2001 Mercury 25 hp 4 stroke MID section removal

hansonaj86 · 07 September 2015, 22:43

Hello all! I just picked up a 2001 Merc 25 hp 4 stroke Big Foot that has is giving me no water flow through its tell tale hole. After hours of problem shooting and dismantling I am now stuck at this point...

Power head has been removed and cleaned out, thermostat replaced and exhaust cover taken off and cleaned out, lower unit has been removed and water pump repaired (the old Impeller was fine but there is a new one in it now).

I am now almost certain there is a bad gasket right at the top of the water supply tube that is in between the top of the driveshaft housing and the adaptor plate. I attempt to shoot water up the water tube but I only get a small trickle of water up through the adaptor plate. Now here is the question... I have all the bolts off the adaptor plate and all bolts from the bottom of the driveshaft housing but I cant separate the two from each other! Is there some trick I'm missing???

Any help will be appreciated.

Nightfisher · 20 September 2015, 12:10

Check the water output tube for obstruction.

hansonaj86 · 20 September 2015, 14:17

Thanks for the reply. I already pressurized the water supply tube from the top and bottom with no water getting up or down it. I can't get the drive shaft unit to seperation from the adaptor plate to vet eyes on the gasket on top of the water supply tube.

Nightfisher · 26 September 2015, 06:40

Sit the skeg on a brick, using and ONLY using a Copper 1" or so flat round punch or solid copper small block. Sit the copper 1" punch or block on the top spline and using a 5 lb hammer with the skeg supported on a brick, whack down hard once. That should do it. The copper being soft but metal will ensure No Damage to splines. Good Luck.

phantom 19 · 26 September 2015, 07:42

Common problem on these- The water tube is secured to the sandwich plate and sealed between a rubber grommet. Corrosion and poor rubber cause the grommet to swell inwards and gradually block off the water flow.

It is very common in Mercury 25/40/60hp four strokes where they use a decent Yamaha derived powerhead and mate it to one of their own shonky legs.

You need to strip the lot down and replace the 50p (70cent) grommet. Good luck with the engine mounts!