stainless steel valves in cast iron guide - Model Engineer

14 Jul.,2025

 

stainless steel valves in cast iron guide - Model Engineer

I'm not sure if this is the best thread to ask but my problem is actually on a s Moto Guzzi engine with exposed valves. I had new guides and valves professionally fitted in a cast iron cylinder head. Expert advice is that a stainless valve will 'pick up' in an iron guide so they fitted phosphor bronze guides. The exhaust valve stuck after 2 miles. The guide was reamed out to give more slack. this time it lasted 20 miles then stuck. Originally this engine had iron guides as they are self lubricating which the bronze ones are not. Any advice please? Thanks.

Goto Yaxing Valve to know more.

What clearance did they ream the guides to, between the valve stem and guide? A lot of those old engines ran massively larger clearances than what modern automotive machine shops are used to providing. Same with piston to bore clearances, which have caused problems for several restorers I know over the years.

Those old engines with exposed valve gear and no positive lubrication could run .003" to .005" (0.075mm to 0.125mm) exhaust valve guide to stem clearance, which would be considered "worn out" in a modern engine.

The stainless valves I have used in bike engines all had hard-chromed stems, presumably to prevent "picking up". And usually not phosphor bronze for valve guides as it is said the phosphor can tend to leach out under extreme heat in an air cooled engine. Aluminium bronze such as Ampco 45 is more commonly used. But that factor is unlikely to be causing you problems at such short mileage. Probably has more influence over length of service life. So I would look first at what clearance you have.You already found that more clearance lasted longer before seizing so I would look at trying a bit more.

Edited By Hopper on 16/02/ 21:57:48

Edited By Hopper on 16/02/ 21:59:09

Agree with Hopper and Chris above, old engines had much larger clearances than modern valves/ guides, I took a Triumph Bonneville head to a so called expert on classic bike cylinder heads who insisted that bronze inserts in the existing guides and machining the seats on his massively expensive Serdi machine was the only way to go. After 20 miles the an exhaust valve siezed in the guide and pulled it out of the head. Damaging the bore for the guide on the way out.. Turned out he used the same clearances as for a modern engine as an "improvement", Made a new set of guides ( one with an oversize O/D) with much more clearance and it ran fine with no smoke or siezures, this was with Nitrided valves rather than stainless, but I imagine the principle is the same. Looking at some forums found that others had had the same experience with the expert , now retired I believe.

Thank you so much for all the replies, some good information there which is much appreciated. The Company concerned is South Cerney Engineering near `Swindon. They have an excellent reputation, working on the highest quality and rare vehicles so I took them at their word. I'm sure the chap doing the job said he'd opened the guide up to give .003". I've since found a Moto Guzzi chart from the period which recommends nearly .008" at max tolerance! So that's the first thing. Is there a way to tell if a valve stem is chrome plated? or is it obvious?

Incidentally, the inlet guide has an oil drilling for valve lubricant but the exhaust has to just get on with it.

Thanks again for the knowledgeable and informative replies.

Clearance of .003" on an unlubricated valve stem could quite possibly be too tight, I reckon. My Harley with cast iron heads has a factory spec of . to ." valve stem clearance, new from the factory. Then they allow another 2 thou of wear beyond that before replacement is called for. And that is in a much more modern engine with higher revs, enclosed rocker gear and pressure fed oil to the rocker spindles and arms which then sprays out over the guides and valve stems.

So I reckon you could try something like .005" clearance and see how it goes. Maybe even a thou more. Just make sure they give the valve stem a darn good polish up after it has nipped up so there is no roughness left to start galling again.

I don't know if the chrome is really visible on stainless Harley valve stems, I never really looked at them that hard. What brand of valve did you use? I think most of the high performance aftermarket valves like Manley come with chrome stems if they are stainless. But they are made for high rpm high power use with heavy valve springs etc so your lovely olde-worlde single banger will probably not need it.

