pressure in upper gear case

[luckys pinstriping]

I have a 1984 Mark Twain with a OMC 2.5 liter motor. The out drive is a 400/800 stringer. When i went to change the oil in the upper gear case it had pressure in the case. I first unscrewed the top plug/dipstick and oil came out with pressure behind it. I then pulled the bottom plug and a small amount of water came out only a couple drops. the was milky white once drained clearly a sin of water. I recently resealed the upper gear case and made sure the four water pump bolts had plenty of permatex #2 sealant on them when installed. I did not change the impeller or housing at this time. Any ideas where this water is comign from and how to correct? I assume the pump is forcing water into the gear case somewhere.
Thank you Nick

 

[southkogs]

I agree: the impeller is my first suspect. I would get a new kit and replace it. Drain the drive, check the o-ring on the upper dipstick, refill and see what you get.

If you have the tools and know how, pressure testing the upper gear case would be good too. (I had to have it done for mine)

 

[kenny nunez]

OMC upper gear cases must also be vacuum tested. Most times the outer seal area on the ball gear is the problem. If that is the the cause you will see small imperfections on the outer seal contact surface. The seal surface on the lower pinion shaft is a chrome sleeve that can begin to peel off and cause a leak. It is normal for gear cases to have a positive pressure if the drive is in the sun, I have been splashed quite a few times checking them.
OMC upper gear cases also generate a positive pressure when running on plane due to the spinning of the gears but go to a vacuum when the boat slows off plane, that is how the water gets drawn in through the ball gear outer seal.

 

[luckys pinstriping]

Awesome thank you guys for the input. I did replace both seals behind the ball gear as well as the two seals on the lower pinion shaft. I will inspect them both again when install the new impeller kit. Could the impeller be producing enough pressure to force water thru the lower pinion seal? I also read about making sure the four bolts on are well coated with Permatex which I did
When I installed the two sets of seals I did not coat the metal edges with any sealant, should I have?

 

[luckys pinstriping]

Also after the motor has been run and has pressure in the gear case. I do not have any oil leaks anywhere. I guess I could assume the case holds pressure at this point but i have not vacuum tested it.

 

[Scott Danforth]

my stringer 400 had a small hole worn in the impeller housing from a stone that wedged itself under a blade and managed to pump force enough water into the gear box and pull enough gear oil out that the bearings seized 1/2 mile from the ramp.

 

[luckys pinstriping]

That is exactly my concern. The boat is in amazing condition for the age and so is the engine and outdrive. I am worried about the water cheeping in the gear as I don't want to wear out the gears or destroy a bearing.

 

[luckys pinstriping]

Water pump kit should be in on Monday. Anything specials i need to pay attention to while installing new pump?

 

[kenny nunez]

# 2 Permatex on both sides of the stainless steel plate and on the mating surface where the pump housing mates to the lower pinion housing in to the bolts as before. Torque the 4 cover bolts to 35 lbs. Inspect the splines for wear, if over 50% are worn away you will need the following.
ONC# 909753 pump shaft
Sierra #18-2185 Pump shaft
OMC# 909121. Pinion shaft
Sierra # 18-2183 Pinion shaft
OMC # 907866. Lock nut
Sierra# 18-3731 Lock nut
OMC#. 982949 Upper seal kit
Sierra # 18-2667 Upper seal kit

 

[luckys pinstriping]

Kenny thank you. When you say both sides of the stainless steel plate, do you mean the new one under the impeller? If so does that impact the performance of the impeller?

 

[kenny nunez]

Just be sure that the Permatex is on all the sealing surfaces and not on the impeller running surface. Also on the bottom outer surface of the pump housing to the swivel bearing engagement cover.
Be very sure that the 1/2 moon key has a tight fit in the pump shaft, a tap with a ball peen hammer will tighten the slot to keep the key from “rocking out” of the shaft.

 

[luckys pinstriping]

Awesome thank you very much for this information it was been very helpful. Will report back once i the new kit installed and hopefully sealed up water tight.

 

[Scott Danforth]

Check your shaft splines of the 3-piece shaft. If the splines are peaked, then they are about to strip out

 

[luckys pinstriping]

Inspected the splines when I tore it down the forest time and all looked in dry good condition. I am going to also replace the seals on the steering gear just to be sure that is not the culprit. Scott thank you for the advice much appreciated now just waiting for pumped to be delivered today

 

[kenny nunez]

The “O”rings at the rear of the upper gear case are under the cast support of the steering worm retainer. Do not try to un screw the threaded retainer under the support. It is bonded with Loctite and a special tool is required.
The quad ring seal behind the small steering gear can be pulled out with a small pick.
Be sure to coat the splines with some heavy grease.

 

[luckys pinstriping]

Good morning. Ok go the new impeller housing in last night with all the advice that you guys have given, thank you. I do have a couple questions
1) The impeller kit included 5 O-rings I used three of them. The large one around the base of the pump housing, the quad ring where the pump drive shaft goes into the upper drive shaft, and the last one in the the bottom end of the pump drive shaft inside. The last two are about and inch in diameter and according to the instruction sheet that cam with the pump kit these are to be used on the impeller shaft. According to my factory shop manual there are no other O-rings in the assembly that I can see. Am i missing something here. The kit I used is from Marine Engine OMC part number 983218.
My only thought is because this kit covers multiple years those two maybe used in different set ups.
This is the model of my out drive

• Model 252STHRCRA

 

[luckys pinstriping]

Ok put it all together. No will not pump water. Followed the manual very close to make sure all part were installed correctly with impeller in the correct way.
Any ideas here? I’m stumped
Thank you

 

[southkogs]

When you tested it for water, are you actually putting the boat in the water to see if the impeller is circulating?

On the hose, the pressure from the hose should push water through the system - if you're on a hose and not getting water, you're blocked somehow.

If you're trying to stick the drive in a big bucket o' water ... it's not gonna' draw. You've got to have the drive mostly submerged like when the boat is floatin'.

 

[kenny nunez]

3 things could be the cause. The stainless plate or the pump housing is upside down or the 1/2 moon key slipped fron the slot.
Just take your time and go over the job, you will find the problem.

 

[luckys pinstriping]

Thanks for the replies. Found the issue it was me of course. Only had the hose on half open. Took a break went out and retried with full pressure on hose and now have good flow. Will lake test it Saturday and hopefully all is well. After running in of the hose I did not have any water in the case hopefully this will not change when I lake test it. Would it be safe to say if running on the hose does not introduce water then it is most likely not the pump that pushing water in? And if in the lake i do pull water it it would be coming from either the ball gear seal or the steering worm gear seals?
If that makes any sense
Thank you guys for all of the help this is my first stern drive system i have always had outboard, old outboards.