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Help! Please! broken intake valve Spring on 2001 mercury 15hp bigfoot four stroke

J

Jhanratt

Regular Contributor
I need some advice please.

I have diagnosed my fail to run fail and fail to idle issue. The upper cylinder intake valve spring is broken in several pieces. The upper intake valve seal is also destroyed. I pulled the valve and it did not come through the guide smoothly. It took some twisting and pulling by hand to get it out. The valve has a clear wear point above the seal and below the keeper which has a slight shoulder. I think it will need to be replaced along with the valve spring.

Questions:

Do mercury replacement valves come drop in ready? I have never worked on valves and have no idea how to grind or lap?
Do I need to replace the valve guide?
Should I replace all of the other three valve springs while I am in here? Is this a common failure point?
The two rocker shafts have some minor staining / corrosion where they are exposed. Should I try to clean them up or ignore it?
There is some wear at the top of the valve guide under the valve seal. I think it will be ok. It would require replacing the entire head to repair.

Any other advice while I am in here?

I have done re and re on automotive heads but I might be in over my head here.

Thanks in advance for your help! Please!

Jeff
 
If you want to do the work yourself you need to get a good service manual. Fully disassemble the head and keep everything in order it was taken apart. I am sure the tolerances are pretty tight. You may get away with just replacing the valve, spring and all the seals but you want to check everything is within tolerance like valve stem clearance and seat width both intake and exhaust. I would replace all the springs and anything else thats out of spec. How do the cylinder walls look do you still see a cross hatch on the cylinder walls and no ridge on the top of the cylinders. Were you over reving the motor or did it get hot? Did you figure out why it happened? Definately clean up the rockers and shaft and inspect for wear was there any metal shavings in the oil? Sounds like a fun project take your time and price out the cost of repair parts if the head can be rebuilt compared to a good new/rebuilt.
 
THANK YOU!!!

No it was never over heated and never over-revved. I am the only captain and I have had it nearly all it's life. It is a kicker used for fishing and the tattle tale works fine. It is somewhat high usage at 800 - 1000 hours but it is all at idle or very low power.
The cross hatching pattern in the cylinders looks like new.
No ridge in cylinder. but I could be wrong due to un-burned carbon at the top of the cylinder.
Some damage to the piston from striking the valve but I think it's okay. How thick are the pistons anyway??
Some oil in the exhaust port of the lower cylinder. Nothing but carbon in the upper cylinder.
No History of oil consumption. Some history of making oil and running WAY too rich. I fixed that last year and it did not make any oil last year.
Yes some metal fragments on the oil pump pick up screen and some in the bottom of the crank case. Nothing I would consider excessive though.

It ran great the last trip out and I shut it down as normal. The next day it cranked and cranked and when I finally got it to start it was running on one cylinder.
I can't understand why it failed. The mercury dealer said he has never sold a valve spring???

I cannot take my time as it is sockeye season and my boys want to fish so I want to get up and running FAST!

My neighbor came by an hour ago and helped me drive out the valve guide it had some wear on it from the broken spring and it was looser than the lower intake valve so he said change guide too. He suggested I replace the valve and guide and all springs and seals. I am about to search for a kit but my merc dealer quoted $120 each for valve seals. I hope he got that wrong!

Thanks again!

Jeff
 
Last edited:
I have a good .pdf manual for the engine.
I just looked at the link you sent me. I suspect my dealer got it his pricing wrong on the valve seals! The rest seemed reasonable-ish...
My serial number is 0T2897## I hash tagged the last two digits but if you need them I will post properly.
I will probably order parts from him tomorrow because I NEED this motor fixed yesterday!

right now I am thinking I will replace the following:

All four valve springs.
All four valve seals.
The damaged intake valve.
The damaged intake valve guide.
The head gasket/
The power head - base plate / crank case gasket (whatever it is called)

I realize I am short cutting a bit but I am in a hurry to fish with my kids and sockeye season is only open for a bit here and my summer vacation is wasting!!!

Thanks again!

Jeff
 
Sockeye season tells me your in WA? Seawaymarine in lynnwood may have what your looking for open weekdays only. I would want to replace the upper cam seal also while it is apart.
 
I am in Summerland BC Canada. My local dealer is Dockside Marine.
I thought he quoted me for valve guides.
I am now worried that they are not available seperately from the head.

I would hate to have to buy a complete head for this engine.
 
IMG_3031.jpg
cylinder head. Valve seats look to have even wear which corresponds to even wear on the valves.
IMG_3029.jpg
cylinders two minor score marks on the bottom cylinder
 
IMG_3024.jpg
Lower cyl intake valve. note wear on the valve stem from contact with valve adjustment screw.

IMG_3025.jpg
Upper cyl exhaust rocker note wear from cam shaft.
 
The best way to measure the valve stem clearance is with a dial indicator and very important. You may want to mill the ends of the stems nice and flat and get new adjusters when the end gets a dent in it it keeps the valves from spinning when it is running. It depends on how far you want to go I dont see you can get oversize pistons I wouldnt want to spend too much money on a motor that needs rebuilt when you rebuild the head. Clean it up as best you can and run it till it pukes?
 
It's been quite project but It's back together now. I had a machine shop do the head because I was out of my league. New head gasket new valve springs. new valve seals. I put it back together but now I can't remember the wiring inside the engine. It seems like the start solenoid is an orphan?
I connected same colour wires together but is doesn't have a corresponding match?
The start solenoid has a tan brown wire which is attached to a brown and white short wire which doesn't seem to have a match?

Anybody got any ideas how to wire it?

I'd like to get it running.

Thanks

Jeff
 
Ok found a brown wire hiding out under the starter motor.
It ran smooth and sounded fine but puked a liter of oil out in about 5 minutes.
I realized i forgot to tighten the valve cover bolts.
I tightened them up and restarted it.
it puked out another liter of oil.
I pulled the power head and noticed the oil pump gasket is loose.
it is tightened to spec and still "floats"
it cant be right.
The only way to get it to seal is to remove the o ring?
but the parts diagram and manual show an o ring. There is no clearance for it and it keeps the oil pump down and away from the head which prevents the gasket from contacting.

i'm stumped on that one for now.
 
Oil pump issued solved by installing without the o ring. Just the oil pump gasket and a thin bead of rtv silicone. I ran it for about four hours and it runs like new so far. At the end of the day I probably should have just bought new motor and parted this one out. Live and learn. New valve guides 4, new valve 1, new valve guide seals 4, new valve springs 4, new head gasket, new powerhead gasket, new oil pump gasket.

Sounds good and runs good but it's still a high hours well used motor.
 
Mercury 15 hp 4-stroke manual

Hello, I hope you got your Murcury 15hp fixed.

You did mention you had a good pdf manual.

Any chance you could send me a copy?

It would be very much appreciated,
Thanks,
Alan
 
Update. This motor has continued to run like a champ since the rebuild. No sign of oil consumption. No excessive contamination of the oil. The leg seals went last year and I replaced all the seals in the leg successfully.
It seems to have been worth the money I spent on parts.
Thanks for the great advice all.
 
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