It is a common problem with modern machine shops working on true vintage machinery. They think that because they have done work on Honda 4s and Kawa 900s from the s, and maybe a few old Norton Commandos or BSA twins and the like, that they know all about "vintage" bikes. But those old engines from the pre-War era ran everything loose and are a whole different world again. They were still operating very much in the steam age to a certain extent . They did not have the machining or the metallurgy let alone the lubrication, to run modern tight clearances.

Edited By Hopper on 18/02/ 04:17:31

Edited By Hopper on 18/02/ 04:29:00

At the price (not the postage!!) and at the news of the stellite pad coming off the end of the stem, even under severe hammering, I would have to wonder about the quality of the valve. Good quality Harley valves run about $50 each and Norton valves can be as much as almost $200 each for the super magic ones. But I suppose you don't get much choice with ancient Guzzi parts. I have seen a few hung up valves on Harleys and Brit bikes but have never seen a pad come off the tip of the stem. But not sure they even have such a thing. I don't suppose you have an alternative supplier ?

Yes surprising your machine shop would make it so tight on such an old machine. If they opened it up to 3 thou after the first seizure it must have been 2 or 2 somehting to start with. Did you find what the original Guzzi clearance specs were?

Edited By Hopper on 18/02/ 07:30:34

Posted by Hopper on 18/02/ 07:27:37:

At the price (not the postage!!) and at the news of the stellite pad coming off the end of the stem, even under severe hammering, I would have to wonder about the quality of the valve. Good quality Harley valves run about $50 each and Norton valves can be as much as almost $200 each for the super magic ones. But I suppose you don't get much choice with ancient Guzzi parts. I have seen a few hung up valves on Harleys and Brit bikes but have never seen a pad come off the tip of the stem. But not sure they even have such a thing. I don't suppose you have an alternative supplier ?

Yes surprising your machine shop would make it so tight on such an old machine. If they opened it up to 3 thou after the first seizure it must have been 2 or 2 somehting to start with. Did you find what the original Guzzi clearance specs were?

It is a sacrificial 'pad', a separate item that literally just sits on the valve stem. The only thing preventing it falling off is the rocker

Edited By Hopper on 18/02/ 07:30:34

I get involved mostly with JAP V twins on Morgan Three Wheelers and one or two other odd balls, and more recently JAP 500 singles. Safe valve guide clearances for these engines are considered to be 2 thou on the inlet and 4 thou on the exhaust. Some practitioners opt for 2 thou all round, and some get away with it.

Valve guide material was Meehanite, although Colsibro is currently offered as an alternative. Valve guide lubrication is a bit hit and miss – there are drillings through the head into the valve guide and small pipes feed oil from a collector on the back face of the rocker box into these. Lining up the hole in the head with the hole in the guide is important. The rocker box may or may not be positively fed with oil. The worst case is no positive feed (like my engine), oil “mist” is thought to find its way up the pushrod tubes from the timing chest which communicates with the crank case, into the rocker box, some then finds its way to the valve guides. I add a bit of oil to the the exhaust valve guide each morning before setting off but the rocker box is always wet inside.

The little cap on top of the valve stem we know as lash caps. These are currently being machined from EN24T rather than EN36 hardened.

Measuring valve guide bores reliably can be tricky enough, but parallelism is critical. One engine that we dealt with recently that nipped up when working hard was found to have plenty of valve guide clearance at the ends but the middle of the valve guide was tight – the bore was barrel shaped. I think also that adjusting valve guide bores can be a game for any number of players….reamers like to have a bit of work to do and taking an extra thou out with a used reamer, especially in the bronze like materials, may not work. Adjustable reamers don’t always behave either.

Ian

Complete Guide to the Different Types of Valves - Gemini Valve

In the simplest terms, a valve is a device used to control the flow of a medium — liquid, gas or solid — through a piping system. Most commonly, valves are used to stop and start the flow of media. Some valves are also able to control the rate of flow, these are commonly referred to as control valves.

Because there are so many different uses for valves, they are available in a wide range of mechanical variations. Using the appropriate valve in a given scenario means your application will run smoothly and safely, accomplishing the intended goal most efficiently.

Though there are many different valve classifications, most valves fall within three categories: rotary, linear and self-actuated.

