Mercury 850 lower unit compatibility problem.

[halfbeat]

Hi all.
Firstly, happy new year to everyone!
Ok, i have a Merc 850 outboard, and i think i have a problem with the lower unit......
Me being a smart arse decided to rebuild the water pump after having one or two problems with the lower end of this engine that i picked up cheap on the back of a small boat.
Anyway, charged straight into the job as usual, pulled it apart, and everything went well up until there. Came to order the bits for it, still going ok Bits arrived, great!
Went to fit the bits.... or to be precise oils seals and impeller.... damn!! they are the wrong size. Checked with the dealer, i have the correct parts for my engine though
I am wondering if my lower unit has been replaced at some point, as the drive shaft is a smaller diameter than my replacement parts were made for... i hope that makes sense to you. The impeller is loose on the shaft, and the oil seals.... well, don't seal.
Is there any way of finding out what lower unit i have? as i don't know what replacement parts i need to order now. Are there any different designs or part numbers that i can tell from?

Many thanks for any advice given,
Simon.

 

[Laddies]

Re: Mercury 850 lower unit compatibilty problem.

Re: Mercury 850 lower unit compatibilty problem.

All pre 84 large 4 cyls and inline 6 back into the 60s use the same impeller and without a serial number you won't get any help for a specific engine.

 

[halfbeat]

Re: Mercury 850 lower unit compatibilty problem.

Re: Mercury 850 lower unit compatibilty problem.

Hi Laddies.
Thanks for the reply. Sorry, never thought to put the serial number of my engine. It's a Belgium Merc no: 9076814
Would there be a part number on the lower unit? I have had a look round it but cannot see one.....am going to have another look today though, as i didn't have much time yesterday when i looked. Do any of the Mercs use a smaller diameter driveshaft at the base? Mine seems to be the same size where the gears are cut into the top, or it would not fit into the powerhead, but the base seems to be smaller.
I am somewhat stuck now until i can identify which parts i need.

Many thanks again,
Simon.

 

[halfbeat]

Re: Mercury 850 lower unit compatibilty problem.

Re: Mercury 850 lower unit compatibilty problem.

Hi Laddies.
Thanks for the reply. Sorry, never thought to put the serial number of my engine. It's a Belgium Merc no: 9076814
Would there be a part number on the lower unit? I have had a look round it but cannot see one.....am going to have another look today though, as i didn't have much time yesterday when i looked. Do any of the Mercs use a smaller diameter driveshaft at the base? Mine seems to be the same size where the gears are cut into the top, or it would not fit into the powerhead, but the base seems to be smaller.
I am somewhat stuck now until i can identify which parts i need.

Many thanks again,
Simon.

Just been and looked at it again and have now found the part number of the gear casing. 1623-5245. Says Mercury Fleetmaster next to the part number too.
Anyone know what this might be off now? Maybe i can order some spares then and get it going again.

 

[Laddies]

Re: Mercury 850 lower unit compatibility problem.

Halfbeat, if your unit is a fleetmaster it would be one of few they were built by mercury high performance as a racing unit. I have checked by you serial number and it should have a stock unit that uses a 47-89984T4, if in fact it is a fleetmaster I don't know where to find a parts list or parts. Would it be possible to post a picture of the unit, shaft and etc.

 

[halfbeat]

Re: Mercury 850 lower unit compatibility problem.

Halfbeat, if your unit is a fleetmaster it would be one of few they were built by mercury high performance as a racing unit. I have checked by you serial number and it should have a stock unit that uses a 47-89984T4, if in fact it is a fleetmaster I don't know where to find a parts list or parts. Would it be possible to post a picture of the unit, shaft and etc.

Oh blimey!!
Sounds like this is going to be a bit of a buggar!
Will get some close up pics asap and put on here. I think i already have one of the lower unit somewhere that i took a while ago.....

 

[Laddies]

Re: Mercury 850 lower unit compatibility problem.

Halfbeat, that a standard unit. I just went back and reread your post and I may have made a wrong presumption. When you said that the impeller was loose on the shaft if you meant that it was just finger tight but the key still drove it they are all that way and when you said the seals didn't. Could this have been the problem they did make 2 drive shafts they both used the same upper seal that keep water out of the case 26-94038 is 1' ID x 1 1/2' OD but the lower seals that seal the gear lube are different on uses 26-55682 that's .875" ID x 1.250" OD and the other uses 26-16977 that's 1" ID and 1.253" OD so if the large ID seal was used on the small shaft the seals would leak. If this is the problem I must apologize for the poor info.

