1987 Looper v4 140 RPM only 4000

sound like a Frankenstien motor. I reember the 140 seadrives had the big lower unit, OMC ran a special on the motor assembly(every thing but the Seadrive bracket) for repowering an existing set up for a while back in the late 80s. They were selliing the motors for about what a new powerhead cost. We sold quite a few, just left the swivel bracket off the old engine, and put the seadrive stuff on, kept the standard OB cowl and lower covers
 
Update

Guys , lets face it maybe the lower unit was swap out for a v6 gearcase 15 spline , If this is the cause for my lack of RPM at WOT 4000 max then I have a lower unit from 1978 v4 140 I can bolt up to it , I brought this boat and engine from a guy that had about 20 plus motors, Who knows what he did or did not do. Please see nymack66.com page 2 and on I have photos of the engine , 140 is stamped on the block over by the throttle shift lever , I can bet it is a 140 due to the Pack, Sator, Trigger that was installed and is working. The stamp on the carbs as mentioned before is for a 140 . Could it be the gear ratio on the larger gear case be the cause ? Or should I just intall a 14x13 prop to offset the difference ?
 
I went back and looked at your pictures, that is definately NOT a 25" leg. It's a 20" leg, you can tell by the lower engine mount spacing. And it looks to be a V4 lower unit, not the hybrid unit that used a V6 prop. Have you counted the prop shaft splines? Or roughly what is the outer diameter of the prop hub? If it is a V4 lower, it is pretty much certain to be a 2:1 ratio which is proper for that engine. The 1.86:1 ratio in the V6 lower would KILL the V4 looper by taking it out of it's power band vs prop speed. Your prop sizes also sound like a V4 lower. I still think you need to try a 15 or 13 pitch prop. My 140 slings a 17 pitch to 46 MPH at 6100 RPM's, and a 19 pitch to 53 MPH at 5600 RPM's. It would spin a 15 pitch to around 5800 at 34 MPH on my old boat, wich would have been close to a V20 in weight.

What is your current WOT and speed at that RPM?

If your reaching 28 at 4000 RPM's your tach is pretty much dead on. 4000 with a 15% prop slip comes out to 27.4MPH. Sounds like the engine may not be tuned properly, or there is something amidst in the engine itself. You say you have 120-130 pounds of compression, have you checked this against another guage. I'm running 150-155 pounds in my 140 with a .020 over bore.

And all of the electronics are the same from 120 to the 140, no differences in between the 2 up through the 90's. The differences were internal. The numbers stamped on the block where you say is a casting stamp as I believ mine is stamped 138 there. Even if it has some 120 parts, it don't make a big difference. Both of them are torque monsters very well suited to a v I think. The problem being is these engines don't make much power up until around 3500 RPM's. If your overpropped and not letting the engine hit it's peak, it will be WAY off on RPM's. These engines are rated @5600 RPM's.
 
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Update

My prop is a 15 spline for sure , I counted the splies on the shaft also,
My max RPM is 4000 , I will take it out with my GPS to clock the speed , I will post the results later
 
Your pictures and your model number comes out to a 20" shaft, and your certain you have a 15 spline shaft. So this means like LORD SKOOLS said, you got the wrong lower most likely. The 15 spline 20" leg lower is one RARE bird to find, so somebody probably swapped in a V6 leg. Problem being that the V4 don't have the power to spin a 1.86:1 ratio and make any power. Sounds like your gonna need another lower unit. The first thing I would do at this point is get a rough idea of your gear ratio. Take the cowling of the engine off and remove the spark splugs from the engine. Rotate the flywheel by hand until the #1 top dead center mark is lined up with the timing marker on the front of the engine and mark the 2 points. Now put the engine in forward and mark where the propeller is at. Now rotate the flywheel by hand counting the revolutions of the flywheel and propshaft until the prop makes 1 full revolution. If you rotate the flywheel just shy of 2 full turns to one rotation of the prop you have a V6 lower unit. If you get 2 and 1/4 turns of the flywheel to one revolution of the prop, you have the V4 lower.

