Water Getting in Top Cylinder Yamaha 40hp Twin

[fleetwin]

quote rickrodt:

Check for a broken reed on the top cylinder…..same thing happened to me on a 6 horse OMC motor. Drove me crazy. With the reed gone, the top cylinder acts like a pump and sucks the water up into the cylinder from the exhaust manifold dump.

Another excellent point! It is amazing how messed up exhaust pulses can pull water back into a combustion chamber…This always amazed me on stern drive engines also.

[joesnuffy]

Getting closer I will post pics 2 morrow once they go to the icloud. 2 screw heads were missing on the top cylinder reed valves closest to the rod the 3rd and only screw left was barely holding the reeds and back stop on the screw being bent kept it from unscrewing. My bet is the rod knocked the screw heads off. Here is an auction on ebay right now for a used reed valve assy for that motor notice how the middle screw has been getting hit by the rod. http://www.ebay.com/itm/381402128198?_t … EBIDX%3AIT leads me to think it is a problem with these motors especially when compression is over 170 on each cylinder.

I put a used rod on the upper cylinder when I rebuilt it due to cost of new one which was in specs with a new big rod bearing assy. It is possible when it threw the rod it loosened those screws since the rod cap bolts had loosened causing the engine failure and they unscrewed and the rod hit them I didn’t notice that when I had it apart. I felt the rod with my finger where the two halves of rod come together it still feels tight. I decided to roll the dice and fixed the reed assy best I could and added new screws and lock washers re-installed it and the motor ran a lot better almost getting to WOT. I am going to pull them back out 2 morrow and see if the rod has pecked on the new screws if so the motor will have to come back apart and I haven’t wasted my new head gasket that is coming if not I will look for some good used reeds assy.

Thanks to all for the help,

Joe

[fleetwin]

Well, it certainly is possible that the flying rod debris initiated the reed problems. Looks like you/we were right about the reeds, but for the wrong reason! In any event, I would certainly change that reed block with a used one that you have ordered. That ebay reed block/manifold assembly looks a little rusty, but I see the rub marks on the screw. It is hard to say whether reed manufacturing problems caused the rod to hit the reed block, or whether that engine came apart like yours did slapping against the reed block. I’m sure the used rod you are using is OK.
I would probably use the reed block that was not hit along with a new gasket. I don’t know about Yamaha, but I am usually fearful of disassembling reed blocks. Altering leaf valve positioning, or flipping the leaf plate over usually causes the leaf valves to break. I would probably check all the screws to ensure they are tight, and make sure the leaf valves look OK and are seated properly/not rusted. If the screws seem loose, you could remove them one at a time, then carefully reinstall the screws with a drop or two of Loctite. I would probably use a few drops of Loctite on the two screws that hold the reed block to the manifold plate with a new gasket as well.
Unfortunately, I don’t know if this was a known Yamaha problem, hopefully someone will chime in.
Do you know what caused the original rod failure on your engine? It doesn’t seem like rubbing on the reed screws would cause the rod to fail, I’m thinking the messed up reed block was collateral damage.
I don’t know just how much clearance there is between those reed blocks and the rods. You could try assembling the new reed block to the manifold plate without the gasket first, then snugging the manfold in place. Now, slowly turn the crank listening for rubbing. If the rods hit the reeds without the gasket in place, I’m thinking there isn’t enough clearance, and you should investigate with Yamaha for known problems/fixes for this situation.
I’m glad you found the problem, sorry you had to rip into this thing after rebuilding it, but happy the powerhead is not damaged….

[billw]

I have seen a couple of heavy use Yamasakis where the bearing cage for the upper crank bearing goes away. (It’s plastic, sometimes.) Then all the rollers work around to one side of the crank, causing it to thrash around and generally be noisy, spew some oil out of the top, but exhibit no other symptoms. Wondering if this is why your rods hit the reed screws?

Long live American manufacturing!