Rotary

Rotary valves utilize a rotating closure component to block flow within a piping system. Most often, this rotation is limited to 90 degrees, which is why rotary valves are also commonly referred to as quarter-turn valves. These types of valves are closed at 0 degrees and open at 90 degrees.

Some rotary valves can operate with a larger degree of rotation and include more than two positions. Common examples of rotary valve types are butterfly, plug and ball valves.

Linear

Linear valves use a flow obstructer — such as a disc, slat or diaphragm — that moves in a straight line to start, stop or adjust flow through a piping system. These valves can be separated into two distinct types: rising stem (multi-turn) and axial. 

Multi-turn linear valves work particularly well in control applications and include globe valves, gate valves and needle valves. Axial valves, such as coaxial and angle seat valves, are fast-acting and used primarily in on/off process applications. 

Compared to other categories of valves, linear motion valves tend to have longer cycle times than rotary valves.

Self-actuated

Unlike linear and rotary valves, self-actuated valves do not require direct input from the operator. Instead, they use the pressure within the process line to open or close a pressure control valve. This valve type is commonly used as a pressure relief valve and only opens once maximum allowable pressure is reached within the system. As a result of this mechanism, self-actuated valves are common safety requirements in certain applications.

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Common self-actuated valves include relief valves, safety valves, check valves and steam traps.

Since quarter-turn valves allow for a wide range of motion with the turn of a handle, these valve types are commonly used in applications that prioritize quick and easy opening/closing over precision.

Ball Valves

Ball valves can be used in most applications where a fluid flow needs to be shut off. In fact, they are the most widely used process control valve. These rotary valves use ported spheres that swivel in the pipe stream, working to start or stop flow.

Since the valve’s port can be fitted precisely to match the pipe’s diameter, ball valves offer low head loss. Ball valves may be more expensive than other rotary valve options, but they offer better sealing than types such as butterfly valves.

Butterfly Valves

Butterfly valves work using a center-mounted, disc-shaped obstructer that sways in and out of the piping system’s flow. These quarter-turn valves are frequently used with larger pipe sizes and in wastewater plants, power plants and other process plants where shut-off, regulation, and isolation are called for. 

Advantages of using butterfly valves include lower cost and smaller size. However, these common valve types are more vulnerable to leaks and head losses than ball valves and may not work as well against high-pressure flows.

Plug Valves

Plug valves are very similar to ball valves in their construction and function. However, instead of using a ball-shaped obstructer, plug valves obstruct or allow flow via a tapered cylinder that swings into or out of the flow stream. There are two main types of plug valves: lubricated and unlubricated.

This type of rotary valve is frequently used for shut-off and as a control valve for chemical processing industries, processing plants and wastewater treatment facilities. Plug valves may be favored for their lack of voids and cavities, and their ability to be adjusted for leaks that develop over the long term. As a result, these valves are often used in extreme service scenarios — think corrosive environments like oil refineries and chemical plants.

Commonly used in flow control applications, multi-turn valves work by cranking a handle to move an obstructer element into the flow path. This restricts flow within the piping system. Some types of multi-turn valves enable the flow to be released or blocked at variable speeds. These types of valves are commonly referred to as control valves.

Globe Valves

Globe valves work by using a globe-shaped disc to block flow when closed against a restriction orifice. These multi-turn valves are commonly used in on/off and throttling applications. Globe valves can seal both against or with fluid flow.

Two-way globe valves are recommended for precision, while 3-way globe valves are suitable for combining media from two inlet ports and sending the resulting mixture through an outlet port. Globe valves are frequently used in wastewater plants and food processing services. Although this valve type is available in many variations, the most prevalent is the Z-style valve.

Gate Valves

Gate valves are multi-turn valves commonly used to block flow streams and occasionally (and sometimes ineffectively) for throttling. This multi-turn valve type utilizes a plate-like barrier to block a flow stream. 

Gate valves offer lower head losses when open compared to other valve types. Although their operation is comparable to globe valves, gate valves offer less flow restriction and regulation capabilities. 

