90hp evinrude compression

[SHAWSHANK555]

I have an 86 EVINRUDE 90 HP (4-cylinder) OB that recently had idle problems. I took it to the local OB repair shop and they advised that I need a new powerhead. The guy who worked on it said one of the cylinders was getting poor compression, and he looked in sparkplug hole with a mini camera . I took a look myself and there is a small chunk of metal that appears to be peeled back from the edge of the piston head. The cylinder doesnt look scored, but I am by no means an expert on this. The guy at the repair shop said that I could probably find someone who could replace just the piston, but that he wouldn't do it any other way than replacing the powerhead (at $3k estimated cost). Since I only have $2500 in the boat/motor/trailer, I am thinking this expense is quite a bit more than I want to sink into this. I did a little research and a new piston is about $106. I have a Clymer's shop manual that doesnt provide very good step by step other than pulling the whole powerhead and getting the engine about completely apart. My questions are:

1. What is involved in replacing the piston? I imagine I'll have to buy a torque wrench, and possibly other tools as well as gaskets to replace any that I unseal in the dissassembly process.

2. Is there a better book (or website or antyhing that is idiot simple) to use for the step-by-step process of replacing a PISTON? I am mildly mechanically inclined, but this will be the biggest project on an engine that I have tackled.

3. Is it possible just to change one piston and not the whole powerhead.

4. ANY GOOD ADVISE WOULD WOULD BE APPRECIATED,
Thanks for the help!

4. After taking off the cover, T

 

[fixmyevinrude]

Re: 90hp evinrude compression

I would at the very minimum take the heads off and get a good look at what you have. You may just have carbon build up and just need to de carb the engine. The rings could be sticking from all the carbon. I believe you could replace one piston but I would replace the rings on all the pistons.

 

[tashasdaddy]

Re: 90hp evinrude compression

replacing a piston is not simple. you have to split the case. disconnect from the crank shaft. you must have the Evinrude manual == outboardbooks.com.

 

[cbcmarine]

Re: 90hp evinrude compression

This is not an impossible problem for you to deal with.
First I would order a manual this is a must.
Next Take the Heads off and find out what you are dealing with.
Take lot's of pictures with a digital Camera as you take apart( this will help when you are putting everything back together. But invest in lunch bags and label all parts and put them in these bags as you disassemble.
Start with the heads and find out what is the problem is first before going ahead with Pistons ect. May be simple or a big project but lets start there first

 

[SHAWSHANK555]

Re: 90hp evinrude compression

anywhere i can get a book to get started? What the best book i could get for explaining step by step?

 

[wilde1j]

Re: 90hp evinrude compression

OEM shop manual is the only one to own: outboardbooks.com or fleabay

 

[bob johnson]

Re: 90hp evinrude compression

has the motor been run in salt water at all???

if not...try and pull both heads off...( could turn into disaster if you start snapping head bolts!!!) warm up the engine a few times while sparying the head bolts with PB blaster...over a few days...then the last day when you are set warm up the motor get it hot and shut it down and start to pull the head off...the warm aluminum block may make it easier to take the head bolts out....

then you can check out the problem.....

but in the end you can solve low compression just by taking the head off...

the only way you could get LUCKY would be that a ring is stuck from carbon and you can free is with a decarb process...

if you see damage in there.....I am gonna say...that if you are a not a tool guy and mechanically inclined...that a power head rebuild is not something you want to tackle

just because many have done it as first timers, doesnt mean it was easy or fun..and it probably wont be efficient!!!!

many things can be fixed by the weekend -boat mechanic-if he needs to be guy.....but some are best left alone.....pistons and rods and stuff like that...

forget it... for the average joe.

I am very mechanically inclined.. and i took a 70 hp apart.... it is in boxes and seems to be a daunting task to put it back together...

because I should use new parts so many places the cost just keeps going up and up... and if It doesnt go back super clean or just right...it all turns to trash!!!

youd needs to sernd the block out to get honed and cleaned.. you would have to have a way to check the condition of the bores...ID, out of roundness, you would have to check the head for flatness.....

you would need a few specific tools

you could find out by buying the book, then reading about all the special tools you will need and measurements that need to be taken...

I would say after reading the rebuild proceedures...MOST coming here for recomendations o their first rebuild will forego the project... as well they should


the parts to rebuild are about 1/3 the cost of a rebuilt power head... then you have to make sure you dont ruin it... and you have to actually do it all!!
the you have all that doubt afterwards....

go on craigslist and look for rebuilt power head( professionally done)

there is a place that has three sites on the east coast that will take your block in trade and give you a new power head for less than $2000

outboards 1 or something like that...they can do it while you wait too!!!

bob

 

[emdsapmgr]

Re: 90hp evinrude compression

Before you spend the money on the overhaul, you may want to determine the reason for the failure. You don't want to do the overhaul and have the same problem again.. An original factory manual is the only way to go, as everyone has mentioned. Ken Cook Co., in Milwaukee is the original publisher and will sell you one. It is permissible to replace just one piston, even if you have to overbore that one cylinder. You really should put in 4 new ringsets as long as you have it apart. If the head it badly pitted, I would replace it. You will need an engine powerhead gasket kit. After the overhaul, suggest you put in two new thermostats and a new impeller before you start it up. (if the failure was related to the oil/fuel pump-you will need to replace it, too.)