Merc 500 Head Removal

[TwinMerc500]

I am working on twin 500's. I have one going and am working to remove the head on the other to replace what I suspect are faulty reed valves. I have removed the 6 nuts that hold the head in place. The head appears to be seized on the left side of the motor. I have been trying to work the head loose with a pry bar and have a little movement. Otherwise I have been hitting all possible points with penetrating oil. Whenever I have the patience I go out for an hour or so and give it some more attention, but after a month of patience I have not had any success.

Any suggestions?
My shop manual suggests that I pull the engine from an eye bolt attached to the top of the flywheel and lifting with an engine hoist. The head seemed light enough that I haven't done this yet.

I cant see anything that I have missed. Anyone have some wisdom to offer?

 

[Chris1956]

Re: Merc 500 Head Removal

First of all, reed vavles hardly ever go bad. Secondly, although you did not post the year of that motor, most(likely all) Merc 500 motors do not have a removeable head, and the reed valves are at the carb end. You cannot see the reed valves unless you pull the crankcase cover (under the carbs), and you cannot remove the crankcase cover unless you pull the powerhead.

You might get a Merc Service Manual.

 

[Yepblaze]

Re: Merc 500 Head Removal

They may be referring to power"head".

 

[TwinMerc500]

Re: Merc 500 Head Removal

I am attempting to remove the power-head, I am sorry I did not make that clear. The reason I am exploring the reed valves is because I seem to have gas, and spark, but there seems to be no suction from the base of the carburetors. I was at a loss for what else may be my problem so thought Id inspect the reed valves.

I have a shop manual for my Merc as stated in my original post.
My s/n 7080900 suggests that it is a late 70's motor, but I could be wrong on that.

So once again. Any wisdom or suggestions regarding freeing up the seemingly seized power-head. All I could deduce from my shop manual is 6 nuts to remove, and still the power-head does not appear to be free on the left hand side of the motor.

 

[Chris1956]

Re: Merc 500 Head Removal

Some Mercs have two power head nuts much further forward, than expected. They straddle the steering arm, but are above it. Do you have these? Are they out?

Sometimes you can use a pry bar to pry up the stud ends. Be gentle. Did you drop the lower unit? If not you will want to do that. it makes reassembly so much easier. An overhead hoist is a real good idea as well. it is a fairly clumsy unit.

 

[7920hpMercury]

Re: Merc 500 Head Removal

Check and see if the slide shifter on the port side is still attached. You can tear up this plastic part if you do not remove before pulling powerhead (ask me how I know!)

I just removed two 50hp powerheads on a 84 and and 88. I found using the flywheel screw in hook or puller and a hoist seemed to help rock the gasket loose easier for me. I used a wonder bar (90 degree hook in the end) to break the powerhead free in the rear. Tapping the powerhead in a safe place with a rubber hammer helped too. You might make sure you are not hanging up around the front shifter mechanism too. I thought there were 4 nuts on each side.

One thought and not a happy one either, is that your lower unit drive shaft male spline might be frozen in the crank female spline. Hopefully you already have the lower unit off, so this is not the case!

Hope this helps.

 

[TwinMerc500]

Re: Merc 500 Head Removal

Thanks for your responses.
I did find the two forward nuts and have removed them.
I have not dropped the lower unit, looks like I will start there then get the eye bolt and try the hoist to rock the head loose.

Hopefully I haven't made things worse yet.

 

[TwinMerc500]

Re: Merc 500 Head Removal

I dropped the lower half this evening and luckily there was no damage to the drive shaft. Things still seem a little stuck, focused on the second bolt from the back on the left side.
Looks like I will try the eye bolt and a hoist on the weekend if all goes well.
It did seem like the drive shaft was playing a role in my problem.
Thanks again for the helpful sharing of experience.

 

[kartman]

Re: Merc 500 Head Removal

you really dont need the eye bolt. i just pulled my 80 with a buddie helping me lift it. their not that heavy, maybe 150#'s, just awkward. just work it loose by prying a little on each stud. make sure the nut is on the end of them to protect the threads. it will take some time. try taping on the stud holes with a rubber mallet, it might be full of rust or corosion. if that dont work, you can always try some heat. but not so much that you burn the paint, or melt the aluminum.