Valve guide choice

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rjk40
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Valve guide choice

Post by rjk40 » Fri Feb 02, 2018 1:55 pm

I know, this argument has gone on a long time, and here I am revisiting it.

As I have just found terminal wear on the now (ovoid) exhaust valve guide, I am faced with the decision on which type of guide to replace with: iron or bronze.

Since the engine (#851539) came with bronze guides, and since the vertical head had good guides with no need for any new parts, just a cleanup and new valve seals, I am unclear. The bike is/has never been used for anything but fun street use.

So, have looked on various forums (fori?), and what I see is: iron guides last longer (according to some folks) and are easier to machine when necessary, and bronze ones are popular in competition, but require more expensive machining tools. Many posts argued in both directions, pro and con, for both iron and bronze. So, nothing definitive gained by those posts (doing a Google search for "valve guide material choice").

Exhaust valve is quite galled, so will have to be replaced.
Intake valve cleaned up just fine, but has what looks like microscopic galling on its face. Probably will replace.

Shopping list now includes"

1. new intake and exhaust valves
2. new intake and exhaust valve seats (in case of needing replacement after new guides are in).
3. new intake and exhaust valve guides (what kind?).

As always, I defer to the wisdom of experience you gents might wish to share.

My current mentality is to use the bronze guide, since that was what the factory used. But, I am open to any comments.

Thanks in advance to all of you gurus.

May Vishnu smile upon you.

Richard Kovach
Malabar, Florida USA

wdietz186
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Re: Valve guide choice

Post by wdietz186 » Mon Feb 05, 2018 11:01 am

I'm not aware of anyone producing iron guides for Ducati bevels. The stock bronze guides seemed to have been made of Parmesan and were lucky to have made 6,000 mi. before allowing oil to run into the exhaust system. Kibblewhite Precision make very good replacement guides for Ducati and are widely used in the industry. It's unlikely the seats will need to be replaced if they haven't been cut before. They will need to be cut though,the original guide bores were rarely concentric with their outside diameters.

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Craig in France
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Re: Valve guide choice

Post by Craig in France » Wed Feb 07, 2018 3:11 am

Hi Richard

I claim no particular expertise in this area, but FWIW;

1. I've always understood that aluminum head = phosphor (or manganese) bronze guides. Close co-efficients of expansion, you understand.

2. Another determining factor is the valve stem material. This needs to be compatible with the guide material - again, think co-efficients of expansion.

3. Valve guide failures in Ducrappi heads is normally attributed to them being a) a tad on the short side; b) lubrication failure, the latter being perhaps due to people insisting on running monograde oils in cold temperature environments ... I say no more.

If it were me, I'd contact Nigel Lacey, ask him what he recommends/uses - and then buy them from him!

P.s As Bill says, try not to replace the valve seats - unless they're pitted, that is. Hopefully, they won't need re-cutting, either - altho' you should expect to have to ream the new guides. And lap in the valves, of course.

HTH

Craig

P.s I see Steve also sells guides. Maybe he'll come along soon ...

rjk40
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Re: Valve guide choice

Post by rjk40 » Wed Feb 07, 2018 2:25 pm

Youze guize are great! God Bless you all!

The world is a better place for your knowledge, and we yanks appreciate that.

Looking at Nigel's stock, he stocks three lengths, and I guess that I would have to remove the old guide to measure its length, then go from there; that's a bit confusing to me, especially with your comment, Craig, on one of the two typical causes for failure being a tad too short; ?. Too much side force strain? What does too short mean?

I've ordered new exhaust valve (one plus a spare; those durned exhaust valves are the ones that go...) from Nigel, will check the stem-to-guide fit, and go from there. Still haven't found any intake valves; thankfully, mine are good; are they made from the two rare elements: unobtainium and unaffordium?). I'm a bit naïve on how to ream the guide (is this before cutting the seat if necessary, or before the new guide is installed, while still out in the open?? Also, I would do a trial lap to see if the seat really needs a cut...).

Ordered bronze guides from Steve, original Domi Racer stock, will see how they fit with the new valve.

Rocker faces that the cam rides on are showing breakthrough in the contact area with the cam lobe, so am sending them to the chrome shop to be re-chromed; hopefully, that will add a few kilometers to their life cycle; cam lobes are just fine; have you noticed that those durned springer rockers are nowhere to be found?

I'm not in a hurry on this project, so can incorporate any wisdom that you gents can offer.

Again, thanks from Malabar, Florida.

