Reverse problem Merc500

[GonzagaCRO]

Hello,

I have a blue band 1974 Merc 500 50HP 2 stroke 4 cyl, serial number 4078037, gear ratio 2:1.
Motor has started to slip from reverse, I pull the handle from neutral to reverse and it shifts without problems but when i give it a little throttle a can hear really bad grinding sound from my lower unit.
Example; when shifted to reverse the propeller starts to turn and when applying throttle little by little its starts to accelerate to a certain point when it slips from reverse and starts to grind.
There is no problem with forward gear and achieve WOT without problem.
I took the boat to mechanic and he checked the cables and said that there are OK but the problem is in LU.
I didn`t fully understand what he was talking about so please can you help me.
I saw on ebay some gear sets for my LU but I don`t know what I`m looking for.

http://cgi.ebay.com/ebaymotors/MERC...7621927QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

http://cgi.ebay.com/ebaymotors/MERC...9072625QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear



Best regards,

Igor

 

[Texasmark]

Re: Reverse problem Merc500

Geez, has been a long time since I was in a LU. I know that if I make a big enough blunder experts will jump in and rescue me....that's my intent. Ha!

The lower unit has a driveshaft and a propshaft. Drive pressure is transferred from the drive gear on the driveshaft to one of two gears mounted on the propshaft; the F and R gears.

The F gear is different than the R gear because the F gear has a slip clutch that allows the engine rpm to be lower than the rpm of the prop when you are decelerating....the prop just accepts the spin that the passing water puts on it....On land, with the engine off, turning the prop in one direction (in F gear) will produce the click, click, click of the clutch.

R gear has either 3 or 6 ('74 probably has 3) square teeth/sockets that mate when the shifter is placed in the R position. The shifter is a sliding shuttle that the shift shaft causes to move back and forth along the prop shaft selecting the desired gear.

In your case, I'd assume that either or both your sliding shuttle R teeth are worn and probably the mating teeth on your R gear. Another possibility would be that and the shifter spring that keeps pressure against these two gears keeping them mated when R is selected is weak....and for an engine if that vintage seems probable.

Regardless, you are after a lower unit tear down and probably two gears plus seals and all. Just a WAG but I'd have a $1000 in my pocket when I took the engine to your local Merc dealer. I wouldn't attempt this personally as there are adjustments that have to be made to the assembly so that gear engagement and clearances are correct and this requires special tools which few do-it-yourselfers have.

Mark

 

[GonzagaCRO]

Re: Reverse problem Merc500

TNX Texasmark,

Crap...

This motor doesn`t worth 400$ at best so ether I buy complete good used LU or just ignore the grinding sound.
Do you know which LU will fit my motor, maybe from newer outboards from 80`s?
Gear ratio is 2:1.

Best regards,

Igor

 

[Texasmark]

Re: Reverse problem Merc500

I don't think that ignoring the grounding sound is your best answer. The noise is made by metal on metal which means metal chips caused by the parts wearing off every time you hear the noise. Eventually these particles will get into your bearings and gears and cause a bigger problem later.

Can't help on finding a replacement but if you find one in good shape that probably would be the best answer as surely you could get out for several hundred $$$.

Mark