'74 merc 500, water in #4 cylinder

Rulost

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Tried searching, but not having much luck. Mercury 500 Thunderbolt, serial 3817126. This boat/engine sat up for several years before I purchased it. Compression is OK (120 range on all cylinders). After new wiring harnesses, and plugs, fired right up. With a new impeller I finally got a chance to really let it run today. After about 45 minutes, things seemed to be pretty well, but I thought there appeared to be more "shake" to the engine than I felt it should have (like not firing smoothly). I remembered that I had only put the plugs in finger tight after the compression test, so I went to tighten them down. As I put a wrench on the #4 plug, I can see a milky oil around the outside that tells me water is getting in from somewhere. No such evidence on other plugs. Had other things to do at that point, so I didn't get to look into it any further. What are the most common causes of something like this? Never worked on an outboard powerhead, and may not know all of the terms, but have been spinning wrenches most of my life, so as long as it's not catastrophic (cracked block?), I'm hoping a little direction will help me get it squared away. Thanks!
 

GA_Boater

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Often a lower crankshaft seal can cause water in #4. What does the plug look like, clean with no carbon? That's also a sign the seal is bad. The powerhead has to come off to replace the seal.
 
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Rulost

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Not sure what the plug looks like yet, as I haven't had time to get back to it. I would imagine they should all be pretty clean since they have less than an hour of run time on them. I wouldn't mind it being a bad seal, need to look at manual and see if I can get an idea of how bad pulling the powerhead is going to be. Thanks!
 

racerone

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Install the sparkplugs.---Test run the motor and look for a leak on the waterjacket cover.---This may be an easy fix.
 

Rulost

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After idling for 45 minutes yesterday, I didn't see any external water leaks. Pulled #3 & 4 plugs today and I will try to attach pics. Pretty obvious which is which. Well, for some reason the second pic won't upload, but I think this one shows the problem pretty well
 

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Rulost

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Racerone, to be sure I am not overlooking something, do you think having the plug tightened down all of the way would perhaps cause an external leak to become visible? Thanks for the replies so far!
 

racerone

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If the plug is tight and you do not see an external leak than it proves that you have a leak internally.------Possibly gasket on exhaust cover.---Possibly a hole caused by corrosion.----Possibly a bad lower seal.------You need to look at this without delay as internal corrosion occurs quickly on precision bearings and crankshaft..
 

Rulost

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Thanks, I will be pulling the powerhead as soon as the weather will settle down. Until then, I loaded the cylinder up with Deep Creep on the slight chance that it might help just a little. I will try to pull the exhaust cover too while it's apart. Really hoping that I can get it off without breaking bolts.
 

Rulost

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Finally got time, and fair enough weather to pull the powerhead off today. Just to clarify, the lower crank seal y'all are talking about is the gasket between the powerhead and the housing, correct? I don't see any obvious tears, but of course that gasket is dried out and hard. It will probably take a few days to get the exhaust cover off, as there are 6 bolts that have enough resistance that I expect they will break if I force the issue. Any good tips for helping them to come loose without breaking? I did spray around them several times with Deep Creep, but they aren't very loose so it's not like the lube can get in the threads real well.
 

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racerone

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No , the seals are in that housing around the bottom of the crankshaft.
 

Rulost

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Thank you, I'm going to try to find a good parts breakdown this afternoon.
 

emckelvy

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Here's a link to parts diagrams for your motor:

http://www.marine engine.com/parts/mercury-outboard-parts/500/2858814-thru-4140999-usa

Since this site parses any references to other sites, you'll need to copy & paste to your browser's address bar, then take out the space.

This is a breakdown of the end caps, manifold & exhaust covers:

http://www.marine engine.com/parts/mercury-outboard-parts/500/2858814-thru-4140999-usa/end-caps-manifold-and-exhaust-covers

You can remove the lower bearing end cap without splitting the crankcase, to replace seals (if you find they are bad). The end cap is held onto the block by (3) bolts. When you wrench on these bolts, if they don't move with normal force, Stop! Get a propane or Mapp torch and apply heat to the bolt & surrounding areas, to loosen it up. If you twist back-and-forth on a stuck bolt without applying heat, you'll break the bolt and the repair for that is no fun at all!

Once the end cap bolts are removed, take a thin, wide blade (such as a paint scraper or drywall tool) and carefully tap it in-between the end cap & block. The end cap should start to move. When it gets high enough, use 2 prying tools, on opposite sides, to evenly pry the end cap. A wide, flat surface such as a Wonder Bar works best. Small screwdrivers will dig in and gouge the surfaces of the end cap or block. DO NOT pry on the bolt tabs, as they are easily broken.

You'll note that there are 3 extra holes in the end cap, you may be able to tap those for bolts, and use a harmonic balancer puller, which is far better than prying-up the cap.

