56" omc cooling

[thornl01]

Got a stock rebuild to do on a 1986, 70 hp, 56" rude.

need any additional info on cooling upgrades for the middle cylinder.

Have already "backed out" the bridge on all the exhaust ports and have drilled piston for bridge cooling.

Any more suggestions ?

LT

[brichter]

There was a kit available at one time, some fatter main jets. The remedy at the time was to "cool it with fuel". Most customers were not happy....lost 50-100 Rpm. I think some still stuck with the kit.

[Per]

I'm not 100% sure this applies to the -86 engine but I know it was recommended to my -91 56CI.

Relocate tell tale outlet to top of water jacket.
Rejet, as mentioned before
Reduce timing to 17degree, think 19 is std.
I think there is some kind of mod to be done to the thermostat and /or seat as well.
There is still an upgrade kit available but I don't remember the part# (bought one myself for a couple of years ago)
Waterpump?


There's lot of information on this topic on Iboats OMC repair forum. Think most of the mods / part# above are described in detail there.
Also if not already done search for service bulletins on the topic, there is several...

Most important, don't lug the engine!

I bought my engine with seized middle (and scuffed upper) cylinder, the previous owner told me that it happened while he was towing another boat, I'm sure you will find other stories just like that if you google...

Good luck

Edit: found what I was looking for...

Seahorse5 over at Iboats wrote:


60 & 70 hp service bulletins for cooling and overheating

SB 2221 Temp sensor new sensor pn 584166, tan/blue stripe wire.

SB 2225 thermostat seat new seat pn 336416, may not need this in fresh water.

SB 2271 jet and timing kits ds

SB 2276R1 relocate tattle tale nipple to top of block.

SB 2276R1 and new pressure relief springs comes in waterpump kit pn 432955.

[Powerabout]

do you have a copy of 2271
the rest we can work out
thanks

[Per]

do you have a copy of 2271
the rest we can work out
thanks

I will go to my workshop tomorrow, maybe the paper is still in the box the kit came in...

[Bill Gohr]

There were no mods for the 1986 motor, the issues were mainly with 1991 thru 1993, we changed the block for the fall of 1993 which the 94 build, that's when it went to a single exhaust port. If you read those bulletins they should not pertain to an 86' what the 86' did have was a tighter head, and would take out the middle cyl, but if it lived this long its probably OK, if you're worried go up 1 on the main in the middle carb.

For your engine as far as cooling, buy the 432955 water pump kit and follow the instructions

[thornl01]

Thanks Bill,

This engine definately took out the center cylinder & head.

Got a later model head for the rebuild.

Should I still drill the pistons (1/16" hole) to oil the bridge ?

Lawrence Thornton

[Bill Gohr]

Well I have to recommend the factory oversize piston for that repair, I had the cam shape changed on the piston for the service part as well as the holes added

[Per]

Sorry to ramble in this thread:o[

B]Powerabout:[/B]

Went to the workshop but the box with the kit was not really what I was looking for, it was the waterpump kit...

I did find some of my own notes in my workshop manual for my -91 56CI stating that a ignition should be reduced to 17degrees like i previously stated the notes also stated that the info was from a SB but not wich number:o
In the end I didn't bother to rejet or reduce timing since I figured it would work anyway with my light boat and cold waters:D
Also the fuel consumption was already ridiculous compared to my old Volvo Penta VP700:rolleyes:

PS: Powerabout, your PM inbox is full...

[Bill Gohr]

If the head you are using has a "G" stamped after the part number that would be the later one,

As far as those service bulletins from 90, 91 92, and early 93, most of them can be disregarded, lots of those were quick fixes trying to cover engines that were failing like popcorn so we really don't need to do all of them and remember if you have a 90-93 with a replacement oval port powerhead and the correct water pump you need to disregard them all.

[calvin]

Which year/years 56 inch motor is the best for mods or stock rebuilds?

[Powerabout]

Thanks Bill

PM box fixed

[Bill Gohr]

Which year/years 56 inch motor is the best for mods or stock rebuilds?

You are going to build a powerhead for stock I would use nothiing but an Oval port powerhead

[sharpeye Mike]

That sounds great but can you mod an oval port?
If so what kind of mods can you perform?
Has anybody ever ran a stock motor on a sst60 exaust tunner?
Thanks.

[Powerabout]

I am about to try a sst60 tuner on a stocker but I am pretty sure I will;
loose bottom end
get nothing on top
need to rejet
so waste of time on stock porting

[ima75man]

I am about to try a sst60 tuner on a stocker but I am pretty sure I will;
loose bottom end
get nothing on top
need to rejet
so waste of time on stock porting

why would you lose on bottom end? how about mid-range? i thought everybody ran stock moters.....i found out just modifying a stock tuner would help some..

[Per]

If the head you are using has a "G" stamped after the part number that would be the later one,

As far as those service bulletins from 90, 91 92, and early 93, most of them can be disregarded, lots of those were quick fixes trying to cover engines that were failing like popcorn so we really don't need to do all of them and remember if you have a 90-93 with a replacement oval port powerhead and the correct water pump you need to disregard them all.

Excellent information!
If I only had known that when i rebuilt my engine. I've spent countless hours on the Internet trying to find all info from those service bulletins :rolleyes:

[Bill Gohr]

Well depending on the boat you would most likely lose bottom end with the 60 tuner, because, it is designed for peak power on a tunnel boat, at high rpm's.

If you're looking for absolute peak power when you mod one of these you would be best to use a pre-90 bridgeport, that was before the casting got changed, or the most reliable would be a 94 and newer with the revised cooling system.

[calvin]

Which year motors are oval port?
I have a 87 and a 88 56 incher.

[Bill Gohr]

Which year motors are oval port?
I have a 87 and a 88 56 incher.

1994 and up are oval port

[Cubman]

Does anyone know where I can find a copy of the service bulletins mentioned previously?

[Bill Gohr]

Does anyone know where I can find a copy of the service bulletins mentioned previously?

Hopefully any good OMC dealer would have them, I think I may have a copy of the Memo I wrote, proividing the info to everyone in house regarding this matter, it was a big topic back then

[Nemesis75]

If you were going to build an OMC 56ci and you were looking for max top end what combination of stock parts would you use? Block, head, crank (4 spline is OK), rods, pistons, intake, reed blocks, carbs, ignition and exhaust tuner. I have several of these motors I can use as doners. I already have a '72 65 flywheel but I will need a powerhead adaptor to go to a 15 inch, 49ci exhaust housing as the stock one is about 3/4 inch too tall. Thanks for your thoughts. Tom