1975 350 MKIII camshaft drive seized.

[themoudie]

Aye Ian, please don't be confused, bloody meerkats!

The item that I have described as a "bearing carrier" in my image, is described as a "bush" #37 in the link below. It sits on top of the "bevel tube" #22 in your linked diagram and is held in place between the top of the bevel tube and cylinder head by two cap screws M6 x 35mm, coming from inside the upper bevel area in the cylinder head.

Ducati_wide_case_cylinder_head_parts_diagram

As you can see in my layout image, not ony do I have shims between the bushing and the top of the bearing (when in situ), but also three shims between the lower side of the bevel gear and the top of the bearing, with a further shim and washer below the bearing and the whole assembly held in place by the circlip, which in this instance had been assembled with the curved face, rather than the flat face supporting the washer.

Thank you for your interest.

Good health, Bill

[IanHood]

To be fair, I’m easily confused

[blethermaskite]

Bill, to me your picture of the bearing and shaft as dismantled suggests a mixture of attempts to set top bevel clearance, I personally don't really see anything particularly wrong with this.......however I would normally expect the shimming to be regulated on the actual shaft itself.
If of course you are maybe? going to use another cylinder head then it would be shimming from scratch again so what you have there as removed is highly unlikely to be of any use.
Cheers,
George

[themoudie]

Ian, no confused, just a wee bit discombobulated!

George, that was my way of thinking George, shim either side of the bearing, but not the bearing in the bushing, especially as the shims in situ appear to have taken up the radius of the bearing outer circumference.

Having had another look at the "alternative" head, I think that I will be giving it a go. 32mm inlet angled stub, gas flowed, twin plugged and with no broken fins, it just had part of the alloy bridge across the top of the inlet valve rocker chest rewelded after it was broken off by the previous owner using the tyre lever wheeze to hold the cam whilst undoing the nut! So I will need to check across the face of the rocker chest to make sure that the cover will seal. The original casting wasn't the prettiest, but this is going to be a runner/user, not a trailer/polisher.

Thank you for your thoughts and good health, Bill

[blethermaskite]

I have used several heads damaged like that, as long as its welded 'oil tight' it shouldn't be a problem........that part of the head isn't doing very much structurally other than keeping the oil inside.
Cheers,
George

[themoudie]

Aye George, the weld has been well puddled.

Cheers, Bill

[Duccout]

Hi Bill,

Those very thin shims between the bearing and its bush are a bit of a mystery; afaik, all the vee twins came with them and my Spanish 250 had one there as well, but I don't know what the purpose of them is. I cannot see that it is for shimming the bevel clearances, so they must have another purpose.

Cheers,

Colin

[themoudie]

Aye Colin, thank you for the info.

I can only think that they were there to bring the lower face of the bearing, so that it bears directly onto the top of the camshaft drive tower raised rim, rather than having a gap, after tightening the tower, up into the bottom of the bushing/cylinder head.

ADDENDUM
I have just been and mic'd up the components and they measure as follows:
Depth of bushing (internal) = 11.20mm
Depth of bearing (overall) = 11.00mm
Shims = 0.23mm and 0.21mm
Raised inner rim of tower = 0.10mm
Gasket = 0.10mm

So, no wonder the second shim was being squeezed from between the bearing and the back of the bushing. Trying to squeeze 11.44mm of bearing/shims into 11.20mm of bushing + say half the depth of the gasket after torqueing = 0.05mm, means 0.29mm of pre-load on the outer bearing track!

The gasket surrounds the rim of the tower and is of the same depth, so when the tower is torqued to the cylinder head I would have thought that would provide sufficient load to the outer bearing race to hold everything snug, with only the 0.21mm shim in place behind the bearing in the bushing.

Engineer's comments welcome.

Suspect worn tooling, mismatching Spanish/Italian components and clumsy assembly at the factory! Sounds familiar to those who have studied the UK motorcycle industry debacle and actual Italian "engineering", rather than the "rose tinted" gloss!

More micrometer work at the assembly stage.

Good health, Bill