Engine help

[tonycccc]

Anyone know if it is possible for water to get into a 1976 mercury 500 50hp engine while it is running,and if so is it only through the exhaust cover.My engine gradually lost power.Then i found it siezed when I next came to try it 2 weeks later.:nerd:

[whitesnake]

Anyone know if it is possible for water to get into a 1976 mercury 500 50hp engine while it is running,and if so is it only through the exhaust cover.My engine gradually lost power.Then i found it siezed when I next came to try it 2 weeks later.:nerd:
probably lack of oil caused the problem mate,apparently petrol breaks down the lubricating properties of oil if its left pre-mixed for too long.
was you using old fuel/oil mix?:mellow:

[tonycccc]

No,only been mixed an hour

[ChrisP]

sounds more like a lack of water, did you have a strong flow out of the pee pipe whilst it was running?

[blueskip]

If the engine has seized because there is water in it, then you must have a gasket gone, (cylinder head maybe)? so that water flowing around the head to cool it, is getting into the compression chamber?
Either that or was it the opposite? a SHORTAGE of water that made the engine overheat? was there water coming out of the tell-tale? did you commit the cardinal sin, & forget to put 2 stroke oil in it?????
Sounds bad, & no cheap alternative comes to mind I'm afraid!
blueskip

[Nos4r2]

If the engine has seized because there is water in it, then you must have a gasket gone, (cylinder head maybe)? so that water flowing around the head to cool it, is getting into the compression chamber?
Either that or was it the opposite? a SHORTAGE of water that made the engine overheat? was there water coming out of the tell-tale? did you commit the cardinal sin, & forget to put 2 stroke oil in it?????
Sounds bad, & no cheap alternative comes to mind I'm afraid!
blueskip

FYI-Merc 500's have a blind bore-ie no cylinder head. What looks like a cylinder head is just a removable water jacket cover. It's possible on these engines to overheat/sieze them even if the telltale is working as the telltale exits from the bottom of the block and will still work if cooling water isn't getting to the top 2 cylinders. The telltale will be weak but there in that case.

BTW, there is a way of eliminating this possibility-extend the telltale hose inside the cover so it comes out of the block it comes up level with the top of the top cylinder then run it back down to the usual outlet. Once this is done, the telltale will only work if the impeller can provide enough water to cool the top cylinders.

There's actually no way on these motors bar a cracked cylinder liner for water to get into the combustion chamber-unless it's removed and left with the leg up higher than the block which will cause water to run back up the leg and in through the exhaust ports.

[blueskip]

Wasn't aware that the water went via a blind bore, I knew that it was possible for the two top pots to cook whilst the tell-tale still showed water, it happened to a mate of mine, but his mixture was water & steam, & he knew something was amiss!
The bit about putting a loop of tell-tale piping ABOVE the upper cylinder is very interesting, what you mean is that the top of the loop, has to be above the top cylinder for it to work properly? similar to a siphon pipe? I understand the principle, that if the water isn't reaching the upper cylinders, it cant get over the top of the loop to feed the tell-tale! Fiendishly clever! It could also mean that the top 2 cylinders may have partially "furred up" water galleries, due to water not getting there, or only getting there in a dribble!
First thing tomorrow my tell-tale tube will be extended & go "high rise", & hopefully when I start up I will see the full stream! I wouldn't be at all suprised to find there is some deposits in there!
Mr Moderator I reckon this info is worthy of being a "Sticky", it may need a little work to make it crystal clear, but there are lots of Merc owners out there who wont be aware of the danger of the top 2 cylinders getting no water! this could save a lot of people a lot of money, & make your engine safer & more reliable, 10 out of ten for this one Nos4r2!
blueskip

[tonycccc]

Water definatley comming from tell tale,I suppose there is the outside chance that I picked up the wrong oil and put it in the tank but i definately put 500ml of something in 25l of fuel. I only had it in the water for 20mins,started losing power after about ten minutes got us back ok.Tried to flush it out ,very hard to start, was not siezed when I left it.
Have taken carbs off to rebuild and found a lump of dried salt in bottom carb just behind throttle disc where it bolts to the block ,trying to work out how it got there. There is a passage in the manual that says that during an overhaul of the powerhead the exhaust cover gasket should be changed to avoid getting water in the engine??????? This is why I am confused.
Anyone know if these power heads are worth overhauling?

[Nos4r2]

Anyone know if these power heads are worth overhauling?
No, don't bother.Bear in mind you're looking at £500ish for a rebore and pistons-without labour.You can buy a whole engine for that much. Look around and you can get a 2nd hand powerhead for a pittance-I paid £30 for one last year. Most outboard dealers wouldn't even know what a 1976 engine is :(
The parts are prohibitively expensive and hard to get too. :(

[Nos4r2]

The bit about putting a loop of tell-tale piping ABOVE the upper cylinder is very interesting, what you mean is that the top of the loop, has to be above the top cylinder for it to work properly? similar to a siphon pipe?

Yes.If your impelller can pump water that high then it's also able to pump water as high as your top cylinder.
If you're furred up round the top 2 pots in the water jacket it might still show a telltale though-all it does by routing the hose that high up is increase the amount of water pressure needed for the telltale to come out because it has to lift the water higher to get over the loop of pipe.

[tonycccc]

Just a thought , if the peepipe outlet was slighty blocked and the exhaust cover gasket had a leak,would it not be possible for the pressure caused by the blockage to push water into the engine very slowly.Basically imagine putting your finger over the peepipe with the engine running thus pressurising the cooling circuit surely this water would try to get out through any way possible . any thoughts on this theory ????

