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Timing Belt Change - Bent Valves?

2010 Views 18 Replies 8 Participants Last post by JEFFRPM, 2 mo ago

twelvexs

Discussion Starter · 2 mo ago

Cross-posted in another forum as well...

Apologies for the lengthy post. Need some advice if possible. New to Ducati maintainance, so hoping I did not screw things up.

Went to replace timing belts, watched videos, researched forums, felt confident I could do this. Got some tools ordered and figured I'd go at it. Everything went smoothly with disassembly, got engine to TDC on horizontal, marked pulleys, pinned cams, removed old belts, everything stayed in position. On went the new belts, but didn't apply the tensioners. Think this is where I made my key mistake. Pulled the pins, then applied the tensioners and set them to ~100Hz. Failed to recheck the timing marks on pulleys. Rolled engine over by hand with crank tool and it wasn't smooth and seemed to 'catch' at specific points. Did this about 4 complete revs and knew something was wrong.

Was able to get engine back to TDC on the horizontal and both cam pulleys were 1 tooth off.

@#$#$%

Scoped the bores and the valves do appear to have touched the pistons on both cylinders.

#$%^#$%^

Pulled the belts and reset the cams back to original marks. Belts back on, tensioners on, then pulled the pins. Nothing moved off the marks this time. Rolled the motor over by hand and smooth as silk. Set the belt frequency again to ~100Hz, few more turns, no issue, checked the frequency and still good.

Reassembled the few pieces needed to get it to run, inserted key and it fired right up, sounded OK, warmed up, and revved fine. No weird noises, backfires, smells or smoky exhaust. Did this a couple of times as a follow-up.

I only rolled it by hand never by starter.

Guess my question/concern is - did I bend the valves?
Was my mistake pulling the pins before applying the tensioners?
Am I looking at an issue down the road?
Since it starts up and runs, did I dodge a bullet and not do significant damage?

Any feedback, jeers, shaming welcome.

Thanks!

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1 - 19 of 19 Posts

casor

· #2 · 2 mo ago

What bike is this?

twelvexs

Discussion Starter · #3 · 2 mo ago

Oops, important point.

Monster 796 - 2V motor

Ricko

· #4 · 2 mo ago

If you just turned it by hand I doubt it was enough to bend metal.

Maybe do a leak down test if you want peace of mind. You should be ok.

Reactions: 1

ducvet

· #5 · 2 mo ago

You likely will be fine , BUT....

To be sure do a leakdown test on the motor to verify, if you have a bent valve the leakdown test will dump air out the bent valve.

Reactions: 1

Andreaz

· #6 · 2 mo ago

What pins did you pull? Did you losen up the cam pulley adjusters? If you did this, you migth want to make sure your timing isn't out of wack by degreeing your cams or follow the work shop manual instructions using the cam lock pin

twelvexs

Discussion Starter · #7 · 2 mo ago

Ricko said:
If you just turned it by hand I doubt it was enough to bend metal.

Maybe do a leak down test if you want peace of mind. You should be ok.

That's a good idea. Can't hurt to have that data point just to confirm things. Thanks!

twelvexs

Discussion Starter · #8 · 2 mo ago

ducvet said:
You likely will be fine , BUT....

To be sure do a leakdown test on the motor to verify, if you have a bent valve the leakdown test will dump air out the bent valve.

Will do. Think I need to do this just to have confirmation one way or the other. Thanks!

twelvexs

Discussion Starter · #9 · 2 mo ago

Andreaz said:
What pins did you pull? Did you losen up the cam pulley adjusters? If you did this, you migth want to make sure your timing isn't out of wack by degreeing your cams or follow the work shop manual instructions using the cam lock pin

Thanks for the comment! I didn't loosen the 3 bolts on the cam pulleys if that's what you're meaning. I used these from Hdesa to pin the cams thru the access hole described in the manual.

Font Audio equipment Fashion accessory Titanium Electric blue

I removed these too soon I think and the cams rotated a tooth when I tensioned the belt. I didn't recheck before turning over by hand, but should have.

I'll do the leak down test and see what that shows.

