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Need some help with my 3 cylinder 65 HP mercury outboard with power trim.. i believe its around mid 70's engine. has a plastic cowl not the metal one found on pre 70's.

Bought my boat 2 years ago with this engine. fired right up but was leaking water out of the side cover. so i bought gaskets and tore it apart to find it was cracked inside and water getting into the crank through the exhaust side.
So i went to a friends who works on boats and he happened to have a whole 70 HP stripped apart in a box, the head and pistons are the same as the 65 HP, the extra 5 HP came from different carb jetting and newer electronics that got rid of the distributor. So i used the 70 HP head put the best looking pistons i had from the 2 engines into one and got it back together and wouldnt start. Key on not turning it over you could hear it sparking randomly in the distributor cap, i messed around with it for a while and never figured it out and gave up for the season.

Last summer i never even touched it.

This year i got back at it and throw a battery in it and it fired right up but ran rough. i got browsing online and found a whole engine the same for 100 bucks with low compression on 1 cylinder. so i bought it and put all the electronics onto my engine and it ran great in the back yard. i done a compression test on it... 150 psi on all 3 cylinders.

Finally got it in the water this past weekend, wouldnt rev past 3,000 rpm on the water but sounded to be running smooth, just didnt want to go anymore. after a few runs around it opened up and just screamed across the lake then would slowly die back down but never failed on me.

Went back out again Sunday and same problem, so i thought maybe bad plugs, pulled them out and found one that was loaded with crud. cleaned it up and way i went just screaming again for 5 minutes then slowly die down again.

When i got home i ripped the engine off tore it apart and found the top cylinder.. (#1) the piston was starting to melt in the center and had bad scoring on both sides. not exactly sure what the problem was.. i just put a new water pump in it and it works great so i dont think it was overheating.

.......
my Theory of the burn piston is leading more towards the timing not being correct.. too far advance possibly causing pre ignition, but its only the one cylinder thats bad..
.........

I tore down my spare parts engine i got this summer. and only had slight scoring on 1 cylinder so i ran my hone through it and cleaned it up, still some marks in it but its 100 % better then it was.
All the pistons have 3 rings in this engine.. the parts engine had 1 new looking piston with only 2 rings and the gap in a different location and a chip out of the ring so im assuming it was catching on a port.

I took the 2 good pistons from the blown up engine and put into the parts engine today, finally got it all back together, what a PAIN.. lol. the worst part is getting the pistons back into the head i done it all by hand, even if you had a tool for the rings you would not get it down in there because the head and one side of the crank case is 1 piece so its pretty tight getting even your finger in there to push the rings in. and changing the pistons is a nightmare LOL, the wrist pin bearings are all separate little needle bearings that are not in a raise so i load them up with grease to hold them in place while getting the wrist pin pushed back in then you have to check that the dam things didnt fall out LOL.

So after all this.. got everything all back together, primed the gas, touched the key and way it went, but i couldnt pull the throttle all the way down where it normally would be at an idle or it would stall out and start pinging.

I am not sure exactly how to set the timing on this thing.. it has a distributor that runs off a belt to under the flywheel, it does have a timing mark on it, when the mark is lined up #1 is TDC but for it to run i have to advance the throttle way up as to advance the timing.

So i tryed this..... took the belt off, turned the distributor gear 1 took back. Did run but was worse. so i took it off and put it one tooth forward. and now it runs MINT. ..

Sat there and idled for 2 hours while i was cleaning my mess up, took the plugs out to check for junk on them and still clean so i guess i done something right LOL.

The help i need is how to set the timing properly on this thing so i dont burn up more pistons or do other damage and kill this engine.

The throttle lever at the same time also advances the timing as you throttle up, but as some point the timing has to stop advancing it has screws to turn in and out for where the spark advance should stop.. im pretty sure the timing at idle is pretty dam close to being right on, i have a spare distributor and sat beside the engine looking at where it would be firing. so with the timing actually 1 tooth on the gear (belt) forward i think im retarding the timing. its firing either right on TDC or just slightly after. Previously i think it was firing before TDC

The way it was before i left it lined up with the marks and adjusted the crap out of the advance lever so it would run and i think this is why i burned that piston out of it. i want to make sure this is right before i get it out on the lake and run it full board.

