Confirm My Tilt/Trim Understanding

[AguaSki]

I am still a bit of a newbie so bear with me. My motor is a 1978 140 hp Johnson V4. I noticed that when I trim up while underway the trim reaches a point where it will not go up any farther. There does seem to be a range that the trim will move up/down, but at a certain point I can’t go up anymore. I do have the full range of tilt/trim at idle and with the motor off. After reading my Clymer’s manual I found the following sentence.

“The power tilt will temporarily maintain the engine at any angle within its range to allow shallow water operation at slow speed, launching, beaching or trailering. At about 1,500 RPM, however, an overload switch will automatically lower the engine to its fully trimmed out (15 degree) position.”

I assume that this overload switch is also preventing me from raising my motor any higher than it does. Do I understand this correctly and is it normal for the trim to stop at a point while underway? I assume this is probably a safety feature to prevent idiots like me from frying the motor by getting the motor too high and loosing water pressure.

On another note, I have read all over these forums that my motor should be running near 5,800 RPM. I have had a heck of a time getting my RPM’s up. The best I have seen is 5,300 with a 13.25 X 15 Rapture. The motor is healthy with 120 PSI compression on all cylinders. I bought this motor totally rebuilt from a local Johnson/Evinrude dealer. The rebuild included a brand new power head. I followed the break-in procedure exactly. The tach is a new OMC with a digital display. In an effort to get my RPM’s up I raised my motor by two holes. I may have picked-up 100 RPM’s with the lift. Water pressure is still good. The boat handles about the same except the prop does loose its hold in sharp turns. Given that I don’t really understand tilt/trim, should I have done more playing before raising the motor? I noticed there is a spring loaded pin on the bracket where the motor is mounted. What does this pin do and how might it affect trim? I am wondering if I should have started moving this pin around and tested before raising the motor.

 

[Joe Reeves]

Re: Confirm My Tilt/Trim Understanding

The limit of trim is set by the hydraulic system, not the electrical system.

The unit has 15° of trim movement (down/up) which it will hold at any rpm. After that 15°, the unit switches from the trim mode to tilt mode and the tilt mode is not designed to hold under the thrust power of the engine's prop.

On units with operational PTT, the pin is really not needed as the tilt angle would be set via the hydraulic setup. However, you could set in in the hole closest to the transom.

On units without PTT, that pin would be used to manually lock the engine down when underway so as not to have the engine raise up when in reverse. It would also be used to set the most favorable engine setting when underway..... usually with the cavitation plate in the closest parallel setting/releationship to the bottom/keel of the boat.

 

[Texasmark]

Re: Confirm My Tilt/Trim Understanding

Trim is sandwiched between tilt extremities......like you would have 40 degrees of tilt and 20 trim so it would be tucked all the way in out to 5 degr then 6 thru 25, then 26 thru 40. If in tilt, there is some sort of hydraulic pressure relief or mechanical override to keep you from trimming out of the specified range (Merc uses a pressure relief valve and as you trim out at high speed, once you hit that point, pushing the up button farther gets you nothing........till you slow down).

Yes, tilt is made to be used only at the lower rpm's.

Yes you should have exhausted the trim options first.

Expect some blowout when high on the transom in tight turns with high trim angles. If you don't like it, drop the engine or trim in till it quits.

Since you have dinked with the height and engine is in good shape, sounds like you are in order to drop a couple of inches of pitch to grab those rpm's, but expect to loose a few mph.....hole shot will improve; popping up skiiers will definitely improve.

You didn't tell us what boat you have or how you use it so no one knows whether a 15 is too shallow or not.

HTH

Mark

 

[Texasmark]

Re: Confirm My Tilt/Trim Understanding

Forgot something. The spring that I remember on OMC was for the minimum tilt bar...located between the motor mounting clamps on the rear side. You could move the tilt bar to different tilt (minimum...tucked in setting) positions and the spring would hold it in place. On the higher hp engines they just use a bar that you slide out and back in to get another hole.....but lots of folks just remove the bar when they have PTT to get more tuck in tilt.

Otherwise there may be a spring on the tilt bracket where the engine is tilted up, on engines that don't have PTT and there is nothing else to hold it otherwise.