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Chuckracer

· #10 · 2 mo ago

I once bought a perfect ST3 super cheap because the shop that changed the belts on it did the same thing, but they didn't check their work first, just started it.

Goodbye exhaust valve.

That bike was running, but with an audible tick, which was the exhaust valve hitting the piston.

twelvexs

Discussion Starter · #11 · 2 mo ago

Chuckracer said:
I once bought a perfect ST3 super cheap because the shop that changed the belts on it did the same thing, but they didn't check their work first, just started it.

Goodbye exhaust valve.

That bike was running, but with an audible tick, which was the exhaust valve hitting the piston.

@Chuckracer Yikes! Glad I didn't attempt to start mine. Fingers crossed it was just a dumb oversight by me!

JEFFRPM

· #12 · 2 mo ago

Last year while doing my winter maintenance in my greed for more bottom end grunt I advanced my cam timing from 3° advance to 5° when doing so I bent my vertical cylinder intake valve by.. oh... say... 0.001" when turning over by hand needless to say I didn't repeat that stupid idea on the horizontal next.

Why I didn't pull that stunt on the "easy" to replace horizontal cyl first was my penance for having to tear my engine down changing the PITA vertical intake valve.

I seem to occasionally have lapse of judgment.

Reactions: 2

twelvexs

Discussion Starter · #13 · 2 mo ago

JEFFRPM said:
Last year while doing my winter maintenance in my greed for more bottom end grunt I advanced my cam timing from 3° advance to 5° when doing so I bent my vertical cylinder intake valve by.. oh... say... 0.001" when turning over by hand needless to say I didn't repeat that stupid idea on the horizontal next.

Why I didn't pull that stunt on the "easy" to replace horizontal cyl first was my penance for having to tear my engine down changing the PITA vertical intake valve.

I seem to occasionally have lapse of judgment.

@JEFFRPM Wow only a 2 degree difference! That's incredibly tight tolerance.

twelvexs

Discussion Starter · #14 · 2 mo ago

Well, setup the leak down test tonight and both cylinders tested good at their respective TDC. No loss of pressure during the test and no audible hissing or escaping air that was noticeable. Think I got lucky here and any damage was superficial.

Time for a slow and thoughtful reassembly over the coming days.

Very much appreciate everyone's comments and feedback.

Ride safe everyone!

Reactions: 3

JEFFRPM

· #15 · 2 mo ago

twelvexs said:
@JEFFRPM Wow only a 2 degree difference! That's incredibly tight tolerance.

12.1 pistons & big cams is what caused the tight clearances, stock pistons with big cams you probably could go 8 or 10 degrees advance.

There's a pretty big difference in domes from whatever 1100 stock pistons are compared to these things.

Oh yea the 47mm intake valves didn't help either.

Reactions: 1

twelvexs

Discussion Starter · #16 · 2 mo ago

Thanks again for all the replies.

One last question regarding setting the tension on the belts.

I see occasional references to 'floating' the cam pulleys while the cams are pinned to equalize the belt tension using the 3 fixing bolts on the pulleys:

Wheel Circle Font Illustration Art

However there's just as much or more videos and forum posts about just pinning the cams, swapping the belts, and not floating these. Video I see referenced most is the Brad Bike Boy video and he does not appear to do this procedure:

Which one is correct?

Any comments or feedback would be appreciated!

Thanks!

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ducvet

· #17 · 2 mo ago

You have the pulleys and tools to do it if you wish, I think you are simply adding increased risk if you make a mistake and the benefit would be so small it would likely be imperceptible.

belter

· #18 · 2 mo ago

2.27 > in this video is why i don't do it the factory way. that and tool accuracy or lack of. and if someone has done the cam timing, and you do this you'll undo that. at a simple belt change it's a total waste of time at best imo. as eric says.

JEFFRPM

· #19 · 2 mo ago

I've never seen anything so stupid in my life now I know why every virgin bike I've checked cam timing on was off by a mile from the factory.

I'll stick to setting valve clearance first then cam timing with a degree wheel & belt tension last.

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