Tech Tip: Measuring, Selecting & Installing Valve Guides

 

Don't forget to watch the video above and read the following post..

Selecting and choosing a replacement valve guide is not as simple as having a "replace what came out of it" mentality..

Valve guides play a very important role in your valve train and care must be taken when choosing and installing a replacement guide 

As the old saying goes... "your valve job will only be as accurate as your valve guide.."

In todays Tech Tip post series we will dive into some of the following topics that will help you become a better machinist and cylinder head rebuilder 

 

• What is a valve guide?
• How to inspect a valve guide bore 
• How to measure a valve guide bore
• How to select a valve guide 
• Installing a valve guide 

Although this info we will be covering today is relevant for most applications, it will be specifically targeted for vintage British motorcycle riders and owners

With that being said, lets get to work..

 

What is a valve guide?

Valve guides "guide" either an intake or exhaust valve ensuring the centerline is concentric to the valve seat, guides also shed heat throughout the cylinder head and guides also keep the valve straight acting as bushing 

If you have sloppy guides, your seat work will be just as sloppy...

 

 

How to inspect a valve guide bore

A valve guide bore is the housing in which your valve guide resides in

When measuring a valve guide bore you must first remove the old valve guide 

Upon removing your valve guide, you must check the quality of the valve guide bore by visually inspecting the bore

We are looking for any damage which includes scratches, gouges, or steps 

Any of the above damage could contribute to a guide working loss, lack of heat transfer and oil retention 

If your guide bore happens to be damaged, please consult a machinist for the best option for repair...

 

How to measure a valve guide bore

 Assuming that your valve guide bore(s) are in good shape, lets get ready to measure the bore..

To measure a valve guide bore you can use the following tools

• Telescopic gauge 
• Dial bore gauge 
• Split ball gauge 
• Caliper / Micrometer 

 The most accurate way to measure a valve guide bore is to use a dial bore gauge, however obtaining a dial bore gauge can be expensive; the most affordable option is to use either a telescopic gauge or a split ball gauge which can be found on eBay or Amazon for pretty cheap..

For this exercise (and video) I will use my dial bore gauge

When I insert my dial bore gauge inside the guide hole I am looking for a few things

1. Straightness 
2. Roundness 
3. Taper 
4. Over bore size 

Now in a perfect world, we would like to see "0" on the indicator at every point we check, however that will more than likely not be the case on a used head 

For those NOT using a dial bore gauge, you must use a split ball gauge or telescopic gauge and check your measurements at different locations to check for taper, etc

Assuming that your bore is in good shape, get the overall inside diameter hole dimension as this will help us select which guide we need 

For this demonstration, my valve guide bore measures .500" (1/2")

How to select a valve guide  

Now that we have the valve guide hole size (1/2") we must select a replacement guide 

For most Triumph, BSA, Norton heads .500" (1/2") is known as a "standard" bore size 

For those that measured your head and came up with a different size, lets say .502", .503" or larger, then you would need a larger valve guide to accommodate the larger hole...

Mind you that every time you remove a valve guide, some material is lost which will result in an oversized hole condition.. 

For most Brit bikes press fit when installing a valve guide is .001" - .0015"

The "press fit" is what keeps the guide locked in place..

Going back to my .500" hole size, I will need to find a valve guide that will offer the proper press fit - a simple math equation below will inform you what size guide you need 

Equation 

Valve guide hole size .500"

Press fit                      .0012"             

+____________________________

 = .5012" 

 

By adding the bore hole size and the press fit desired will give you the proper valve guide outer diameter size you need 

For my example, I would need to order a guide that has an OD of .501"

Installing a valve guide 

Now installing valve guides can be a controversial subject

Everyone seems to have there own way to install guides, and to be honest, there are indeed multiple ways to do so 

The goal is to install the valve guide into the cylinder head without damaging the valve guide and guide hole 

I will list a few different ways to install a valve guide, you choose what works best for you..

 

• Freezing the valve guide and heating the head
• Using a drift to drive in the guide
• Drawing in the valve guide 

 

The method I will be using (which I think is the best method) is drawing the valve guide into the cylinder head while the head is hot 

This method / tool I use centers on the valve seat, and allows the guide to be inline during installation 

As always, I heat the entire head and use some lube (Sunnen press fit oil) to prevent galling to the cylinder head bore.. 

Once your valve guide is installed let the head cool at room temperature - now your guide is ready for sizing 

Parts for purchase

Now that you know the process of installing a valve guide, always remember to check and inspect your cylinder head before you order replacement parts 

Below is a link to a similar tool that Kyle used in the video above 

Tool Type	Link
"Heavy Duty" Valve Guide Installation tool	Click Here

Thanks for reading

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Should you have any questions, please drop us a comment using the comment section below 

 Ride safe!