Mercury 20 HP Reversing problem

fuzzyduck

Recruit
Joined
Oct 23, 2004
Messages
2
Hi all, i'm shouting to you guys over in the US because i'm stumped (probably because i'm a stupid european. :))<br /><br /> OK, here's a puzzler.<br /><br />I have an aging Mercury 2 stroke 20 HP outboard.<br /><br />Serial No:- 9195125 (note this engine was made in Belgium) my research tells me that this engine was probably made in the late 70's (78)<br /><br />at some point over the weekend it's decided that reverse sucks. when reverse is selected from the remote, the outboard just seems to rev as if she's in neutral.<br /><br />However, if i look into the outboard well and select reverse the prop turns in the correct direction, and even stirs the water a little, but then adding any further revs just results in very quickly increasing the engine revs to ear splitting volume. and doesn't increase the thust.<br /><br />With the engine off the boat i put it in forward gear and turned the prop (sparks disconnected) the prop turns the engine to the point where i cannot turn against the compression. (seems ok)<br /><br />In neutral the prop spins freely.<br /><br />In reverse the prop turns fairly freely with a bit more resistance than neutral (peaking at two points each rotation)<br /><br />Observation is that the propshaft is turning, and not the propellor relative to the shaft. (this rules out bushes and sheer pins right? (I don't appear to have a sheer pin))<br /><br />So conclusion is that i have a gearbox problem, and not something simpler, but what kind of problem?<br /><br />Also are <br /><br />Comments / suggestions folks?<br /><br />Thanks in advance.<br /><br />Alan
 

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: Mercury 20 HP Reversing problem

Sounds like the prop needs to be rehubed even tho it appears to be working ok in fwd gear. Props on those 20-25 hp motors are notorious for having hub problems.
 

fuzzyduck

Recruit
Joined
Oct 23, 2004
Messages
2
Re: Mercury 20 HP Reversing problem

Thankyou IBNFSHN, i'll get a new prop and see if that sorts the problem out.
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Mercury 20 HP Reversing problem

an easy way to check and see if your prop hub is sliping on any engine is to ***** punch the prop and the prop hub with aligning marks and test run then recheck the marks if they are not aligned you have a slipping hub this is cheaper that just buying a prop---bob
 
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