If you have a V6 lower your engine will NEVER run right. LAND N SEA did a nice write up on prop curves vs engine power curves and how you have to match the 2. If your engine isn't at it's peak power point when the prop is at it's peak efficiency point, then it runs like crap. Simply changing your prop pitch won't give the desired effect as changing the gear ratio will. Make sure your of what your ratio is first, and then go from there.
 
i just looked at your pics that's a V6 lower unit for sure. i just looked at all 3 of mine none that same case. but yes same case on my many v6 225's
 
Thanks a million for all your help I will follow your instructions and post the results . Question I have a 13 spline 1978 140 v4 lower unit as a spare . Will this work ? I am guessing I will install a new water pump kit change the oil and bolt it up ? The current unit will not be a problem since I had it remove and service last July ..
 
the 78 will fit but you will have to swap the shift rods as the older one was off a cross flow and newer motor a looper they just use a different shaped shift rod that's all. they just screw in and out.

Now on a 20" lower unit the shift rod when you swap should measure 21 & 15/16 inches measuring from the surface where the gear case and midsection meet to the top of the shift rod when the gear case is in neutral.
 
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Skools Out said:
the 78 will fit but you will have to swap the shift rods as the older one was off a cross flow and newer motor a looper they just use a different shaped shift rod that's all. they just screw in and out.

Now on a 20" lower unit the shift rod when you swap should measure 21 & 15/16 inches measuring from the surface where the gear case and midsection meet to the top of the shift rod when the gear case is in neutral.
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What he said:beer:. If you have the 1.86:1 gear ratio, that 140 will never run right. It makes sense that a smaller prop should correct it, but the problem then will be that your top end will be slow even though your RPM's are there. And it will not pull well out of the hole.
 
THEFERMANATOR said:
Your pictures and your model number comes out to a 20" shaft, and your certain you have a 15 spline shaft. So this means like LORD SKOOLS said, you got the wrong lower most likely. The 15 spline 20" leg lower is one RARE bird to find, so somebody probably swapped in a V6 leg. Problem being that the V4 don't have the power to spin a 1.86:1 ratio and make any power. Sounds like your gonna need another lower unit. The first thing I would do at this point is get a rough idea of your gear ratio. Take the cowling of the engine off and remove the spark splugs from the engine. Rotate the flywheel by hand until the #1 top dead center mark is lined up with the timing marker on the front of the engine and mark the 2 points. Now put the engine in forward and mark where the propeller is at. Now rotate the flywheel by hand counting the revolutions of the flywheel and propshaft until the prop makes 1 full revolution. If you rotate the flywheel just shy of 2 full turns to one rotation of the prop you have a V6 lower unit. If you get 2 and 1/4 turns of the flywheel to one revolution of the prop, you have the V4 lower.

If you have a V6 lower your engine will NEVER run right. LAND N SEA did a nice write up on prop curves vs engine power curves and how you have to match the 2. If your engine isn't at it's peak power point when the prop is at it's peak efficiency point, then it runs like crap. Simply changing your prop pitch won't give the desired effect as changing the gear ratio will. Make sure your of what your ratio is first, and then go from there.
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You were right on, Its a V6 gearcase base on the instructions ,just like you said shy of full turns I have one complete rotation !!Thanks man , Like it sys many will be called ,few will be chosen , you are the chosen one !! The best of the bes looked at this and could not have figured this out ..Once again thanks , I will prep the spare v4 unit and bolt up ..Will keep you posted . Thanks guys keep up the good work ..
 
Shift Rod

Guys , I worked all weekend with the Shift rod issue , I am replacing the V6 gearcase see previous notes , I am now replacing it with a lower unit from a 1978 140v4 , Bolts up fine problem with the shift rod off the v6 gear case its over 22 inches in N , If I connect it to the shifter I can't shift into Forward , Reverse is fine the rod approx 1 inch 2 long,
Question is do I need to buy a new 1987 v4 140 shift rod or the shift rod from the large gearcase should work ?
 
