1986 115 tower of power cylinder wear

[ryan 98]

Ok, so i picked this 86 115 up to go on an old wildcat. I bought it off someone i know and if he said it ran well i believe him completely. the trouble started since ive been running it on the watermuffs(just mounted it up on the boat). i noticed a water leak at the exhaust cover where the gasket had blown out, turns out the bolts were not tight and it had simply blown the gasket out. so easy enough repair, ordered gaskets and i plan on using a product similar to yammabond? on the bolts. i think that was what it was called when i rebuilt my jetski and that's what it ran on all the head bolts ect... im assuming that mercury used a similar product when new on these bolts. The gaskets have obviously been replaced in the recent past and the last guy didnt use any form of lock tight and actually wire wheeled the threads clean. but checked with a snap on straight edge all of my mating surfaces are near dead flat, so no problems there. trouble is when i looked in to the exhaust ports, the second cylinder from the bottom shows a good bit of scoring around the center exhaust port. now i dont remember the numbers but when i bought this i compression tested it and they were all close to even around 120, looked like a really healthy motor. so im sure compression numbers and damage havent changed in 5 minutes if running it, this damage is old. so my basic question is just an opinion of if this things going to eat itself. i mean I'm a tech for ford and have built many a motor, and I've pulled quite a few snowmobiles that ran decent down and seen similar stuff. i just have zero experience on mercury stuff, been a hardcore omc 3 and 4 cylinder fan my whole life. so basically just looking for someone who knows these motors and if its going to live, just a go fast boat, dont care about a bit of bad idle. now the last thing is i have a same year 90 hp of unknown condition, it came off a pontoon boat and looks super good and low hour. is this the same block and internal aside from reed blocks and carbs ect..? if so i could pull that one down and look in to it, a powerhead swap is no big issue, and as far as ive read their all 99 cu in powerheads. if their truly the same i would obviously pick the best looking one to run. i just dont want to get in to a full rebuild for a 35 year old motor, but at the same time they are great motors and ive loved running them on boats before. pics attached. thanks for any input.

 

[Faztbullet]

She has been hot once or twice, and motor has some hours as piston shows wear from side thrust. Just give it a good decarbon and run it. The 90 block is different as no transfer port in cylinder sleeve and exhaust ports height a tad lower.

 

[ryan 98]

She has been hot once or twice, and motor has some hours as piston shows wear from side thrust. Just give it a good decarbon and run it. The 90 block is different as no transfer port in cylinder sleeve and exhaust ports height a tad lower.

That's pretty much along the lines of what I was thinking. But I will say that damage has nothing to do with side thrust. The rings and piston have scoring on them that you can pick up with your fingernail, and only at that middle exhaust port on that cylinder. It picked something up at some point and as usual one little nick in a ring leads to more material going. Sad actually since the other 5 cylinders show pretty well and actually still have the factory rings running around the pistons clearly. So it could have been a super healthy, all be it well run old motor. Thanks for the reply about the 90 powerhead also, I figured on them having different porting but I was still hopeful they would be the same. My brain wants to pull it all down and do a full rebuild since it's a clean last of the breed motor. But money wise I could pick up a nice 150 omc for the price of the machine shop and pistons, so it's kinda fighting common sense there. All just button it up and run it, the funny thing is if I never saw in there I would have been totally happy with a little lump in it at idle. but now it will be in the back of my mind everything I run the thing.

 

[Texasmark]

That's pretty much along the lines of what I was thinking. But I will say that damage has nothing to do with side thrust. The rings and piston have scoring on them that you can pick up with your fingernail, and only at that middle exhaust port on that cylinder. It picked something up at some point and as usual one little nick in a ring leads to more material going. Sad actually since the other 5 cylinders show pretty well and actually still have the factory rings running around the pistons clearly. So it could have been a super healthy, all be it well run old motor. Thanks for the reply about the 90 powerhead also, I figured on them having different porting but I was still hopeful they would be the same. My brain wants to pull it all down and do a full rebuild since it's a clean last of the breed motor. But money wise I could pick up a nice 150 omc for the price of the machine shop and pistons, so it's kinda fighting common sense there. All just button it up and run it, the funny thing is if I never saw in there I would have been totally happy with a little lump in it at idle. but now it will be in the back of my mind everything I run the thing.

