rebuild head questions

[fsds123]

I have a 1979 Evinrude 115hp v4 motor that I have owned for 5 years now. It ran fine until last summer when it starting to act up. It would still run fine, but was harder to start, especially after sitting. I did a compression check last night, and got the following. (The gauge I used for some reason doesn't "clear" lower than 30 psi, so I assume you have to subtract 30 psi from these readings.)
Starboard top: 150
Starboard bottom: 150
Port top: 35
Port bottom: 135

So corrected, this would be 120, 120, 5, 115.

I pulled the head on the starboard side and saw damage to the piston and some scratches on the cylinder on the top side (the one that read 35 psi, or 5 psi corrected), and also what looks like a single "nick" on the bottom piston, but no damage to the cylinder walls.

I do all my own work when it comes to car repairs, but haven't done much as far as 2 stoke boats are concerned.

My questions is...cost wise and reliability wise, is it best to pull the head and bore just the one cylinder/piston, both cylinders with new pistons, do all 4, or just get a new or used head on ebay etc?

 

[tashasdaddy]

Re: rebuild head questions

i look at it this way. first the availability of parts for a 30 year old motor. the cost to have the outside work done. i think you need to go further into it, and check the crank and bearings. then decide. you may find a good donor on ebay, and build one out -of two,

 

[emdsapmgr]

Re: rebuild head questions

You'll probably have to bore at least one hole. If the engine is worn and there is a lot of taper to the other pistons and sleeves, you may need to do all 4. Likely the crank and bearings are OK. I personally wouldn't use the pitted head. You can find good used replacement heads around-they made thousands of your engine around those years. .030 over piston ring sets should be readily avail. 5006669 piston around $90. You'll need a gasket set, about $120. When done, the engine should run like a new one, for significantly less $.

 

[fsds123]

Re: rebuild head questions

Any idea which powerheads will work with this motor? years and hp?

I also came across a rebuild kit on ebay for $550 that contains:
# 4 New Piston kits in your choice of sizes; STD. .010, .020, .030, or .040
# 4 New connecting rod bearing sets
# 4 New wrist-pin bearing kits
# 4 New wrist-pins
# 4 New piston ring sets
# 4 New wrist-pin circlip sets
# 1 New crankshaft seal kit
# 1 New thermostat overhaul kit
# 1 New overhaul gasket set

Are any parts missing should I decide to go this route? Is that a good price? Anything else you would replace while the motor is apart? I'd also be rebuilding the carbs and waterpump.

 

[emdsapmgr]

Re: rebuild head questions

When you overbore with genuine Bombardier pistons, you can use the service manual to determine the required overbore clearances for the machinist. If you use off brand pistons, you need to know their required overbore specs to give to the machinist. Pistons will vary in their expansion rates, by manufacturer, so you need to be concerned with this. (So that the rebuilt piston to cylinder clearances will give good service life.) If you aren't comfortable with their information, stick with factory parts.

 

[fsds123]

Re: rebuild head questions

After a little better inspection, it looks like only the one piston is bad. (I still need to pull the powerhead and take a better look). From what I've read, my 1979 pistons are the high ring piston types with higher compression that were discontinued after 1979 or so. So would replacing the one piston be a bad idea, since the replacement would not be a high ring type?

 

[emdsapmgr]

Re: rebuild head questions

It is permissible to bore just one cylinder. The other cylinders will have to be honed, and you should at least put new rings on the other 3 pistons. I doubt the difference in the ring height will make any noticeable difference to the engine operation. All replacement pistons weight the same, for interchangeability. OMC discontinued the use of the high ring pistons for a reason. They were prone to ring failure, esp with the low lead fuels that came out in the early 80's.