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zoe Offline OP
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What do I need to know, i.e. brass vs. cast iron, guide inserts vs. replacement, removal of old guides, inserting new guides, etc?
I've done numerous VW and Porsche heads over the years so I assume it would be similar. Drill the old guide with a step drill, heat the head, tap the old guide out and tap the new one in.

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i used cast iron on mine .......no problems , was lucky to get some NOS Hepolite ones which i figured would possibly be better than anything after market


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zoe Offline OP
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I now understand why few responded to this topic. Googling it provided much info.

For starters I'm a diehard DIYer and if it's physically possible for me to do a job myself that's what I'll do.

Please feel free to make comments based on your experiences.

For anyone who cares I'm going to document my experience.

1. Drilling the port side of the guide to thin it out is very difficult and after trying, I now feel, is a waste of time.

2. I used a 3/8-16 tap to cut about 1" of threads into the rocker arm ends of the guides, screwed bolts into the guides and then used a punch placed inside the guide from the port end to pound the guides out once 300* was reached. This eliminated any possibility of mushrooming the port ends of the guides.

3. Using temperature pencils to determine how hot I was getting the head with my Bernzomatic propane torch worked very well. I made every effort to apply the heat evenly all over the head. At 250* I couldn't pound the guide out but at 300* it came out without too much trouble.

4. The next step will be to mic the old guides and then decide which new guides I want to use.

5. I like the idea of using a screw type tool, available on Ebay, to pull the guides into position rather than to pound them in with the special drifts that are also available on Ebay but I'm open to comments on this.

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If I were to undertake this task I would grind away the visible guide in the port back to flush. Heat the complete head in the oven, and then drift the guide out with a stepped punch ( so it fits and holds within the guide and ensures direct centred removal).

New guides would be fitted with the head heated to a point where they are a push fit.

A small plastic mallet can do all the work required for drifting, if it's not enough to remove it then the head isn't hot enough.


Being honest, I haven't done this job but it is the route I would use.


Life is stressful enough without getting upset over the little things...

Now lets all have a beer!

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zoe Offline OP
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So, each guide measured .566" and all were pretty difficult to remove with the head heated to 300* and at 250* I don't think I could have gotten them out.

I'm going down to my local BSA shop today to mic the new guides he has. If his measure .566" is there any reason for me to buy .002" oversize guides, which I assume would measure .568" as I think mine are stock size?

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Unless your guides were loose stay with .566 .

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zoe Offline OP
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Thanks, Kommando, that's just what I am doing. It turns out that .566" matches up to .002" oversize at my BSA shop. I'm placing cast iron guides in the exhaust and bronze in the intake because I'm told the exhausts tend to wear a little faster and cast iron wears better and that's what was available to me.

Now I have to fabricate a puller to pull the guides in my heated head without having to pound on them even with the special drift.

It's all part of the fun of being a dedicated DIYer like many of the rest of you.

Your advice is always appreciated.

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zoe Offline OP
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I bought the guides today, two cast iron and two bronze all measuring .566".

I made a puller using 8mm all-thread, some nuts and a tapered centering device made from an old drill chuck I had laying around. I cleaned the guide bores out thoroughly with an appropriate sized round brush, heated the head to 300* and tried to pull the first guide into the bore. I did get it well started and straight but I could only pull it about 1/2 way in and then I couldn't pull it any further so I hammered it in the rest of the way by banging on the nut on the rocker arm end of the all-thread. I got all of the guides in all the way and they seem to be nice and straight and they are super tight.

I bought an adjustable 9/32" to 5/16" adjustable reamer on Ebay which I should receive next week so I can ream the bronze guides. The cast iron guides won't need to be reamed. I'll buy a Neway cutter to re-cut the seats and I'll be ready to reassemble the heads with the new valves I bought on Ebay.

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Watch the adjustable reamer, on larger diameters they do not give you a parallel bore but give a belled effect on each end, at this small diameter they should give a better bore but try to make sure the reamer goes in straight. Mounting the head on a milling table with the reamer in the head set to the correct angle and hand turned would be the best way of making sure it does not happen. The neway cutter is the way to go on the seats, you may not even have to grind the valve seats.

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Heating the head (and guide at the same time), makes almost no difference to difficulty of guide removal. Coring the old guide out with a drill (as described), makes much more difference.

