Engine help

**tonycccc** · 22-01-2006, 23:08

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.

**whitesnake** · 22-01-2006, 23:16

Originally Posted by 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.

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?

**tonycccc** · 23-01-2006, 00:08

No,only been mixed an hour

**ChrisP** · 23-01-2006, 01:07

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

**blueskip** · 23-01-2006, 01:09

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** · 23-01-2006, 02:01

Originally Posted by 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

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** · 23-01-2006, 19:14

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** · 23-01-2006, 20:07

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** · 23-01-2006, 21:43

Originally Posted by tonycccc

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** · 23-01-2006, 21:55

Originally Posted by blueskip

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.