to hone or not hone

[dutch420]

Hey guys so i have to replace two pistons in my outboard . Now as u can see two have started to melt . And im assuming this is from timing thatwas so far off i cant believe it ran.... Now cyl 2 is in good shape and i figure it was not damaged do to a lack of compression from a almost stripped spark plug hole. So im going to de glaze cyl 1and 3 before i replace the pistons but should i also remove piston 2 and de glaze this cyl too..
the pistons i got to replace the damaged ones are from my parts motor a 1971 70 hp , the motor they are going into is a 1973 85hp

Pics are in order of cylinder 123

 

[Frank Acampora]

Re: to hone or not hone

You Need to deglaze 1 and 3 so you may as well do #2 also. You can remove the pistons by removing the carbs and intake manifold. Reach in the openings and using a 12 point 1/4 inch socket remove the rod cap screws These are matched so keep them separate and with their respective rods. Push the pistons out through the head.

Use a little oil when you hone and clean very well after--that way you will not need to disassemble the engine.

Be a bit obsessive with the roller bearings. 16 go on each rod. Count them before and after and don't let any fall into the exhaust ports. Look up posts on replacing pistons for more details. Timing may have caused to problem but since #2 is not damaged, there is also a strong possibility that carbs are set too lean. look up synchronizing timing and carbs in FAQs sticky to see how to correctly set them

 

[dutch420]

Re: to hone or not hone

Hey frank. Ya i knew about the intake to get at the rod caps. Im pretty sure i got that from a post u made a few years back.lol. The carb sync i have been looking into and if its anything like the info on timing u gave me it should be a no brainer..

Now i have a question.
I have been researching these motors for quite some time now and have come to find that parts from the 70 to 105 or 120 cant remember can be interchanged some but no all. Is this true, this is why i purchased the 70hp .
No if i need a carb part can i use the whole carb or are the jets and carb body different to make the difference in hp. Or is it a combination of carb and intake and exhast porting

 

[Frank Acampora]

Re: to hone or not hone

The 70 up to the 105 and some 120s are all swappable as far as pistons. all three cylinder cranks are the same.

The 70 has 1 3/16 diameter venturis and the 85 has 1 5/16 diameter venturis. Jets are bigger on the 85 carbs too. DO NOT swap jets into the 85 carb

You can swap the 70 carbs onto the 85 and yes, you will lose a little power, but most of the power difference is in the porting. The 70 has circular exhaust ports milled into the cylinder wall while the 85 has elongated ports with greater area. I never measured but I will bet that the port timing (when it opens) is different too. All these engines have circular bypass ports milled into the cylinder wall If you want to disassemble it you can port both bypass and exhaust. This will make it deliver an honest 90 HP at the prop. More photos next answer.

 

[Frank Acampora]

Re: to hone or not hone

 

[dutch420]

Re: to hone or not hone

Hey frank or anyone else..
So i removed piston 1 got it deglazed no prob looks new. But i ran into a problem
.... My 85hp is running 2 ring pistons and my parts 70hp is running 3 ring pistons. Now my question is can i run two 3 ring and 1 2 ring piston and have no problem.
I will post pics when i get home ran out of time had to go to work

 

[Frank Acampora]

Re: to hone or not hone

Yeah, it probably doesn't make any difference and the engine will run well.

BUT --I tend to be a bit obsessive/compulsive and anal/retentive. Running (two) three ring pistons and (one) two ring piston would severely offend my aesthetic sensibilities. Translated into english: I would never do it because even though they are inside the engine---I WOULD KNOW! I wouldn't be able to sleep at night. Adrian Monk (Tony Shaloub) is my role model.

If you want a little more sharing, I eat M&Ms in even numbers and by color. I buy things in even multiples. Crooked pictures on the wall drive me crazy--well, a little crazier than I already am. Get the picture?

Thus, I have never done this type of repair and probably never will. SO: Why don't you use all three (three ring) pistons?

 

[dutch420]

Re: to hone or not hone

Hey frank...

Ya i know i like to be all the same when i do something too. But this motor has been alover the place with the parts.. I have been replacing as much as i can but in this instance im kind up a certain creek with out that paddle. One of the 3 ring pistons is scored on both sides so all im left with is a two ring. . And what a pain it is to put the bareings and races together and try to assemble. Went at it for almost two hours and all i got was a headache......
Will post pics tomorrow

 

[Jiggz]

Re: to hone or not hone

I concur with you in re-installing the rod caps to the crank! Although this can be done by one person it will be easier with a partner who pushes the pistons while the other is spotting the rod into the crank. I had to use a long 3/16" rod wire to guide the rod into the crank. The bearings need a lot of triple guard grease which by itself is really sticky to hold the race and needles in place. When the upper rod cap is in place use the guide rod to install the bottom rod cap before removing the guide rod. From there it's all about carefully installing the 1/4" bolts!

 

[dutch420]

Re: to hone or not hone

Lol i know what u mean took me a total of 3 hours to put one piston in. What a pain in the arse lol. Im hoping now that i have an idea of how to do it i can deglaze and install the #2 and 3 before i go to work, also hope i can reuse the old head gasket last thing i want to do is buy a new one and have to pull apart the motor again if i have an issue. Still have not got to posting the pics but soon i hope to get to it....
Anyone got any ideas if ya can reuse the head gasket it or not both that i have look to be in great shape and both motors were hitting pretty good #s in the compression department .....also i torqued the bolts to about 195 but am useing an older wrench she maybe a bit off so could be around 200

 

[Jiggz]

Re: to hone or not hone

I reuse my head gasket and everything is working well with 125# compression on all 4 cylinders. The trick is to do a serious and in-dept inspection of the gasket ( I checked it with a magnifying lens just to make sure). any indication of dents or leakage or if you have any doubts at all, replace it! It's well worth $40 not to re-do the head again let alone the torquing! Note, with a new gasket, you will need to re-torque after the break-in hours.