It is necessary to heat the head (and preferably freeze the new guide in a plastic bag) before fitting.I also coat the new guide with moly grease.


You'll need 0.00125" minimum cold interference fit but less that 0.00175"for bronze guides, maybe 0.0015" -0.002" for iron.

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zoe Offline OP
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It would seem to me that heating an aluminum head would cause the aluminum to expand more than the bronze guides allowing them to come out easier.
I didn't bother miking the guide bores as I figured if .566" guides came out of the 300* heated head with some difficulty then new .566" guides would also be a very tight fit and they were.
I kept the new guides in ice water prior to installing them but I expect they came up to the 300* of the head pretty rapidly once they came into contact with the aluminum.
Anyway all seems to have turned out well.
I tried coring the old guides but even with a new drill bit it proved to be a nearly impossible task so I abandoned that idea early on.

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Thanks for posting up your experience with this Zoe.

I can't help but believe 450-500^f is the "magic number". I always go with the highest my ovens will reach, and freeze the mating part for at least 24 hours prior. This has worked very well for me on every interference fit part I can think of.

I only have one other addition to the thread... Rather than Molly grease, LokTite makes a green version that is specific to bushings. It works wonders as a lubricant during installation, and like all the other LokTite products, heat will release it. No worries on valve guides or seats with the combustion heat as long as your tolerances are correct.
If you have loose tolerances than Ceramic filled epoxies work wonders. Many of them work up to 4000* f.
I try to never assemble interference parts dry. Many will cringe at the thought but I've had too many failures with dry parts. Even Dawn Dish soap is a blessing for a mechanic if nothing else is available. Try press fitting stainless in stainless sometime.

This is a cool thread, and it took much of the fear of this work out of the equation. Mystical Brit bikes...

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I'd put 450 degrees to 500 degrees F. head temperature at hot enough to cause damage (permanently).
I wouldn't exceed 150 C head temperature (about 302 F.), to fit a bronze guide.

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Several observations.

"In the day" Hepolite never supplied valve guides. If you bought Hepolite guides it is from someone using the Hepolite brand name to sell there products.

Valve guides should be between a .001 to .0015" press fit in the head. Any more and you risk cracking, or stretching, the head.

If I removed guides and found them .002" oversize I would measure the head before selecting the size of a new guide. Many so called mechanics will routinely "stuff" a .002" oversize guide in the head as a matter of routine. This is not a good practice!

The Triumph factory installed (pressed) the guides in a cold head.

I am with Pete on the heat. I use a 200° F Temperature crayon and rarely let the head get higher than 250°F.

Not all guides are made from valve guide material. Both cast iron (high in nickle) and Bronze guides made from real valve guide bar stock are difficult to machine. There are an awful lot of aftermarket guides made from what is called Free Machining materials. Especially bronze guides.

If you are trying to draw a guide into a head and fail, you haven't checked the guide to head clearance. Those tools will only work when you are using the proper interference fit. For most British bikes this is .001 to .0015". This is not a case where more is better!!

If you are attempting to drill out the center of the guide to aid removal without damaging the head, you will have to use a sturdy jig to hold the head and carbide tooling. Diving out the guide can lead to creating deep grooves in the head which will allow oil to flow into the port.

Drawing the guide into the head with a tool that uses the valve seat as a reference insures you will not have to grind your head away trying to find you new valve seat. Most of the valve pocketing found in our heads is the result of valve guides that were improperly installed.

Guides should be purchased with a small i.d. and sized to the valve stem after installation. Depending on the quality of the guide material you will have to use a carbide ream or a diamond hone. If you can size a guide using a High Speed steel reamer you do not have gudes made from real valve guide material.

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Thank you for adding the Info. Pete, and Mr. Healy.

I do see most people stay around 300*f when heating parts. Perhaps I should state for the record that the most common metals that we deal with in engine building are Alum., Cast Iron, and Steel.
All of these (including specific alloys have a set thermal expansion.
Meaning they will expand at a set ratio no matter what Temp. is applied. For example T3003 Alum. is 12.9 microin. Heating to the melting point will not change this. Adding excess heat does not increase the ratio or the total amount of expansion.

I also understand I am pushing the limit of heating an un-mounted part. Engine cases or heads with varying thicknesses can warp or even crack when cooling down. I am by no means advocating that everyone should take these chances BUT to date I can not remember one failure of a part from my heating/chilling process.

