1976 mercury 115 pistons???

Shadow1234

Cadet
Joined
Jul 17, 2008
Messages
8
I just bought this engine yesterday. My dad did a compression check on all the cylinders and all had 120psi except number 3 which was 60psi. So he thought no big deal replace that piston and good to go. Well we just took it apart and I now need to replace three pistons one is cracked one is burnt and the other number 3 is really burnt up. The pistons that came out of the engine are 3 ring pistons. And when i put the model number in on the internet to buy new pistons they are only 2 ring pistons. Did they just switch to 2 rings??

I have a couple of questions for you guys/girls on here.

1. Will the 2 ring pistons work?
2. What caused the pistons to burn up like they are in the picture my dad thinks it might be the timing.
3. 4 of the pistons have notches on them and 2 do not. My dad thinks that it has been rebuilt before.
4. What all do I need to buy? I need a shopping list. I am a broke college student trying to get out as cheap as possible but I do not what to cheap out on the engine so what ever needs to be done needs to be done.

P.S. if you need anymore information just ask.

Thanks,

Shadow


NO LIP
IMG_0306.jpg


Crack
IMG_0305.jpg


#3 piston
IMG_0303.jpg


With lip
IMG_0302.jpg


All 3 that need to be replaced
IMG_0300.jpg
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,100
Re: 1976 mercury 115 pistons???

Looks like they were running lean and have detenation issues. The 2 ring piston replacements can be mixed with the three ring original pistons. You will need to bore out any cylinder that is damaged and install an oversize piston and ring set. Shop around as pistons can be pricey. You should find some for about $90/each.

You must clean all carbs, rebuild the waterpump with gaskets, orings and impeller and wearplate, as well as set timing to factory spec, or you will have a repeat of this damage.
 

Shadow1234

Cadet
Joined
Jul 17, 2008
Messages
8
Re: 1976 mercury 115 pistons???

Cool. Thanks for the info. Ill clean the carbs. And do everything you say to do here.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,930
Re: 1976 mercury 115 pistons???

Thats pre-ignition damage due to a bad trigger, replace it.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,100
Re: 1976 mercury 115 pistons???

Hey Fazt, That 1976 motor has a distributor. Is it still the trigger?
 

arsenalpsu

Petty Officer 1st Class
Joined
Dec 1, 2008
Messages
290
Re: 1976 mercury 115 pistons???

I sent you a PM in reguards to your pistons.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,930
Re: 1976 mercury 115 pistons???

Hey Fazt, That 1976 motor has a distributor. Is it still the trigger?

yep ..replaced about 30 or so over the years for the same issues..
 
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