Building A looper Beast

[Steve Litzell]

Dick a quick question, Are the rods of a cracked cap design or are they smooth across the parting line? Thanks Steve

[narrowminded]

Modern pro racing outboards went to one piece rods and press together cranks to get reliability at increased rpm and power output. I believe a one piece rod would make the engine more reliable and secure the investment of your efforts. ( you are to be applauded for running the engine) There are a lot of sizes of one piece stock rods, and also the custom route and considering what you built ,if any body can build a inline 6 press together crank you can . Hope the best for you solving this, the power from this thing is incredible I thought it was a animal before you bumped up the timing.

[Steve Litzell]

Modern pro racing outboards went to one piece rods and press together cranks to get reliability at increased rpm and power output. I believe a one piece rod would make the engine more reliable and secure the investment of your efforts. ( you are to be applauded for running the engine) There are a lot of sizes of one piece stock rods, and also the custom route and considering what you built ,if any body can build a inline 6 press together crank you can . Hope the best for you solving this, the power from this thing is incredible I thought it was a animal before you bumped up the timing.

Because of the indexing of the six cylinder crank, twisting of the crank while running is a major problem. This is why the six cylinder Konig did not work so good. Been there done that. Dicks project here is the most dependable way. besides there are plenty of 14 to 15 thousand RPM motors with rod bolts that are tough and don't break, Steve

[Fast Fred]

production cost is the reason for one piece rods. rods just hang on for the ride, unless upset. at 10,000+hp alu rods are used, two piece at that.

[R Austin]

Dick a quick question, Are the rods of a cracked cap design or are they smooth across the parting line? Thanks Steve

Steve

The rods are the later style cracked caps with the 1/4-28 12 point cap. Does any one know the latest MERC torqueing spec for this rod assembly?

PS I did look at the SPS bolt line up and found a bolt but the flange is to big in diameter. Which I suppose could be ground down., but the flange face would loose the 45 degree chamfer and need to be replaced

[Powerabout]

Dick
You might want to get some bolts and do some torque to stretch to see where they stay elastic so you find out the correct torque spec regardless of what Merc say
At least you can them check them before use.

[champ20B]

Bolts in general have a standard torque rating based on sizes and grade as already tested. There is info that can be found on the net. But if you go beyond the rating of a particular grade bolt, it can or will break every time.

As for the rod issue, If it were me I would research what rods the Mercury Twister II used. It was a 100cid six cylinder that made 200+hp in racing tune, maybe more. Anyway, that was a race engine and the rods and crank may have been better suited if it were a quality "purpose built" engine.

[baldad45]

Same rods as a stock 115-150 inline .

[Fast Fred]

i looked around, 180 inch pounds which is 15 foot pounds is what i saw for that rod. seems weak, that may not be right. they used a torque spec in them days, you could check installed length (of bolt) to uninstall of a new bolt, it did say use new only.

[Yellowjacket]

That same size bolt on the 44 cubic inch motors is torqued to 18 foot pounds (216 inch pounds) so yes 15 foot pounds is a bit low....

The merc motors run in the modified classes run pretty high speeds and it isn't an issue. I think the rods are probably not an issue. Not sure what potential issues there are running high speed, but if you get into a torsional vibration mode the crank would let go in very short order.