OMC 400 Series Outdrive

1983, OMC 400 Series, 2.5 lt, 4 cyclinder, mechanical shift<br /><br />It appears that this outdrive is skipping gears. No matter what RPM it is in, every three to five minutes while in forward gear the shift seems to jump gears. The Intermediate and lower gear houseing has been removed, inspected and found nothing wrong (gears, cogs) and no wearing in any thing. The Upper housing has now been removed and inspected, again nothing seems to be wrong. I need some assistance or suggestions at to what to look at next!!!

Re: OMC 400 Series Outdrive

Please explain a little more in depth... what do you mean by "jump"??

Re: OMC 400 Series Outdrive

It seems to be like the drive is shifted out of gear and back into gear, VERY Rapidly. Like you would expect from a bad engagement of the clutch and forward gear. However, after complete teardown of intermediate and lower gear cases there is no indication of this actually occuring.

Re: OMC 400 Series Outdrive

Dude, I've been chasing that same problem since the middle of june. My 81 hydro does the same thing. It's almost like an engine skip. It never jumps out of gear, it stutters without any rhythm (meaning it's not a tooth in a gear). Questions for you, can you;<br /><br />1. idle in the water? (mine yes)<br />2. what is the lowest rpm it does this in? (mine 800-1000).<br />3. does it do this on a hose in gear? (mine runs perfect on the hose).<br />4. does it do it in reverse? (mine doesn't).<br /><br />I have been through my boat so much trying to find this that I am seriously thinking of parting my boat and putting the omc motor up to an 86 Chris Craft with a merc. <br /><br />please I want to hear what else you tried. My season is just about done........-Jeff

Re: OMC 400 Series Outdrive

Have you guys ever looked at the coupler on the back of the crankshaft?

Re: OMC 400 Series Outdrive

Either Keith or Boomer suggested it, but I have not checked it. I can turn my prop in gear by hand (with the plugs in) and it turns all the way to the belt. If it was a coupling might it spin doing that? That is honestly about the only thing I have not done. My understanding is the motor has to be pulled to check it, which if I'm going to pull the motor, it's probably going to find itself mated with an "easier to repair" drive, with easier to find parts, easier to find mechanics if needed, etc etc.

Re: OMC 400 Series Outdrive

Now when you say jump out of gear... are you feeling a temporary loss of power?<br /><br />Does your RPM go sky high?

Re: OMC 400 Series Outdrive

My RPMs don't change. I know your asking the other guy, just throwing mine in to see if it could be an identical prolem.

Re: OMC 400 Series Outdrive

Originally posted by jh19:<br /> My RPMs don't change.

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Then IMO you are not going out of gear. If you "jumped" out of gear, the revs would jump too.<br /><br />Somebody surmised in your previous posts that you have an engine problem, not a drive problem. The engine is skipping and you are confusing that with a drive going out of gear. I tend to agree.

Re: OMC 400 Series Outdrive

no change in RPMs. jsut a "jump" and then back into gear

Re: OMC 400 Series Outdrive

The jump seems to happen VERY fast. I have replaced the points, so now I'll look at replacing the plugs. I have removed the shaft that engages with the coupler at the back of the engine, not a mark on it!!!

Re: OMC 400 Series Outdrive

Oak Cove...<br /><br />I fail to see how your engine RPM's would not increase if you were literally jumping out of gear while underway. Even if your prop hub was slipping the revs should increase. <br /><br />If you have no increase in RPM, then the "jump" as you call it, has to be the engine dumping a cylinder or two for a moment and then refiring. <br /><br />That's all I can think of at the moment.

Re: OMC 400 Series Outdrive

Keith, what do you suggest? Coil? points? I did cap, rotor and plugs. Don't have a dwell meter so can't do the points properly.

Re: OMC 400 Series Outdrive

also, not sure if it makes a difference, but the boat runs perfect on land, and at idle in the water. This only happens upwards of 1000 rpms. Gets no worse the more rpms there are.

Re: OMC 400 Series Outdrive

Originally posted by jh19:<br /> Keith, what do you suggest? Coil? points? I did cap, rotor and plugs. Don't have a dwell meter so can't do the points properly.

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I suggest a complete tune-up. The points are the heart of the system! If you do not have a dwell meter and timing light it is impossible for you to replace the points and expect the engine to run properly. If you are not familiar with the procedure, take it to a mechanic.

