Questions about replacing gaskets and seals

[mlbinseattle]

Hopefully, someone who has rebuilt and engine or has done what I've described can answer these questions.

Acquired a '76 Mercury 850 that needed some attention. I've already installed new plugs, rebuilt the carbs, and replaced the checkvalves/diaphragm. It has good spark, and I've got it to where it will start and idle. Compression is good (110, 105, 105, 110). However, when I first started getting into this 2-cycle, I noticed the bolts on the transfer port cover were loose. Not knowing what the transfer port were used for at the time, I went ahead and tightened up the bolts ... at least the ones I could get to. Whenever I put it in gear, it would bog and quit running. Now that I've had time to study how 2-cycles actually operate, I've come to the conclusion that outside air is getting sucked into the transfer ports and screwing up the gas mixture causing it to run extremely lean. Additionally, there was water coming out of the water jacket cover around the plugs. I figured this wasn't too serious ... all I should need to do is to replace the gaskets.

I've decided to pull the powerhead and replace the port side exhaust plate gaskets, "head" cover gasket, water jacket cover gasket, and the transfer port plate gasket. I was going to pull the powerhead to do all this, and before re-installation, I'd replace the exhaust gasket (located on top of the lower unit). I also need to replace the water pump/impeller.

Question 1) I'd like to replace the oil cap seals on the top and bottom, and I'd also like to replace the crank cover gasket while I have the powerhead removed. Is this feasible, or is there something that I need to worry about regarding the crankshaft? Seems like I should be able to replace these seals without touching anything on the crankshaft.

Question 2) Does all this sound feasible? I mean, from what I've explained (especially with the transfer port cover plate bolts being loose and the possibility of a leaky gasket allowing outside air to get sucked into the transfer ports), does it sound like that what I've described doing will help? I don't want to throw money at a problem that can never be fixed.

Sorry to be long-winded. I just wanted to thoroughly describe what I've found since I was never really familiar with 2-cycle engines. Doesn't seem like there is much to these compared to a 4-cycle, and in my mind, as long as the block/pistons/rings/reeds are in good shape, then everything else shouldn't be too much of a problem.

 

[mlbinseattle]

Bump.

 

[Chris1956]

Gee, if it were me, I would tighten the transfer cover bolts. If there are gaskets between the transfer covers and the block, they should not leak. Put some silicone on the leaks on the cylinder head water jacket. Then I would adjust the carb idle mixture properly to allow the motor to accelerate cleanly. You will find that the carbs need to be richened about 1/4 turn out from initial setting (1.5 turns out). But the adjustment needs to be done in the water, motor warm and idling.

If you see signs of water on the #6 spark plug, the lower crank seals will need replacing. If not, no need to fix that. The top seals hardly ever go bad.

 

[mlbinseattle]

I did try to tighten the transfer cover bolts ... the ones I could get to. The bottom ones are next to impossible to get to. I went ahead and ordered a new gasket set and a lifting eye. Going to raise the powerhead and replace all the gaskets. Thanks for the tip about the lower crank seals.

 

[Chris1956]

You should be able to get to all the transfer covers, without lifting the powerhead. Remove the cowling support, remove the 4 ss screws that hold the very bottom cowling (where is says 85HP), remove that cowling and push the lower cowling down. it will move enough to get a box wrench on the transfer covers.

 

[mlbinseattle]

I'll try that, although, the plan is to replace all the gaskets and seals. I'm actually curious to poke at the rings to see if any "spring" (tension) remains on those, and I want to take a look at the reeds, as well. I don't believe there are any issues with the rings or reeds, but I want to see what condition those are in, anyway. It has good compression, and I've read more than a few articles that say the reeds rarely go bad. I'm fairly sure that I have a leak on the transfer port cover gasket that's either pushing out the gas mixture or sucking in more air. Additionally, I'm sure this thing has been in salt water, before, and I want to see what it looks like and to clean it up if possible.

 

[mlbinseattle]

The parts were suppose to arrive, today. "Out for delivery", but "Next business day", of course, so it'll probably be Monday before I see anything ... including the lifting eye.

Chris1956, with respect to tightening the bolts without pulling the powerhead, the covers are all supposed to be torqued in three stages. With that in mind, I would need to pull the powerhead, anyway, just to be able to get a torque wrench on the bolts that are located at the bottom inside the lower cowling.

