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good01

Regular Contributor
I had a 96 225 ocean runner. I was told that the engine was no good. I had a loud banging noise at about 4000 rpm cut back to under 2000 rpm and it would stop. Engine would jump and then run a bit then bang again. So I was told I needed to re power so I found a 225 ocean pro with 600 hours and ran fine on stand. I should tell you I had my lower unit re built. Everything but gears. So engine shows up and I am told the lower has water in it. Mind you I have a receipt that says it was just serviced also. So I was told to put my lower on. Went out and the same problem. Now I am a heavy equipment mechanic and I feel like the problem has been the lower all along. I am 7 grand in the hole and a wast of a summer. Any suggestions. My patience is starting to wear thin.
 
have you ever rebuilt a gearbox? Did you keep the other engine? You may be able to just rebuild both gearboxes and just sell the other engine for a net gain?
 
"Rebuilt, everything but gears". Does that tell you anything? That banging is caused by a worn clutch dog coming out of forward gear, rotating a bit, and slamming back into gear. Every time it does that, the wear increases. Rapidly. Replacing the clutch dog is a waste unless the presumably worn gear is also replaced. It is repairable at far less cost than replacing the whole motor. Far less.
 
You're describing a lower unit that is jumping out of gear and back in again.... usually because the lower unit was off for some reason (water pump ??) and someone turned the shift rod out of adjustment which is critical to the 1/32 of an inch.

The lower unit shift rod needs adjusting properly at a minimum repair.
 
Here is what I am not understanding, why would it run perfect on way out. I went around 3 miles. Fished for a couple minutes and headed back as I was really checking the new motor out. And the banging started. Now after writing my first post the mechanic says he thinks I have another cylinder problem. I checked the compression on this engine and all cylinders were 115 and good. I know you say do it myself but I do 12 to 14 hour days and it is hard for me to have the time. I don't mind paying some one but this has been going on for 2 months. Yes they did rebuild the lower unit on the first motor. No they did not do the gears. Re did the prop and prop seals, water pump. Put it back on first engine. Same problem. Buy new motor and change my lower to new motor same problem. I agree the common denominator is the lower. So why does he say the motor is bad again. When I went out it ran great. Just not on way back. Also I paid attention to the tach and when this happens it does not drop rpm. Yes I have rebuilt gear boxes. I have also built 500hp circle track engines. I can do the work. but I have all this money tied up and still down.
 
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I can well understand your frustration, and I can't answer why the engine ran okay on the way out and go bad midstream so to speak but your explanation does coincide with a lower unit jumping out, then back into gear.

However... you do speak of the problem as a banging noise..... Think about this for a minute... does the engine act like it might be hitting a submerged object every so often... BUT... only at the higher rpm side of the engine, that is... all is well at the lower rpms and this problem only rears its ugly head when the engine really has a load on it throttle wise?

If so, you'll experience a real jerking sensation on the transom like you're speeding through a log jam.

If not... this banging noise you speak of is a mystery.
 
The motor will jerk on the transom until I find a slow enough rpm to stop it. If I try to get back up on plane it starts jerking again. Kinda feels like some one hitting the pack of the boat with a sledge hammer. But again two motors doing the exact thing. And the only link is the lower unit. Thank you for your time.
 
I’m wondering if it could be a fuel supply issue? For giggles pull the suction tube in the tank and see if the strainer is dirty. Remove the gas cap and see if the engine reacts to that? The chance of both engines having the same issue is slim to none. That leaves you with fuel supply or gearbox. Connect it to a portable fuel tank and give it a run? Maybe worth a try?
 
kimcrwbr1 said:
I’m wondering if it could be a fuel supply issue? For giggles pull the suction tube in the tank and see if the strainer is dirty. Remove the gas cap and see if the engine reacts to that? The chance of both engines having the same issue is slim to none. That leaves you with fuel supply or gearbox. Connect it to a portable fuel tank and give it a run? Maybe worth a try?
Click to expand...

