Problem, Mercury 500, start at home, won’t start at lake

[Nandy]

Mercury 500<br />50 hp<br />1968<br />Continuation of the initial post.<br />Ok, I took the motor apart and found that the one reed petal for each piston 3 and 4 was broken. These pieces made it to the two mentioned above pistons. Cylinder 3 did not get scratched but the top ring was damaged by the reed piece. Cylinder 4 got barely scratched but all the rings got damaged and stuck to the piston. The piston was also damaged. This is the one that measured 15 when I was measuring the compression.<br />I took the power head to a friend that works on cars a lot and he told me to definitely replace piston 4 and the rings, that I am better off also replacing piston 3 and the rings and to while I am at it replace the rings for the other 2 pistons. He told me to just hone the cylinder unless I wanted to really spend more money and have the cylinder bored and then I will need oversize rings for sure.<br />What do you think?

 

[phatmanmike]

Re: Problem, Mercury 500, start at home, won’t start at lake

if the cylinder walls are still good, i think you just answered your own question<br /><br />oh, one more thing... invest in some boysen power reeds, i hear that they are not made of metal and if they break off they wont chew up your cylinders, any body else know this...

 

[Chris1956]

Re: Problem, Mercury 500, start at home, won’t start at lake

Nandy, I recommend you replace the rings on both pistons, break the glaze (lightly hone) each cylinder and get some new reeds. Whether you want to invest in Boylesen (and if they fit) is your decision. Personally, I would get some used stock reeds and let it go. Also, usually when cylinders are bored out on outboards the pistons are replaced with oversize piston and ring sets. This new piston prices are at least $75/piston.

 

[Dead Eye]

Re: Problem, Mercury 500, start at home, won’t start at lake

I would move to the lake. <br /> Just couldn't resist.<br /> Good Luck, Dead Eye

 

[Chinewalker]

Re: Problem, Mercury 500, start at home, won’t start at lake

In my experience the broken reeds are usually caused by "revving" the motor in neutral when the operator is attempting to "warm up" the motor. Revving the motor can actually slap the reeds back into the reed block, causing them to fracture. Reeds rarely break on their own...<br /> You should be able to find some used good pistons out there. Same ones were used in the 20hp Merc 200, too. I beleive Wiseco makes new ones if you go that route.<br />- Scott

 

[Nandy]

Re: Problem, Mercury 500, start at home, won’t start at lake

Thanks for the input. I took the motor to the shop where I buy the parts. The guy there gave me prices for all the parts. He told me to just hone the cylinders and the pistons, put new rings and forget about buying the pistons. I am not sure about that though... Economically makes sense and he is supposed to know what he is talking about, right? The pistons are $161.00 each. I check weisco and the closest thing are $100.00 but I must check if those really fit. Can I get the cylinders honing stones from a automotive store? Is it the same stones for the pistons?<br /><br />Standard Size Piston Rings Set $45.70<br />Piston Assembly $161.85 each w rings<br />REED KIT $44.00<br />O-Ring $1.15 each<br />Seal $9.30 each<br />Big Seal $18.65<br /><br />These are all mercury parts of course.<br />The boysen reed is 82.00. I think I wont buy that one for this old motor.<br /><br />Any more Ideas?

 

[Chinewalker]

Re: Problem, Mercury 500, start at home, won’t start at lake

Hi Nandy,<br /> You can't "hone" a piston. If the scorched one has any damage to it, replace it. I think I may have some good used ones if you're interested.<br /> Hone the bores and see where that gets you. A regular small engine hone (three bars, spring loaded) should be sufficient, or better yet see if you can borrow someone's Sunnen straight hone. <br />Scott csr112-n@prodigy.net

 

[Nandy]

Re: Problem, Mercury 500, start at home, won’t start at lake

Chinewalker, I do not have email set up on this computer. I will send you email once I get to the main computer.

 

[Nandy]

Re: Problem, Mercury 500, start at home, won’t start at lake

Email is on the way!

 

[Nandy]

Re: Problem, Mercury 500, start at home, won’t start at lake

UPDATE:<br />I finished rebuilding the motor yesterday. I installed new rings on all pistons, honed the cylinders, buffered pistons 3 and 4 and replaced all the reed valves. I ran the motor yesterday at low speed for about 40 minutes, everything sounded and felt ok. After running the boat I checked the cylinder pressure and it was the same on all the cylinders; 115. <br />The questions now are, how many hours do I need to run the motor to do the breaking before using the motor at full speed? What should be the water temp coming off the motor? Can I use a regular (automotive) timing light to check the timing?<br />Thanks!!!

 

[Clams Canino]

Re: Problem, Mercury 500, start at home, won’t start at lake

Run at least 10 gallons through it before you hammer it at all. WOT timing outta be 35 degrees before TDC, yes you can use a light on #1.<br /><br />-W

 

[KCLOST]

Re: Problem, Mercury 500, start at home, won’t start at lake

You may want to go with a 25/1 or 35/1 gas to oil mixture until it's fully broke in....

 

[Nandy]

Re: Problem, Mercury 500, start at home, won’t start at lake

10 galons! Wow, that will be all summer for me! I was also thinking to change the mix but was not sure of all the effects on the motor. Looks like it is ok then... Any more inputs...

 

[Trent]

Re: Problem, Mercury 500, start at home, won’t start at lake

Like was said. You need to double up on the oil for at least the first tank full.