I went ahead and got started. Pulled the transfer port covers and looked at the rings. Those appear to have "spring" (tension), so none are broken. From what I could see of the pistons/rods/etc, everything looked clean. Not bad shape for a 39 yr old engine. The transfer port gaskets had become so flattened that all the cover bolts had lost tightness. You could see where gas had been leaking out around the bottom as well as the corners. I'm sure this was the reason that it would bog and quit (not able to maintain idle) when put into gear. Either gas mixture was getting pushed out, or it was sucking air, or both.

I removed the wiring harness from the side plug back to the starter/solenoid. Took care of some frayed wiring. Also removed the gas line from the input back to the fuel pump. Going to replace that line as well as the line going to the carbs with new hose.

Next, I started to loosen the head cover bolts, and ran into problems. I knew these bolts would be "baked" into place, and being small bolts on the rusty side (port/exhaust/water jacket gasket leak side), I figured there was a chance that one or two would snap on me. Well, I hit the jackpot. At least six snapped. Was only able to get two out without doing any harm. The remaining four are still in there as I wasn't able to get a socket on those until I pull the powerhead. After I get the cover off, I'll drill out the bolts and retap the holes. Pain in the backside, but, oh well. It's an old engine, and I was halfway expecting this. I just hope I don't run into the same problem when I pull the exhaust cover. Those are bigger bolts, so there's a better chance of those not snapping.

As soon as the parts/lifting eye arrives, I'll get started, again. I'll report back with results as soon as I can get a few more things accomplished.

 

[Bill kubiak]

I was reading your posts and I see you are doing basically what I am doing, see my post, hot or too hot, when I took the head cover off four of those 1/4 inch bolts snapped off drilled two out and re tapped. I learned a little lesson today I think, and that is to grind back that bolt stub enough so you can find the center of the bolt before you center punch it and start drilling,

 

[mlbinseattle]

lol ... I just finished posting on your post about the same time I saw your post on my thread. I had actually looked at your post, earlier today before I got started, and it had me thinking that I'll probably snap a few of those 1/4"ers. Those things get baked into place, and being small, it's almost inevitable one or several are going to snap. Thanks for the tip about grinding back the bolt stub and then using a center punch before drilling. Makes sense. I have a Dremmel tool, so I'll be putting that to use. Doesn't look like it'll be too bad getting those suckers drilled and tapped. Good luck on your end.

 

[Bill kubiak]

Drilling them out is the easy part, re-taping them is another story, the remnants of the old bolts are in the holes original threads and getting a tap thru there is a *****, the worst thing you can do is snap a tap in there and then you are off to a machine shop to get it fixed. You cannot drill out a tap. I drilled a small center hole and then I enlarged it as much as I dared to before I started with a tap, the tap will find it's way into the old threads but you gotta be slow and careful with it, I have two to go and one is at the very bottom and I have not yet figured out how to get to it. Don't know what those bolts are made of but Mercury charged me 1.65 each for them. They are made of some tough stuff but as you say, they are baked into the block and have become part of the block.
Gopd luck

 

[mlbinseattle]

Thanks for the heads-up on tapping. There is nothing really special-looking about these bolts. The full torque value on my head cover/water jacket bolts is only 83 in/lbs (approx 7 ft/lbs). Not that much to torque, and unless these bolts are made out of something special, I'm going to the hardware store and using regular steel hex head bolts. Probably why those cost you $1.65 each is because those came from Mercury.

If I run into a problem, I may consider using a helacoil insert. I think there may be enough meat to drill the hole out large enough for this. My brother-in-law had to use these on his F-250 truck after it blew out a few plugs from the aluminum heads. Worked great for him.

 

[GA_Boater]

I think the bolts are stainless. I wouldn't use ordinary steel in an aluminum block. If you think you snapped a few this time, wait until you snap all of them because you used the wrong bolts. Every once in a while the engineers and designers get it right.

 

[mlbinseattle]

I wouldn't expect stainless to snap that easy. And as far as snapping all of those, I've already snapped six out of eight so far. (Four more to go once I get the powerhead out.) Oh well. In any case, I'll go back with stainless.

 

[mlbinseattle]

I just checked one of the snapped bolt heads on a magnet, and it stuck right to it. So, unless it's 400 series stainless (which I doubt), it's not stainless. Plain old steel bolts on an aluminum block. I've heard some manf's do use carbon steel bolts on aluminum blocks and other use stainless. Apparently, in 1976, Mercury used carbon steel.

