lower unit gear clash

[jeff_smith_0423]

Forgive my ignorance on this. I'm pretty new to boating (as my post count and previous questions have exposed). How much gear clash, if any, is normal when engaging the lower unit into forward and reverse? I need to decide if a lower unit rebuilt is in order before putting my boat into the water for the first time. The motor is a 77 Merc 850.

 

[achris]

Re: lower unit gear clash

Hi and don't be embarrassed about asking questions. We were all ignorant once.

Ok, your question... The gear systems are dog clutches. When shifting them they have one of two states, in or out! I cringe when I hear people 'ease' the engine into gear. I can visualize the bits of metal being ground off The way you shift gears is with a single positive movement. You may hear a slight 'crunch' at times, that's normal. Mostly it's more a 'clunk'.

If you're running it on the flushers then you will hear a lot more noise. Again, normal. I would recommend you don't go straight from forward to reverse, or vis-a-versa. Coming out of gear, allow time for the prop to stop spinning before engaging the opposite gear. I realise that there may be a situation on the water where you really do need to go straight from forward to reverse, like to stop hitting the moron who's just cut you off at the ramp. That's not going to kill your gearbox, but doing it regularly may. Also bear in mind that the gearbox on your engine was also used on all engines up to 150hp, so your 85 really doesn't have much of a chance of hurting it. apart from the idle speed being too high. You should have about 650-700rpm in the water in forward gear unhindered (not tied to a jetty or on the trailer!).

Cheers and I hope that's answered your question. If not, feel free to post again.

Chris................

 

[jeff_smith_0423]

Re: lower unit gear clash

Thanks chris! I'm hearing a minor crunch while on muffs, but i also believe i'm not being as positive with it as I can be. Also, i need to get a tach so i can get the idle speed set properly. I think it's a little high.

 

[Texasmark]

Re: lower unit gear clash

Yeah a clunk or a thunk is what I call it. One big factor, in addition to achris' comments is engine rpm. Don't be shifting with your fast idle on.

Remember, you have two gears spinning at engine rpm (F and R). Between them is a sliding gear called a clutch dog (again as achris mentioned). The faster the rpm's when you shift, the harder it is for the teeth to engage. Course the rpm's have to be high enough to keep the engine running. My 3 cyl 90 is spec'd at 650. Your 4 cyl could tolerate a lower number. You can adjust on the linkage stop screw under the cowl on the left side of the engine.

Mark

 

[flabum]

Re: lower unit gear clash

When the engine is out of the water, it will be idling higher. Shifting gears at a higher idle is not recommended as it can cause damage. There is no real reason to shift the engine while flushing unless you juat had the lower unit off and are checking that it got put together properly.

 

[trey]

Re: lower unit gear clash

Jeff, i have the same motor you do. Mine also grinds whenever i shift from forward to reverse. Do you have any trouble with your carbs.? I have to tap my throttle down slowly to build up speed, but when i start moving everything is ok...

 

[jeff_smith_0423]

Re: lower unit gear clash

Jeff, i have the same motor you do. Mine also grinds whenever i shift from forward to reverse. Do you have any trouble with your carbs.? I have to tap my throttle down slowly to build up speed, but when i start moving everything is ok...

Haven't gotten it in the water to really know yet. I rebuilt my carbs and fuel pump before attempting to start the motor though, so i can't really say yet.

 

[Texasmark]

Re: lower unit gear clash

trey, explain how you shift and what is happening when you do.

If the boat has forward motion and you attempt to go into R the prop shaft (hence clutch dog) is spinning as is your R gear and they are going in opposite directions. If the boat is stopped, and you make a definite stop in N and the engine rpm's are as mentioned, it should be a pretty quiet process, but still expect to hear gears engaging.

On Mercs (that I know of) there are square teeth, 3 on some 6 on later engines that have to engage to obtain R gear. Think about it. You have a square hole spinning in one direction and you are trying to plug a square peg into it spinning in the other direction....if boat is in motion, hence prop is turning by the force of the water against it. The faster the boat is moving the harder it is so you could expect to hear some noises while the holes are trying to match up.

Clunking and grinding and crunching are vague terms and what one means to you someone else may blow off. Only way to really know is to be there and witness the event to really know if there is a problem or this is just normal behavior.

Wish I could be of more help, but I'm not there.

Mark

 

[MercFan]

Re: lower unit gear clash

If it's any help, I'll try to exlain how I do it on my 1150. The experts here can also comment on my shifting procedure.

Since my engine is over 30 years old, the reeds arn't what they used to be. So I tried and tried to get get the engine to idle at around 850rpm in gear, but I just couldn't. So I opted for the next best I could think of. I now have my engine idling at around 800rpm in neutral in the water. I have to compensate for this be just shifting positively into gear and a little onto the throttle to keep the engine at around 850-1000rpm in gear. It just gets the boat moving. So about 0.5-1sec later I've already pulled the throttle back to the in-gear-idling position. Works like a charm. But unfortunately I can't go from neutral to just ingear-idle while the boat is at a stand still, the engine just dies.

 

[Texasmark]

Re: lower unit gear clash

Let me clarify something. When I said 650 the manual says that it is when you are idling in F gear in the water and the boat is slowing moving ahead. Anything else and you get a higher number.

Mark