Only firing on one cylinder after belt change - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 30 (permalink) Old Aug 17th, 2019, 3:45 pm Thread Starter
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Only firing on one cylinder after belt change

Hi everyone, I changed the belts on my 2003 ST4s ABS today (only 5400 miles on it but original belts!) and everything went fairly smooth but now it's only running on the horizontal cylinder. I marked the old belts then transferred the marks to the new belts and everything lined up perfectly, the one unknown is which direction the intake cam spun on the vertical cylinder when tension was removed, I thought it spun back so I moved it forward until the marks aligned but that must have been wrong. How do I make sure it's where it should be now? Is there something I could be overlooking? I know it has spark. Any insight is appreciated!

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post #2 of 30 (permalink) Old Aug 17th, 2019, 3:56 pm
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Hi everyone, I changed the belts on my 2003 ST4s ABS today (only 5400 miles on it but original belts!) and everything went fairly smooth but now it's only running on the horizontal cylinder. I marked the old belts then transferred the marks to the new belts and everything lined up perfectly, the one unknown is which direction the intake cam spun on the vertical cylinder when tension was removed, I thought it spun back so I moved it forward until the marks aligned but that must have been wrong. How do I make sure it's where it should be now? Is there something I could be overlooking? I know it has spark. Any insight is appreciated!
You know the cylinder that isn't "running" (vertical cylinder) has spark? And yet it's only "running" on the horizontal cylinder?

Hmmm.

First place I'd go would be to see if there is "air" blowing out of the intake tract of the vertical cylinder while the engine is turning over. If so, you've either got your belt/cam out of time on that cylinder or you've bent a valve on that cylinder due to the belt/pully/cam being out of time on that cylinder. I wouldn't run it any more until you troubleshoot this though.

Bigger brains are sure to pipe in on this soon.


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post #3 of 30 (permalink) Old Aug 17th, 2019, 5:01 pm
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Agree with Rex. I had a cam spin one tooth against the helper springs once when I wasn't looking. I got lucky and didn't bend a valve but it ran real bad on one cylinder.

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post #4 of 30 (permalink) Old Aug 17th, 2019, 5:13 pm
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... I had a cam spin one tooth against the helper springs once when I wasn't looking.
Sneaky little bastards ....


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post #5 of 30 (permalink) Old Aug 17th, 2019, 5:31 pm
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The vertical intake cam will rotate forwards i.e clockwise when tension is removed if you started off with the motor in the "home" position.

Did you rotate the crank by hand after installing the new belts?
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post #6 of 30 (permalink) Old Aug 17th, 2019, 5:41 pm
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for a quick visual check the camshafts 3 notch's, should align with each other per cylinder.there is a tool you install to verify but you should be able to see if a pulley is 1 tooth off. https://www.ducati.org/forums/techni...ng-timing.html
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post #7 of 30 (permalink) Old Aug 17th, 2019, 6:49 pm Thread Starter
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Thanks everyone! Yes, I rotated the engine over by hand several times using the rear tire in top gear, no sign of trouble. I checked for spark using the original plugs that were in it, as I replaced them with brand new NGK Iridiums. It had Champion plugs in it, is that what these came with? I also installed a new AGM battery, the Yuasa that was in it still worked great but it was dated 2011 so I figured now was the time.

If I'm not mistaken, my forward upper gear is off one full revolution so even though all the marks are aligned I don't know if I need to turn it one back or three forward or whatever other option.

I'm going to head out to the shop and triple check everything now while I try to wrap my head around how to tell where the valves should be in that position.
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post #8 of 30 (permalink) Old Aug 17th, 2019, 7:43 pm
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It's 360 degrees of rotation. There is only one spot. You could spin a cam several times in ether direction and when you get it back on the mark, it will be the right spot. The thing to be careful of is the lay shaft pulley (drive gear). It has to be on the mark pointing towards the clutch AND the flywheel mark for TDC compression at the horizontal cylinder has to be in the left side window. If you're not sure the correct cylinder is at TDC, with the belts off use a small wood dowel in the plug hole. You'll know when the cylinder is at the top of the stroke. If the lay shaft timing mark and the flywheel mark agree, you're at TDC compression for the H cylinder. That is where you install both belts and tension the horizontal belt. Rotate to TDC compression for the vertical cylinder to tension that belt.

Aside from potential the timing mark issues, be sure you didn't forget to connect anything you disconnected to get at the belts. ECU ground comes to mind as a start...

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post #9 of 30 (permalink) Old Aug 17th, 2019, 8:08 pm Thread Starter
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It's 360 degrees of rotation. There is only one spot.
That's what I was hoping to hear! I am fairly certain I figured it out, I was off one tooth on the drive sprocket so both cams were advanced one tooth. I re-marked, removed tension and moved each cam back one tooth, now everything is aligned properly. I can't believe I did that but live and learn. I ran out of time tonight but will let you guys know how I make out in the morning. Thanks again everyone!
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post #10 of 30 (permalink) Old Aug 18th, 2019, 5:37 am
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Originally Posted by 2004 999s View Post
for a quick visual check the camshafts 3 notch's, should align with each other per cylinder.there is a tool you install to verify but you should be able to see if a pulley is 1 tooth off. https://www.ducati.org/forums/techni...ng-timing.html
that's only on a testa evo 2009 -ish onwards. on your 999 for instance (all testa pre 2009) , the vertical cams will have the t leg pointing to 4:30 instead of 12, as they're 135 degrees rotation (rotating anti clockwise) before what the picture shows when the crank is at horizontal tdc firing. rotate the crank 270 degrees, which is 135 degrees timing shaft and cams, to vertical tdc firing and the t slots on the vertical cams will then be as the above picture shows. if that makes sense.

the desmoquattro don't have the t slots at all. they have dots.
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know all wanker

Last edited by belter; Aug 18th, 2019 at 5:55 am.
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