The sole reason I do use the heat I do is to maintain the heat longer. Many times a part will install partially, and go no further. You need time to remove, and re/align the piece. I find this especially true with bearings, and case 1/2's or bearings an crank shafts.

Back to the specs for the valve guide... I would have to believe that at 0.001, a frozen guide in a heated head would fall into place. I am looking for a scrap head to "practice" on.
When it does come time to refurbish my permanent head I will use a first rate machinist to do the work for me but I would like to learn what all the fuss is about, and at least give the process a go on a scrap piece.

One last thing... Being in the marine trades I only own Cobalt drill bits. Carbide is good for many jobs in a machine shop or home type shop but NO ONE should keep standard steel bits (ie: Home center/cheap). For the few dollars more a Carbide bit will do almost everything except Cast Iron, and Stainless so it should be your "go to" if you do not want to spend the bucks on Cobalt bits. Cobalt drill bit can outlast your project list, and drill everything you are likely to come across.

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When you say "Cobalt" drill bits, are you referring to a specific brand, or a specific type of steel bit?

Lots of people, including the cheap folks at Northern Tool (Northern Hydraulics) sell what they call "Cobalt Drill Bits".

Are these all "created equal" or are some better than others?

I really need to upgrade my drill bits from the mongrel collection I've built up over the years of various quality from "chalk" to "pretty good I think" ...

Lannis


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Quote
All of these (including specific alloys have a set thermal expansion.

When an engine part, which started as a casting, and machined when cooled down to ambient,
has drilled or reamed holes, these holes are exactly round at ambient temperature.

However, when the part is heated up, these holes are not necessarily round any more, but depending on the surrounding amounts
and thicknesses of the surrounding metal can be slightly oval.

The hotter the part, the more out of shape...

2c


Ger B

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Originally Posted by Zombie
the most common metals that we deal with in engine building are Alum., Cast Iron, and Steel.
All of these (including specific alloys have a set thermal expansion.
Meaning they will expand at a set ratio no matter what Temp. is applied. For example T3003 Alum. is 12.9 microin. Heating to the melting point will not change this.
A few things you wrote aren't quite right. It's worthwhile addressing a few points in greater detail to make sure all is clear

First, I can't think of a single exception to the fact that every metal we deal with on our motorcycles is an alloy, and typically a variety of alloys is called by a common name. For example, we say "aluminum," but the alloy used on a given motorcycle for the cast cases is typically different than that used for the head, and certainly different than that used for a forged bracket. If you do a simple google search you will find a single thermal expansion for "aluminum." In most cases that number is good enough to use for whatever alloy we're dealing with (and we seldom know the composition of those alloys, anyway). However, Boomer is currently dealing with the issue of the thermal expansion of a "cast iron" cylinder liner for his ZB Gold Star, where a more accurate number is needed than turns up with a simple search of the generic term.

Next, it's a useful approximation to use a "coefficient of linear thermal expansion," i.e. a single number that tells us how much an object expands per unit length per change in temperature. In fact, though, the coefficient of expansion is not linear; it's somewhat different at, say, liquid nitrogen temperature than it is near the melting point.

The value "12.9 micron" you mention for aluminum is a reasonable average value to use in the temperature range of interest, but only when used with the full set of units, i.e. 12.9 microinches/inch/oF. Taking an "aluminum" head as an example, and using this average value, it means a 0.566" diameter hole in it when heated to 200 oF will expand by 12.9 microin./in/oF x 0.566" x (200 - 72) oF = 0.00093", i.e. a bit less than 0.001". Doing the same calculation for a "cast iron" valve guide cooled to 0oF finds it will shrink in diameter by only ~0.0002" so it's hardly worth the effort to stick it in the freezer. However, with dry ice it shrinks by 0.0006" which, in combination with the expansion of the hot "aluminum" ends up with a nice push fit of a guide oversize by the 0.001-0.0015" that John mentions in his post.

"Differential thermal expansion" also comes into this. If you decided to heat your head to make it easier to remove the current "cast iron" guides, the hole in the head will expand by 0.00093" but the valve guide also will expand, by 0.00043". The difference, i.e. the differential thermal expansion, is only 0.0005". So, heating will help when removing the valve guides, but it won't help by much (and you'll have to work with a large chunk of hot metal).