Kim... Yes, I would agree "if" it pertained to "two" completely different engines... BUT... "good01" is speaking of a replacement powerhead sitting on top of the same lower unit... OR... having his powerhead rebuilt... OR a different engine BUT with his original lower unit (difficult to judge which).... not actually two engines.

The common denominator here is his lower unit in all cases.

********************
(Jumping Out Of Gear - Manual Type)
(J. Reeves)

This pertains to lower units on all OMC manual shift outboard engines, or any OMC engine with lower units defined as a Shift Assist or a Hydro Electric Shift unit which incorporates a "Shifter Clutch Dog".

Within the lower unit, splined to the prop shaft is what is most often referred to as a clutch dog, hereafter simply called dog. The dog has at least two lobes protruding from it on both ends, facing both forward and reverse gear. The forward and reverse gears also have lobes built into them near their center area. When the engine is running, in neutral, the gears are spinning constantly via the driveshaft being connected directly to the powerhead crankshaft, but the propeller does not turn due to the fact that the dog is centered between the two gears, and the dog lobes are not touching either of the gear lobes.

When the unit is put into either gear, shift linkages force the dog (and its lobes of course) to engage the lobes of the gear. The lobes of the spinning gear grab the lobes of the dog, and since the dog is splined to the prop shaft, the propeller turns.

The lobes of the dog and gears are precisely machined, most with right angled edges that could be installed in either direction, and some with angles slightly varied that must be installed in one direction only (one end only must face the propeller). Dogs that can be installed in one direction only, if reversed, even if the dog and both gears were new.... would jump out of gear almost immediately. Keep in mind that the lobes are precisely machined with sharp angles!

Due to improper adjustment or worn shift linkages, but usually due to improper slow shifting, those precisely machined sharp edges of the lobes become slightly rounded. Now, with those lobes rounded, as the rpms increase, the pressure of the gear lobes upon the dog lobes increases to a point whereas they are forced apart (jumping out of gear), and due (usually) to the shift cable keeping tension on the engines shift linkages..... the unit is forced back into gear giving one the sensation that the engine has hit something, and the cycle continues.

Some boaters with manual shift engines have the mistaken belief that shifting slowly is taking it easy on all of the shifting components..... Wrong! Shifting slowly allows those precisely machined sharp edges of the dog and gears to click, clank, bang, slam against each other many times before they are finally forced into alignment with each other..... and this is what rounds those edges off! The proper way to shift is to snap the unit into gear as quickly as possible.
********************
 
kimcrwbr1 said:
I’m wondering if it could be a fuel supply issue? For giggles pull the suction tube in the tank and see if the strainer is dirty. Remove the gas cap and see if the engine reacts to that? The chance of both engines having the same issue is slim to none. That leaves you with fuel supply or gearbox. Connect it to a portable fuel tank and give it a run? Maybe worth a try?
Click to expand...

I will pull strainer today, both filters are new so I don't suspect that, also talking to the guy I bought the boat from he asked if I had them check the wiring. I had not. So last night I rode down and pulled the key switch out and the was a yellow wire with red tracer that looked like it went to the solenoid and down to the coil packs. It was not hooked to the switch very well. But I was told that has nothing to do with my problem. I did tighten the connector and wire tied it so it wont be a problem.
 
Joe, I will tell them to put the lower unit back on or put gears in the this one.

Again thank you all for your help.
 
The people that you're having do the lower unit work...... If they're not aware of it....Advise them that the shift rod must absolutely be adjusted to a certain specified measurement from the top surface of the lower unit surface to the center of the shift rod hole.

No, I don't know what that measurement would be. Hopefully another member jumps in here with that number.
 
Ok, received a call today. We put your lower unit back on and the jumping in and out of gear is gone. But wait there is more. Now it wont go over 4000 rpm. If Not repaired by Friday going to recycle yard.
 
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