HELP! YZ450F won't start after valve adjust

[dkortje]

I love my 450f, but my greatest fear has been working on it. I am new to 4-strokes and feel very lost. I decided to adjust my valves this weekend. When I put it back together, it wouldn't start. I think I probably did something wrong with the timing chain, so here are my questions:

1. The service manual says TDC is when "I" mark on rotor is aligned with pointer. Is this the "I" after the "H" or is this the punch mark on the rotor?

2. Once you have TDC, how do you know which direction to place cams, ie. since a four stroke has two complete revolutions for each spark, how do you know if the punch on the cams should be "out" or "in" for the particular part of the cycle :eek:

This is all very confusing to me, I tried a search without much help. This is the funnest bike I have ever ridden, but boy, my old 125 was much easier to work on.

 

[Rich Rohrich]

1. The service manual says TDC is when "I" mark on rotor is aligned with pointer. Is this the "I" after the "H" or is this the punch mark on the rotor?

Yes. it's the mark that looks like an I.

2. Once you have TDC, how do you know which direction to place cams, ie. since a four stroke has two complete revolutions for each spark, how do you know if the punch on the cams should be "out" or "in" for the particular part of the cycle :eek:

If you look at the cams from the left side of the engine the exhaust cam should be pointed at about the 10 o'clock position and the intake cam should be at about 2 o'clock.

The top dot on each cam gear should be at 12 o'clock, and there should be 12 cam chain pins between the top dots on the cam gears..

 

[nikki]

Next time before you remove the cams, put the bike at TDC and use a paint marker to mark where the chain lines up with the cam punch marks. Makes reassembly a little easier.

There should also be a picture in the manual on how the cams/punch marks should be aligned at TDC as Rich described above. There is also a picture showing the "I".

Also, make sure the new shim pads are sitting in their groove and that one didn't get wedged under the cap. I had that happen to me once and it took us a little while to figure it out. If you measure all of your valve clearances at TDC and they are in spec, then your shim pads should be sitting correctly in the groove and you have another problem.

 

[dkortje]

If you look at the cams from the left side of the engine the exhaust cam should be pointed at about the 10 o'clock position and the intake cam should be at about 2 o'clock.

Rich, doesn't the timing mark rotate twice for each cam rotation, in other words I thought that at one point the cam would be 180 degrees off, or have I just been inhaling too much 2stoke exhaust? :think:

 

[Rich Rohrich]

Rich, doesn't the timing mark rotate twice for each cam rotation,

After re-reading what I posted I realized it might not be totally clear.

When the piston is at TDC if you look at the cams from the left side of the engine the exhaust cam lobe should be pointed at about the 10 o'clock position and the intake cam lobe should be at about 2 o'clock.

With the lobes positioned this way the top dot on each cam gear should be at 12 o'clock, and there should be 12 cam chain pins between the top dots on the cam gears.

This is proper cam timing for the YZF, if you reinstall the cam chain tensioner and rotate the crank 360 degrees at this point the engine will again be at TDC but the cam lobes will have turned 180 degrees.

The service manual shows some pretty clear pictures and outlines the procedure really well.

Hopefully this helps some.

 

[dkortje]

Thanks Rich, that's what I thought, but what I still am having a hard time with, is when you set the piston at TDC, how do you know if the cams should be installed at position 'out' or 180 degrees 'in', ie. how do you know which TDC in the timing cycle you are at?

 

[Rich Rohrich]

, is when you set the piston at TDC, how do you know if the cams should be installed at position 'out' or 180 degrees 'in', ie. how do you know which TDC in the timing cycle you are at?

OK, now I understand where the sticking point is. Let me see if I can clear it up. There is really only ONE TDC if you ignore the cams for a second. TDC is TDC, so once you have the piston positioned there, the CAMS really decide the timing.

Try this. Remove the cams, hold up the cam chain and put some tension on it with your fingers and rotate the engine. As you can see, as long as the engine is at TDC you are ready to install the cams with the lobes at the 10 and 2 position described above. The cams don't know or care how many times you've rotated the engine, they just care about TDC. The main thing to remember is, the CAMS control the timing. The crank just gives you a reference point to work from.

One last thing, don't forget to check the shim seating that Nikki suggested. It's a really common issue that people run into and I should have mentioned from the start.

Thanks Nikk :worship:

 

[dkortje]

Thanks Rich and Nikki,

Sorry I'm so slow. :clue: I'll check the shims and try to get it together this week. You folks are a great help!! :thumb: :thumb:

 

[biglou]

My favorite tool for bucket & shim removal/instalation is the magnet on a stick. Keeps things where they should be. :thumb:

 

[dkortje]

My favorite tool for bucket & shim removal/instalation is the magnet on a stick. Keeps things where they should be. :thumb:

Brilliant Biglou, it took me forever to get them out with my slippery fingers, and the needle nose seemed too rough :eek: . Now how can I get all you guys and galls to just do my mechanic work for me :laugh: !!!

Seriously, your experience really helps, thanks again.

 

[biglou]

lol, ask anyone that knows me-just bring it over to the house and I'll gladly wrench on it for ya!

 

[High Lord Gomer]

I was very worried about how the engine would know if it was at TDC at the end of the compression stroke or at the end of the exhaust stroke. I finally called EGorr and he told me it didn't matter as the bikes fired on every revolution....both the compression and the exhaust strokes!

 

[dkortje]

I was very worried about how the engine would know if it was at TDC at the end of the compression stroke or at the end of the exhaust stroke. I finally called EGorr and he told me it didn't matter as the bikes fired on every revolution....both the compression and the exhaust strokes!

Aha!!! :clue: :clue: :clue:
This is making more sense all the time!

 

[Rich Rohrich]

Exactly, it's called a lost spark ignition and it's common to most four-stroke singles.

 

[dkortje]

PTL !!!! I put it together this weekend and it starts!!!! :aj:

Thanks for all the great help, I'm starting to feel more like a thumper mechanic everyday. :)