21 SF V4 Cam Timing

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baggerman

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I finally got around to checking the cam timing before I reshim the heads. Factory spec is exhaust 56-13, 13-49 intake (26 degrees overlap). As delivered front head exhausts 54-15, 13-49 intake (28 degrees overlap). Rear head exhausts 64-5 (ouch), 11-51 intakes (16 degrees overlap). Opening the exhaust early loses part of the power stroke. The rear cylinders were literally blowing some of the torque out the exhaust pipe. And intake filling is worse due to the loss of overlap. Loss of about 5-6 hp relative to the factory spec methinks. Normally I've found that the superstock racers sort out where you really want to time the cams but I've been unable to find anything online.
 
Searching online for information? You dirty dog 😂 andy is going to hear about this and scold you for your lack of engineering acumen.

The front cyls are within spec (3° wiggle room) but the rears aren’t close. Would Ducati be that lax to let an engine out like that? Maybe check your rear tensioner? What about just bringing it back to dead nuts spec and see how it runs?

Best bet if you wanted to get into the weeds would be to hit up DucShop or Luigi Moto. Or Andy since he is the Ducati repository of all knowledge…
 
The tensioners were ok. Pretty typical ducati relative to the cam timing. Never had one that was timed to spec as delivered. I'm not sure Sutton is building these. Maybe I'll email him and ask. I think I'm going to advance the intakes 4 (17-45) and set the exhausts to spec.
 
I had a duh moment so went and pulled one of the rear exhaust cam pulley bolts. It was sitting at the end of the slot in the pulley. The bolts were tight and glued so it was an assembly thing. Thank god for VAG induced quality control. I've decided the heads of my bike were shimmed on a friday afternoon after a little too much vino at lunch.
 
Nope the bolts were tight. When you're assembling the cams the closer springs want to rotate the cam towards the end of the slot. Claudio wasn't paying attention and tightened it there. I was talking about the valve shimming (openers and closers) being all over the place with essentially no wear on the valve train components. Just a sloppy assembly job. In contrast my 1098 came out of the factory with the shims perfect. Even the cam timing on that motor was good (enough) as delivered. Unfortunately it had too much rod bearing clearance and the crank bearings had way too much preload.
 
Gotcha. This is what you’re talking about.

IMG_0451.png



Could that explain the out of spec? Why even have slots in the drive gears?
 
Yep the rear cam was sitting at the end of the slot. That was why it was out of time. You have to have some level of adjustability to correct for tolerance stack up. But most of the slot is there for tuning purposes. A motor with the potato's (converters) removed from the exhaust may like some altered timing.
 

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