Mark

 

[AguaSki]

Re: Confirm My Tilt/Trim Understanding

The boat is a 1978 Glastron SSV-188 (18 feet in length). I use the boat mostly for water sports. Top GPS speed is 37 mph. The long-term health of my motor is my greatest concern, so getting the RPM's up is the primary goal, but I am hopeful this can be accomplished by working with my set-up and not dropping in pitch. I see many others on this forum with similar rigs running 17, 19, and even 21 pitch props at 5,800 RPM. I will do what I have to, but hopefully I can at least keep my 15 pitch.

 

[AguaSki]

Re: Confirm My Tilt/Trim Understanding

I have also wondered about water saturated foam adding weight to the boat. A boat this age could have some water weight that is robbing my RPM's. The floor and transom are rock solid, and I would expect that any wet foam would be also be accompanied by soft or rotted wood. The evidence of water logged foam just is not there, but I suppose it is possible.

 

[tashasdaddy]

Re: Confirm My Tilt/Trim Understanding

went to NADA guides, your dry hull weights 1200 lbs, you 140 about 320lbs. dry weight is as it left the factory, without accessories. fuel tanks empty, so compensated for that, and you can go there and find the weight of your trailer, if not have the whole unit weighed, and then launch the boat and have the trailer weighed. usually a $10.00 fee a a public scale.

 

[Texasmark]

Re: Confirm My Tilt/Trim Understanding

Sorry, your pitch didn't register. Wouldn't go any lower in pitch; maybe, like you said, after you find the bug and fix it, you may even be looking at a 17. :%

I had an 18' Caravelle open bow tri hull (medium depth v) with a 125 Johnson in '72. The boat was propped at 17" and I could pull 2 slaloms up or run 39 alone in the boat. I think the gearbox was 2:1; should be about the same as yours. Hole shot was pretty quick (5 sec or less kind if thing)

So it sounds like you have something else troubling you. Weight is a good place to start. Course, your SSV could be a deep V , like a really deep v which take a lot of power to push that hull.......and get that smooth ride that they're famous for.

But I don't remember a really deep V in the Glastron lineup.....they have a web site, I'll look.
---------------------------------
NO! Just pulled up the history of Glastron. (www.glastron.com then go to the 50th anniversary pdf and lower left of page 9 of 16).

The SSV (Super Stable V) came out in '77 (remember it). That is a high performance hull and should run easy with your setup and see mph in the 40's lightly loaded with a higher pitched prop. They said that the hull was so successful they incorporated it into all their boats in just the next few years.

What they also did was got the wood out of stringers, decks and all and that may have been part of the SSV. Don't know, but if it is, weight should not be a problem as the stringers are gone and surely they had enough sense to use closed cell foam and surely didn't use an air chamber (like boats of the '60's) that would fill with water (BTDT on an old boat).

Maybe you need to check your tach. I'd say a 15 prop on that hull would have your rpm's well over 6000 on that hull at WOT.

HTH

Mark

 

[Rancherlee]

Re: Confirm My Tilt/Trim Understanding

Your tach has to be off, IF the 37mph is GPS speed then you are only running a 1.7% prop slip with a 15 pitch prop. Bumping up to the 10% accepted slip your turning about 5800rpm @ 37mph with a 15 pitch prop. If the engine is purring like a kitten I would suspect the WOT timing advance is turned was back OR your boat is waterlogged.

 

[AguaSki]

Re: Confirm My Tilt/Trim Understanding

Thanks for the feedback.

The motor does purr like a kitten. It will idle between 650-700 RPM. At WOT it is smooth and without any type of hesitation.

I agree that my speed is too high for the low RPM's I am seeing. At the recommendation of Walleyhead in the prop forum I replaced the original tach with an OMC tach this last spring. I still had the same RPM's with the OMC tach. About a month later I replaced that OMC tach with a digital OMC tach. I am still seeing the same RPM's. So 3 tachs in 3 months with the same RPM's tell me my tachs are working properly. All 3 tachs have the dial on the back set pointed at the 6. Is there some type of sending unit that could be bad? Tell me more about the timing advance mentioned by Rancherlee. The reason why I have considered the water logged boat idea is because I am stumped and can't think of anything else. As mentioned before, there is not a sign of soft wood or rot, so I don't know that that is my issue. This boat is extremely solid and no signs of moisture anywhere. Additional thoughts and ideas are welcome.