1975 500 Powerhead removal and general work.

[oba97]

I have been doing some repairs on my old Merc and ended up snapping the tattle tale fitting that is attached to the power head. At this point I need to remove the power head to replace it. I have a shop manual to help but I was wondering if anyone has any tips that might save me some frustration and cash. I do have a couple of specific questions to start....

1. Should I remove my lower unit prior to taking out the power head?
2. are there any gaskets between the power head and lower unit? my manual talks about a exhaust extension plate gasket but im not sure if that is required as Im not tearing apart the power head. Don't even know what it is for that matter.

Thanks in advance for your help.

 

[merc850]

Isn't the fitting between the 2nd and 3rd cylinders and the outlet on the lower cowl? If you have to remove the powerhead make sure that you can get the PH to exhaust plate gasket (Nr. 7) because it will be damaged from removal. I would remove the LU because it might have a bearing pre-load pin that could be damaged too. I separated mine by hammering a thin knife between the 2 units and moving it around, after removing the 8 nuts that hold it together.

 

[oba97]

No Title

I believe for my motor it would be #10 that I would need? The numbers are hard to see but it's the top gasket that I think I will need. It is available to buy.

 

[merc850]

Yes; the image I posted is for an 85 hp I didn't realize there was a large difference in construction. You should also check the upper shift shaft( long shaft in middle of image) for corrosion if there is any and it's bad replace it , mine failed last summer and all I had was N and F.

 

[oba97]

Will do. Unfortunately my tattle tale fitting is located at the bottom port side of the power head which is why I have to pull it. any tips on how to extract the piece broke inside? With all the work that I am doing I am thinking about cleaning the carbs while I'm at it but last summer the motor seemed to run good and I hate to mess that up. Is it worth redoing the carbs and risk messing up the adjustments? I ended up ordering a new internal wiring harness because my wires were cracked in a lot of places. I am learning a lot but a little nervous that I'm not going to get it back together . Fingers crossed.

 

[racerone]

You might consider replacing lower crankshaft seals.------Perhaps the lower bearing if it slides off the crankshaft.

 

[oba97]

No Title

racerone - Are you referring to part #'s 2 and 3? Is this something that can be replaced without tearing the power head down? This is all new to me.

 

[oba97]

Before I actually pull the power head I should ask if there is a way to access the lower port side of the power head without removing it?

 

[merc850]

If you undo all the lower cowl supports and the nut cover and the shift/throttle cables you might be able to lower the cowl enough to access the fitting.

 

[racerone]

No---It is not parts 2 and 3 on that parts page !--------Look on the page that shows end caps.---Bearing # 15 and 2 of the same seal as # 3 on that page.---I have replaced those without tearing the engine apart !!

 

[oba97]

No Title

I have the powerhead removed. Looking down the exhaust there is lost of crusted build up. Is it worth my time and effort to remove it?

 

[racerone]

That will only get worse.-------------Clean it out now !

 

[merc850]

That's why I use synthetic oil! That buildup will cut your performance significantly, remove the lower unit and chip it away and put the LU on after you put the powerhead on; see that pin on the driveshaft it might be broken if you put PH on last.

 

[oba97]

Will do. Unfortunately the lower unit is stuck on! I've never had an issue removing it in the past year I've owned it.

 

[oba97]

Ok, I'm an idiot. I missed one nut . The lower unit is off. The heavy carbon was only at the top of the shaft, I have got that off now. Time for a bourbon and hockey game. Next step is cleaning the inside of the cowling while I wait for my parts.

 

[oba97]

When I install my new fuel line should I put some type of dope one the fittings?

 

[oba97]

Ok, I have everything back together but I cannot get it to start. It doesn't even seem to try, just cranks. I'm not sure if it's the spark or fuel? I replaced the fuel lines and the wiring harness. Any tip on how to start troubleshooting?

 

[merc850]

Remove a spark plug, ground it to the block and turn engine over to check for spark you can also put a timing lite on the Nr. 1 wire and aim it at the flywheel it should show 4* on the decal. To check for fuel I tilt the engine up all the way and pump the fuel bulb until gas comes out of the carb(s); are you lifting the cold start lever all the way up and holding the choke button at the same time?

 

[oba97]

My choke only works if I manually pull it up. It is very stiff. I did lift the cold lever and manually have the choke on. I'm wondering if I did something wrong re-wiring the harness because there was one black wire that I believe is extra so I didn't connect anywhere. It's a smaller gauge (guessing 18).

 

[merc850]

The choke is supposed to be stiff so it doesn't fall down, here's a wiring diagram the only black wire is a large gage one that grounds the engine.