Mercury classic 50 HP - part 2

[JohnTRI]

Low compression - 1986 Mercury classic 50

I’m having low compression on cylinder #1 at 95 PSI when warm and 50 when cold. Cylinder #2 is at 125 Cylinder #3 is at 125 and Cylinder #4 is 115 Here’s a video of the engine running. I have an understanding that an engine with low compression tends to misfire and not start and if it does...

forums.iboats.com

This is the original post and I’m making a sequel to that. In that post I basically discover that my top cylinder is giving me a compression of 30 to 40. When hot 100 I suspected there was something wrong with my piston rings. After investigation these are the photos that I’ve come back with. First picture piston 2, second picture piston 1, third picture 3rd piston and forth picture 4th piston. I’m looking for advice with next steps

 

[racerone]

Motor needs to come apart for inspection.----Then repair as needed.-----Looks like something broke INSIDE the motor.-----That resulted in the damage seen in the second picture.----Not difficult if you can do the work yourself.-----Hard to find a shop that will take on this kind of work.----And you would be shocked at what it would cost at a shop.

 

[Faztbullet]

Agree....Looks like maybe a piece of reed went thru cylinder. Nothing in a can or spray will fix this. Needs a piston and possibly bored

 

[JohnTRI]

Motor needs to come apart for inspection.----Then repair as needed.-----Looks like something broke INSIDE the motor.-----That resulted in the damage seen in the second picture.----Not difficult if you can do the work yourself.-----Hard to find a shop that will take on this kind of work.----And you would be shocked at what it would cost at a shop.

How would I go about repairing this piston? It looks like this piston is never EVER supposed to come out of this engine block.

 

[cyclops222]

If you decide to remove pistons or rods ? Be very sure of any direction marks on each piston and rod assembly. Some do have directional marks on them. That need to face front or flywheel of the engine. Some engine are designed to cause trouble when opened up. Taken apart. Cleaned. Measured Buy new parts. Then reassembled.
" I wish I had never opened up the engine. " Has been said by many DIY people.

 

[racerone]

????----Of course the piston comes out of this engine !----It just comes out in a different way.----This motor must be taken apart.

 

[Faztbullet]

No repair ot the piston itself only a new one

 

[merc850]

Pull the powerhead off the DSH then strip it down to the bare block follow these instructions

I'm assuming that a Classic 50 has no cylinder head.

 

[racerone]

None of the Mercury motor inline models have a cylinder head , until they developed the V-6 models

 

[cyclops222]

How to repair a very small casting hole in a Aluminum piston. the Evinrude 30 hp 2 stroke. Pull the sparkplug out & looked into the cylinder. Hey !! Is that a tiny hole in the piston ? Yes Pulled the head off. Tiny casting hole.
What to do. It is not above the rod area. Get a drill bit a little bigger the hole but same size as my Aluminum nails. Cut off the pointy tip .Slight rounding of the end. Press the nail in snug. Cut off excess and filed stub flush.
30 ? years ago ? Still in place.

 

[Willyclay]

Thanks for sharing this. It is part of why I love two-strokes!

 

[racerone]

Many pistons have a small ---" center hole "---Used to position piston when machining.----Normal.

 

[JohnTRI]

Thank you for all the valuable information that you all have taken the time to share to me. I want to learn further into taking apart my engine even further. As it stands I’ve taken off the exhaust cover, the bypass cover. I believe with enough time and tinkering I could put it back together as it is. I would need to find the torque specs for the bolts for the exhaust and water jacket cover but I believe I could put it back. The issue that I’m worried about it the fly wheel and the timing on the flywheel. To put it simply I have absolutely no ideal what I’m doing or getting my self into when it comes to removing the fly wheel and truly taking apart the engine in its entirety. If there was a step by step guide that I could find anywhere that would be optimal for my highest chance of success. It’s just that before completely opening her up I would want to know all the most probable and likely things there is to go wrong and things that I can take preventative maintenance on to avoid miscomings.

 

[racerone]

The powerhead MUST be removed from the exhaust housing in order to do a proper repair.

 

[chrisgt]

Thank you for all the valuable information that you all have taken the time to share to me. I want to learn further into taking apart my engine even further. As it stands I’ve taken off the exhaust cover, the bypass cover. I believe with enough time and tinkering I could put it back together as it is. I would need to find the torque specs for the bolts for the exhaust and water jacket cover but I believe I could put it back. The issue that I’m worried about it the fly wheel and the timing on the flywheel. To put it simply I have absolutely no ideal what I’m doing or getting my self into when it comes to removing the fly wheel and truly taking apart the engine in its entirety. If there was a step by step guide that I could find anywhere that would be optimal for my highest chance of success. It’s just that before completely opening her up I would want to know all the most probable and likely things there is to go wrong and things that I can take preventative maintenance on to avoid miscomings.

Such a step-by-step guide exists; you need to buy a factory service manual and it'll walk you through the process.

 

[racerone]

Judging by statements so far , you need a proper manual in order to understand how these fine / smooth running motors are put together.----There are no short cuts.----Mistakes will be expensive.