Needle Valves

Needle valves closely resemble globe valves aside from several key factors. First, they are smaller than globe valves and allow for more precise flow control within smaller systems. Additionally, they consist of a cone-shaped needle — as opposed to a disc-shaped plug — that moves into and out of an orifice to start and stop flow. 

Needle valves offer a precise way of modifying fluid flow through a system. They can be used for on/on applications but may not be the best option in such instances, as they require many turns in order to close. 

Much as the name suggests, on/off valves are fast-acting devices that either enable unrestricted flow or block flow entirely. Though these types of valves do not allow for precise flow adjustment, they are useful in various applications where speed is essential, for example when used for situations that require emergency shut-off.

Solenoid valves

Solenoid valves use a linear sliding obstructer to open or shut the valve or redirect the flow from one outlet to another. These valve types are available in many different sizes, from as small as one millimeter to as large as 100 millimeters. Furthermore, they can be composed of various materials such as cast iron, stainless steel, aluminum, plastic and brass.

Solenoid valves are commonly used in emergency shut-off service applications and high-pressure systems. They can also handle a wide range of temperatures, with some models able to handle temperatures as extreme as -418° F to ° F, making solenoid valves a popular choice for cryogenic processes. 

Coaxial valves

A coaxial valve is a 2-position valve that can be either pneumatically or electrically actuated. Electric coaxial valves use an electromagnetic coil vs. a spring. Pneumatic coaxial valves use either air pressure vs. a spring or double acting air pressure (air pressure that comes from both directions). These valves use a shuttle obstructer to open or close and to divert flow to the correct outlet. 

Coaxial valves are a good substitute for ball valves in many on/off applications. In fact, they are a more affordable, smaller, lighter, safer and faster alternative. Disadvantages of coaxial valves include lower flow capacity and limited fluid compatibility.

Angle seat valves

Closing out the list of different types of valves and their uses is the angle seat valve, another type of valve that can serve as a substitute for a ball valve in on/off applications. Seat angle valves use a built-in pneumatic actuator that can be double acting or spring return

This 2-position valve includes an obstructer plug that goes into the valve at an angle in order to fit into the angled seat situated within the flow path. When the valve is open, the plug is retracted almost entirely out of the flow path, making this type of valve the highest flow fast-acting valve with the lowest pressure drop. 

Compared to ball valves, angle seat valves are faster, less expensive and just as durable. The primary disadvantage an angle seat valve has when compared to a ball valve is that angle seat valves do not perform as well with media that carries particulates. Due to their linear nature, an angle seat valve is more prone to trapping objects against the seal when closing, which can lead to failure to create a tight seal and can damage soft seal components. Ball valves, on the other hand, will tend to wipe away any particulates as they close which keeps objects from getting caught between the ball and soft seals. Angle seat valves also tend to be better suited for applications with lower operating pressure.

Why is it important to choose a certain type of valve?

Different valve styles will perform differently in any given application. This may mean differences in both functionality (cycle speed, position control, etc.) and the lifespan of the valve. Some types of valves may be entirely inappropriate for certain applications.

What’s the difference between linear valves and rotary valves?

Rotary valves utilize a rotating closure component to block flow within a piping system, while linear valves function by raising or lowering a flow obstructor, such as a gate, globe or diaphragm. Rotary valves typically require only 90 degrees of rotation to cycle on or off, whereas linear valves require multiple rotations of the shaft to move the closure component.

Why should I consider an on/off valve?

On/off valves should be used in applications where the intended function of the valve is to stop or start the flow of media. On/off valves should not be used to modulate flow rate.

Why should I consider a control valve?

Control valves should be utilized in applications where more precise control of the media flow rate is required, though not all control valves are recommended for throttling.

Can all linear valves be used as control valves?

No; gate valves, for example, are not recommended for control applications and are intended to either be fully open or fully closed.

Why are some valves more expensive than others?

Cost is influenced by a wide variety of factors including materials of construction, manufacturing processes and the complexity of the design. There are many different features and options that may influence cost as well. For example, actuated valves will generally be much more expensive than manual valves.

Still not sure which valve type is best for your application? With decades of experience and expertise in the valve industry, Gemini Valve is here to provide the right solutions for your system. Contact our team today to get started.

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