mercury 50 (500) grey goo, runs bad and snapped bolts.

[modopopcorn]

Hi guys! I'm back again having issues again with my 1970 Mercury 500 thunderbolt

It only runs on the top two cylinders and the lower cylinder doesn't fire. When started cold it starts really easy and idles well but as the pressure in the coolingsystem increase the lower two cylinder stops firing.

I have

* Good compression on all four cylinders (A bit high on cylinder nr.4)
* Rebuilt the carbs (jets were all clogged up)
* Checked the ignition were in sync
* Good spark on all plugs

I got a tip that this model could suck water backwards into the combustionchamber if the exhaust-cover fails, I just removed the covers and the gaskets looks like s#!t but I can't see any obvious leaks (and of course two bolts snapped....), the passages between the cooling channels or whatever it is are all corroded and ugly but I can't see any holes.

The inside of the middle cover and the cylinder were covered in this grey goo (exhaust gases mixed with water?)

Boat in water for a quick test-run (excuse my mothers loud voice, the horrible quality and my mothers even worse recording-technique. https://www.youtube.com/watch?v=bhKVxvvdbM4

Idling warmed up (water leaking from a broken plastic fitting) https://www.youtube.com/watch?v=xexh7dVQC70

Appreciate all the help I get, best regards!

 

[Chris1956]

In picture 3 the bottom two exhaust ports look real clean, unlike the top two. I would think that they were washed off by water getting into the cylinders.

It could be the bottom crankcase seal, or one of the exhaust covers, but it looks like something is allowing water into the motor, putting out the fire in the bottom two cylinders.

I would pull the powerhead and replace the crank seals, and insect the covers for holes. If they are sound, clean up the gasket surfaces and check the exhaust baffle for straightness.

You are supposed to put the gaskets on dry, but I would recommend some silicone to help them seal, in their old age.

Try to get the broken bolts out. Vice grips, pipewrench etc can grab their ends. Otherwise you need to drill 'em out.;

 

[modopopcorn]

Hi Chris and thanks for you response. It isn't clean actually, it's rather covered in this grey gooey slime.

I'm thinking that I'll replace the baffle and the gaskets (about $140 plus shipping) either way now that I'm this far into it.

I have some heat and coolant resistant silicone that I intend to use when I'm reassembling the exhaust, but I'm thinking that I'll use very little so I'm not risking clogging up the cooling.

I've never removed a powerhead before, and this outboard weighs a ton so I guess I'll need an extra set of hands to do it in a safe way. But as I just mentioned, being this far into the process what more harm can I do?

About the broken bolts, I used to have a special drill, weird shape that drills out stainless bolts like a hot knife through butter, haven't used it in 5-6 years and now I can't find it, turned my entire garage upside down. I have three sets of screw extractors I can't get it loose any other way. Thankfully the broken bolts stand out about 1.5 inch from the engine block.

 

[Chris1956]

Try a vice grip on those broken bolts. Use gentle heat to loosen them some. You can always drill them later.

Powerhead is awkward, but not heavy. I could carry my inline six block, and that 4 will be much lighter.

I put a 1/2 lag bolt and washer into the garage header and use a cable hoist (cumalong) to lift the powerhead. I need to jack up the trailer tongue to make it happen though.

Remove the gearcase first and install it last, so you do not destroy the driveshaft or crankshaft splines.

Try to put 3 seals in the crankcase endcap. Loosen the crankcase bolts around the cover to get it off. Retorque all bolts.