please help to identify OMC powerhead

[wrestler20]

Hello, I want ot order a manual for my motor, but the powerhead on it is not the original. THe freeze plug has the serial number G264255 on it. That freeze plug is located dead center on the back of the powerhead about 6 inches up from the V6 logo. Please help me figure out what year and HP the powerhead is. If that is not the correct place to look, let me know where to find a number that will identify it. Thanks for the help<br /><br />Steve

 

[wrestler20]

Re: please help to identify OMC powerhead

anyone?

 

[rickdb1boat]

Re: please help to identify OMC powerhead

Can't get it from the serial number. Need the model number, which should be on that plug. I don't know of any other place to look, as the number is usually on that welsh plug. Look everywhere on the powerhead for another number.

 

[Dhadley]

Re: please help to identify OMC powerhead

Sounds like a looper. The exhaust is all molded on and there are no covers bolted to the side covering the intake passages, right?<br /><br />There will be some numbers on the cylinder heads. Let us know what those are.<br /><br />Good luck!

 

[wrestler20]

Re: please help to identify OMC powerhead

Dhadley,<br />The only numbers i could find on the cylinder heads were the number 329745 on the right bank thermostat cover, and numbers next to each head bolt that just looked like the torque sequence. Let me know if that is the right number or what i might be missing. Thanks for all the help, don't know what i would do without this forum.<br /><br />Steve

 

[Buckstar]

Re: please help to identify OMC powerhead

Hi, Did you happen to look on the transom brackets to see it there is a tag on one of them with the model number on it? Sorry, had to ask,

 

[Dhadley]

Re: please help to identify OMC powerhead

OK, close enough for the moment. Its either a small or big bore open deck looper. Look at the top of either cylinder head and there is a tab on the head gasket that sticks up past the head and block surface right in the center. Is the tab straight across or does it have a semi-circle cut in it?<br /><br />There are numbers cast/stamped in the heads. You may have to look fairly close to see them. Once we get those numbers we can determine which model you have. The tab will tell us the bore size.<br /><br />Hummmm......there is a flat part in the center of the head (on the outside) that goes top to bottom in line with the spark plugs. Doess this area still look the same as the rest of the head (casting) or has it been machined completely flat? <br /><br />Also a factory replacement p/h (or one from a factory authorized remanufacturer) would not have that plug with that nimber. <br /><br />Good luck!

 

[Dhadley]

Re: please help to identify OMC powerhead

^Zip!

 

[dick]

Re: please help to identify OMC powerhead

Check that number .On a replacment p/h the number usually starts with a 4 and is 6 numbers long.Engine serial are 7 numbers long.

 

[wrestler20]

Re: please help to identify OMC powerhead

sorry for the slow response. The tab on the head gasket is straight across and the part of the head in line with the spark plugs is machined smooth. I still cannot find any casting numbers on it at all though. I talked to the shop and they said that the powerhead was rebuilt, not a replacement. They said to bring it by and they could identify the powerhead, but from what they remembered, the powerhead was a 93 or 94 closed deck 200. The motor itself is a 92 200 johnson gt. Hope this helps, let me know what else to do. thanks,<br />Steve

 

[Dhadley]

Re: please help to identify OMC powerhead

The gaskets with the straight tabs are for the small bore motors produced in 1986 and 1987. They have a 3.500" bore as standard.<br /><br />The thermostat cover number you gave us is used on the open deck motors, not the 93 and newer closed deck motors.<br /><br />The "machined" cylinder heads you are describing came primarily from Second Effort - the old OMC race division. They werent all that great but not bad. But that explains why you cant find the numbers - they are machined off.<br /><br />Looks like you have a small bore looper with cut heads. They ran pretty well, especially if you have a boat that responds to torque.<br /><br />BYW - how does it run? What type boat?<br /><br />Let us know!

 

[wrestler20]

Re: please help to identify OMC powerhead

Actually i have had some problems with the rig. I have a post that is outdated in which you were working with me on reducing slip, but then everything froze over up here and i havn't gotten a chance to go out and try some different things. The boat is an Astro fish and ski. No problems jumping out of the hole, bu the top speed is horrible. Turning a 24 pitch brand new raker at 5600 rpm and the boat is only topping out around 52 mph. I have a hydrualic jackplate that hasn't been a ton of help to me yet because the motor is also having some overheating issues. We pulled the lower unit and checked the water pump and impeller and they are fine, replaced both thermostats, but the thing still is running hot. Not really sure what else to check. I talked to my mechanic and he is going to go through it again to try to figure out what is going on, any ideas??? thanks,<br />Steve

 

[Dhadley]

Re: please help to identify OMC powerhead

If its overheating replace the entire pump assembly no matter what it looks like. Use a factory kit only! Replace both head gaskets. Install a water pressure gauge.<br /><br />Let us know how it does when you get done.<br /><br />Good luck!

 

[wrestler20]

Re: please help to identify OMC powerhead

He said he was going to replace the water pump assembly to start with. Forgive me if i sound ignorant, but the only way i'll learn is by asking, so why should you replace the head gaskets? The overheat buzzer went off once and i shut it right down, but does this mess up the head gaskets? I did go take a look at it with my dad today and he pointed out that the head gasket tab DOES have a little half moon cut out of it. Sorry for the wrong information earlier, don't really know how i didn't see it the other night when i looked, guess i was expecting something different. I had the mechanic install a water pressure guage and he put a tee in on a hose that comes from the bottom of the bock by the indicator and goes to some sensor on the throttle arm. That is the correct place isn't it? Hope this info helps and thanks again for all the help you have given me and everyone else on this board.<br /><br />Steve

 

[Dhadley]

Re: please help to identify OMC powerhead

OK - that head gasket tells us its a big bore open deck looper from 1988 to 1992 with a standard bore of 3.685".<br /><br />Since you are experiencing an overheat the head gaskets should be replaced especially if they havent been replaced in a while or if you dont know when they were replaced last. A slightly leaking or burned gasket can allow exhaust into the cooling system. If it gets worse and water enters the cylinder you could have bigger problems.<br /><br />It sounds like the water pressure gauge is installed correctly. The line you are refering to should actually come from the adaptor plate the block is mounted on and go to the throttle controlled water valve. <br /><br />Good info! Let us know how you make out!

 

[wrestler20]

Re: please help to identify OMC powerhead

how can i tell by sight that the motor is an open verses closed deck motor? I want to be able to have some type of info to back my statement up when i go back to the mechanic. Thanks in advance, <br />Steve

 

[Dhadley]

Re: please help to identify OMC powerhead

The closed decks have a "blow off" valve just to the inside of the port head near the top of the block. Its a little cap held on with two screws and has a hose going to each head. The open decks have no such place to put this cap and valve. I think, but may be wrong about this, the closed decks dont have the threaded bosses to mount your water control valve just aft of the throttle. I believe the bosses are there but they arent tapped. <br /><br />Or you could just pull one head off and look!