Originally Posted by Zombie
Adding excess heat does not increase the ratio or the total amount of expansion.
Increasing the temperature most definitely increases the amount of expansion. For example, heating from 72oF to 172of (a delta-T of 100oF) causes a certain amount of expansion, but heating to 272oF (delta-T 200 oF) doubles that expansion.

Originally Posted by Zombie
I only own Cobalt drill bits. Carbide is good for many jobs in a machine shop or home type shop but NO ONE should keep standard steel bits (ie: Home center/cheap). For the few dollars more a Carbide bit will do almost everything except Cast Iron, and Stainless so it should be your "go to" if you do not want to spend the bucks on Cobalt bits. Cobalt drill bit can outlast your project list, and drill everything you are likely to come across.
I think there are a couple of misprints in what you wrote. You probably meant to write "For the few dollars more a Cobalt bit..." As I'm sure you know, carbide bits are more than a few dollars more than cobalt. Also, because it is so brittle carbide is a very poor choice in anything but a milling machine (or lathe) with the part rigidly mounted. Unless you are referring to carbide-tipped steel "masonry" bits(?), but they would be a poor choice for drilling metal.

Anyway, speaking for myself, if I only could have one set of drill bits I would have cobalt in the common 135o split point jobber length. Without taking the time to look it up I don't know what the requirement is on the amount of (expensive) cobalt that has to be in the steel for a bit to be classified as "cobalt," but I'm sure cheap sets have the minimum. Since it's the cobalt that gives the bits their ability to retain a sharp edge a cheap set would be money poorly spent.

But, standard steel bits are far from useless for what we do and they would last a very long time on aluminum and the occasional steel bracket. However, only with a milling machine or lathe is carbide useful. Even for Bill Gates it would be a waste of money to buy complete number, letter, and fraction drill sets in carbide since it is very unlikely more than a half-dozen sizes ever would be needed in a lifetime of working on motorcycles. If one got further into it they would find uses for specialized bits, like long "aircraft," left-hand spiral, spade drills for sheet metal, etc.


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Cobalt drills are made from HSS (high speed steel), with a percentage of cobalt included in them.
ie 5%,8% depending on application, both cobalt and carbide drill bits are more brittle than HSS.
If you need to drill a gear say a B31 mag gear to convert it to a Gold star timed breather gear you would need a carbide drill.
Also flute helix and point angles differ with different application drills.
Do not buy carbon steel drills, taps,or dies they are sh**e, money buys quality!!

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Originally Posted by GS DAVE
both cobalt and carbide drill bits are more brittle than HSS.
I've never had a problem using cobalt bits in hand drills so, whether or not they are more brittle, they aren't brittle enough to have been an issue for me. I treat them just like standard HSS bits. Carbide, on the other hand, is just waiting for the slightest misalignment as an excuse to snap.

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Originally Posted by Lannis
When you say "Cobalt" drill bits, are you referring to a specific brand, or a specific type of steel bit?
Lannis



Here's a good, and short explanation on Cobalt bits...
http://home.howstuffworks.com/cobalt-drill-bits.htm

There are cheap copies that claim to be cobalt. The real ones are easy to recognize. The almost look like Titanium. Sort of a mottled gold color.
Stay away from the ones that look like gold plating.

Also PB Blaster is the best cutting fluid I have found with these bits. Keep them cool, and they can last indefinitely.

For example... A standard high speed steel bit in 1/4" can cost $1.50. The same size in carbide is about 2.50, and Cobalt is around 4.50.
When you consider the life span of Cobalt, it's a no brain-er. It might take 100 carbide bits to cut 1" stainless or cast iron. One cobalt bit will cut it 100 times or more.


Thanks for expounding on these topics Magnetoman.
I tend to paint images in broad strokes, and leave the finer details for the reader to ask or seek out.

Mr. Healy mentioned carbide bits. They are pretty common, and easy to find in most hardware/home centers.
Cobalt is more a specialty item, and may be more difficult to find but not to the point of making them not worth the effort to find.
Actually our Ace Hardware in town carries them. They cost more than Carbide but not much.

Thermal expansion is an interesting topic in itself.
As mentioned by Ger B, it all depends on the surrounding material, and as Magnetoman points out the alloy is important.
ENGINEERING tOOLBOX has the charts... http://www.engineeringtoolbox.com/thermal-expansion-metals-d_859.html

An old trick I used to apply was to "shock the parts out. A can of freon was enough to quickly shrink a part inside another heated piece. Say you heat a head in the oven to 450... Turn the head face down, and spray freon into the seats. They fall out one after the other.

