Suspension rabbit hole

baggerman said:

Wait you let other people work on your bike? I don't trust nobody else's work. Andy said somewhere that he spun a bearing and ventilated the case. Bearings spin for primarily two reasons; lubrication failures or rod big end stretch (they get pulled into an oval). Careful assembly will negate that kind of stuff. So now I'm tempted to check the bottom end since the bike is mostly apart anyway. Can't trust the factory either. Maybe I'll just take the oil pump out and blueprint it.

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which Andy......... not me!

andyb said:

which Andy......... not me!

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I guess my memory is a thing of the past. Someone posted this awhile ago saying the motor puked a rod due to a bearing being spun at about 5K miles. Due to sloth I'll blueprint the pump and turn the rev limiter down.

baggerman said:

I guess my memory is a thing of the past. Someone posted this awhile ago saying the motor puked a rod due to a bearing being spun at about 5K miles. Due to sloth I'll blueprint the pump and turn the rev limiter down.

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That was probably me.

Did you take pictures of the parts or do you have them on the shelf of shame in the garage? Sometimes you can see the differentiate the cause of failure from the heat signature on the back of the bearing or in the bearing bore. Where'd the replacement motor come from?

baggerman said:

Did you take pictures of the parts or do you have them on the shelf of shame in the garage? Sometimes you can see the differentiate the cause of failure from the heat signature on the back of the bearing or in the bearing bore. Where'd the replacement motor come from?

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Yes, far as I know we still have the motor (torn apart for inspection). Looked like the bearing got hot and then spun, broke the rod which then keyholed the block.

Found a used 1000 mile motor on eBay.

The bearings spin for 2 primary reasons lubrication failure or big end stretch. The big end stretches oval and the sides pull in and contact the crank (rpm related). And assembly related as the clearance was insufficient. Lubrication is usually a feed issue not enough pressure or volume. And lubrication failure can be related to excessive clearance that lets too much oil out the sides of the bearing usually combined with a pump with too much end float and/or an incorrect pressure limit. When it's caused by rod stretch there will normally be telltale heat signs near the bearing and bearing bore parting line. A lubrication failure is no oil it spins but the parting line heat signature is usually missing. If the bike has the capability to record oil pressure during a season (it must have right) I'd check the new motor for pressure fluctuations in the data especially if the track you frequent has a g-out. Sound like yours was a lubrication failure. Ultimately, it's better to run clearances on the small end of the spec but prep the rod bore as an oval across the parting line then as the big end stretches it goes round and you have lessened oil flow requirements due to the tighter clearances. Good luck hope you got a good one.

BTW I would do a thorough post mortem. Particularly pull and the rods mate (if the sucker is intact) and measure the clearance (should have been close to the same as it's mate) and pull the pump assembly and check the oil pressure relief and pump clearances. If you measure the pump reliefs spring rate, spring installed height and the orifice size you can calculate where the relief valve was set. Should provide some clues.

baggerman said:

BTW I would do a thorough post mortem. Particularly pull and the rods mate (if the sucker is intact) and measure the clearance (should have been close to the same as it's mate) and pull the pump assembly and check the oil pressure relief and pump clearances. If you measure the pump reliefs spring rate, spring installed height and the orifice size you can calculate where the relief valve was set. Should provide some clues.

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Good thought. I’ll share with my builder. Fwiw, Mark at DucShop said he wouldn’t expect much more than 5k track miles even from a built motor. Obviously not intending that to be gospel, but he knows a thing or two about Ducati motors.

Must be a long job just to remove the engine, let alone rebuild it. Sounds like a LOT of money, and quite terrifying.

craig bush said:

Good thought. I’ll share with my builder. Fwiw, Mark at DucShop said he wouldn’t expect much more than 5k track miles even from a built motor. Obviously not intending that to be gospel, but he knows a thing or two about Ducati motors.

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Mark's simply a great guy. But I think he means between refreshes not holed cases. I'd pull the old pump and check it thoroughly including the scavenge sections. If the motor had enough oil in it something was wrong. A clue is which rod. If the rod is the one furthest away from oil pump feed then you probably ran out of volume to sustain the oil wedge. So it's mates bearing should be starting to show some trauma. Are you going thru the replacement? Bare minimum I'd turn it over pull the pan and carefully inspect the pump.

I suspect there will be piles of sworf on the screens above the oil pump but look for something that may have ended up there first like a piece of dislodged sealant. Something killed the feed probably and the rest of the bearing woulds have to have big clearances to kill the oil pressure and I bet you don't find that. If this happened after a quarter mile wheelie then all is moot the oil was in the heads.

Bruce Wayne said:

DM me with your settings and i will put it into our motospec software, offset, fork height, shock length, wheelbase, front and rear springs, the V4 is very susceptible to low COG, Happy to give you settings from Philip island with front running asbk rider from Last year on the V4

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“The V4 is very susceptible to COG changes”

Can you educate me a bit on that, I’m putting in a tank seat combo that’s going to move my center of gravity a bit down and a good bit further backward on the bike.

The tank is slightly translucent unpainted so you can see how the fuel sits in the bike, I’m going to put fuel cell foam in there to prevent most sloshing.

