Leaking Cylinder

[Troy_from _Oz]

Hi all, I recently replaced the impeller on my 71 merc 650 (4cyl) (see other post). On checking the engine running on muffs, I noticed water seeping out of the top cylinder between the spark plug threads . on pulling the spark plug out, the outer section (thread area) looked corroded so I guess this may have been going on for a while. (Ive only owned the boat for about 6 months and replaced plugs then) I guess this means its time to pull the powerhead off? <br /><br />I did a compression test on the top two cylinders and each measured 125psi.<br /><br />Does anyone have any suggestions or thoughts as to where the problem is likely to be?<br /><br />cheers<br />Troy

 

[Troy_from _Oz]

Re: Leaking Cylinder

Update - I just rang a marine wrecker asking about the availability of a powerhead in case mine was toast and was told that the water is just seeping out between the top cover and the spark plug recess. Is this like a water jacket over the top of the cylinder? this guy also indicated that if there was water in the cylinder the plug would look steam cleaned (which it didnt). does this sound correct too?

 

[dkondelik]

Re: Leaking Cylinder

The STEAM CLEANED plug comment is likely correct. <br />From compression numbers and NOT steam cleaned plug, not likly that water was in cylinder. New gasket on top might get you where you wanna be.<br /><br />Good Luck

 

[Walker]

Re: Leaking Cylinder

Those water jacket covers on the Mercs are a bad design. I guess you noticed that there are no bolts at all except around the outside edge. Nothing to really keep the cover and gasket tight in the centers.

 

[Trevor]

Re: Leaking Cylinder

be care full when removing that cover broken bolts are very comon during this repaire lots of heat even warm the engine up before attemptiong this job good luck

 

[Gold Bear]

Re: Leaking Cylinder

Troy_from _Oz <br /><br />You've gotten good advice already. When you get the cover off, make sure it is not warped. You may have to take it to a machine shop and have them mill it just enough to clean it up.<br /><br />Good luck, Gold Bear

 

[RICKRICK1]

Re: Leaking Cylinder

Troy--<br />Had the same problem my dealer told me that if I replaced the gasket to use 2 gaskets instead of one. Also he told me that if I got some high temp RTV and with the plugs removed and the motor cold that by forcing the RTV in to the area between the jacket cover and head using my fingers I could possibly remedy the problem. I used the RTV and it has not leaked in the last year. Just be carefull and not get the RTV into the cylinder and not on the plug threads and sealing surface.<br />Good Luck

 

[Troy_from _Oz]

Re: Leaking Cylinder

Thanks for all the excellent advice guys.<br /><br />Walker - yep It does seem a bit silly having only bolts on the outside of the cover. Hopefully they have learnt since then <br /><br />Trevor - thanks for the tip on using heat. Ive been a bit wary of undoing anything on the motor. Most mechanics around here wont touch it at all for that reason.<br /><br />Gold bear - good idea. Ill remember to check to make sure it is true before it goes back on - otherwise il get it machined.<br /><br />RickRick - If you'll excuse my ignorance - what is RTV? Did you use this instead of replacing the gasket? If so, this may be preferable - as my parts guy is having trouble even finding a gasket for it. It seems they may no longer be stocked in Australia any more.<br /><br />thanks again for all the good advice. Ill keep ya posted on the outcome.<br /><br />cheers<br />Troy

 

[alcan]

Re: Leaking Cylinder

Hi Troy<br /> RTV is a silicone sealant. You can get at any auto parts house. Doubling the gasket may be a good idea and then it may not. I have found a lot of times, twice the gaskets,twice the leaks. If you clean up that plate as good as practical, (you may not be able to get it perfect) use a new gasket and do a neat job with the rtv, you'll probably be in good shape. Let the rtv set-up a little before installation.

 

[Hooty]

Re: Leaking Cylinder

You might be able to true up the cover yourself using 320-400 grit emory cloth and a FLAT surface like a surface plate or a piece of 1/4" plate glass. Oil the flat surface real good so the emory cloth will stick to it, squirt some WD-40 of the cloth and sand the surface of the cover using a figure "8" pattern.Use plenty of WD-40. This keeps the cloth from filling up with aluminum. After a dozen or so strokes, you can look at the cover and see the high & low places. Continue this until the cover is true.<br /><br />c/6<br /><br />Hooty

 

[Troy_from _Oz]

Re: Leaking Cylinder

cool- thanks guys. It sounds like it should be pretty easy to clean it up, make it true and get it all back together again. Thanks for all the suggestions and good advice. Fingers crossed that I can get a new gasket easily now.<br /> <br />Cheers - Troy

 

[DJ]

Re: Leaking Cylinder

Troy,<br /><br />FYI, RTV stands for (Room Temperature Vulcanizing)<br /><br />All that means is that it cures at room temp's.<br /><br />It's great stuff. Here's a tip: less is better than more when using it.

 

[speed29668]

Re: Leaking Cylinder

I have the same design on my 1974 75hp chrysler. But the factory discontinued the gasket for the cover soon after production for some unknown reason. The manual calls for using RTV to seal the cover on my motor. I think you will be fine with a new gasket if one is available. If not then RTV will work fine I think.

 

[Chinewalker]

Re: Leaking Cylinder

I would not use the double-gasket fix, as it can actually lead to more warpage of the cover. The bolts will compress any paper-based gasket used - more paper, more compression. Being that the bolts are on the outer edge of the cover, it will in effect cause a bulge in the center where it isn't being compressed as much. Over time, it'll leak again... Use one gasket and the sealant and you'll be good to go...<br />- Scott

 

[Scooch_2]

Re: Leaking Cylinder

I had the same problem on my 1984 Merc 35 after replacing the water pump. Scared the devil out of me (new boat owner of course...) I removed the plate and old gasket, cleaned up the surface, and replaced the gasket with a new one(with a little bit of sealant). Hasn't leaked at all since. I also did spy a little leak from the hose attached to the top of the block leading to the tell tale. Had to tighten up the plastic connector that screwed into it.<br /><br />Scooch

 

[Troy_from _Oz]

Re: Leaking Cylinder

djohns - Thanks - I think ill have to get me some of that. We do have stuff specifically for sealing gaskets here (called gasket goo). Would there be much difference?<br /><br />CW - I think I will go with the single gasket option with sealant first. It does make sense that two gaskets could prove to be troublesome - especially as there is no tension in the middle of the top plate - which is where the problem is.<br /><br />Thanks again for all the good posts. Im learning lots every day from this forum!<br /><br />cheers - T

 

[Davidandkerrie69]

Re: Leaking Cylinder

I haven't heard of gasket goo in years! It's different stuff - tends to stiffen over time compared to the RTV which remains flexible.