HELP! motor engages in reverse but not forward

[makoshark]

Was running my '85 mercury 90hp inline 6 OB today, running at around 25 MPH when I felt a thud. I threw it in neutral and trimmed up the motor to look at the prop, looks fine but the boat ONLY engages in reverse gear now, forward it just revs but no forward propulsion. Had to ride it in 2 mi in reverse to get back to launch. Got home and check cables, prop cant figure it out, prop spins in forward and reverse when on a hose. Removed the prop and verified the shaft is spinning in both forward and reverse. So I am down to faulty shift cable, spun hub, or busted lower unit forward gear. From my symptoms do you have any ideas or can you tell me of those 3 can I eliminate any since it DOES go in reverse and bite the water just fine? Thanks

 

[JB]

Re: HELP! motor engages in reverse but not forward

Almost surely a spun hub, makoshark. FWD (in the water) is the only time you put a heavy enough load on it to make it slip.

 

[tashasdaddy]

Re: HELP! motor engages in reverse but not forward

i vote spun prop. good luck. a prop shop can fix it.

 

[makoshark]

Re: HELP! motor engages in reverse but not forward

Hey guys, thanks! I will get my prop into the shop and have them pack a new hub.

 

[AMD Rules]

Re: HELP! motor engages in reverse but not forward

If access to your launch ramp is convenient, you can check for a spun hub by marking a line on the prop across the hub and extending out to the outer shell. Place it in forward gear under load. If the line you marked is no longer in alignment, you've confirmed the spun hub theory.<br /><br />The 'thud' you refer to may indicate other issues. Does the lower unit make any unusual noise when it is in fwd gear on the hose?

 

[makoshark]

Re: HELP! motor engages in reverse but not forward

Yeah, I am going to try the marking test. As far as the thud I THINK that might have been us striking an object or getting tangled in a line but thats a guess. I am in Biloxi, MS so there is debris everywhere in our waterways.

 

[makoshark]

Re: HELP! motor engages in reverse but not forward

Damn, turn out its not a spun prop. When shifted in forward and can turn my prop counterclock-wise and it feels like the teeth are slipping, flywheel doesnt turn. Must have blown out the gear-case in the lower unit. I think I am done with this boat, 1969 17' Boston Whaler Katama, '85 merc 90hp inline 6 (with busted gearcase). Anyone interested I am in Biloxi.

 

[JB]

Re: HELP! motor engages in reverse but not forward

CCW rotation, with clicking, is normal when gearcase is in FWD, shark. It is a deliberate over-run feature built in to the dog clutch.<br /><br />Can you turn it CW? Did you do the marking test?<br /><br />I still think you have a spun prop.

 

[AMD Rules]

Re: HELP! motor engages in reverse but not forward

Are you sure JB?<br /><br />From my notes:<br /><br />If prop won't rotate in either direction - lower unit is in reverse.<br /><br />If prop rotates freely in either direction - lower unit is in neutral.<br /><br />If prop wont rotate counter-clockwise, and simply ratchets when turned clockwise - lower unit is in fwd gear.

 

[JB]

Re: HELP! motor engages in reverse but not forward

You are right, AMD. <br /><br />I assumed that the CCW was percieved from the front of the engine rather than the rear.<br /><br />In the absence of reports on the marking test, prop behavior in N and in REV I chose to get more info.<br /><br />I suppose it is possible that the FWD gear or the dog is completely stripped, but when have you ever seen that? How would it behave in REV or N?<br /><br />I just don't want Max to trash an engine that can easily be repaired.

 

[AMD Rules]

Re: HELP! motor engages in reverse but not forward

I agree... it probably is a just spun prop, but to assume... well you know what that does.

 

[makoshark]

Re: HELP! motor engages in reverse but not forward

OK, I have not done the mark test, have not had time to take th boat back to the water but here is what I have so far:<br /><br />1. Shift in forward, prop RATCHETS when spun CLOCKWISE. When spun COUNTER-CLOCKWISE is I feel resistance but I can pretty easily turn it, and it feels like teeth are 'slipping'<br /><br />2. Shift into NEUTRAL, prop spins freely in both directions<br /><br />3. Shift into REVERSE, moving the prop COUNTER-CLOCKWISE actually turns the flywheel.<br /><br />The problem is that the engine just revs but I get no forward propulsion, I can however engage the reverse gear amd move through the water. Its item #1 that I believe means I have a busted gearcase in my lower unit, no?

 

[makoshark]

Re: HELP! motor engages in reverse but not forward

I should also mention that when shifted in reverse the prop locks either way the prop is spun (turns the flywheel). I am also doing this while standing to the rear of the prop out side the boat.

 

[JB]

Re: HELP! motor engages in reverse but not forward

Okay, makoshark. I concede.<br /><br />Something inside the gearcase is broke, but that is not reason to throw away your engine or your Whaler.<br /><br />Get a Service Manual and get her apart.<br /><br />Good luck.

 

[Motor Boater Bill]

Re: HELP! motor engages in reverse but not forward

I bow to the wisdom of the others here, but I would also take the shift cable loose and try shifting it by hand before tearing the LU apart. It sounds like the fwd clutch dog teeth are not fully engaging, which could be a linkage problem rather than something internal to the gearcase. Or the gearcase could be hosed. But I'd check the linkage first.

 

[makoshark]

Re: HELP! motor engages in reverse but not forward

Yeah I took the shifter cable nut off and can manually throw it into forward, N, Reverse, same results and no luck. As it turns out my wife (yes you read this correctly) wants to repower the Whaler with a new motor! "Aw geez hun, I guess so."