Valve guides.

[Duccout]

I may be wrong about Ducati reverting to phosphor bronze on the belt twins; whenever I've worked on my modern Ducatis (750 SS, GT1000 and 620 Multi) I've assumed that the guides were bronze because they were brown colored, but that may have just be oil staining. Next time I adjust the valve clearances I'll check. It would make sense to use iron on the more modern engines because the guide seals are very effective and the guides will not get much oil!

[CanuckDuc]

This thread is providing some wide-ranging, hands-on shop experiences undertaking a seemingly simple task of valve guide replacement. As Nigel has eluded to in his posts, most of these castings are over a half-century old, well used & often abused in use and or past assembly. I'm sure everyone undertaking this will develop their own methodology with what techniques works for oneself and the tools at hand. So here is another method to share to others.

To remove the old guides from the head I now use a 15/32" coring drill having a 5/16" piloted tip. The 5/16" end is close enough to 8mm, allowing the drilling out of most of the guide body, just leaving a thin-walled section remaining in the head. While I prefer using this tooI in the mill, it works effectively just using a hand drill. I usually drill from the port side out, removing about 80% of the guide length, leaving a step for a punch to lightly tap the guide free. Making the guide into a thin sleeve removes the clamping force at place, minimizing chance of damage to the guide hole. Stock removal is fast, the original phosphor bronze guides cuts out like butter, taking only a minute or so. Of course it goes without saying, any carbon/cleaning media packed about the guide boss, etc. has been taken care of beforehand.

The replacement guides I use are typically a zinc/manganese bronze from bar stock made here in Canada by AV&V Valves. I find they can be fit with very tight stem clearances to maintain long valve seat integrity & do not stick or wear rapidly like many bronze types, while dissipating heat much better than cast iron guides.

One of the goals I want to address when installing the new guides is in maintaining decent concentricity with the previous valve seat. Most of these heads I see suffer from already sunken valve seats; mainly due in my opinion to past valve guide replacement that placed the guide axis skewed from the old seat, requiring cutting an even deeper seat to cleanup. The deeper seat influences airflow, compression, rocker arm & spring geometries amongst others.

I use a basic fixture method that I believe helps the valve seat-to-guide alignment in check. I have an arbour press large enough to fit the head with mock valve in place on a pedestal on the valve head while the guide is pressed into place from above. This assists the guide to be drawn along the stem axis as the valve "cones" onto the original valve seat surface. I've found minimal material needs removal to recut the seat this way. I also install my guides at room temp these days, the 1-1.5" thou fit I find heat unnecessary. However, the cylinder head hole bore needs to be round, straight & properly chamfered, along with a properly sized, smooth bullet shaped guide entry, well coated with press fit lube & no galling etc. will occur. The hand applied press allows great feel in how fitting these parts go together compared with the heat/shrink/hammer methods I was taught back in my formative years. My techniques have been an evolutionary process over 4 decades of in working in this trade; they have worked for me.

Of course, once the guide is fitted a whole new issue of preparing the guide hole for the valve, as well as the methodology in preparing a proper valve seat is a whole new subject. However, regarding that I can't begin to highlight how many "new" valve guide installations I have seen that have been sized using cheap and/or dull reamer tools and/or "ball hones" to size the guide id's. Most of us doing this type of work have acquired a substantial investment in tooling to measure, alter & install these components as quality outcome without quality tools is difficult at best. My two cents, hope this helps others.

[Duccout]

Good info, thanks for posting. Your guide installation tool sounds very much like the one that Steve Wynne used, it would be nice to see a picture. I have never had trouble fitting the Singles guides, but I have with bevel twins, that have a tiny amount of support in the head, so I would never again attempt to fit them.

[Ventodue]

Good stuff, CanuckDuc. Appreciated.

[blethermaskite]

That's much appreciated information and advice.
Cheers,
George

[LaceyDucati]

CanuckDuc

An excellent reply and I agree with all you say, it's near impossible to cover every aspect of these subjects and finishing guide bores and cutting seats as you say is a whole different subject. The seemingly simple job is not always as simple as it would appear.

I'm interested to hear your methods of fitting guides at room temperature and it bears out my thoughts on the matter that I mentioned. Makes perfect sense, maybe time to rethink my methods some time.... Of course you need the necessary equipment, possibly beyond most home mechanics.

Regards Nigel

[Eldert]

hi guys

i press the guides in cold . press fit is 0.05 mm

i do use a stepped mandrel and Sunnen B-200L press fit lubricant to prevent galling .

Eldert

[Duccout]

This thread gets more interesting every day! We've gone from discussing removing guides cold, to fitting them cold.

[Jordan]

I'm glad to learn about press fit lubricants for cold work.
I would like to read more about them but can't find any detailed descriptions.

I'm not sure if I missed it, but is there any good reason not to use an oven for guide removal?
This is evidently the classic way to do it with light alloy heads.

Seat re-cutting after fitting guides is standard procedure.
I've had no more complication to do it on Ducati (non desmo) singles than with any other engine.
It might help to avoid skewed valves, to use guides with accurately parallel and coaxial inner and outer diameters.
The ID should be close to finished size, before installing and reaming.

[LaceyDucati]

Jordan,

No reason what so ever why not to follow traditional methods. Pressing guides in at room temperature will require good alignment and lubrication, which is unlikely to be achieved using simple hand tools in the average home workshop (unlike hot options). All methods will require care and fitment will only be as good as the hole it's going in.

You are correct that the guide bore needs to be close to size before installation and guides will always require reaming to the required clearance after installation. That should ideally be done with incremental (0.01mm) piloted reamers and also possibly a hone. Accuracy, parallelism and concentricity of the guide is critical, which is why our guides are finish turned and bored together rather than reaming when manufactured (Reamers will generally wander on a machine, especially in wrought bronze). However you can achieve accurate guides with a reamed hole, if you mount the guide on a true running mandrel and finish the O/D afterwards. You can use tapered mandrels intended for valve seat cutters mounted in a collet chuck. I've set up various mandrels and centred them so I can run a running centre to support the end. I then slide the guide on till it bites and then check the mandrel itself either side of the guide. When I'm happy with the run out (preferable none) I can then spin the O/D down to size (obviously we are talking small amounts here). This is an ideal method for quickly knocking up specials, which I end up doing quite frequently. If I remember I'll take some pictures of the sort of set up, next time I make a special.

Nigel