[Nos4r2]

Just a thought , if the peepipe outlet was slighty blocked and the exhaust cover gasket had a leak,would it not be possible for the pressure caused by the blockage to push water into the engine very slowly.Basically imagine putting your finger over the peepipe with the engine running thus pressurising the cooling circuit surely this water would try to get out through any way possible . any thoughts on this theory ????
Can't happen. If you block the telltale it won't overpressurise anything as the great majority of your cooling water comes out through the prop in gallons.That's why you sometimes have to rev the engine gently while running on muffs to get the telltale to show-the impeller (when healthy) can pump more water than a tap can provide. The telltale is just there to show you that there's water being pumped.

The only way it CAN happen (having thought about it) is if your bottom crank seal is shot-this will cause your engine to suck water in on the intake stroke through the damaged seal and may well sieze your engine.It would definitely cause the loss of power you describe too. Take your bottom spark plug out and look at the piston crown through the hole with a mirror-if this has happened your lower piston will look nice and clean compared with the others as the steam will have removed any carbon deposits. Might well cause the symtoms you describe too. I'd almost lay money on the salt water that got in being the reason your engine was siezed after a couple of weeks if thats the case.

[blueskip]

Even if I have "furring" in the galleries, (which will only exist if I am not getting flow), the chances are that this will dissolve, when I start shoving water through through them again, especially if its run in a freshwater drum, & allowed to run until the water gets quite warm!
I have found that the best solution to salt water crystals, is hot fresh water! so its vroom , vroom tomorrow!
blueskip

[Nos4r2]

Even if I have "furring" in the galleries, (which will only exist if I am not getting flow), the chances are that this will dissolve, when I start shoving water through through them again, especially if its run in a freshwater drum, & allowed to run until the water gets quite warm!
I have found that the best solution to salt water crystals, is hot fresh water! so its vroom , vroom tomorrow!
blueskip

Apparently adding vinegar helps with dissolving salt crystals too-but make sure you run it up again with fresh afterwards to flush the vinegar out.Never tried it myself but the southern yanks say they do it a lot and they have a lot more trouble with salt crystals than we do-hotter conditions.

[tonycccc]

I use salt-away works fine. Thanks to everyone for thier help, I am still a little confused as my manual clearly says "when overhauling the powerhead the exhaust cover gasket must be changed as many times water in the engine is caused by a leaking gasket" I will let you know what I find when I get a chance to strip it down.Cheers

[Nos4r2]

"when overhauling the powerhead the exhaust cover gasket must be changed as many times water in the engine is caused by a leaking gasket"


I'm guessing here but by 'water in the engine' they may well mean water under the cowl-not inside the engine block itself.

if the exhaust cover plate gasket leaks it will leak water out into the cowl.

By the way, don't try and unbolt the cylinder head water jacket or the exhaust cover plate unless you're prepared for a whole load of snapped bolts. Salt environment isn't kind to the threads on these engines-and the bolts are UNC thread not metric so aren't very easy to get hold of.

[tonycccc]

I know what you mean I had a jetski for 7 years so I know about salt corrosion,would you suggest an impact driver or heating them up before trying to remove them?

[Nos4r2]

I know what you mean I had a jetski for 7 years so I know about salt corrosion,would you suggest an impact driver or heating them up before trying to remove them?

An impact driver may well snap them too-they are only the UNC equivalent of M6 or M8 if I remember correctly.

What I'd do is:-

Wire brush the hell out of them til they look nice and clean-it's surprising what a difference it makes. Spray them with electrical freezing spray then spray them with diesel (it's thinner than WD and doesn't evaporate as fast so penetrates better over a period of time) while they are frozen. Repeat the freeze/spray a few times during a week then try undoing them. A little bit of heat won't hurt afterwards either-but make sure it's even or it'll warp the plate. It cleans the diesel off the bolt heads too. Freeze them again, and while they are cold try to undo them.

If they snap after that you'll never get them undone :(

[tonycccc]

:boat: :wallbash: Thansk again Ill let you know how it goes

[tonycccc]

Well it warmed up a bit today so i went down to the boat and stripped down the engine,not a single siezed bolt to be seen everything came off without any fuss.I spoke to the guy at maddox marine in the week and asked him what he thought ,he said that water could have got in through a hole in the exhaust cover or a faulty bottom seal. Would u adam and eve it ,thats exactly what I found,a hole in the exhaust cover and evidence of salt around the exhaust ports.Siezing was due to a little surface rust on one of the bores ,soaked this in 2 stroke and gently turned engine free by hand compression tested the motor only 5 psi differance.Will rebuild next weekend

[whitesnake]

you must have more jam than hartleys to get them bolts out.:clap3:
i have snapped bolts on a 5yr old engine

[blueskip]

I thought Mercury put those bolts in with "Loctite" on them:spiteful:! I have tried every method possible, including the "long wait" method, heat, WD40, boiling water, a hand steamer from Lidl's (cleaned the engine a treat, but I dont think it helped), best return I reckon about 50% snap offs:sad:, & loads of Hermatite when you put the cover back on!

[tonycccc]

Like i said in an earlier post I had a jetski for 7 years and know the joys of seized bolts.But even the self tapping screws under the bottom cowl came out like they had been put in yesterday. The weird thing was that the exhaust cover gasket was original and salt had corroded through the exhaust baffle behind the deflector. I wonder if the previous owner had removed and greased every bolt when the engine was new ????????

[tonycccc]

Engine Running Fine Now Job Done