 

[mlbinseattle]

I checked Fastenal's website for pricing on these bolts. Not sure if those are 1/4-20's or 28's as I haven't measured any. Those must be a grade 5 or better because max torque for a 20 only goes to 8 ft/lbs and a 28 only goes to 10 ft/lbs. In any case, the price for stainless steel bolts is horrendous. A box of 10 was like over $40. The price for grade 8 carbon steel chrome plated bolts was much better, but it was still up there. I looked up the actual bolt p/n and price on the local marine store's site, and they are priced for a little less than what Bill paid for his ($1.48/bolt). Then, I found a place in Lake Placid, FL that sells these for .72/bolt. I suppose I'll go with them. Oh well, was hoping to have this thing running in a few days. Guess I'll have to wait a little longer.

 

[Chris1956]

The cylinderhead water jacket bolts are 1/4"-20 grade 5 or 7 steel. If you look closely at the block, you may find you can drill thru the casting and install new bolts and nuts. Some of the older motors even had thru bolts and nuts. If you would have asked, I would have advised that the bolts often break, just as the water jacket cover bolts over the exhaust ports. Never remove these unless absolutely necessary, IMHO.

 

[mlbinseattle]

Chris1956, thanks for that info. If I had thought to ask, I would have. In any case, the water jacket cover gasket had to be replaced. Water was dribbling all down the head and around the spark plugs while the engine was running. Yesterday, I saw that the holes (expect for a few on the port side) go clean through, and I was also thinking of using a nut on the backside of those that I could do that with. The design is such that the opening on the backside doesn't look quite wide enough to place a nut back there.

Also, I haven't taken the exhaust cover off, yet. What can I expect when I go to remove those bolts? Hopefully, no more bolt heads snapping off.

 

[Bill kubiak]

I finally figured out the water flow thru my 40 hp 4 cylinder 2 stroke. It was different then I had originally thought, I pulled the lower unit, gonna change the impeller anyway, and jury rigged a hose to the copper water tube which goes from the water pump up into the power head and took some pictures.
Here is what it does, the water enters a curved semi circular channel at the bottom of the cylinder head cover but is then sent thru a hole to a channel behind the gasket in the exhaust cover and the water then travels upwards, and as it does there is a series of holes sending water directly over each cylinder head dome, once the whole dome is filled with water it exits to the top and is directed, some to the pee hole and rest to another channel behind the exhaust gasket and downwards to the bottom of that channel and out a small hole into the exhaust, along the way it also picks up some water from the forward part of the cylinder head dome thru three holes strategically placed. I took pictures of the whole thing with water both flowing and not flowing. You cannot post them here so you can message me and I will email them to you.


If you think about it for a minute, which I just did, the copper feed tube inside diameter is the same sizs as a AAA battery and the water being ejected out of the engine is thru two main places, the pee tube and that exit hole in the bottom of the exhaust cover which is much smaller in diameter then a AAA battery, there is actually a third place and that is the very bottom of the exhaust cover gasket aforementioned at the beginning of this that channels some excess water pressure also directly into the exhaust flow but thru a much smaller opening then the main exit hole. I directed water pressure to both holes and the main hole took the water directly out and out the exhaust and the other one took very little water and sprayed all over on me but I could see water coming out the exhaust too but in smaller volume

I am gonna try to rig something to see if I can pressurize that small hole, It just might be partially blocked, or not

 

[Bill kubiak]

I just checked one of the snapped bolt heads on a magnet, and it stuck right to it. So, unless it's 400 series stainless (which I doubt), it's not stainless. Plain old steel bolts on an aluminum block. I've heard some manf's do use carbon steel bolts on aluminum blocks and other use stainless. Apparently, in 1976, Mercury used carbon steel.

My manual say to use Loctite when installing the bolts, perhaps that is why they are so hard to remove

 

[mlbinseattle]

Bill, I'll email you. I'd like to see those pics. Also, I'm sure Loctite doesn't help any with those bolts. (My service manual didn't mention loctite for these bolts.) Since these are plain ole carbon steel bolts, they are prone to corrosion and rust. Even if these were chrome plated, it would have been better than nothing at all. I seriously wonder why Mercury didn't use stainless in an aluminum block where it's prone to high temps and water.

One thing I am going to try before I wack those bolts flush with the block is to spray some WD-40 on the threads and let it soak in overnight. Then, I'll try to loosen with a pair of vice grips. If I can get the remaining bolt out of the head without having to drill and tap, then great. I'm not holding my breath, but it's worth a try.