OMC powerhead interchange

[masondr]

Are the 90-140 v-4 crossflow( powerheads physically interchangeable bolt up to same base}? Same question re SEADRIVE vs "non-seadrive powerheads? I'm looking for a powerhead for a 115 SEADRIVE, and am getting mixed answers locally to both questions. My most credible source says all from 1978 on will bolt up, but i would like to confirm, if possible. thanks

 

[Dhadley]

Re: OMC powerhead interchange

That is correct -- 1978 on will bolt up. Flat or bubbled exhaust. Actually the 1977 powerheads from a 25" motor will too. <br /><br />The only issue is how your shift linkage is mounted on the powerhead. Take a look at your existing powerhead. On the front half of the block assembly there is a pan mount on each side at the bottom. The pan mount will be an "arm" that has a rubber mount in it. The starboard one has been machined on some Sea Drives to allow the attachment of the shift linkage. <br /><br />Outboard powerheads from 1979 on have the same type of lower front pan mounts. But not all had the extra "meat" needed to drill and tap for the shift clevis. If you need to, simply measure your existing mount and then cut, drill and tap the outboard mount to match.<br /><br />It all has to do with the angle at which the cables come into the motor. If yours comes straight in and has nothing to do with the pan mount then you can use the outboard powerhead without modification. <br /><br />Your next question will be if you can use your existing front half. I'm not saying you can't switch them but they are intended to be kept as a match to the block they came on. <br /><br />Good luck!

 

[masondr]

Re: OMC powerhead interchange

Dhadley: thanks for the help. Need one more thing- help me with what exactly the front half includes. Thanks.

 

[Dhadley]

Re: OMC powerhead interchange

The front half is what bolts to the block and the two pieces hold (surround) the crank. Anyway, like I said -- look at your existing motor and tell me if anything bolts to the pan mount. All pan mounts have a rubber insert with a bolt going down (verticle) to the pan. What we need to find out is if anything bolts to it horizonaly. <br /><br />Let us know!

 

[masondr]

Re: OMC powerhead interchange

Dhadley: thanks for reply. My linkage does bolt to the mount. As you indicate, I also would be "leery" of using my front crankcase on another block. I was thinking more of bolting an assembled powerhead to my base, swapping " external" pieces as necessary/feasible. I have been told That as long as a powerhead came with its own linkage, i could hook up to my cables, even though the linkage had a different boltup to block?

 

[Dhadley]

Re: OMC powerhead interchange

On an outboard the cables come straight in. On your Sea Drive I believe the cables come in on an extream angle. It's going to be a lot easier to use the Sea Drive linkage on the new powerhead assembly. If you find a used outboard powerhead, just drill and tap the mount to use the linkage you have. If you order a powerhead simply specify that it's for a Sea Drive. A quality remanufacturer will supply you with the correct part and no mods will be necessary.<br /><br />Good luck!

 

[masondr]

Re: OMC powerhead interchange

Cables on mine come straight in {horizontal}. THanks again for the help.

 

[masondr]

Re: OMC powerhead interchange

Dhadley: what is the story on omc hp ratings? I noticed in your reply to another seadrive question that an 88 235 seadrive was rated 235 hp at flywheel and 175 at propshaft. Can't believe losses between flywheel and propshaft are 60 hp? Must be more to the story. Thanks, Dave.

 

[Dhadley]

Re: OMC powerhead interchange

The sad truth is that a 235 never was 235 at the flywheel. That's why I said "about" 235 HP. But all the 160 CID crossflows were 175 at the shaft.<br /><br />Oh well!

 

[Hooty]

Re: OMC powerhead interchange

dhadley,<br />I've been watching this post and I'm curious. Is my '76, 149 cid, 200 hp 'rude 200 hp anywhere?<br />Thx. for the reply,<br /><br />c/6<br /><br />hooty

 

[Dhadley]

Re: OMC powerhead interchange

The 1976 200 was rated at the flywheel. You will typically lose about 12 to 15% to the prop. The 76 200 made decent power with those heads. <br /><br />Good luck!

 

[masondr]

Re: OMC powerhead interchange

Dhadley: Thanks. I'm a long-term car nut and more recent boat nut, but am learning. One last question on this posting. What is the status of current outboards rating? Ratings accurate and consistent between manufacturers,or is this a case-by-case thing?

 

[Dhadley]

Re: OMC powerhead interchange

The NMMA stepped in back in the early 80's and by 1984 everyone (outboard) was propshaft rated. They allow a 10% variance from advertised to actual horsepower. There have only been a couple of models that got out that were more than advertised but only for one year. Kinda fun to watch all these things going on.<br /><br />On the OMC side, Sea Drives were classed under Drive Systems as were stern drives and inboards. That's why they don't have model year or horsepower designations from the factory. They simply go by model number. But they are directly related to the outboard line. Interesting, huh?<br /><br />How's yours coming?

 

[masondr]

Re: OMC powerhead interchange

Dhadley: Thanks again. Going slowly at the moment. Watching for a good powerhead to wander by. Mine is beyond rebuilding-crank bad, block questionable. Have several other old boats, one is operable at the moment, so I still can get on the water. Hopeless "junkie", I guess. Dave.

 

[Dhadley]

Re: OMC powerhead interchange

Dave -- A friend of mine who has a machine shop has two Sea Drive V4 powerheads. You still need one?<br /><br />Let me know!

 

[masondr]

Re: OMC powerhead interchange

Dhadley: Thanks. Condition and price? Can e-mail me at masondr19@yahoo.com. Dave.

 

[bertherr]

Re: OMC powerhead interchange

Dhadley, I am in a similar situation. One of your earlier replies states that a long shaft 1977 would fit also. I am looking at a 1977 115HP Johnson 25" shafted powe head to fit onto my 1981 90HP Johnson. Is the 25" the longshaft? Thanks, Bert.