1973 50hp no start no spark one cylinder

[shorehugger14]

All,

I have a 73 50hp that is not getting any spark on the top cylinder and will not start....

Here is what I did: It would not accelerate past idle in the water so ran it on muffs three days ago to try and get it up to max rpm which it appeared to do but then died and hasn't started since. Gas and gas path is good. Pulled spark plugs and cranked it over and found no spark to top cylinder and orange spark to bottom. Swapped orange leads on power pack and verified that top coil is good with spark @ plug. Swapped sensor leads coming from stator but spark didn't swap over so I am thinking the power pack is bad. My only concern is whether or not I screwed anyhting up by running the thing to it's possible death on muffs. I have ordered a power pack thanks to several posts and responses from natashasdad (thanks bro...I owe you) but need to know what else to consider. shrimp are starting to run in my neck of the woods and I want some for the 4th of July.

Shorehugger14

 

[tashasdaddy]

Re: 1973 50hp no start no spark one cylinder

never rev the motor above, 1500 rpms, on muffs. the power pack is where i would start.

 

[shorehugger14]

Re: 1973 50hp no start no spark one cylinder

Thanks for the advice...you have posted numerous hints and clues that I have used over the weekend to troubleshoot my problem. Do you think that there is a possiblity of doing any head damage if it goes above 1500 RPM off muffs, I dont have a tach but I am pretty certain that I exceeded that limit. Would a compression check give me a good diagnosis? The only reason I am worried is that the motor would atleast start with one cylinder before I tried to run it out (blow it up) I am from the burg afterall....

shorehugger14

 

[shorehugger14]

Re: 1973 50hp no start no spark one cylinder

Good news and bad news....I know why my motor isn't starting, the cylinder that was originally firing with spark is only getting 30 PSI now, the other cylinder is 125 PSI. Lesson learned: Dont run your motor on mufs very much above idle and if you do then you will have compression problems. So my next dilema is to decide on a head gasket or cylinder rebuild. I am thinking the latter seeing how the top cylinder is tight and I sauspect the pressure is leaking through the bottom of the bottom cylinder.

 

[shorehugger14]

Re: 1973 50hp no start no spark one cylinder

Pulling head to determine loss of compression on lower cylinder. After removing water cooling plate on top of head it is apparent that it hasn't seen water in quite some time because the valve seal was blocking the water passage. Snapped the two center head bolts and have a third one that I cannot get out. Will finish pulling tonight. Does anyone know if the engine mounts for the head have guide studs on them or will I be able to slide the head off with snapped headbolt studs?

 

[shorehugger14]

Re: 1973 50hp no start no spark one cylinder

Can't get head off with broken and corroded head bolt studs in it. Soaked with liquid wrench for two days, drilled holes and tried to extract with EZ-out but no joy. Now I need to pull complete powerhead for more access to head. Head is cracked @ one of the center head bolt holes due to corrosion and or over torquing. Just keeping this going so that others may learn from my shade tree mechanics mistakes. As it stand right now I am replacing everything on the top end of the power head. Need to order manual to figure out how to remove power head with out creating anymore $$ damage. Still have operating trolling motor and will be out on 4th of July morning for shrimp.

 

[tashasdaddy]

Re: 1973 50hp no start no spark one cylinder

that sucks. where are the shrimp running?

 

[shorehugger14]

Re: 1973 50hp no start no spark one cylinder

Installed new power pack and now getting spark to both plugs. Still waiting for manual to perform head maintenance. Started drilling out head bolts but taking my time because it is like a surgery to keep from hitting the block.

 

[shorehugger14]

Re: 1973 50hp no start no spark one cylinder

Head is finally removed after side drilling 3 snapped head bolts but the outcome is bad, lower piston sustained catastrophic material failure. The outer edge of the piston brole off and bounced around in the cylinder. The cylinder wall looks to be in good shape but the piston has about20 impact dings in it. Now need to determine whether it is better to swap out with a rebuilt power head or attempt to change piston myself, I would imagine that it is best to change both postons while I'm in there. Is there any other oh by the way things that would be wise to change when this this is broken apart?