Yes it is illegal now, and I might be the guy that made the ozone hole over your garden but in the 70's it worked.
Today I use liquid oxygen but it gets expensive, and dangerous if you are not 100% careful.

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Originally Posted by Zombie
For example... A standard high speed steel bit in 1/4" can cost $1.50. The same size in carbide is about 2.50, and Cobalt is around 4.50.
When you consider the life span of Cobalt, it's a no brain-er. It might take 100 carbide bits to cut 1" stainless or cast iron. One cobalt bit will cut it 100 times or more.
OK, you must be referring to carbide-tipped masonry bits when you say "carbide," because a proper 1/4" carbide bit would cost more than 2x more than cobalt. Also, the profile of the tip on a masonry bit is completely wrong for something like stainless (or Al, or steel). But, a proper carbide bit would outlast cobalt by far (held rigidly in a milling machine).

Looking at the McMaster-Carr catalog who, unlike Ace or Home Depot, can be counted on to stock high quality items like this, 1/4" jobbers-length bits go for:

HSS $2.84
Cobalt $4.98
Masonry bit $5.07
Carbide-tipped (but not masonry) $15.08
Carbide $25.08

Actually, it would be worthwhile for anyone interested in this to look at the over 50 different types of drill bits available on the McMaster-Carr web site before spending their money following my, or anyone else's advice, in this thread.

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I just went through my drawer of masonry bits and found one still in its original Ace Hardware blister pack. The package says "For drilling brick and cinder block," but it does also say "Carbide tipped for long life." I confess I never tried to use one on metal, but it did a surprisingly acceptable job on Al.

Some types of stainless work harden so they have to be drilled with a high feed to avoid this, and I don't know what type is what in my SS scrap box (and I was unwilling to damage a perfectly good piece on the shelf for this experiment). That said, the profile of the tip didn't allow for fast feed and it didn't do very well at all on the scrap piece I fed it.

So, you can use a carbide-tipped masonry bit to create something that passes for a hole in some metals, so you might be fooled into believing these bits are appropriate for this purpose. But, just because you can do something doesn't mean you should. If trapped in your garage during the zombie apocalypse and your only way to escape is if you drill a hole in metal using a carbide-tipped masonry bit, by all means go for it. Otherwise, there is no question involving repair on a motorcycle where the correct answer is 'masonry bit.'

p.s. A search of Ace Harware's web page for 'carbide bit' turned up 27 items, all of which are masonry bits.

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I learned to change guides in aircraft cylinders. we put the cylinder on a stand and used a thing like a weed burner to put heat inside the barrel (this is a commercially made setup). heat the head until spit would fly off with a slight sizzle... if it sticks.... too cold. in later years the company that makes the tool recommended 600 F degrees.

once the cylinder is hot, we insert a slide hammer with a mandril that fits the guide.... square to the guide but a slight bit loose in the bore. the mandril is hollow & drilled so that water can flow briefly before hitting the hammer. install the mandril, flow water for about 10-15 seconds.... one hit, maybe two & its out. and the guide bores are not damaged.

we'd freeze the guides, dip the end in engine oil & slap them in..... again one or two hits. the longer it takes, the more likely you are to damage the bores. if it's not in in 3, stop & take it back out. and with a cast iron guide, if the temp difference isn't big enough chances are good you will crack it.

intakes were fit at something like .0007 to .0025 and exhausts maybe .002 to .004 interference fit (tight). bare in mind that some aircraft engines allow cylinder hear temperatures as high as 500F

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More good info Magnetoman. I just looked around, and found the missing link in my thinking. Masonry bits are out of the picture for what we do (metal cutting).

I was confusing Carbide drill bits with Titanium drill bits.

Carbide drill bits ARE about 100 times the cost of any of the lot, and are generally reserved for stationary machine use.
The Titanium bits are the one I confused... These are sold as an upgrade to standard High Speed Steel bits but they are in MY opinion not worth buying. They might last longer (slightly) in steel or Alum. drilling but do nothing on harder metals.

For a real life recommend, it's cobalt bits for me. They cut everything we need, and last.


I've got to stop drinking at 7:00am. I'll wait till 9 for awhile, and see how that goes...

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