Valve guides.

[Beach Life]

Thank you all for your advice. I can see the wisdom of cold removal now. I do like the idea of warming the head and freezing the guide, do they drop in as with a bearing on a shaft? This would help with alignment?

[DBDBrian]

Just one further point, before drifting the guides out, make sure they are clean on the port side, so as not to take any debris through the head bore.
Very unlikely the guide will drop in, hence my suggestion to install the guide in one quick operation before it has time to expand.

[Duccout]

The head HAS to be heated to a high temperature, hot enough so that water sizzles when it hits it, and the guides must be kept in a freezer overnight, but skill is still required to get them in straight.

[Jordan]

AFAIK, phosphorous bronze has a higher expansion rate than aluminium, so heating the head first seems wrong.

See this list of expansion rates
https://www.engineeringtoolbox.com/ther ... d_859.html

Aluminium and its alloys 12.8 to 13.1
Phosphor bronze 9.9

[Beach Life]

Heating the head for installtion makes sense, untill the guide picks up the heat. Lining it up sounds tricky, and sods law..... so Im thinking about a jig located into valve seat then into the guide hole and reducing to guide the guide in straight. Hmmmm thanks again for all the advice

[Beach Life]

Its been a good topic for discussion and theres always (well usually) more than one way to do things. Just one more thing, what sort of interferance fit would you reccomend? I'm thinking 0.025? Considering as stated that the phosphorbronze expands more which makes geat sense to use in aluminium heads.
Cheers

[Jordan]

I'm not sure if it was clear, but I was pointing to info that aluminium expands with heat more than phosphor bronze does.

[Duccout]

Thanks Jordan; I got my info about phosphor bronze expansion from Steven Eke's book on Ducati twins, it seems he was wrong!

Beach life: the idea of a jig is good; Steve Wynne used such a jig when fitting guides.

[Beach Life]

Thanks Jordan, I skimmed over that and have just had a chance to sit down and go over it properly. In the back of my mind a voice said, but aluminium has one of the highest expansion rates. But I do take advice on face value sometimes, and thought, well phosphor bronze must be the exception. Learning every day, and so glad I found this forum!
Duccout, yes and the jig would help stop the valve seats from dropping out as well, time would be a wonderful thing!!
Thanks.

[LaceyDucati]

Hi "Beach life"

I always remove guides cold, being careful to try and remove as much hard carbon deposits as possible from the exhaust guide before doing so. I have in the past tried to heat heads before removing guides and frankly it didn't make any significant difference. Always use a piloted drift to remove guides and ensure the O/D is significantly smaller than the guide O/D. A slip with a "pin" punch is likely to wreck the bore.

I will add here, bead and grit blasting ports can impact media around the guide. This can prove impossible to remove before guide removal and potentially can score the guide bore in the head during removal. Hot or cold the result will be the same... I don't recommend blasting any bronze bushings in situ for this and other reasons (best masked off if possible).

I always install guides in a hot head, freezing guides can help, but my experience is the benefit is minimal and it hinders lubrication of the guide during insertion, the oil/grease goes sticky which probably then helps transfer heat and aids sticking. I always lube guides as invariably the guide will grab before it is fully down and at that point you will need to follow it down with a thump. If the guide/hole is dry, that's not going to be nice!

As for interference, I work to 0.03mm +/- 0.005mm. Guides in these engines will always tend to pull off centre due to differing support either side of the guide hole, greater interference will only make this tendency worse. Relieving the "fit diameter to the length on the shortest side of the guide bore can help with this. Pulling the guide in with a an alignment tool will not stop this.

Using "pullers to fit guides is to my mind pointless if you are going to heat the head as the second the guide makes contact with the hole it will expand and you will then have to pull it in all the way.....You might as well pull it in cold as far as I can see. On the subject of fitting guides cold, I swear when I visited the factory some years ago, I saw a guy fitting something that looked like guides with a large club hammer and no indication the head was hot! I guess if the guide has a good lead and is well lubricated then why not? Most would not flinch at fitting other bushes in the engine cold....... Mostly I guess the issue with our guides is the shortness and lack of lead in, to allow good progressive alignment.

I always use a tubular driver to insert guides that drives on the flange, that way you won't damage the guide bore.

Measurements for guide holes and guides need to be done with micrometers and at minimum bore gauges, better still a bore micrometer. Using a digital vernier is just not going to cut it. With regard to this, be prepared to find oval and tapered holes. You will then need to either compromise on fit or rectify, judgement and experience at this point will be key.

The Desmo single guides are a particular pain and need to be aligned. I use a tubular driver that has a cross hole in it which I place a pin through, the pin sits in the open slots in the top of the guide. I then use the pin to judge whether I'm "sort of straight" with the rocker chamber. I will mention here a driver that fits snugly on the guide and doesn't drop off, is a bonus during installation. Using a cross pin with flats to engage with the slots at the top of the desmo guide will allow the guide to be held on the driver during installation. Mostly aligning this way works but occasionally due to a slight misalignment, there is a need to trim the odd few thou from the sides after installation to allow suitable clearance to the closing rocker. Unless you are miles out, removing the guide and refitting is likely to cause more harm than good, again this is where judgement is needed.

Needless to say when fitting guides hot, speed is of the essence. If you place the guide in the hole with your fingers, by the time you have reached for your driver/drift, the guide will be well and truly stuck! It's a matter of guide on the driver, good alignment and "IN", with hammer in hand ready to follow it in if it sticks midway in. If it sticks just in the entrance to the hole, best stop, remove the guide and start again.

As for temperature I work on just above 150 degees C, unless it's a Misano head (a replacement race head) then I keep below 140 degrees as they are heat treated alloy. In that instance the guides go in the freezer as a compromise. If the valve seats drop out at these temperatures, count yourself lucky that you found out now, not when the engine was running.... In short they shouldn't!

The above are my methods, figured out for my needs over many years. I will add I've fitted several hundred of guides to Ducati bevel single and twin heads and so far no complaints or issues as far as I know.... so I'm guessing I'm not to far wrong!

Hope some of this helps with your idea's of what you want to do.

Regards Nigel