90 and 115 distributor-less block differences.

So I am repairing a 1986 90 inline 6 that has a cracked block.
I looked up the Mercury number, and it is 8311a4.

I won a 115 block on ebay, distributorless also, the mercury part number is 8310a4.

I need to know what the differences are between the two and if the block I won will work with my motor.

If you have any knowledge any help will be appreciated.

Thanks alot guys,
Paul.

Re: 90 and 115 distributor-less block differences.

The blocks should ne near identical, the difference being the port timing and piston diameter, the 115 has a bit more timing and bore to make more power than the 90.

See http://www.mercruiserparts.com/Show...4&bdesc=CYLINDER+BLOCK+AND+CRANKCASE+ASSEMBLY

Re: 90 and 115 distributor-less block differences.

The bore, stroke and timing are identical on those two blocks. The intake porting and exhaust scavanging of the 115 block is likely a bit better. Compression may be a bit higher due to high dome pistons, but that should be verified.

Re: 90 and 115 distributor-less block differences.

Chris1956 said:

The bore, stroke and timing are identical on those two blocks. The intake porting and exhaust scavanging of the 115 block is likely a bit better. Compression may be a bit higher due to high dome pistons, but that should be verified.

Click to expand...

Both Chris and Charlie have answered, just a small correction. The pistons are the same bore, your new block will have finger ports which work along with the power ported pistons. If you have non power ported pistons from your 90 you will still have 90 HP. If you have power ported pistons you will gain hp as long as you set the reed stops to the 115 setting. I suspect you have low dome pistons in your 90, not high dome.

Re: 90 and 115 distributor-less block differences.

Fart,
I thought I had sourced a cheap block.
Turns out after talking to the seller further the motor did a have a distributor.
He is an used parts dealer, seems to know what he is talking about. He seems to think that the block is the same between the two, as long as I use my front cover off of my motor I can use the distributor style block.

Quoted from email.

""I'll tell you a secret about this unit-it'll work on a 1985 inline 6 if you have the front cap to replace on this one. The only difference between the 1985 models and the older models like this one are that the older ones have the front cap for the distributor to mount on. The newer ones have a front cap without the distributor. I can probably come up with a good newer model block but it's the same as this unit here, for the 150.""

True, false, Or is the jury out?

I haven't worked on enough of these to know, heck this is the first "tower of power" I've ever looked into extensively.

So what do we say? Is it possible? If I use every last piece from my 1986 90 HP to not have to fart with trying to rig a distributor on it?

Re: 90 and 115 distributor-less block differences.

There is one thing to be aware of ( I was reading about interchanging parts) when it was pointed out to me that engine block and intake covers are married to each other from the factory.I tried using my 80 horse intake on my 85 hp motor and notice that top and bottom of the engine block and intake did not come together smooth (they were a little offset) meaning that the top and bottom bearing carriers wont seal up the engine like it is supposed to be. Other than that its identical.