Sorry. Drop the lower to see if it has cratered.

Update , pulled lower off and engine started up easily killed it right away.checked compression and it's still 120 120 130 130

I have lower in a vice and if I put in reverse or forward and apply pressure and make it turn you can hear and feel the gears chewing up

Good deal. Locate a good used lower. Almost all of the V4`s will work just compare length. The shift shaft can be changed out of your old lower. Just remember when you screw the shift shaft all in then back it up 6 rounds before installing. Someone closer to you should have a good lower unit.

One I found is in Dequeen Arkansas and its 375 but I'm gonna trade him a blown 90 model 90 hp mercury for it ....man I'm gonna be sick If I do this deal and the motor still knocks I may have to shoot it then

You can connect a water hose to the copper tube coming down in the mid and run it.

Draw out, sometimes a knock can be due to predetonation in one or more cylinders. I'm sorry I am not familiar your hp and year motor. Most of my experience is the OMC 25hp and smaller hp from the 1950s,60s, and 1970s motors.

You should seek out advice from

www.aomci.org (vintage and antique motors)

Or www.iboats.com

You should get very good advice and guidance there.

Good luck

Sac-a-lait man I don`t see what your problem is? Draw if the 90hp is blown a 375.00 lower unit sounds like a good trade to me. You will need to make sure all seals are good and install a new waterpump. Remember to check the shift shaft.

It's most likely the lower unit

Thanks guys I'll update sometime next week after getting the lower unit and installing, Gary what do you mean by check shift shafts ?

Drawout, sent you a PM

1. I think that engine idles on 2 cyl, if I'm not mistaken.
2. Sounds like the clutch dog is gone from the way you described it. A gear set is around $400 if my memory serves me well. But you can buy a whole engine for $600-800 and have some other spare parts too. Check craigslist.

For the record, I ran 1980 model v4 for many many years. Always kept a spare coil and starter solenoid in the boat, along with spark plugs. Had to swap each out on the water at one time or another.

You will need to use the original from your motor, back it out 6 rounds after you screw it all in.

Ok heres the latest update, got the lower unit installed and took it to the lake no knocking and drives and shifts good ! Seems to misfire occasionally while idling not sure where to begin on that but I do plan to get some inline spark testers . Also considering getting some seafoam since Gary mentioned carbon build up, anything else I should check ?

Good go catch a biggun.