Any recommendations off the cuff on possible suspension or geometry changes?

Steven31371 said:

“The V4 is very susceptible to COG changes”

Can you educate me a bit on that, I’m putting in a tank seat combo that’s going to move my center of gravity a bit down and a good bit further backward on the bike.

The tank is slightly translucent unpainted so you can see how the fuel sits in the bike, I’m going to put fuel cell foam in there to prevent most sloshing.

Any recommendations off the cuff on possible suspension or geometry changes?

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I think what he means is that the PV4 takes a bit of effort to initiate the lean. You have to work to get it leaned over. But once leaned it'll hold that angle. It'll also want to return to the vertical more readily. This is most likely due to the seating position and mass centralization of the exhaust under the bike.

My 675 was the opposite. You feel like you sit above the bike and having the weight under tail exhaust kind of exaggerated this effect. It feels like it would readily tip into the corner with just a little input. R6 was similar. GSXR if I remember correctly felt low cg (you feel like you're sitting "in" the bike).

Correct me if I'm wrong, @Bruce Wayne.

You can raise cg by lowering the fork tubes through the triples and raising the rear ride high an equal amount. And vice versa. That shouldn’t affect the geometry. I can imagine it would be easy to get lost doing this

SuperDomestique said:

You can raise cg by lowering the fork tubes through the triples and raising the rear ride high an equal amount. And vice versa. That shouldn’t affect the geometry. I can imagine it would be easy to get lost doing this

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You mean rabbit hole ?

Well my experience with the v4 was the opposite, coming off my 1299 onto the V4 it took a bit of getting use to because it would fall into the corners . I put it down to the counter gyro forces the v4 engine has rotating opposite to the wheels.

Steven31371 said:

“The V4 is very susceptible to COG changes”

Can you educate me a bit on that, I’m putting in a tank seat combo that’s going to move my center of gravity a bit down and a good bit further backward on the bike.

The tank is slightly translucent unpainted so you can see how the fuel sits in the bike, I’m going to put fuel cell foam in there to prevent most sloshing.

Any recommendations off the cuff on possible suspension or geometry changes?


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A guy at my local tracks has this tank, pretty cool ! he said it felt quite narrow and unsupportive braking, but said he could really lock on leaning off the bike . i questioned him about fuel slosh and he said it was baffelled inside ?

Steven31371 said:

“The V4 is very susceptible to COG changes”

Can you educate me a bit on that, I’m putting in a tank seat combo that’s going to move my center of gravity a bit down and a good bit further backward on the bike.

The tank is slightly translucent unpainted so you can see how the fuel sits in the bike, I’m going to put fuel cell foam in there to prevent most sloshing.

Any recommendations off the cuff on possible suspension or geometry changes?


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We found a sweet spot with the vertical COG where we raised both the front and rear to get the bike to change direction especially picking it up from full lean, my motospec licence is being used by a friend ATM should have access this weekend and will post the settings, i will email the OP them too. We first set GOG at the upper level and bike turned really good but when pushing through a fast change of direction the bike would slide we dropped 2mm and bike was pretty good, our rider at the time broke the lap record by a goo margin. Bike geometry was fairly flat too.

SuperDomestique said:

I think what he means is that the PV4 takes a bit of effort to initiate the lean. You have to work to get it leaned over. But once leaned it'll hold that angle. It'll also want to return to the vertical more readily. This is most likely due to the seating position and mass centralization of the exhaust under the bike.

My 675 was the opposite. You feel like you sit above the bike and having the weight under tail exhaust kind of exaggerated this effect. It feels like it would readily tip into the corner with just a little input. R6 was similar. GSXR if I remember correctly felt low cg (you feel like you're sitting "in" the bike).

Correct me if I'm wrong, @Bruce Wayne.

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Definitely helps return to vertical, makes big difference on change of direction, bike feels lighter, a bike falling on its side isn't usually a high COG but more steering angle and suspension settings, like if the front falls through the stroke mid corner, in my opinion the COG is the first step to get right and then build from there.

SuperDomestique said:

I think what he means is that the PV4 takes a bit of effort to initiate the lean. You have to work to get it leaned over. But once leaned it'll hold that angle. It'll also want to return to the vertical more readily. This is most likely due to the seating position and mass centralization of the exhaust under the bike.

My 675 was the opposite. You feel like you sit above the bike and having the weight under tail exhaust kind of exaggerated this effect. It feels like it would readily tip into the corner with just a little input. R6 was similar. GSXR if I remember correctly felt low cg (you feel like you're sitting "in" the bike).

Correct me if I'm wrong, @Bruce Wayne.

Click to expand...

My V4 and Gixxer feel the opposite…the Ducati I feel high off the ground on top of the bike and it tips in and changes direction way better than the Gixxer, whereas in the Gixxer I feel like I’m lower to the ground and in the bike, it doesn’t turn in or change direction nearly as well as the Ducati, but feels more stable and confidence inspiring mid-corner and everywhere else.

I love the agility and power of the V4 and I love the lower feeling ergos and stability of the Gixxer. The ideal bike would have both lol