Merc 40 4 HP question

[upstairsdave]

I have a 1974 Merc 40 4 HP single cylinder engine with a serial number of 3938383. I am in the process of replacing the water pump and installing the lower unit to the upper unit. There is the copper water tube that goes into the water pump housing from the upper unit. My question is about the plastic tube guide. Is there supposed to be a rubber hose that goes around the copper water tube and the plastic tube guide?
I thought there was one there when I took it apart and can not find it or remember if there was one there or not. Too much beer out of aluminum cans killed my memory.
Thanks,
Dave
:?:

 

[Frosty]

I fully sympothise with your prediciment yes beer can do that, best not to partake of alchaholic beverages whilst working on machinery. However ,--regarding the water pump feed pipe, No there is not a rubber pipe, I think you will find that the copper pipe fits snug in the water pump outlet. However if you are still unsure you could measure by how much the copper pipe is short of the casing and measure by home much the water pumps sticks out of the gearbox.

 

[upstairsdave]

Merc 40

Thanks for writing. Perhaps someone prior to my ownership replaced the water pump. I thought I showed my son the plastic guide with a hose attached. I assume the plastic is only a guide for the pipe to direct it into the pump housing seal. I don't see how you could put a snyg fitted rubber hose on the piece of plastic and not cause the water pipt to further go up into the houseing instead of directing the pipe into the water pump housing. I mean, the rubber piece of hose put onto the plastic guide would have no purpose as far as sealing the water pipe at each end, Right????
I should have taken a picture of the assembly for reference. I did that for the water pump assembly but the plastic piece was on the tube and I thought it was held on there with a piece of hose.
Thanks again
Dave

 

[Frosty]

You Know you might have some thing there. Some one may have put a pipe on the pump to guide it in. It is a bit fidely, Thats a good idea. Unless some one has made a mod to your motor I am pretty sure the copper pipe goes right in the pump housing. Just make a bit of pipe up then as a guide !!

 

[upstairsdave]

Merc 40 Water Pump

Hi,
Well, I finished putting the engine back together and the water flows nicely from the flush hole under the top of the housing. It has been so long that I have run the engine I forgot where the water is supposed to come out. I thought is was supposed to come out of the exhaust releif hole and started to panic. It appears that there is more exhaust coming our of the bypass than the lower part of the engine. Do I have an exhaust bypass problem now. I put my finger over the bypass hole and the exhaust came up out of the water. Maybe this is normal. How does the bypass system operate and what parts are in it to go bad. It seems all of the rubber parts are a bit crispy.
Thanks again
Dave

 

[Frosty]

Your terminology is confusing me a bit here "flush hole'? in the bottom of the engine cover should be a small rubber pipe that skuirts water out of a small jet . This comes from the bottom of the engine. This is called a 'tell tale' and is meant to show that water pressure is sufficient. If you have a nice flow from here then its probably Ok unless there is a blockage deaper in the engine that would only show up as a problem if you got an over heat situation. Does your model have an overheat alarm, If it does I would try it on the water. Carefully-- very carefully feel the temperature of the cylinder head after the engine has run for a couple of minutes with the flat of your hand.

 

[upstairsdave]

40 Merc Pump

Then it sounds like everything is working OK. I just thought there was too much exhaust coming out of the exhaust relief in the top of the engine. Maybe once the RPMs are up and the prop is spinning faster it will pull more exhaust out of the bottom of the engine. I'm reading throught hte factory manual to see if I can get info on the exhaust relief system
Thanks