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Nytro Engine Timing

The chain will jump off the gears just as he describes if you do not tie wrap them. Then tensioner is a hydraulic type, that is why it will jump the chain on first assembly, it needs oil pressure to keep tension. Again, if you feel you don't have the items lined up properly then rotate the motor over one time using zip ties to hold the chain on the cam gears. Then install the motor and fire it up and you will be fine.
 

the first stroke of a four stroke is the exhaust stroke the second stroke is the intake. The problem is that the exhaust cam lobe is not fully off of the valve and the intake cam is starting to compress the intake valve spring. The exhaust cam wants to turn and the intake cam doesn't which causes slack between the gears and results in the chain jumping a tooth. I normally rotate the engine a couple of times with ties then without to make sure the tensioner takes all the slack out of the chain. If it keeps skipping on you then the tensioner, gears and/or chain has a problem.
 
grizztracks said:
the first stroke of a four stroke is the exhaust stroke the second stroke is the intake. The problem is that the exhaust cam lobe is not fully off of the valve and the intake cam is starting to compress the intake valve spring. The exhaust cam wants to turn and the intake cam doesn't which causes slack between the gears and results in the chain jumping a tooth. I normally rotate the engine a couple of times with ties then without to make sure the tensioner takes all the slack out of the chain. If it keeps skipping on you then the tensioner, gears and/or chain has a problem.
Click to expand...

That's what I'm thinking. I don't want to start the motor and bend a valve. I've done as everyone is saying. One full revolution with the tie wraps, and as soon as I take them off and turn by hand, it jumps. Tensioner is tight and eveything looks fine but still jumps. Maybe it is related to the oil pressure and tensioner. Seems to me that the tensiorner is spring loaded but that might be just enough to hold until the motor starts and builds oil pressure, not sure. Not trying to over think things but if the chain won't hold on the gears when turning over by hand I don't want to try and start it. Maybe the vector motor has less agressive valve timming and doesn have as much tendancy to jump as the Nytor motor? Anyone actually timed a Nytro motor and if so was it different than a vector or the 05-07 models?
 
You said in your other thread this engine was new to
you. Did you replace the gears, chain and tensioner or
is this the old stuff? Even the vector has the nytro style tensioner now I believe. The older ones were
different. I wouldn't start it either until the problem is
resolved. Might be a pita to set up but can you pressurize the oiling system through a port somewhere? And may be a dumb question but are you
rotating the engine clockwise or counterclockwise looking from the left side of the sled. (as if it were installed)
 
Rotating counter-clockwise looking from left side but clockwise looking at the mag side.
 
I haven't done one of these motors yet so I just can't say. I would be asking the same questions. Now I see why you said the rub block in the valve cover is
going to hold it down. I think you are right and everything is ok. It's not actually jumping. Pretty experienced group here someone will know. Clean
work and a very good video by the way.
 
Thanks. Sometimes its just difficult to explain things. It might be as SRXspec had said, that once oil pressure is built up it will hold but its so close to skipping a tooth that I'd be worried starting it like this.
 
Oil pressure doesn't have anything to do with chain tension. The tensioner is not hydraulic, its spring loaded. Once the tensioner takes up the slack in the chain it should lock into place and not allow slack to reappear. Chain guides are their to prevent the chain from slapping and coming in contact with the engine block. I think Yamaha normally recommends replacing the tensioner if the engine is apart. Did you replace the tensioner?
 
Well the tensioner pushes the chain guide against the chain to take up the slack. The tensioner is working fine as I tested it before putting it in. I took the mag cover off to check and the tensioner is out as far as it can go with the amount of pressure it can apply. I agree the tensioner is spring loaded but I wonder if this is just enough to get things running and then the oil pressure assists. There is what looks to be an oil passage going from the block into the back side of the tensioner. Either way, do you think what's going on in the video is normal?
 
I'd also be concerned especially after seeing your video. From what I see in the manual it appears that there is an oil port to the tensioner. I haven't had the Nytro tensioner out yet so I'm not totally familiar with its operation but it may depend on oil pressure to maintain it's position. When the chain gets slack in it can you see the tensioner rod moving back? I think as long as the tensioner is released, extending out against the tensioner guide and with the valve cover on there's not enough clearance for the chain to jump time.
 
I am sure it is oil dampened, the new ones are hydraulic in 2011 or 2012 I believe. The manual says
to bleed all the oil out before installing so the spring
must do the job. A spring would bounce all over without oil in it and wear out quick. They can only be cycled so many times.
Just as a note the 2005 through 2007 bad tensioners could not be checked out of the motor. They would check out
good.
 
I wonder if the chain is bad...did you checking that before you put it back together...maybe some of the links are tight....ive seen it do that with a bad chain
 
Yeah, checked the chain. It measures good as per the manual. Nothing seems tight. Its very consistent in how it does it. Same spot every time. I'll take a video tomorrow night showing whats going on with the mag cover off. Might shed some light. I guess the fact that not too many people have run into this shows how reliable these motors typically are. With a 2 stroke there's tonnes of people getting back to you with responses on motor trouble lol.
 
Srxspec said:
The chain will jump off the gears just as he describes if you do not tie wrap them. Then tensioner is a hydraulic type, that is why it will jump the chain on first assembly, it needs oil pressure to keep tension. Again, if you feel you don't have the items lined up properly then rotate the motor over one time using zip ties to hold the chain on the cam gears. Then install the motor and fire it up and you will be fine.
Click to expand...

Well, must be hydraulic for sure as the spring in the tensioner just isn't strong enough to hold. Everytime the chain pushes away from the gear the tensioner is moving out allowing slack in the system. I think the spring must be to hold enough initially for the engine to fire and then oil pressure takes over. Fingers crossed.
 
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