View Full Version : Engine rotation

04-01-2004, 04:37 PM
I want to repalce my OMC 165 with a chevy short block but am confused about the rotation issue. Lets say that my OMC 165 engine since it is an inboard turns CCW. what do I need to change to make the replacement motor work?

04-02-2004, 01:11 PM
" First - all I/O's are left hand rotation, unless you have a twin screw boat.
The firing orders are completely different, which means the camshaft, distributor gear, advance weights, etc.. are opposite. A standard car motor will implode itself in very short order. Marine motors have a different torque and horsepower curve among a ton of other things.

Best advice to have to bite the bullet and have the original rebuilt or goto chevyengines.com - they put out some extremely nice marine rebuilts for a decent low cost. "

CJ Inglis
04-08-2004, 03:15 PM
" Scott,
Quick question. When you say 165, is that the same as a 3.0L? Also, in reference to the above reply, I have had several boats in my time. Some with marine engines and some with auto engines that had marine cams. There was zero performance difference between them. In fact, I just replaced my 4.3L OMC by rebuilding a Monte-Carlo 4.3L and using the cam from the OMC. Works like the original. As for multiple differences in the blocks???? Not true with Chevy. Even the heads are the same. Years past would have more nickel in the cast for the marine applications, and larger valves. These days, that's not always the case. Lastly, the firing order is the same as well. I didn't even have to change the crank.
So, in response to your question, you would need a marine cam because the torque requirements are different. Depending on what size engine you want to use would be a more apt factor in answering your question. Let me know if you would like more info.
CJ "

04-12-2004, 07:48 AM
"I want to repalce my OMC 165 with a chevy short block but am confused about the rotation issue. "

All the Same........
Go for It.............

04-21-2006, 08:54 PM
I have a 1975 OMC i/o with a 165 in line 6 cyl I have a problem with engine over heating there is lots of water coming through the exhaust and flowing out the tatle tale however the engine doesn't seem to be getting any water I removed the thermostat but it still heats up at slow speed if I rev it up to about 900-1000 rpm's it cools down could this be the water pump on the engine the impeller seems to be putting lots of water up. any help woul be greatly appreciated
Thanks Ralph

04-22-2006, 07:19 AM
"Check for air getting into the pump. Just had this on mine--bad gasket on the strainer. It pumped water, but no where near enough.