Clunk Click when reversing, is it right?

[Guest]

Is it true that the Merc engines 'Clunk' a lot more than the volvo ones going from forward to reverse, and if so what causes that, it just doesn't sound right to me, like changing gear with no clutch. (I bought a volvo 4.3ltr) Does it cause any damage if you reverse a lot?

 

[hlb]

Well they all clunk and click a bit. Especialy with outdrives. going from forwards to reverse quickly cant do alot of good and putting a lot of power on in reverse is not a good idea. Everything is pushing in the wrong direction. Dont forget, you are changing gear with no clutch.

<font color=blue> Haydn

 

[Russell]

The alpha drives r much noisier than the SX drives, which is why I bought a Volvo after trying them both.
I believe its because the SX uses a cone clutch, and the merc uses dogs 2 engage the gears.
Also the water pump is in the leg on the mercs, but on the engine on the Volvos, which makes impeller changes much easier.

 

[jfm]

Dirty Dogs

The clunk is the dogs, not the gears. The forward and reverse gear wheels are permanently meshed with the drive pinion all the time, they dont move in and out of mesh. Just as on a car, the gearwheels dont move in and out of mesh, all 5 gears are permanently meshed all the time.

The dogs have got lots of wear capacity, and it doesn't matter if they clunk. It doesn't affect performance even if they have rough edges. As mentioned above, the absence of clunk on the volvos is because they have cone clutches that make the dogs spin at the same speed as they approach each other, so both dog faces are spinning at the same speed (approx) when they engage. Just like a car. This is obviously a nice refinement but it's not that big a deal

 

[DavidJ]

Reduce your tickover speed a bit, this will reduce the 'kick' but of course don't take it down so low that it stalls.
The Volvo cones do seem to be effective.
David

 

[Guest]

Russell, you are dead right about the impeller, it is a piece of cake to change on the volvo as it faces you on the lower right as you look at it. The Merc however is a whole different story with it being in the leg. Just for info and correct me if I am wrong, but when the impeller goes, there is a change in the engine sound as if revving high, and the temp gauge starts to rise dramaticaly, am I right here. I have bought a speare impeller, but would like to know from some of the more experienced on here what causes them to go, I have heard about the plastic bag on the leg one, but anything else?

 

[Guest]

Only indication will be the overheat alarm going off, I'm afraid. If the intakes get blocked, then the impeller runs dry and burns out. More likely is the raw water strainer blocking with silt, if you drag the skeg through the mud...

 

[Russell]

I've never had 1 self destruct, but the engines do run hotter when they start 2 get knackered. It can also scorch the rubber coating off of the exhaust water shutters if they get 2 hot, then they start rattling 2. More expense....

Theres a good failsafe if u have raw water cooling & run on LPG though, when the water stops flowing through the engine the vaporiser ices up and the engine stops !

 

[spannerman]

Regarding Mercruiser gear shifting, a common practice I see in marinas which makes me cringe is people trying to engage gear gently which results in a clonk,clonk, clonk as the clutch dogs bounce off the dogs on the gears which can knock the corners off. Eventually there is no flat face for the dogs to engage each other, and it will jump out of gear, this applies to most outboards also. The only way with Mercruiser is to shift quickly and positively into the gear detent on the control box so it goes in first time.Same with coming out of gear, on Alpha drives if you take it too slowly the micro switch will stall the engine, or the same will happen if its not setup correctly. There are quite a few mods to this switch that Mercruiser have brought out recently to cure engine stalling.

 

[Guest]

Thanks very much for the replies, the knowledge on here is unbelievable, I think it is fantastic and the great thing is the people seem great as well.

Cheers

 

[jfm]

firm movement of the hand

Absolutely right Spannerman. The correct way is a firm shift of the gear lever so you get one firm clunk, not a gentle or slow movement so the dogs rattle together several times. This applies for both forward and reverse. As I recall mercury specifically advise this in the operators manual

 

[Guest]

Re: firm movement of the hand

Good advice, but you can't blame newbies for think 'what the hell is going on here'. (so different to a car) At least we know it is normal now.

Cheers,