My 749R is in for a 15K valve clearance check. The dealer just rang to tell me that 5 of the closing clearances were out of limit at 0.33 to 0.35mm. In order to remove the shims/adjust the clearances, I was aware that the heads need to be removed as the collets are difficult to remove since the valves need to be supported to do this. This is best done with the heads on the bench and using the special tool designed to remove the valve stem collets. So far, so good. What I am confused about is: The dealer said that the excessive clearance could be due to wear of the collets, rather than wear of the shim. I've not heard of this before - has anyone else heard of this? Just wanting to get a better understanding really as I had not heard about this sort of wear. Cheers.
I'm looking forward to the responses to this myself. Taking the heads off is new to me so it must be option of absolute last resort. also new to me is collet wear being blamed. I'd love to know the average cost of sending a bike to this dealer for valve servicing. TB BTW who is the dealer?
Okay, the arguement about heads off or heads on to change shims is an old one. The job can be done without removing the heads but some technicians find the whole process is easier taking the heads off. I have not heard the suggestion that clearances could be affected by worn collets but the mecanical engineer in me is saying, yes but high mileage not in the first 15,000 miles. I do know in my time at MR in parts, collets are changed due to wear. £1400 is about what the shim service on my Multistrada cost with 3 exhaust closer shims being changed. Andy
the collets are pressed in the shim with the valve stem at about +/- 10NM. When fitted they cant be moved and therefor you need to support the valves to losen the collets from the shim. if the collet would wear, they would be lose in the shim and valve stem.
Not questioning the need to remove the heads - I accept that it is the way it should be done. My question was bout the collets really. @mrfurry has a good answer.
I think that the berylium valve seats wear out and therefor the clearance of the closer rocker become larger.
This bike doesn’t have the Kit cams however my other 749R has the super sport kit heads/valves/cams etc. Do you have a spare copy of the workshop manual that you are willing to share?
Has the 749 got the same wire collets as the earlier engine? If so then it is possible that that the clearance can open up due to 'damage' to them. I have fitted new ones in the past and found that the clearances come back within range. I believe better aftermarket ones are available which do not deform and keep the clearances correct for longer.
Yep , wire collets wear .. not uncommon to replace and find that shim replacement isn’t required until next Desmo service MBP collets are one of the aftermarket brands .. in fact the only one I’m aware of https://www.mbpducati.ca/index.htm?components.htm~mainFrame
Some info and discussion here worth a read... https://www.ducatiforum.co.uk/threads/900ss-cam-pulley-feel-valve-clearances.8872/
Off at a slight tangent, but relevant. An interesting and well written article about valve seat recession: https://oldschool.co.nz/index.php?/topic/20751-valve-seat-recession-explained/
Shims rarely wear that much. It’s usually wear on the seats, valve surfaces, collets etc. that cause changes. The conventional wire collets flatten and open up the closing clearances. The 749R uses tapered collets that are pressed into the shims as they are/were more reliable for higher rpm and were needed to homogolation the R motor for supersport. They can still wear on the tapered sections and it’s likley what’s caused the clearance to open up. The shim has to be tapped to free the collets and this is why it’s best to remove the heads, otherwise you risk bending the valve as it’ll sit at an angle against the piston crown.