1987 Looper v4 140 RPM only 4000

[spareparts]

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

[nymack66]

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 ?

[THEFERMANATOR]

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.

[nymack66]

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

[THEFERMANATOR]

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.

[Skools Out]

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

[nymack66]

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 ..

[Skools Out]

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.

[THEFERMANATOR]

Originally Posted by Skools Out

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.

What he said. 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.

[nymack66]

Originally Posted by THEFERMANATOR

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.

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 ..