[joesnuffy]

Thanks Guys,

The cages indeed are made from plastic on those large rod bearings not a good feeling. I put 2 brand new OEM ones in it one for each rod when I rebuilt it.

What I make out about the original engine failure was the rod bolt/s backed off the rod and slapped a hole in the front of the engine case. I purchased the boat and motor after the failure. The motor looked to have been barely used very clean for that year no oil leaks etc no overheating paint looks new. Originally I thought it might have just spun a bearing do to long storage time but after I disassembled the engine the rod bolts were backed off on the top cylinder.

I am going to take the carbs back off today and hope that the screws on the upper reed block are intact and not damaged which will mean that the rod is working as it should I will then order a replacement reed block assy. The one on the ebay auction I was using as a comparison to show the screw had been getting tapped a bit by what I think would be the rod and your right it is rusted and it wouldn’t work for my application. Their are several one’s on ebay right now that look to be OK. I did use locktite on all the screws even the ones that hadn’t backed off yesterday I didn’t do the ones that hold it to the plate I will do them when I put the different reed block assembly on.

I will also perform a compression check today and check my notes on what it had after about 10 hours of run time.

I did check to see turning the flywheel by hand yesterday to see if I could feel rod tapping the reed screws and I did not feel it. But your right if the screws were tapped today I will be going to see yamaha. And I will put new gaskets on they might even be thicker than before that is something yamaha could tell me and I could micrometer them and compare the thickness of the old one to the new one and know that the new one will get squashed a bit. I do know when I have built sea doo 2 strokes the base cylinder gaskets come in different thicknesses to get your piston to head clearance correct.

I appreciate the help and will keep you posted.

Joe

[joesnuffy]

Got the carbs off and reed valve assy. The screws on the reed block did not get damaged by spinning crankshaft so that’s a good thing the rod is not sloppy. I feel like I am missing something simple so I checked a few things. Both cylinders have over 1/4 inch of spark on each coil so that part is ok. I re-checked both high and low jets in carbs which also were clean. The high speed jets have pretty large holes and go straight up to the carb throat so it should get to WOT if everything else is working OK. The reeds looked good no light was coming through them so I don’t think they are the problem may be that one of the screws on the reed valve assy came loose after rebuild and went bouncing around on top of top cylinder dome and might have cracked cylinder dome or possibly cracked the piston sleeve. I re-checked compression it was 175lbs on the top and 180lbs on bottom with reeds and carbs off.

I am going to order some new gaskets for intake manifold, carbs, etc. I will also order a different reed valve assy. I am thinking about putting 2 gaskets under the read valve assy where it mounts to motor to give it a little more clearance unless someone thinks that’s a bad idea. I don’t think it could hurt and I could always remove it later if it did make motor not run right.

I already have a good used head and new head gasket on order so I am going to just slow down a tad on this project and think about it while waiting on parts. When I pull the head I will take a look at the top piston head to see if it has been damaged by a screw head bouncing around in there. It was a new piston so if it is damaged it happened after rebuild and it could have damaged the head possibly causing a small leak in dome. I will also take a good look at the bore to try and see if it might be cracked might not be able to see it with naked eye would probably need a pressure test.

The top spark plug looked to be washed I could even see the white cermaic part of plug like it is being washed by fuel or water. I think I will replace fuel pump also.

Thanks for the help,
Joe

[fleetwin]

Not quite sure what you are asking, but I seem to remember you saying the engine ran better and "almost got to WOT"….So, just what is the running status now? Does it idle nicely? Does it develop full power in gear? Could just be something simple like carburetor linkage getting screwed up and one or both butterflies not opening fully. The compression sounds OK, so it doesn’t seem like any of the reed screw debris did any significant damage.

