TOPIC: mark 35a impeller replacement

I'm replacing the impeller on my mark 35a and remember reading a procedure when i was surfing the web. I thought i saved the page but apparently not! I remember reading that the motor needs to be in gear.

Does it need to be in forward?
Is there shift linkage to disconnect?
Any other helpful tips?

Found a link, and it happens to be from this website...thanks anyways!
human.papillomavir.us/fiberglassics-forums/home/mercury-outpost/mark-35a-lower-unit-reinstall-help

I tried to remove lower unit with no luck.

I removed two 5/8ths nuts on the side of lower unit and one under the cavition plate area.

I tried knocking it loose with a rubber mallet but it didn't budge. I stopped before i started damaging anything. Is there something i'm missing or is it just on there real good? Any tips for easier removal?

there is an allen screw up the exhaust snout in the rear.

Thanks for the quick reply Dave. I got it off but now i need to rig up something to get that plate with the 4 holes off!

1/4in plate 3in wide 2ft long drill hole for driveshaft drinn holes for at least 2 of the hole and put drive pins in heat and turn tap with a hammer.

Impeller is out but...there is no impeller key! I was careful taking it apart to make sure i didn't lose it so i know it didn't drop on the ground.

Would a dealer still carry this item and if not does someone recommend a vendor that ships FAST?

do you have a flat or a groove in the shaft.merc has them for the flat. check closely in the pump housing for thr key.

look what i found, by the way it is grooved.

When i turned the lower unit upside down to see if the impeller key would fall out the clutch dog fell off the splined shaft. Is this an issue if it's not exactly how it was? I guess i'll find out when it doesn't shift correctly.

Last question for the day...i found all this crap which looks like old grease in the cavities around the clutch dog area. Should this be cleaned out and apply new grease?

How do you guys line up the impeller key with the impeller when installing a new impeller on a mercury mark 35a? I'm tempted to drop the dang motor to the bottom of the lake!

dave bernard wrote:

do you have a flat or a groove in the shaft.

I just re-read the previous post by Dave and see he asked about the shaft not the impeller. The "shaft" has a flat and the new impeller is grooved.

Do yourself a favor and pick up an impeller key for a later-model 50hp 4-cylinder. The improved key has a flat to fit the flat on the shaft, and a "bump" which nicely fits the slot in the impeller.

Mercury did away with the impeller drive pins, 'cause the impeller/pin would "walk" on the flat in the driveshaft and dig grooves in the flat. Some would wear so bad that the pin would spin out and then you'd lose the powerhead from overheating.

The later-style key has a flat with more surface area so there's less stress/ wear on the driveshaft flat. It holds the impeller much more securely.

Plus you can smear a dab of grease on the flat of the impeller key, then it'll better stick to the driveshaft, and also stay better aligned while you're installing the impeller.

Far as getting the impeller in there, some guys have used small tie-wraps around the impeller, to make it smaller than the insert. It just drops in place once you line it up with the key.

I imagine you could use tape to the same end. But the tie-wraps are probably a lot easier to get out once the impeller is in place.

Or, line it all up, and spin both impeller & driveshaft clockwise as you push the impeller into the cup. You do have to keep it aligned or the key will just push out.

One thing that'll help you line it up, is to mark a line on the driveshaft with a Sharpie, indicating the center of the impeller key. Keep the groove in the impeller aligned with this mark on the way down, and it'll go right on the key.

Here's an eBay auction with good description of the key, including the old & superceding part numbers:



HTH & G'luck.........ed

where are you located? close enough to me i can help. or you can drop it my wat and not to the bottom.

curse wrote:

When i turned the lower unit upside down to see if the impeller key would fall out the clutch dog fell off the splined shaft. Is this an issue if it's not exactly how it was? I guess i'll find out when it doesn't shift correctly.

If I recall correctly, the 2 little "tangs" that stick up on top of the shift lockout cam (note it's not a "clutch dog"), should be aligned with the Stbd-side gearcase stud.

The important thing is to make sure the gearcase is in Fwd gear then rotate the shift shaft counterclockwise until it shifts to Neutral. Then, rotate the shift shaft clockwise, just until it shifts to Fwd then Stop!

At that time, install the lower shift lockout cam, aligned as described above.

Next, install the upper piece of the lockout cam assy. It should "nestle" into the lower piece. Such that the 2 opposing tabs on the upper piece are pointed 90 degrees to the centerline of the motor.

You'll notice that there are 2 slots in the exhaust tower (center section) in the shift shaft area. The upper shift cam piece's tabs fit in those slots. This keeps the upper shift cam from turning, but it's free to move up and down.

And this is what makes it all work:

When you shift CCW from Fwd to Neutral, the lower lockout cam rotates with the shift shaft, while the upper shift lockout piece can't rotate.

But that cam is free to move upwards. Which it will do, since it "walks" up the ramp of the lower shift lockout cam, as it turns.

The upper piece pushes on the shift lockout rod; the rod pushes on the tilt pin lockout hooks; and the hooks engage the tilt pin to lock down the motor. Lockout occurs in both Neutral and Reverse.

So, there you have it in a nutshell, hope that all makes sense.

BTW, to answer the question in your other post, the area in the front of the gearcase is just a void, it should have a drain hole drilled in the side of the gearcase towards the bottom of that cavity. The drain keeps water from being captured in there and freezing/busting the castings over the winter.

Best thing to do is clean out all the gunk and make sure the drain hole is clear. No grease or other maint. is required.

So, do grease up the bottom of the lower shift cam; there are grooves in the bottom & I like to fill those up as well. Grease the splines of the shift shaft, grease up the "ramps" where the 2 halves of the shift lockout cam assy "nestle" together.

Spread a little grease in the slots in the center section, so the upper lockout cam piece will slide easily in there. Be sure the remote control is in Fwd when you install, it'll be easier that way. The upper/lower cams will be "nestled" together and properly positioned to fit into the center section.

HTH & Have Fun!........ed

So it is just a pain in the butt! LOL

It makes me chuckle a little bit because i did exactly what you said to do before i posted. I put 2 zip ties on it and struggled so i put a line on the driveshaft with a pencil and tried to rotate both while sliding impeller down...when i did this the key would keep falling before it got lined up.

The newer key is exactly what i ordered off Ebay yesterday, part #28- 56662 and i ordered 2 so i have an extra.

Dave, i live near Kalamazoo in Portage Michigan.

I am in Yonkers NY.
I'll pick it up?

Thanks for the offer Dave but i just went back outside and tried the zip tie method again and it finally worked. Now i just need to wait for the new impeller key and do it again! I noticed the top of the driveshaft is worn but hopefully it will get me through till i find a good one.

Motor is back together and running great but i will be looking for a drive shaft since mine is damaged where it meets the powerhead. I am able to get around the lake but it will need replaced.

If anyone has one please let me know, thanks.