Marine 351 help

tater_51_old · November 8, 2008 at 2:59 PM

I know this is off subject with regards to a hipo 289, but I need a little help, opinions.

My son in-laws family has a ski boat powered by a 351. It's an older boat that had a tired motor so they found a NAPA rebuilt long-block (ebay) to replace it. Being the motorhead father-in-law, I went with him to pick the motor up, which had been sitting for a couple years. Last night the kids had pulled the old motor out and we had a good look at both engines on the garage floor.

First thing I noticed was the timing marks on the old motor, BTDC fell to the left of TDC on the dampner. Checking the firing order it was 18456273, a reverse rotation set-up. Problem is I'm pretty sure the new longblock is a standard rotation, but have yet to verify that.

My question is, can the standard rotation motor be changed to reverse rotation by swapping out the camshaft or is there more to the change over? A fellow had mentioned that the crankshafts are different, beats me?? Of course everyone is looking to me for the answer, hell, I don't know, I only tinker with motors that run on top of 4 tires.

What would be the best way to verify the rotation of the new longblock, it does not have an I.D. tag or dampner on it, timing gears are clearly visible as it does not have a cover on it.

Any help or comments would be greatly appreciated.

Thanks

marv · November 9, 2008 at 12:34 PM

Marine engines do turn in the opposite direction of standard engines. You could turn the the Crank to the right (standard rotation) until #1 is TDC on a Compression Stroke- both Valves are closed; and then, rotate the Crank 90 degrees and see which cylinder is now on the Compression Stroke. Continue this until you have turned the Crank twice, 720 degrees, and you will have the firing order. You can then see if it matches the order on the old engine or if it is an exact opposite. I hope this helps.

C6ZZKGT · November 9, 2008 at 3:56 PM Official Post

My understanding is that the little hash mark lines on the crank at the rear seal area are in the opposite direction on a reverse rotation engine. Those little lines help keep the oil going back toward the inside of the engine. If the crank was turning the opposite direction the lines would help the oil escape from the rear main seal to the outside. That to me would translate to a rear main seal leak.

-Fred-

tater_51_old · November 9, 2008 at 8:17 PM

Thanks for the help. Looks like I'll be looking for another engine or possibly rebuilding the original. Seals, piston slap, camshaft, etc. etc. are more than I care to change on a newly remanufactured motor. At least we have the winter to figure everything out. Thanks again!

marv · November 10, 2008 at 2:30 PM

Yes Fred, it that's 'old right-hand torque rule'...

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