[joesnuffy]

Mainly thinking at this point and trying to figure out what I am missing not really asking a question. The motor still isn’t idling as it should unless the choke is pulled out a tad the idle up a tad also. That kinda makes me think it is still something I am missing. I did disconnect the fuel line yesterday and it didn’t wind up much more if any. I did raise the engine up while underway to try and reduce the water going through engine and it did improve sligthtly. That has me thinking the head is leaking water through the dome on head which is damaged. It did almost get to WOT it just doesn’t seem to want to get over that hump and builds up slowly to the highest I can get it. I have the carbs off right now and am ordering gaskets, reeds etc. I do appreciate the help. This is a hard one for me.

Joe

[joesnuffy]

I have been inspecting the reed valves with a very bright light I forgot I had. The ones that the rod hit I see light coming through all 3 valves so I am feeling good about replacing them. All the other 9 reeds no light coming through them. The motor did run a lot higher rpm’s yesterday with the screws in the reed valves. The compression is so high on that motor I don’t think it will be the head or head gasket. I will replace the reeds first and see how she runs. If that doesn’t fix my issue I will rebuild the fuel pump got a new diaphragm coming at that time I will see if it has any cracks in it. Then if that doesn’t fix the issue I will change the head and put on a new head gasket.

Thanks for helping I really appreciate it,

Joe

[fleetwin]

Well, I really don’t think you have a fuel pump issue, so I wouldn’t spend time ripping that apart. Keep in mind that you seem to have a lean condition while idling, a bad fuel pump diaphragm would cause a rich condition in the crankcase it is connected to. You could diagnose a weak fuel pump by pumping to fuel line primer bulb while the engine is running to see if RPM picks up.
Did the engine have more WOT power RPM when you first ran it, before the reed problem occurred? Or, do you just feel the engine should have more power….
Again, I just don’t want you going crazy looking for a water leak that I’m thinking is not there. When I get frustrated with stubborn projects like this, I have to remember (force myself) to return to the basics. Most problems are basic ones, we create our own confusion by skipping over basic issues and looking for/sometimes creating complex problems that aren’t there.
So, the engine doesn’t idle real well, but idle quality can be improved by feathering the choke, correct? Again, I’m not too familiar with Yamahas, but am assuming it has two carbs, am I correct? If so, you problem could be as simple as a synchronization/linkage problem. On the OMCs, both butterflies must be completely closed when idling….If one is cracked open ever so slightly, the engine will run lean, just like yours. You have had this thing apart several times, it surely is possible the synchronization is messed up. Do you have the Yamaha manual showing the step by step synchronization procedure? Are there any sort of adjustable needle valves for idle, or does it have fixed idle jets?
Let’s just say you check the synchronization and it is spot on…Which cylinder is running lean at idle, or are they both? Manually tickling the choke valves on each carb (disconnect choke linkage between two carbs) can help isolate a problem cylinder. Let’s just say you find that the top cylinder is the problem cylinder by tickling its choke valve to keep RPM up. So, now we are wondering is it a carb problem, or some sort of internal problem causing the lean condition….Well, we could just swap the carbs at this point….Let’s just say the bottom cylinder now runs lean with the carbs swapped, so now we would conclude that there is a carburetor problem seeing that the problem followed this carburetor to the bottom cylinder.
If the problem stayed with the top cylinder after swapping the carbs, then we would conclude we have some sort of problem with the top cylinder/reeds/intake manifold causing the lean condition….
See what I’m getting at here? Let’s try to keep things simple and perform tests that will provide us with fairly concrete conclusions….So, your next step should be rechecking the Yamaha synchronization/linkage procedure thoroughly. I’m sure this is step by step procedure, not unlike OMCs, it is very important to perform every step in the order spelled out in the manual.
Please know I am not trying to "minimize" your problems here, but I just don’t want you to get even more frustrated looking for a major problem when the issue could be something very basic. And, you can safely assume I harp on these things only because I have "relearned" this lesson several times in my life!
Hopefully, a Yamaha guy can chime in if you don’t have the OEM manual showing the step by step synchronization process for this engine.
D

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