 

[halfbeat]

Re: Mercury 850 lower unit compatibility problem.

Halfbeat, that a standard unit. I just went back and reread your post and I may have made a wrong presumption. When you said that the impeller was loose on the shaft if you meant that it was just finger tight but the key still drove it they are all that way and when you said the seals didn't. Could this have been the problem they did make 2 drive shafts they both used the same upper seal that keep water out of the case 26-94038 is 1' ID x 1 1/2' OD but the lower seals that seal the gear lube are different on uses 26-55682 that's .875" ID x 1.250" OD and the other uses 26-16977 that's 1" ID and 1.253" OD so if the large ID seal was used on the small shaft the seals would leak. If this is the problem I must apologize for the poor info.

Phew!!! Thanks for that Laddies! I thought for a while i was going to have a nightmare trying to find parts when you said it may have been one of those special units.
Ah, i think you are spot on with the seals.... the one i have seems about 1" i/d when the shaft in my lower unit seems smaller, probably about the .875" that you mention..... and my invoice from the dealer parts dept lists the larger one... 26-16977. I shall get my vernier out tomorrow and double check it all and then should be able to order the correct seals.
The impeller though still seems rather loose, certainly compared to the one i took off, which was solid.... no movement at all, and i needed to split it before i could remove it. This new one now has maybe .125" of rotation around the shaft in either direction before the key catches it. Is that correct?

Laddies, many thanks again for your help on this!!

 

[Laddies]

Re: Mercury 850 lower unit compatibility problem.

After they are run the silt or salt sticks them to the shaft pretty much and it's not uncommon for them to be stuck, if your w/pump has a drive pin they make a impeller key # 28-43037 that sits on the flat spot on the shaft and takes a lot of the slack out.

 

[halfbeat]

Re: Mercury 850 lower unit compatibility problem.

Halfbeat, that a standard unit. I just went back and reread your post and I may have made a wrong presumption. When you said that the impeller was loose on the shaft if you meant that it was just finger tight but the key still drove it they are all that way and when you said the seals didn't. Could this have been the problem they did make 2 drive shafts they both used the same upper seal that keep water out of the case 26-94038 is 1' ID x 1 1/2' OD but the lower seals that seal the gear lube are different on uses 26-55682 that's .875" ID x 1.250" OD and the other uses 26-16977 that's 1" ID and 1.253" OD so if the large ID seal was used on the small shaft the seals would leak. If this is the problem I must apologize for the poor info.

Hi Laddies. Did i read your post right? Was 26-55682 the oil seal for the 0.875" driveshaft? I just got it in the mail, and it looks like it is made for a 1" shaft.... should i have ordered the other one for the smaller shaft 26-16977?
And this may seem like a stupid question... but if both shafts use the same top seal... 26-94038 which i have also just got in the mail... how does a 1" seal keep the water from passing it when it is on the 0.875" shaft with a 0.125" gap between it and the shaft?

Many thanks,
Simon.

 

[Laddies]

Re: Mercury 850 lower unit compatibility problem.

Simon, when I look at my post on seal position and sizes, my apologies and lets see if I can get it right this time.
First the seals by size and number
Mercury#26-16997/Sierra#18-2013 -- ID .875 x ID 1.1250 upper,for a aluminum pump housing 800-4 cyl.
Mercury#26-55682/Sierra#18-2050 -- ID 1" x OD 1.1253 upper, for a plastic pump housing 850-4cyl.
Mercury#26-94038/Sierra#18-2007 -- ID 1" x OD 1.500 bottom for both housings 800 or 850 4cyl.
800 Aluminum housing Mercury#46-48747A1 800 4 cyl.
850 Plastic housing Mercury#46-58618A1 850 4 cyl.
So you must have a 800 gear case, hope this clears it up. Here's links to both gear cases.
800. http://www.mercruiserparts.com/Show...nbr=170&bdesc=GEAR+HOUSING+ASSEMBLY,+COMPLETE

850. http://www.mercruiserparts.com/Show...desc=GEAR+HOUSING+ASSEMBLY,+COMPLETE+(PAGE+1)