Re: OMC 400 Series Outdrive

Busy day today... but no change. The RPM's do not change one little bit, they remain steady. I have put on new plugs(gapped correctly), disconnected the shift-interrupted swith, even tried disconnecting the tilt switch (in case it was allowing the motor to come up while driving), no changes. The motor literally "jumps" on its motor mounts, so I checked them also. I did notice that it seems to get just slightly worse as the engine warms, but very slightly. The rotor is new and the timing is correct(I do have the correct tools), but have a new cap and plug wires to try next. HELP if you have any other suggestions.

Re: OMC 400 Series Outdrive

Originally posted by KaGee:<br />I fail to see how your engine RPM's would not increase if you were literally jumping out of gear while underway.

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I have experienced this on an old 115hp mercury outboard I used to have. There was significant rounding of the teeth between the clutch and the forward gear, so under load, at planing RPM's, the clutch would break loose from the forward gear for a split second. There was no RPM increase due to the very short duration of the event (fraction of a second). It felt a lot like, "BAM", striking a submerged object.<br /><br />

Originally posted by jh19:<br />The Intermediate and lower gear houseing has been removed, inspected and found nothing wrong (gears, cogs) and no wearing in any thing.

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When I got my lower unit apart, it was difficult to detect anything was wrong. I didn't even notice the clutch/gear teeth were rounded until I compared them to a new set. Don't know if this is your problem, but if so, will likely require new clutch and forward gear.<br /><br />Good luck!

Re: OMC 400 Series Outdrive

Maybe a repost... change the topic and eliminate the OMC. Maybe others will chime in with different ideas.<br /><br />If the dog and gears were rounded, you should see metal in the oil or on the magnetic drain plug.

Re: OMC 400 Series Outdrive

He saw no change in rpm. In mine, if anything, they would reduce, not increase. I did not witness it, but the sound is a reduction. My O/D is also very loud. <br /><br />Question, if the points were that bad, (which btw I did adjust the timing with a light way before the problem started, plugs cap and rotor are new), wouldn't it effect it when not under load too. Timed spark is timed spark. Why not do it under load at 800-900 rpm, why wait til 1000 under load. Load is load right?<br /><br />When a car needs an a tune up or the ponts are bad, it doesn't run any different in neutral than drive. Not meaning to sound like an a$$ but I am a bit confused.

Re: OMC 400 Series Outdrive

To date this is eveything I have tried to cure my customer's pontoon from jumping or bumping while underway in forward gear. It does not seem to occur at idle in forward gear (650RPM) nor does it do it in reverse at any RPM. From 1000 RPM to 2000 RPM the bump occurs every 3-4 minutes. As RPM increases, the regularity increases. As engine temperature increases the frequency increases. The engine literaly "jumps". The engine never goes above 162'. When the jump or bump, whatever we want to call it, happens there is absolutely no change in RPM, neither increase nor decrease. It really feels like the drive has hit something.<br /><br />The stern drive has been removed and both the intermediate and lower gear cases disassembled and inspected. There was no damage visable to any splined shafts, gears, and/or clutch and corresponding engagement points on the forward and reverse gears. There were no metal shavings in the gear lube nor collected on the magnetic pick-up drain plug. Both ball gears are intact with very little wear for 20+ year old boat. The upper housing driveshaft was removed, the splines inspected with no wear or slipage evident.<br /><br />The shift cable was properly adjusted after the stern drive was removed and the disassembly process completed. During one test drive the shift cable was disconnected from the converter housing and shifting was done by hand, maintaining pressure on the shift arm. When the bump occurred with my hand on the shift arm of the converter housing there was no slack in the core wires and no indication of the clutch slipping.<br /><br />Also tried with unsuccessful results:<br />Car rebuild<br />New fuel pump installed<br />Fuel lines from the fuel tank to the carb checked for kinks and in some locations new fuel lines installed.<br />New points, condensor, rotor, distributor cap installed.<br />Dwell set at 34'<br />New plug wires installed<br />Timing set at 4' BTDC.<br />New water pump installed in intermediate housing<br />New thermostat installed.<br />(NOTE: not all of the above were performed as a direct result of the bump/jump conditions, but because the customer insists on using cheap gas and was experencing vapor lock at times.)<br /><br />Also tried:<br />Disconnecting the shift interruptor swith.<br />Disconnecting the tilt motor<br />These also failed to correct the problem.<br /><br />I am out of ideas!!!!!!