If anyone knows about older mercury outboards chime in and give me a clue please LOL.

this engine is on a 15 foot V hull boat. 76 inches wide just a little runabout. it seems pretty fast. the prop on my engine was a 15 pich. the spare engine i got had a MINT 22 pitch so i put that on. for $100 i paid for the other engine the prop was worth that. but in the end i ended up having to fix the spare motor and run it now.

Ill get a few pictured up tomorrow of the engine to show more about the timing crap on it. i was hoping maybe someone would have manual or know more about these mercurys then i do, actually i dont know very much about it LOL, first outboard i have ever stripped down to nothing and put together. but not my first engine or first 2 stroke. im pretty handy with anything that has an engine, and pretty much anything else lol.

Did you try searching for a manual online? Might be surprised to find a few out there.

Sounds like you are on the right track with the problem, as in the timing being off would cause those problems.... But then I'm no boat engine guy. LOL

Research is your best tool.

Some info i found online. might have answered my own questions lol... the marks im talking about on the distributor gear apparently is not the timing mark.. under the cover, and i remember now i seen an arrow on mine that is the timing mark.

"What you need to know here is that there are several different marks. The distrbutor had a notch on top of the belt guide retainer and that is not the mark. Take that off. It is underneath there. The flywheel decal had 3 vertical dot's if they are still legible. Those were the timing marks."

"Set the top cylinder to top dead center, using a screwdriver thru the top spark plug hole to determine TDC. At this point the timing mark on the cowling support should just about match the one on the timing decal on the flywheel "TDC". If not, remove the eight bolts on the center of the flywheel and rotate the outer flywheel until the timing marks aling and rebolt it to the inner flywheel. Now start the motor, and set the idle timing to 4-6 degrees BTDC. This is the timing setting when the carbs should start to open. Max spark advance should be 19 degrees BTDC. "

the part i dont get, is if i had the timing that far out that i was burning the pistons from pre ignition, why would it have sounded like it was running fine. other then one of the plugs was fouling off once i cleaned that 1 plug up it just rippppppppped LOL i know on water it seems faster then it is, but i bet it does 40 MPH or real close possibly more. but turns out that 1 plug was getting backed in aluminum from the piston LOL.

Before i took it out i had done a compression test @ 150 psi every cylinder. just touch the key and way it went every time sit there and idle all day long in my back yard. 2 tanks of gas worth in the last couple weeks messing around with it. but then i get it out on the lake and my piston goes bye bye.

Maybe i didnt have the timing advance stop set right either and it was advancing more then 19 degrees that i just found out it should be set at. so at an idle it was fine i guess and once i got it on the lake and pounded on it then it was advanced too much at WOT

I dont know . im just guessing. but going by what i just found out about how to set the timing. im going to try that tomorrow night.

Hopefully it runs a long time now, i dont want to tare it apart again, its not alot of fun LOL. and i dont have another spare engine i can take apart and build another one out of parts haha.

One way to fix it ...
Buy a tower of power engine LOL
http://toronto.kijiji.ca/c-cars-vehicle ... Z287477425

I bet that would be crazy fast, too bad my boats only rated for a 80 HP. my step dad has that same motor on his boat, im pretty sure its a 6 cylinder

Or cheapest way out.. http://peterborough.kijiji.ca/c-cars-ve ... Z295742810

I could spend more then $400 repairing my engine. if it last then ill be good for a while, i have spare lower end and gears and prop and electronics and gizmos and such. but parts are crazy expensive for these. i spent around $200 on gaskets and seals alone when i first got this motor 2 yrs ago.

this is the same engine.

http://youtu.be/UsnTljn2vH4

Well there are known cases where timing advance seems to create more power, but you create a hell of a lot more heat too. This is why when Nascar guys know their car is about to blow up, because it starts running like a bat out of hell just before it grenades. LOL

After i have though about it, i think i didnt have the advance stop screw in far enough and its advancing way past where it should, so running in my back yard basically idling the whole time it ran great but once i got on the lake and opened it up there goes the piston, i dont think its something to do with the parts i used or how i put it together. the first engine the one that just blew up on me had a bad cylinder too and i had honed it and replaced pistons with used ones and put the best looking parts into it.

