[Donger]

I have a 115 1985 or 1986 mercury. i have a blown piston in no.5 and the piston is locked in the cylinder. Is there any interchangable powerhead for this motor. If not, can i resleeve the gouged cylinder? I have been browsing the internet for motors and have seen some online that are 90 hp mercury motors that look as if they are the same as mine. I wonder if i can get a 90 hp head and use that.

Thanks in advance for the help.

[achris]

The 90 block is different. It doesn't have the power ports that the 115 block has.

I would just knock out the old piston and have that cylinder bored. Unlike 4 stroke engines, it's ok to only bore one (or two) cylinders on an outboard engine. Then buy an oversized piston for that hole.

Chris............

[Donger]

Chris, I think the damage is beyond boring the cylinder out. Do you have any specs on the total boring potential in that cylider? The piston is cooked to the block and has gouged the walls badly

[achris]

I don't have personal experience, but I have heard of some machine shops sleeving the block.... The biggest oversize that Merc do is 0.030". That's quite a lot. I think there is an aftermarket piston manufacturer who goes bigger, but k.r.a.f.t. disease has got me again

Chris............

[Donger]

Chris, i have another block for the motor. It has a 16th of play in the bearing end cap and i was told that that could be welded with aluminum and machined down to proper specs. Do you think that this is an easier approach to the issue than trying to bore out the block. i talked to the dude that i took it apart with and he said it wad f$!%ed. The other block it gouged pretty bad

[achris]

If the crank, with rods and pistons, on the current block is ok, and you don't want to use it, then put them into the new block. Just be sure to keep the crankcase covers for each engine together. They are a machined pair. You can't use cover 'a' on block 'b'....

Chris.............

[daveswaves]

Well Donger you have a couple of options. Chris is correct, the 90 hp is not power ported. You can certainly bolt a 90 hp block on your lower end no problem, you just won,t have the power you used to. Getting back to your 115 block. I have personally rebuilt a few of these and I would be surprised if you could not bore out the one bad cyl. Pistons are available up to 30 over and the weight difference of the new piston is negligible. If you have not pulled it apart yet you will find that it is not going to go together that easy once you do, its truly a labor (labour) of love to rebuild. Complete rebuilt powerheads are available on ebay and unless you are quite adept at rebuilding I would suggest that is the route to go. If you decide to rebuild gasket sets and pistons are available on ebay. Your crankshaft with the 1/16 journal play sounds like it is toast.
If you are going to bore the block you will have to find someone who is willing and capable of doing a "blind" bore. There is no removeable head on that block so it a little tricky to bore.

[hamit59]

As a machinist, I'll tell you Mercs are a real pain to bore. The liner is case in place, so you can't just bore it out and press in a new one .
I have bored over 50 j- rudes but my machine does not do blind bores.
I refer all the mercs to a old machinist the does then on a mill, he charges by machine hour @ 75.00 hr setup runs around two hours per hole, if it's not egg shaped real bad. A .030 oversize bore is very thin cylinder wall on a merc and some are chromed as well so you loose all your chrome.
If you don't have a good Marnie machinist in your area. I would look into a reman power head

Out of round limit as by the book is .0075 max and they do sale a .030 oversize piston, but I would never go that far with a oversize bore.

Just my 2 cents worth
Hamit
BT1 USN ret