while you're at it.

 

[Fl_Richard]

Re: no compression on cylinder, to build or not to build

If shes got some hours on her do the whole thing. Dont wanna do this twice. Dont forget to fix the cause of the problem that caused this. Again dont wanna do this twice.

It's not a particularly hard job. If you can follow directions and keep track of the parts its pretty straight forward. I did my 150 on the patio on a big 3x7 folding table. I was afraid it would get "confused" in the garage.

 

[kenmyfam]

Re: no compression on cylinder, to build or not to build

Depends how much money and time you want to invest in it.

 

[Faztbullet]

Re: no compression on cylinder, to build or not to build

It being a 90 model makes it a open deck block which had better cooling so you dont see as much piston pin migration as in closed deck engines. If engine had set a while it likely had a carb jet lean out a cylinder. For it to close the gap on plug something big like a piece of skirt or large pieces of ring debis got on top of piston as this motor has the "smog heads" as we call them. If it was #6 the bottom bearing came apart which I have seen about 6 of this year. Pull the cylinder head and you can see real quick condition of piston and cylinder walls. Below is pictures of Wiseco looper piston that pin migrated out of allowing rings to rotate and hang in ports then damaging piston and cylinder. Customer had motor rebuilt 5 months before and block did not have water mods(closed deck),and rebuilder woud not stand behind the work.