After i built this other engine and was running it, ice cold tap water running into the bucket and the top of the engine seemed hot to touch still but after i made some adjustments on the timing and got it cranked down some after running for 3 hours it wasnt even warm so im thinking that was my main problem was the timing.

I was also told to run premium gas in it, apparently the ethanol does some damage on outboards and small engines clogging the carbs and stuff. all regular gas has up to 10% ethanol now and premium doesnt have any. but at any rate maybe with the premium fuel i should be running a colder plug as well.

Going to get a timing gun tomorrow and set it up proper. i searched online for the last 2 years ive had this thing and only run across some forums with various info could never find a manual. but last night i found that info about the degrees the timing should be set at until then i had no idea so thought maybe someone here might know a little about those engines.

I was going to take it out tonight for a rip but i think im better to wait until i time it with the light and make sure its set right, also see if i can get a colder plug for it so i can run the higher octane fuel and not worry its going to burn more pistons

A few photos...

"What you need to know here is that there are several different marks. The distrbutor had a notch on top of the belt guide retainer and that is not the mark. Take that off. It is underneath there. The flywheel decal had 3 vertical dot's if they are still legible. Those were the timing marks."

it runs like this.. but i wouldnt be able to correctly set the timing with a light cuz the flywheel needs to be turned...


"TDC. At this point the timing mark on the cowling support should just about match the one on the timing decal on the flywheel "TDC". If not, remove the eight bolts on the center of the flywheel and rotate the outer flywheel until the timing marks aling and rebolt it to the inner flywheel"

Well i turned my flywheel then it lines up like this...


Now im not sure if the TDC mark is at the right side of the sticker thats wore off, or the 1st thick readable line just to the left of there is says TDC... now i can not get the arrow on the distrib to line up with that marking on the flywheel and keep it TDC on #1. just dont line up.

Notice the little nub on the distrib gear outer housing and on the distrib housing itself.. if these are lined up its between #3 and #1 inside the distrib.. right where it is sitting in that 2nd picture is firing right dead on #1

I had lined it up with the NUB on it when i first was trying to set the timing on this thing when i had first bought it and had the engine apart for new gaskets and put the other head on. then it never ran till i tinkered alot with it this year.

Also notice the Belt Alignment Mark on the flywheel.. there is no way it will line up even close to the belt unless the flywheel markings are at 30 degrees on TDC and firing on #1 so i think that mark really means nothing to the timing.

The difference in the 2 pictures on the flywheel.. i took out all the bolts that hold it on, turned it only 1 bolt hole and it moves that much.. my guess is that the 2nd picture is correct and the TDC mark would have been on the right side of that sticker thats wore off.

I found the same engine on ebay forsale, i emailed and asked for a picture of the flywheel markings when the distrib is lined up on that nuby...

Side view....

if it blows up again ill part it out.. holly dam look at these crazy prices for parts.. if they actually sold for that i could make enough money in parts to buy a brand new nice 4 stroke engine LOL well maybe not quit but be a really good start, i have 2 of these engines

http://shop.ebay.com/i.html?_trkparms=6 ... 581&_pgn=1

going to try and trade my Suzuki 9.9 for one of these.

http://ottawa.kijiji.ca/c-cars-vehicles ... Z300828871

http://ottawa.kijiji.ca/c-cars-vehicles ... Z299362050

The older 4 cylinder's were supposed to be a better engine, there apparently was alot of problems with the 3 cylinder ones like mine. that 35 hp looks real nice too but i think is 2 cylinder. should push my boat around but be a little slower long as it runs i dont care lol, mine may very well last a long time but if i can trade my 9.9 for one of those ill have a good backup engine

Had it out yesterday seems to be running fine, never quit on me and when i wanted to go fast there was no hesitation this time. so all seems good so far lol.