Valve guides.

[Jordan]

Thanks Nigel,
No matter the theory, it's hard to argue with your large experience and success.
I will keep heating Al heads before removing guides, as that has worked for me - all the 3 or 4 times I've done it!

[blethermaskite]

Thanks Nigel that's a good shout with the cross drilled tubular drift for the desmo guides I will get one of those made.
Cheers,
George

[Duccout]

A big thank you to Nigel for sharing his expertise! I think that fitting Ducati guides is ranked alongside crankshaft repairs and valve seats, and is not a job for the home mechanic, there are just too many pitfalls, which is why I prefer to have them lined.

I remember talking to Richard Walker years ago, and he told me that when he replaces guides sometimes they go in crooked; but what then? The bore has to be remachined and an oversized guide made.... It is a hell of a job.

[LaceyDucati]

Once the guide bore integrity/position has been lost, you are right, it's a tricky set up on the mill. Trying to figure out which part you would like to line the bore up with....Would you like it true to the valve seat recess, the rocker, the rocker spindle position, the cam, the head face? Anyone who has ever done this will appreciate this dilemma, because nothing is quite inline to start with! The stuff of nightmares and sleepless nights and really not a way to earn money.

I have a 750 head to sort out this week for a customer, It will be at least 2 or 3 hours of set up time, checking and rechecking until my paranoia is partially appeased and then about 10 minutes to clean the hole out. Of course there is a limit to how oversize you can go before the slenderness ratio is lost. I guess this oval and belled out hole is the result of a failed guide replacement, beware eBay...

George, A couple of pics of the driver I made years ago, so you'll get the "drift":-)

IMG_0027.JPG

IMG_0026.JPG

Regards Nigel

[LaceyDucati]

hmm pictures seem to have failed!

Second try:

IMG_0026.JPG

IMG_0027.JPG

[Beach Life]

Thats awesome Nigel, thank you.

[blethermaskite]

Hugely appreciated Nigel always easier to see how you made your one........saves me reinventing the wheel.....whats the old expression" give us the tools and we will do the job" well hopefully?
Many thanks,
George

[gregwils]

Valve guides are often drilled out on older air-cooled Porsche prior to removing cold. The idea was to decrease the structural integrity of the guide and make it easier to remove. Has anyone ever tried this on a Ducati head>

[blethermaskite]

Greg, I have done this myself but hadn't considered doing it on a Ducati or any motorcycle head for that matter.....however on reflection if done with care I don't see any reason why not. I own an early 1930s Morris 8 special sports car with a side valve (flat head) engine, these have cast iron valve guides in a cast iron block and and after 70/80 years of use can be extremely hard to remove without some damage to their support boss in the block, so I now drill them out to within a couple of mm and they come/break out easily........interesting option.

[gregwils]

Your Morris is outstanding!