"All just button it up and run it, the funny thing is if I never saw in there I would have been totally happy with a little lump in it at idle. but now it will be in the back of my mind everything I run the thing."

"We" do tend to do these things to ourselves....leaving well enough alone!
If it really bothers you you might change the oil to 40:1 like some small 2 stroke engines recommend considering their adverse operating conditions. Using Pennzoil Premium Plus semi-syn., you shouldn't notice the difference in deposits or smoking...wally world carries it in the sporting goods dept adjacent to the Quicksilver-Merc. at twice the price. I run it at 50:1 or in a VRO system and have to check the oil tank level to know that I'm burning oil.

 

[Faztbullet]

Just run it and have fun it it craps out then replace it. Likely to run several years without problems. My ole tricked I6 had lil scuff in them also but turned 7K all day long. Just sold the lil rascal last year

 

[ryan 98]

Just run it and have fun it it craps out then replace it. Likely to run several years without problems. My ole tricked I6 had lil scuff in them also but turned 7K all day long. Just sold the lil rascal last year

Yeh, I just did the core in the boat that was a bit of a job. I usually cheat and prop them to rev a bit over with just me in it. But that way I'm not stuck changing props when I have 4 people in it or want to pull a tube. Does this thing have a rev limiter in it? And what rpm is it set at, I assume it has one since it's all cdi. Also any idea on the lower end ratio? I have a feeling it's going to prop pretty different than my old omcs. Thanks for the reply

 

[ryan 98]

"All just button it up and run it, the funny thing is if I never saw in there I would have been totally happy with a little lump in it at idle. but now it will be in the back of my mind everything I run the thing."

"We" do tend to do these things to ourselves....leaving well enough alone!
If it really bothers you you might change the oil to 40:1 like some small 2 stroke engines recommend considering their adverse operating conditions. Using Pennzoil Premium Plus semi-syn., you shouldn't notice the difference in deposits or smoking...wally world carries it in the sporting goods dept adjacent to the Quicksilver-Merc. at twice the price. I run it at 50:1 or in a VRO system and have to check the oil tank level to know that I'm burning oil.

Yeh, I always run them a little rich on oil. In my 61 I run it at about 20:1 since it called for 16:1 sae 30. I learnt my lesson with my favorite 56 running 32:1 in it. She went to heaven, but that was after 10 years of a lot of use. This one will run 40:1 with the cheap tcw gallon juggs from Canadian tire. I figure that oil has to be good stuff since my dads been running it in his 99 since brand new and she's seen one hell of a lot of use.

 

[racerone]

?---20:1 ratio is less oil in the mix then 16:1 ratio.

 

[ryan 98]

?---20:1 ratio is less oil in the mix then 16:1 ratio.

It is less oil. But we have come a long way since the 50s with our 2 stroke oils. When those motors were new they ran standard 30 weight oil in them. With the new 2 stroke oils you can run a bit less. I've actually tried running some old non detergent 30 weight in them at 16:1 and its a truly smokey mess. I think 20:1 is still overkill in them, but at 40:1 they do seem to eventually eat up the bottom end. Sorry about the off topic tangent.

 

[Faztbullet]

Run mix at 50:1 ,use a good synthetic for less smoke, no rev limiter just powerband and ratio of lower is 2:1

 

[ryan 98]

Run mix at 50:1 ,use a good synthetic for less smoke, no rev limiter just powerband and ratio of lower is 2:1

Awesome. I figured they would have put a rev limiter in there, but run up to about 1500 on the water muffs I can sit my drink on top of this thing and it won't go anywhere. So I figured these things would like to rev. Pretty damn smooth motor so far, gaskets come in Wednesday so all get to really find out. Seeing as I have access to tonnes of omc spline props to try, but nothing merc I don't really have a good starting place. All attach a photo of the boat, she's pretty light with all new core and transom, also no coast guard foam to be waterlogged anymore. Its on an adjustable jacking plate so I can mess with that also. All attach a photo of the boat (and yeas its an old photo, she's cleaned up a lot better now). Any rough gestamate on propping this thing? Have to start somewhere.