Merc 850 Inline 6 Piston Scoring

[Deus_Vult]

Hello everyone. Lately I’ve been in the process of tearing down and rebuilding my 1964 Mercury 850 6 cylinder so it is fresh and ready to go for next year.

Today I split the crankcase halves and pulled the crankshaft out and found that some of the pistons had some scoring on the sides. Although I do have quite a bit of experience in the mechanic world (I have actually begun working as an automotive mechanic earlier this year after graduating tech school), I am still young and there are still some things I am not to experienced on that I could use some advice for, this situation being one of them. I am posting the pictures of the pistons here, and I am just wondering if you guys think they are beyond saving. Pistons 1 and 6 are the main ones in question. The cylinder walls themselves looked ok to my knowledge, which to me is a good sign.

I also noticed that the bottom main bearing felt pretty rough and it should be replaced. Does anyone know if there is a good way of pressing the old bearing out of the bottom end cap? If not, I will have to replace the whole end cap assembly, but if I do, would I need to reshim the new one?

Thanks in advance for the help, it is appreciated. Have a great rest of your day.

 

[jimmbo]

The Bearing should be a Service Part, now getting it out will likely involve a Slide Hammer and outward facing Jaws, with the End Cap secured

 

[Deus_Vult]

The Bearing should be a Service Part, now getting it out will likely involve a Slide Hammer and outward facing Jaws, with the End Cap secured

A slide hammer is a pretty good idea, I didn't even think of that. I just need to get a table vise for my garage...

Do you have any thoughts on the pistons by the way?

Thanks for the reply.

 

[jimmbo]

You can't squeeze the Bearing Cap, as that will ruin it, you will need to find a way to keep it anchored

As for the Pistons, they are Scuffed and Scored, and so will likely need replacing. What do the Cylinders look like? Have you measured them for Wear?


2 Stroke Cylinders wear differently than a 4 Stroke. A 4 Stroke will taper, wider at the Top, while a 2 stroke does that too but it will also wear wide at the Ports

 

[racerone]

If you drop the housing in boiling water for 10 minutes , then the bearing might fall out. -----New pistons might be available as well as new rings.------Internet search those part numbers.----Your location?

 

[Scott Danforth]

Doesn't matter what your pistons are like as you will need to get the bores bored and honed and get new pistons and rings

 

[Deus_Vult]

You can't squeeze the Bearing Cap, as that will ruin it, you will need to find a way to keep it anchored

As for the Pistons, they are Scuffed and Scored, and so will likely need replacing. What do the Cylinders look like? Have you measured them for Wear?

View attachment 393180
2 Stroke Cylinders wear differently than a 4 Stroke. A 4 Stroke will taper, wider at the Top, while a 2 stroke does that too but it will also wear wide at the Ports

Visually, the cylinders didn’t look bad. I didn’t have time to measure them last night, as I was fixing my truck as well and moved back to that soon after I got the crankshaft out.

Doesn't matter what your pistons are like as you will need to get the bores bored and honed and get new pistons and rings

I just took a quick look on marineengine.com and found 5 piston/ring sets available. They are around $150 each, so that’s a bit troublesome for me given that I really don’t have that much money to spend on my projects right now due to the fact that I’m living on my own now. I’m assuming if you are replacing a couple pistons it is best to just do them all, but is there anyway I could get away with just doing the two bad pistons and honing all the cylinders? Or maybe even do oversized pistons on 1 and 6? If that’s a bad idea and not recommended I understand, like I said I’m still pretty new to major engine overhauls so I don’t know some of the aspects of it, such as this, too well.

If you drop the housing in boiling water for 10 minutes , then the bearing might fall out. -----New pistons might be available as well as new rings.------Internet search those part numbers.----Your location?

That’s another good idea regarding removing the bearing. I’m located in central MN, why do you ask?

Thanks for the replies everybody, I’m glad I came here with my questions.

 

[jimmbo]

If you can't afford to rebuilt properly it the First Time, how are you going to afford rebuilding a Second Time?

 

[Scott Danforth]

you can do a single piston oversized. however once you find out how much it costs to blind-bore and hone one cylinder or two cylinders. you may as well do the others as the set-up is 90% the cost.

 

[Deus_Vult]

If you can't afford to rebuilt properly it the First Time, how are you going to afford rebuilding a Second Time?

Fair point.

you can do a single piston oversized. however once you find out how much it costs to blind-bore and hone one cylinder or two cylinders. you may as well do the others as the set-up is 90% the cost.

Yeah I had a feeling that was going to be the case.

Looks like I’ll be taking a break from this project to save up some money to do it right. Thanks the advice!

 

[Deus_Vult]

you can do a single piston oversized. however once you find out how much it costs to blind-bore and hone one cylinder or two cylinders. you may as well do the others as the set-up is 90% the cost.

By the way this might be a dumb question but you are saying to just get all the cylinders bored out for all new oversized pistons correct?

 

[racerone]

Step #1 is to find if parts are available somewhere !

 

[Scott Danforth]

By the way this might be a dumb question but you are saying to just get all the cylinders bored out for all new oversized pistons correct?

Step 1 is to find a machine shop that does blind boring

 

[Faztbullet]

What is casting number on block?

 

[Deus_Vult]

Hey everyone thanks again for your help. Sadly, my garage burned down over the weekend taking with it many of my most special possesions, including the Merc 850 and the boat it went on. So needless to say this project has been put to rest.

I do appreciate the advice you all gave me though, even if it doesn't apply to this project anymore. Regardless, I do still love Merc towers, and I plan on purchasing another one someday. That way, all my knowledge I've been building up on them won't go to waste.

 

[jimmbo]

I had a couple of those Inlines. I liked them, even though I was treated with disdain, being in an OMC Family. The Hickling ended when my 90hp and 115 inlines could out pull, have Higher Top Speed, than the OMC 90s and 115 respectively, and the 115 even beating the 135-140s, and doing sp on less Fuel.

 

[racerone]

The inline 6 is a smooth runner.------Had a marina owner say that he could rebuild one in about 8 hrs back in the day.------Now says he does not want to see one anymore.-----Has sold all customers a new motor instead.------

 

[1960 Starflite]

Hey everyone thanks again for your help. Sadly, my garage burned down over the weekend taking with it many of my most special possesions, including the Merc 850 and the boat it went on. So needless to say this project has been put to rest.

I do appreciate the advice you all gave me though, even if it doesn't apply to this project anymore. Regardless, I do still love Merc towers, and I plan on purchasing another one someday. That way, all my knowledge I've been building up on them won't go to waste.

I'm sorry to read of the loss. Tough to lose projects that take hours of enjoyment with them. Tool loss can be a major loss also. I have a list of tools with replacement values. Sadly, it needs updated. I would suggest an inventory list to all. You'll be surprised of the "New" cost value.