Proper Trim Technique

[KRH1326]

Hi All,

Can someone help me figure out the correct way to adjust out trim?

I have an old selectrim system, on my 1976 OMC (OMG ) 235 hp. The front engine mounts of the 351 V8 are hydraulic pistons.

If i press bow up the engine actually lowers in the front. If I press bow down the engine front rises.

This has been a project boat of mine for a few years, and I just wanted to make sure that I haven't crossed wires or solenoids and that this is the intended function.

I know that no two boats plane out exactly the same, but rule of thumb or guide help would be appreciated.

I have been having success with trimming the bow up ( engine front down) to assist getting heavy boat up into plane, then easing engine up ( bow down) to a smooth ride. I had always thought this correct, but have found alot of conflicting testimonies on the forums.

Any input?
Thanks

 

[a70eliminator]

Re: Proper Trim Technique

Your saying the engine itself tilts and not the outdrive? you say it's OMC so I'm quessing not an inboard. Full bow down till on plane, then ease in the bow up till you find the sweet spot. Sound like you have the wires correct front engine down = bow up. If bow up help get you on plane then thats what you need to do.

 

[KRH1326]

Re: Proper Trim Technique

Hey a70

Yeah man, its a pretty wild set up.

The front mounts are actually pistons, the pump is mounted on the front starboard side of timing cover. It is an old electric shift "stringer". The mounts on the int housing are fixed, but flexible to allow engine to pivot there. These old drives have that big black rubber boot all around the outdrive.

The tilt is ALWAYS supposed to be fully down except to clear an obstacle.

Wild right, I have a 1976 "low...ride...ahhh".

 

[NW Redneck]

Re: Proper Trim Technique

Sounds like you have the controls wired correctly. I have a 1975 OMC 175 with the same hydraulic trim as yours. First, always make sure the TILT is fully down whenever running the engine to prevent damage to the ball gears. The TRIM system indeed tilts the entire engine and drive together. Start out trimmed fully in (trim in = engine front up, bow down). Once you get on plane start to trim out (out = engine front down, bow up) until you get to a 'comfortable' running position. If the boat starts 'porpoising' (bow bouncing up and down in calm water) trim the bow down a little until it stops. Trimming 'in' and 'out' refers to the position of teh drive in relation to the transom. 'In' brings the prop in closer to the transom, 'out' moves the prop out away from the transom. Hope this helps! Always glad to see another white anchor owner!

Edit: Here's a diagram/parts list of the trim system to help you out.

 

[KRH1326]

Re: Proper Trim Technique

I have that same drawing. I was trying to figure out how to post it so a70 could see. How did u do it?

I keep getting that my file exceeds.........

 

[a70eliminator]

Re: Proper Trim Technique

Ok yea, I've seen those before, always remided me of an old time kitchen mixer lol, I never knew they worked like that, thanks for the lesson.

 

[NW Redneck]

Re: Proper Trim Technique

I have that same drawing. I was trying to figure out how to post it so a70 could see. How did u do it?

I keep getting that my file exceeds.........

Those were pages I scanned into my 'puter and hosted on imageshack. When you upload your image, set the sizing for message boards. That's the only way I know, and it took me a while to figure that out! :redface: I'm much better with mechanical things than electronic.

 

[windsors03cobra]

Re: Proper Trim Technique

Jesus it is not hard to figure out why OMG is not build I/O's or anything for that matter anymore.
With that said I'm glad for those folks who can keep their old rigs going. I know from experience it can be a bit cumbersome at times.

 

[NW Redneck]

Re: Proper Trim Technique

Yes they do have their faults, but it's not like others don't! Having worked on my OMC stringer and my FIL's Mercruiser, I think the OMC is a simpler system and a little easier to work on. The Mercs may be a little stronger, but are more complex. With a few exceptions most parts are still available and if a person is handy can keep a stringer drive running for a long time to come.

 

[KRH1326]

Re: Proper Trim Technique

I agree with NW R. I think that this older, simpler system is real easy to maintain and take care off. Any parts that I just cannot find, can be replaced with a merc part for same Ford motor.

Last weekend I went on a treasure hunt. I bought an engine, intermediary housing and outdrive, the Exact same as mine. I only took a sawzall with me. On the donor boat (1976 Grady open runabout) I cut the top of the transom off. Then slice down the ramaining transom followed along the stringers, then when clear of the engine front , cut, cut to cut. Had engine held with an engine hoist, while doin it. Hoisted it a little higher and pulled the boat and trailer out from under. Looked great with engine/ int housing still attached to a fiberglass skid hangin there. Backed my old pick up under and away I go.

So thanks to my new friend, Jeff, in Forked River NJ, for 500 bucks I got another 351 to play with, an intact int housing, and another 235 hp elec shift outdrive that had been proffessionally rebuilt 7 years ago, BUT never used. And 3 NEW props as well, not a dent or chip at all. I took a minute to cut the console dash out for good measure. Complete set of identicle guages and tilt switch and trim switch. ------SCORE------

 

[NW Redneck]

Re: Proper Trim Technique

Nice score! I'm always on the lookout for someone scrapping their old drive just to have spares around.