Valve guides.

[graeme]

Yes it certainly is !!!

[Jordan]

I now drill them out to within a couple of mm and they come/break out easily.....

That does sound like a good option with CI guides.
But bronze won't break up like cast iron, and it might be tricky to remove, especially if there's not enough wall thickness to drive out with a double diameter drift?

[blethermaskite]

Yes, that's my reservation too, p.bronze will certainly crush rather than break when it is thin however the principle of reducing the structural strength and in consequence the tenacity of fit by reducing the wall thickness of the guide in theory should be correct, but I am theorising, I havn't tried this with a p.bronze valve guide, certainly I have found some difficulty on occasions removing thin wall p.bronze bush's from alloy housings. I think I have an unimportant scrap Triumph twin cylinder head lying about somewhere with p.bronze valve guides in, if I can find it I will try this out to see if it works in practice.
Cheers,
George

[blethermaskite]

A further thought, does anyone know what grade of p.bronze Ducati valve guides are made from? I remember very many years ago trying to make a p.bronze valve guide for a Moto Guzzi lodola I once owned, I now know the material I was using was called p.bronze 1 which is a coppery colour and was quite simply very nearly impossible to drill through without contracting on and gripping the drill or reamer. Most Ducati guides look to be more brassy in colour than that awful stuff I once tried to use, but I have seen the odd one very coppery looking which (while I like the idea of this) I doubt if you could ever drill out to weaken for easier removal.
Cheers,
George

[LaceyDucati]

George

Don't know the exact spec of the original guides, but most likely PB102 (wrought) phosphor bronze. The brass looking Phosphor bronze is PB1 which I believe is spun cast (machines easier, but softer) . I always specify Colsibro which is a trade marked Bronze which is more specific to Guides. You can also use aluminium bronze, but it's hard work to machine, or more specific ream.

I've noticed Ducati has reverted to using a form of cast iron for guides in later belt drive bikes, which is probably better suited to road applications and can run dry. The problem with Bronze guides is ideally they need oil for lubrication, therefore running tight guide seals is likely to result in a short life. I should be noted when designed originally there weren't any guide seals, they were added in the 60's.

Nigel

[Duccout]

The last of the bevel twins had cast iron guides ( I have a new one in my box of spares) so I don't know why Ducati reverted to phosphor bronze for the belt drive bikes....Maybe the iron cost too much to make!

[gregwils]

Here is a post from my go-to Porsche forum from a nationally-known Porsche engine builder. It's a novel approach for those willing to try a slightly different method. The logic seems reasonable, although a very different than drilling the interior that I posted earlier. I suppose you could technically do both by drilling the combustion end of the guide up to the point that the threaded bolt is tapped into the guide. A little more work, but if it results in a clean extraction with no damage, it's worth it.
___________________________

"If you do enough heads you will find that pushing the guides out will only work if the guides have very little wear.

What we do is run a 10 mm tap in the spring end of the guide and then screw a 10 mm bolt in the threaded hole 15-20 mm.
Next you push the guide out with the appropriate valve guide tool by pushing on the bolt.
If you just beat ( wack-it, wack-it, wack-it) on the valve seat end of the valve guide you may get lucky on a few but eventually you are going to mushroom the end and as the guide moves it will split the boss on the inside of the port."

[blethermaskite]

Hi Nigel, thanks for that spec info on Ducati guide material, Someone pointed me at 'colsibro' bronze before, however I havn't needed to make a valve guide for nearly as long as I can remember , with my work on vintage cars and a lifetime of old Brit bikes cast iron valve guides have often been a common repair item, having said that I have frequently been amazed at how long an exhaust valve and a cast iron guide have survived with little (or in the odd case no) lubrication, particularly in side valve engines which at best are only getting splash at the tappet end of a vertically positioned very hot valve. I ran a 1950s (iron head) BSA B31 for about 4 years and decided to whip the head off for a valve grind....there was only the top 1/3 of the iron exhaust valve guide still there "dry as a bone" the oil feed to the rockers was almost blocked, surprisingly what was left of the ex valve guide was a bit belled but still relatively unworn, in the right application I am a bit of a fan of cast iron guides.
Cheers,
George

[LaceyDucati]

"Quoting"
"so I don't know why Ducati reverted to phosphor bronze for the belt drive bikes"

All the later 2 valve belt drive bikes i've seen had iron guides, but then I'm no expert regarding modern bikes, so I'm unaware if any reverted to use bronze guides.

Regarding the driving out of valve guides if you use a piloted drift of an appropriate size there is no chance chance of mushrooming the guide, at least not on a Ducati single.

Nigel

[gregwils]

Nigel,

Any chance you would have a photo of the type of piloted drift that you use? Do you sell them? I didn't see one in the Tools section of your website.