The seals are pressed into the cap, and the lower crank bearing is pressed in on top of that. So you'll have to remove the bearing before you can get at the seals. Heat the end cap with a torch, around the area where the bearing sits. The bearing will probably fall out.

If not, pad the end cap with a shop rag and gently place in a vice, bearing-side down. Get an old screwdriver and put a bend in the last few inches. Use this bent tool as a driver, on the inner race of the bearing. Drive from the top to push the bearing out the bottom. Once the bearing starts to move, it'll tend to rock in the cap and get stuck; just change the position of the tool to the other side of the bearing, so it's driven evenly out of the end cap.

The seals are removed in a similar manner. Reinstallation is reverse of removal, both seals go lips-down and if you freeze the new bearing, then gently heat the end cap, the new bearing should fall right in.

That's just an overview, highly recommend you get a service manual for more instructions and torque values.

Be sure to check the exhaust side for leakage, since a blown exhaust baffle can spray water into the lower cylinders. Exactly what happened with a motor my good boating bud recently bought to fix up for a G.W. Invader.

The exhaust baffle was rotted thru, and was spraying water into #3 and #4. He's in the process of rebuilding the motor, and it's going back together well. He found lots of good used (and new) parts on eBay. Such as the 90421 inner baffle plate. Lots of clean, freshwater motors being parted-out.

Anyway, hope that helps; let us know if you find any obvious leakers............ed
 

Rulost

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Thank you emckelvy for the link and info! The extra holes in the end cap on mine are threaded, and that explains why. Thankfully I have the puller to make that easier. I hate to pry on pieces like that. Right now, I have all of the bolts in the end cap and exhaust cover soaking, and will take a small torch to them this afternoon after most of the oil is cleaned off. I have downloaded the service manual, and will get all of the torque specs from there. Will update when everything is finally apart and I see how it looks.
 

Chris1956

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You can also loosen the bolts that hold the crankcase cover, near the end cap. That will allow you to get the end cap off easier.
 

Rulost

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Thanks Chris1956. I'm hoping it doesn't come to that, but nice to know in case. Right now I have 3 bolts left in the exhaust cover that I am still trying to work loose without breaking. So far I have tried heat, tapping on the bolt head, Freeze-off, and now soaking with some more Deep Creep on two, and PB on the third to see which seems to work better. Not in a big rush to get it apart as long as I can do so without any broken bolts.
I did get the bolts out of the end cap with no problem, just have to hit the hardware store for the right size bolts to pull it off with. The bolts in both of my puller sets are too big.
 

emckelvy

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On the stuck exhaust manifold bolts, if you get to the point where you feel they're going to break rather than break-loose, best to stop! Far better to drill the bolt heads out and pull covers, than break the bolts off in the aluminum block.

Once the covers are pulled, there will be enough of a bolt stub sticking up that you'll be able to get a pair of Vise Grips on the stub. You'll be able to apply direct heat to the surrounding surfaces and that should help bust those durn bolts loose!

My buddy and I had a heck of a time getting his 50hp exhaust manifold bolts loose, but we got 'em all without breaking. We both felt pretty good about that!

My bet is that your stuck bolts are not on the perimeter of the manifold cover, but are among the row of (3) that are inboard of the outside bolts. They are always the most difficult ones to get, since they're surrounded by water passages and you can't heat them up as well as the outside bolts.

G'luck with that, & Happy Bolt Extracting!...........ed
 

Rulost

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Didn't think about taking the bolt heads off and going from there, thanks. In the pic attached you can see the ones I'm dealing with. The one that concerns me the most is the one holding the plug wires in place. Can't heat that one much without worrying about melting the wires. Of course replacing the wires wouldn't be a bad idea anyway. This evening I'm going to take an air chisel and try to use it to vibrate the bolts more than tapping them does. I will turn the air pressure down so it doesn't hit hard and hopefully will just give me a decent vibration without messing up the head or threads.
 

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emckelvy

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The rubber spark plug boots will pull off (best to lube them with a shot of silicone, etc), then you can remove the little coiled spring thingy within, and pull the spark plug wires thru the clamp. But you'll probably waste the coating on the clamp, if you get the bolt hot enough to release. But better the clamp than burn up plug wires!

The bolt on the outside row just maybe needs more heat. If you have a propane torch and it doesn't have a very hot flame, you can pick up a cylinder of MAPP gas which will put out tons more heat. That's what it took to get the bolts released on my friend's 50hp.

G'luck.........ed
 

GA_Boater

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I went to replace my plug wires and tried to remove the two bolts holding the wire bracket. Mine is an older model and has large phillips screws and an impact driver wouldn't loosen them. I finally just pulled the wires out and used some WD-40 to lube the new wires. Hope you get them, Rulost.
 

Rulost

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I managed to loosen the bolt that holds the wires enough to get them out. I have been working with butane pocket and pencil torches, but I never thought about the mapp gas. Pretty sure I have a cylinder or two of that too, so I will give that a shot tonight. Thanks for all of the suggestions!
 
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