Diagnosing lower unit - Mariner 90hp

[Dans]

Hi Guys,

My father has purchased a new project boat which came with a 90hp mariner 80s tower of power 😩.

We have been diagnosing the engine to see if it is worth repairing along with the boat and by restore (motor) i mean service and run it for a year.

Motor starts and runs which is all good but we were unable to select through any gears.

I have since removed the lower unit to check it all out and probably replace impeller while it is off and have it on a bench, prop is siezed on and soaking for the night to be pulled off tomorrow.

Upon checking gear selection as the cable was destroyed I get the following from the unit

-Neutral - Prop free spins both directions

- Forward - Drive shaft rotates the prop forward and backwards. Turn forward by hand and the prop clicks driveshaft doesn't move sounds like its rolling over the teeth. Turning backwards rotates driveshaft in opposite direction. Dog clutch slipping/not engaging teeth?

- Reverse - Drive shaft rotates prop backwards and forwards. Turn prop in reverse by hand engages no clicking. Turn forwards rotates driveshaft in opposite direction. Seems ok.

I have had a socket on the selector rod and i am fully engaging through the gears.

No fluid has be removed or changed yet.

Would the clicking indicate a worn dog clutch or gear? or does it simply need to engage under pressure/engine running - im actually unsure? Should the prop free spin in the opposite direction when in gear?

Any help would be appreciated before dropping cash into this engine and having lower unit diagnosed and repaired.

Cheers

[noelm]

Not too sure I fully understand your problem, but....it is normal for the prop to "click" when turned opposite to the gear selected, best bet is to reinstall it again, making 100% sure the gear lever and selector are in the correct position and test it properly.

[dunc333]

drain your (fluid) gearbox oil and it will pretty well tell you what condition gearbox in ,milky oil seals no good ,nice clean oil but metal filings present .not good .,if oil good and not to much filings on drain plug and as what you described shes will be good cheers dunc333

[Fab1]

On 8/22/2022 at 12:48 AM, Dans said:

Hi Guys,

My father has purchased a new project boat which came with a 90hp mariner 80s tower of power 😩.

We have been diagnosing the engine to see if it is worth repairing along with the boat and by restore (motor) i mean service and run it for a year.

Motor starts and runs which is all good but we were unable to select through any gears.

Was this testing from the helm or motor?

I have since removed the lower unit to check it all out and probably replace impeller while it is off and have it on a bench, prop is siezed on and soaking for the night to be pulled off tomorrow.

if it were mine there would be no probably and I’d change the impeller for sure.

Upon checking gear selection as the cable was destroyed I get the following from the unit

I’m assuming gear selection was tested from engine not control box?

-Neutral - Prop free spins both directions

- Forward - Drive shaft rotates the prop forward and backwards. Turn forward by hand and the prop clicks driveshaft doesn't move sounds like its rolling over the teeth. Turning backwards rotates driveshaft in opposite direction. Dog clutch slipping/not engaging teeth?

- Reverse - Drive shaft rotates prop backwards and forwards. Turn prop in reverse by hand engages no clicking. Turn forwards rotates driveshaft in opposite direction. Seems ok.

I have had a socket on the selector rod and i am fully engaging through the gears.

No fluid has be removed or changed yet.

Would the clicking indicate a worn dog clutch or gear? or does it simply need to engage under pressure/engine running - im actually unsure? Should the prop free spin in the opposite direction when in gear?

Any help would be appreciated before dropping cash into this engine and having lower unit diagnosed and repaired.

Cheers

I don’t know how handy you are are what tooling you have but I would get myself a manual for your particular outboard and strip/clean/inspect and replace any worn components in that box period.

iIt will have wear to some degree regardless being from that vintage.(But it doesn’t mean it’s  still not usable)

You should always spin the prop by hand with (ENGINE OBVIOUSLY OFF) whilst at the same time selecting gears to test.

Us saying it might be this or that without seeing it in person we are flying blind.

 That manual and you stripping it and looking for things like missing teeth,metal filings,water intrusion,rounded teeth,scours,discoloured components, etc will tell you a lot.

  The manual will give you certain specifications you will need to check too.

  Throw some photos up.