Regards,
Richard

wdietz186
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Re: Valve guide choice

Post by wdietz186 » Wed Feb 07, 2018 3:01 pm

Richard, The rocker faces need to be hard chromed not chrome plated. Regular chrome plating will not last as it is very thin and the copper and nickel under it is very soft. I think Megacycle can repair your rockers, they regrind the profile and apply a stellite surface which is very hard and wear resistant.

rjk40
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Re: Valve guide choice

Post by rjk40 » Wed Feb 07, 2018 4:11 pm

Wonderful!

Thanks for the info; I shall contact them.
I really appreciate this info; it's a lifesaver.

Regards,
Richard

kerrin
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Re: Valve guide choice

Post by kerrin » Wed Feb 07, 2018 11:44 pm

Hi rkj40.
Just a clarification regarding the Lacey valve guides, he stocks three different diameters not lengths. This is to compensate for worn valve guide bores in the cylinder head. And yes, I have noticed the absence of valve spring rockers, mine have just gone off to Joy Engineering to be refurbished. They are going to have stellite pads welded on to replace the worn chrome, at the same time the cams are going to be welded & reground.
Kerrin
KERRIN

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Craig in France
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Re: Valve guide choice

Post by Craig in France » Thu Feb 08, 2018 12:51 am

Hi Richard,
rjk40 wrote:
Wed Feb 07, 2018 2:25 pm
Looking at Nigel's stock, he stocks three lengths … <snip>
No. As Kerrin says, those three sizes are OD diameters, not lengths.
rjk40 wrote:
Wed Feb 07, 2018 2:25 pm
… one of the two typical causes for failure being a tad too short ? Too much side force strain? What does too short mean? <snip>
Good question. The accusation is that the guides aren’t sufficiently long enuf to support the valve properly and this leads to premature wear. It’s not a thesis I particularly support (no pun intended), but what do I know?
rjk40 wrote:
Wed Feb 07, 2018 2:25 pm
<snip> Still haven't found any intake valves; thankfully, mine are good
Nigel has them, no? But don’t replace if you don’t need to.
rjk40 wrote:
Wed Feb 07, 2018 2:25 pm
I'm a bit naïve on how to ream the guide (is this before cutting the seat if necessary, or before the new guide is installed, while still out in the open?? <snip>
You ream the guide after fitting to make sure it’s nice and round. It's good practice, if not always necessary :). Your challenge will be that it’s a delicate job and requires quality/precision tools. You may need to find someone to do it for you.
rjk40 wrote:
Wed Feb 07, 2018 2:25 pm
Rocker faces that the cam rides on are showing breakthrough in the contact area with the cam lobe, so am sending them to the chrome shop to be re-chromed. <snip>
Again, it’s a sign of lubrication failure - and is fairly common. With modern oils, the problem won’t recur. As per Bill & Kerrin, stellite is the dog’s danglies for this operation. (I’ve been told that stellite was, in fact, the original finish, but never by someone whose statements I could 100% believe).

HTH

Craig

rjk40
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Re: Valve guide choice

Post by rjk40 » Thu Feb 08, 2018 1:05 pm

Thanks, Craig,
You and your colleagues are a wealth of info and experience, and have saved my bacon numerous times.
I have sent my rockers off to Megacycle in San Rafael, California to be refurbished with stellite et al. They were very cordial, said that they do a lot of this type of Ducati business; mentioned that the new oils, minus zinc, are likely responsible for the hard surface failue, recommend Motul, and two others I can't remember. Got Motul from Steve at Bevel Heaven, so should be okay there.

I'm embarrassed about my reaming question. I looked on the web, and saw that the reaming may or may not be necessary due to possible slight distortion of the guide bore from the install process, or from birth. Found a good machine shop who will replace the guide, ream, then cut the seat face a bit as needed.
So, all is well, just waiting on parts, and going on to other tasks in the resto project.

Richard in Malabar, Florida

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Craig in France
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Re: Valve guide choice

Post by Craig in France » Fri Feb 09, 2018 1:19 am

rjk40 wrote:
Thu Feb 08, 2018 1:05 pm
Found a good machine shop who will replace the guide, ream, then cut the seat face a bit as needed. <snip>
Good - think this is best :Uwin: . As I'm sure you appreciate, getting the guide concentric with the valve seat is critical, and isn't easy/guaranteed without proper equipment.

if you get a chance, can you ask Megacycle what they think the original finish on the rockers was? Ta!

Cheers

Craig

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