The rod from the V-6 should work. Sounds to me like you have the shift rod threaded in to deep, and it is bottoming and preventing it from fully engaging forward. Thread the rod all the way in until it stops with it in neutral. Then thread it out roughly 2 full turns. Measure from the mating surface to the center of the shift rod bolt hole that connects to the shift linkage. You should have 21 15/16" of distance center of bolt hole to the mating surface. Sounds like your measuring to the top of the rod and so you would be about 2-3 turns to far in.

Another method that I have used in a pinch with virtually no tools available to me is to thread the shift rod all the way in and push downward on the shift rod into forward gear. Thread the shift rod out until you feel it go all the way down and the shift rod isn't bottoming out. Turn the rod outward until the bend faces forward and install it. This isn't the best method, but will work in a pinch.
 
Shift Rod

No Sir , no matter what I do it's just about 1/4 of an inch two long , I am going to re-tread the end of it and cut it , Stay tune :)
 
Are you measuring to the top of the rod, or to the center of the bolt hole? Don't go cutting it just yet, the V4 and V6 loopers use the same rods. Try threading the rod out 2 turns and see if you have forward. If your measuring to the toip of the rod, you should have 22 3/16" of length from the mating base, not the rod base. There is a 1/4" of distance from the center to the top of the rod. Also try a different tape measure as a 1/4" off in a tape measure isn't much, and this measurement MUST BE EXACT!
 
Update

If I place the rod I am trying to use (From V6 Gearcase) next to the rod from the 1978 unit it is approx 3/4 of inch more . I am confuse was it not suppose to be the same ? As for the not cutting the rod when the lower unit is bolted up and shifted in the Forward gear the connector on the end is exactly 3/4 of inch higher and will not allow me to connect it . So my thinking is the damm rod needs to be cut ! Here is what I am thinking is the unit I am removing a v6 gearcase or a v8 gearcase ? Remember I can bet on the 1979 foot I am trying to bolt up because it came from a engine with the serial numbers etc. The unit I am removing who knows maybe from a car at this point..
 
It is highly unlikely you have a V8 lower unit. They are massive to handle the torque that the V8 has. You can't compare the old cross-flow rod to the looper rod, COMPLETELY different shift mehanisms. Your saying reverse works tells me that the shift rod is close. Try the method pushing down on the rod and threading it out until you don't feel the shift rod bottoming out. Then mount it back up. I would say 2-3 turns out will put you close to where you need to be at. If the rod is threaded all the way in, it CANNOT go into forward. Trust me on this one. If you thread it all the way in, only neutral and reverse will engage.

Unthread the shift rod all the way, then thread it back in 3 turns. Now push the rod down until it goes into forward(you may have to spin the propshaft to make sure it goes in). Now thread the rod inward until you feel it begin to bottom out. As soon as you feel it touch the bottom while threading in, rotate it out until the bend faces forward and add 1 more turn out. Try it like that and see if it works. You cannot use the old rod as a reference of how the newq one should be.
 
Skools Out said:
Now on a 20" lower unit the shift rod when you swap should measure 21 & 15/16 inches measuring from the surface where the gear case and midsection meet to the top of the shift rod when the gear case is in neutral.
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do this show us where you are measuring and what you get. this is the only measurment on a Looper you need.
 
I just went out and measured a shift rod that I have in the shop. It is off of an 86 140 looper, but is for a 25" shaft. So figuring you have a 20" leg, the shift rod for yours should measure roughly 30 7/8" - 30 15/16" from the very bottom to the very top. Use a yard stick or something fairly accurate for all of these measurements. But if you have the rod threaded in all the way, then you are stuck in neutral, and the rod will stick up to high to hook up with the selector in forward.
 
not 30" Ferm the measurment i gave above is straight out of the OMC Shop Manual. your 25" isn't 30" the shift rod in a 25" motor is only 26 15/16 "in length installed.
 
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