1974 Mercury 850 Thunderbolt

[santo101979]

I've started the awakening process of my out board. Yesterday I flushed out the lower unit and removed it from the engine. I rebuilt the water pump and have got the cowlings and shields mostly off the engine. I was very happy with the compression reading I got, #1-119 #2-119 #3-120 #4-120.....that gives me some confidence that after all this work I should be able to build some power.

Here is the water pump pic

http://picasaweb.google.com/lh/photo/-JTtH6I4rFsgKslfsk3K-g?feat=directlink

However, you'll see a small rubber coupling piece on what looks like a shift linkage shaft? When I pulled the unit this piece popped off before I could see which way its installed. Does anyone know if this pieces is to be placed with the ears up with the shaft protruding up and through or is it with the ears down with the shaft flush to the top of the coupling? Any thoughts on this would be really helpful.

 

[santo101979]

Re: 1974 Mercury 850 Thunderbolt

Here are several pics of where I am at so far.

 

[santo101979]

Re: 1974 Mercury 850 Thunderbolt

Here is a pic of the anti-ventillation plate that was damaged somehow by the previous owner. I'm thinking of fabricating a patch using some marine tex but the art of how this will be done is still up for discussion. Take a look and let me know if anyone has run into this before.

 

[Chris1956]

Re: 1974 Mercury 850 Thunderbolt

The broken antiventilation plate is not a real issue. I am more concerned that the water tube came out of the powerhead. You need to reinstall that into the exhaust extension. If you cannot get it in, you will need to pull the powerhead to get to the watertube and it's bushing.


That plastic piece over the shift shaft is a guide block. Install it in the midsection. Stick it in with grease if necessary. It wil help align the upper shift shaft, when you reinstall the gearcase.

 

[santo101979]

Re: 1974 Mercury 850 Thunderbolt

The broken antiventilation plate is not a real issue. I am more concerned that the water tube came out of the powerhead. You need to reinstall that into the exhaust extension. If you cannot get it in, you will need to pull the powerhead to get to the watertube and it's bushing.


That plastic piece over the shift shaft is a guide block. Install it in the midsection. Stick it in with grease if necessary. It wil help align the upper shift shaft, when you reinstall the gearcase.

I was wondering why that came out when the lower unit was pulled. Should I be able to slide it back in or will I have to take apart the shroud above the lower unit or? If I free the water tube from the water pump should I slide the tube up and in where it came out of then the plastic tube on top of the water pump will slide back up and over the tube? What do you think?

 

[Chris1956]

Re: 1974 Mercury 850 Thunderbolt

Remember the orientation of the watertube, since you will want to have it in that position, if you can reinstall it into the midsection. The water tube is a slip fit into the waterpump. A few twists and it should pop out. If so, then grease the top of the water tube and try to work it into the midsection. A bit of light will help you figure out where it came from. I do not know if you will be successful, however.

Good luck, and let us know.

 

[santo101979]

Re: 1974 Mercury 850 Thunderbolt

Remember the orientation of the watertube, since you will want to have it in that position, if you can reinstall it into the midsection. The water tube is a slip fit into the waterpump. A few twists and it should pop out. If so, then grease the top of the water tube and try to work it into the midsection. A bit of light will help you figure out where it came from. I do not know if you will be successful, however.

Good luck, and let us know.

Chris you were spot on with the water tube problem. It twisted out of the water pump easy enuff. I put a light smear of synthetic marine grease around the top area and the base for the water pump. I have the engine up on its stand so I tilted the engine up and put down the tilt locks and broke out the flash light. Its tricky going into the power head, it has what looked like a rubber fitting that the tube slides into but its like trying tie your shoes with chopsticks but after a while it'll slide right in. Just so I didnt forget the position I lined it up and with the water tube fitting and masking taped it into position till I get the rest of the lower unit repaired.

 

[santo101979]

Re: 1974 Mercury 850 Thunderbolt

Im trying to figure out how to repair the missing section of my anti-ventilation plate. I was thinking of actually forming a sort of rebar sections putting pieces of stiff wire into a frame work using JB weld then filling in that with Marine Tex. After that Im going to clean it up and scuff sand with the maroon scotch brite pads, prime it and paint it using spray industrial enamel paint.

Any thoughts?

 

[Chris1956]

Re: 1974 Mercury 850 Thunderbolt

What about riviting a piece of light aluminum over the top of the cracked part. Now trowel on some MarineTex to feather the edge of the aluminum plate and match the lower part of the A-V plate. A bit of creative sanding and Paint, and no one will notice that the AV plate is a bit thicker on one side (due tot he Al plate).

 

[Huron Angler]

Re: 1974 Mercury 850 Thunderbolt

I have a '71 Merc 800 so I appreciate you documenting this thread so well. I haven't torn into it but I will eventually once the boat is done if I have any issues.

I'd like to be able to offer some suggestions but I am learning myself and will be following the thread to educate myself a bit

I think Chris has a good plan for repairing the anti-cavitation plate. It should smooth out nicely using his advice.

Good luck with the Merc.

 

[santo101979]

Re: 1974 Mercury 850 Thunderbolt

I've been pondering how to fix the issue with the damaged plate on the lower unit and received some really good suggestions but with a bit of luck I think I may have found a way to not only fix the plate but improve it. I was going through the West Marine store yesterday and stumbled upon a Hydrofoil attachment that bolts right over that plate. Depending on where its mounting holes line up(hopefully not within the area missing a chunk) it should bolt right over top and you wont see the damaged area.

I did some research and it seems most people using these are getting on plane faster, get better handling, and better fuel economy so I figure what the heck, I'll give it a shot. I hope to make it out to the boatpartment tomorrow and see if it fits and I'll letcha all know how it works out.

Heres a pic of the product

 

[Chris1956]

Re: 1974 Mercury 850 Thunderbolt

Those 'Whale Tails' are popular with some. It depends on the boat is they improve performance or not. I would not use on on my performance boat, and don't need one on my fishing boat.

Generally if the A-V plate is in the water or underwater at planing speed, the whale tail will subtract from performance.