73 merc rebuild help.

[Texas Prowler]

Hello all,
I have a 73 merc that I'm going to rebuild with new piston rings and a power head gasket kit. I'm in need of guidance from you great group of guys here. Other then the for mentioned are there any other parts in the power heard that you would replace? I'm doing this build on my garage. I plan to hone the cylinders a little bit and use the standard ring set. Should i try honing until the need for the next size up .015 rings and pistons are needed? Should I get just get a machine shop to bore the power head to fit the over sized rings and pistons? Though I'd like to rebuild the motor myself if it's not going to work I'll take it to a shop. Thanks guys. The motor failed due to one of the coils not firing because of bad power supply wiring.which then gas washed the upper cylinder and resulted in low compression. Any advice is appreciated thanks!

 

[Faztbullet]

What hp?

 

[racerone]

And why would a coil not firing " wash the cylinder " on this 2 stroke motor ??---Investigate and find the real reason for the scoring !!!

 

[Texas Prowler]

Fasztbullet,
The outboard is a 40hp.

Both of the coil power wires coming from the switch box are completely green( corroded). The bottom plug was the only one barely firing. Regardless if it's a two stroke or not it still has gas that is not being ignited. Yea it's mixed with oil but that's besides the point. The only issue found was the coil not firing.

 

[flyingscott]

Wiring corroded like that is normal on that age merc. The plug not firing did not destroy the cyl. You can run a 2 stroke a long time with a cyl down people have done it. 2 Strk oil is designed not to be washed away by fuel. Since it was the bottom cyl not firing great and it is the cyl damaged. You need to find where the water was coming in fairly common on those mercs . The water coming in will cause the exact problem that happend. You will probably need to have the block bored take it to a machine shop. They can tell you exactly how much will need to be bored. Sp my advice would be you either had a carb plug up or water ingestion. Because of the wash you had I would lean towards water ingestion.

 

[Texas Prowler]

I've found a shop to bore out the cylinders after that's done I'll be looking into the correct size piston for the build. The maxrules.com guy I spoke with says the rings might just be stuck from the cylinder not firing. He says now that I've replaced the bad wiring to give it a shot at running it after soaking the piston in cleaner via spark plug. He feels it's possible the rings could be stuck. At this point i have nothing to loose.

 

[racerone]

Remove the bypass cover and inspect the piston and rings visually.---Also make sure you find out why the piston scored or it will simply do it again !!

 

[Texas Prowler]

Hey hey guys before I start tearing the engine apart I want to diagnose the no start issue in having. I've searched but I'm not sure if what i found applies to my engine. Will you guys point me in the right direction to test the stator, trigger switch, and any other things that would cause the engine no to start. Thanks. After i insure everything is working properly I will tear into the engine to see if there's any piston scoring.. Thanks!
And. To add i do not have the remote control box so I'm trying to rig it up to run.

Edit word change.freaking?

 

[Texas Prowler]

Well guys i figured I'd cut the wrap off the 4 wires coming from that stator and found more corroded wires... Guess that's why I'm not getting any fire to the plugs.... Guess I'm on the hunt for a new one.

 

[Texas Prowler]

Found scoring on the upper piston. I'll have the power head completely apart this weekend. And set the machine shop after Christmas. Here's hoping for the best

 

[Faztbullet]

Iline pistons are getting a little harder to find so find you a set of ,.015 or .020 oversize before you have block bored.

 

[quicktach]

Find out what's caused the scoring....excessive play in pins? rings stuck ?

 

[Texas Prowler]

Iline pistons are getting a little harder to find so find you a set of ,.015 or .020 oversize before you have block bored.

I have sourced New pistons in .015 and .030 both from another maxrules.com . that is where I'll get the complete powerhead rebuild kit from. As for the source of the scoring I will ask the guy at the shop that's doing the machine work what he finds to be the cause. I did find part of an old impeller in the powerhead when i removed the ignition coil mount. Maybe that was part of the cause.....ugh.

 

[Texas Prowler]

How can i go about setting the spark advance without the flywheel cover? I read the service manual and it says that cover is needed. Something about a notch on the cover... I will need to know this once i hopefully get the engine back together.

Thanks for sticking with me through this guys. I try to upload photos from my phone but they are to big. If you like you can follow my build thread in the link. I will only come here for questions as the guys over there favor evenrude and Johnson.... Thanks!

 

[Texas Prowler]

Hey guys is there any benefit to using wiseco pistons in these mercs? I've been looking at them and was wondering what you guys think.

 

[Faztbullet]

Stay with a cast piston.....JMO.

 

[Texas Prowler]

Stay with a cast piston.....JMO.

Will do. Do you have an idea of how iI can go about setting the spark advance without the flywheel cover? If not I'll leave it where it is and set it by ear

 

[Faztbullet]

Take a dial indicator and find TDC and then back it off.462.Take a piece of coat hanger and attach it to front motor mount bracket and bend it to point at.462 and you can set timing now...

 

[Texas Prowler]

Thanks!

 

[Texas Prowler]

Ugh guys! Good thing both cylinders were smooth as silk. BUT the bottom cylinder has dimples... Probably from detonation.... See pics in the link

Mod EDIT link removed