In the past, we’ve discussed measuring your valve guides to determine if they’re within serviceable limits. In this article, we’ll get into the various methods for repairing and replacing guides. These methods include:
- Installing thin-wall bronze guide liners
- Replacing insert guides
- Modifying the valve guide to accept oversize valve stems
- Replacing integral guides with false guides
By the end of this article, you should have an idea of the pros and cons of each method. But regardless of the method you choose, it is essential that the valve guide be centered to ensure all components align properly. It’s also essential to clean the head thoroughly BEFORE assembling the valves. Any debris or metal chips left in the head will cause premature failure. You have two factors to consider when deciding which valve guide repair method to use – Cost and Performance. In this context, performance is NOT power output, but the ultimate use (such as diesel, high performance, cast iron, aluminum, etc.). Another deciding factor, which is indirectly associated with the other two) is whether you’re working on all of the valves or only some of them. There are a lot of variables to consider, which we’ll explain in the discussion of each method.
|Valve Guide Knurling
|Low Cost. Requires simple tooling (electric drill, speed reducer, knurling arbor, reamer, guide hone and deburring tool).Spiral groove that’s created helps retain oil in the guide. Operation is performed on the bench not a seat and guide machine.
|Temporary fix. Groove is crushed, not cut. Limited to cast iron guide repair. Groove makes it more difficult to measure the ID of the guide. Limited to guide wear of less than .005 over the specified clearance.
|Lower cost than false guides. Improves performance of cast iron guides. Phosphor-Bronze alloy outlasts cast iron. Replaceable. Operation is generally performed on the bench, not on a seat and guide machine. Phosphor-Bronze alloy has high-strength characteristics and good heat transfer properties.
|Requires dedicated tooling. Multiple steps required for each valve guide. Extra care must be taken to ensure guide alignment is not moved during installation. When installing a liner in an existing non-integral guide, it’s essential that the guide is sound (not loose or damaged) in the head casting.
|Replaceable Insert Guides
|Designed to be replaced when worn. Serviceability – ideal for fleet or other high use vehicles.
|Insert Guides can weld to the head during engine operation making them difficult to remove. Under rare conditions, Insert Guides can shrink during use which may cause head damage if they move up and down with the valve stems. Replacement in this case requires special tooling to install oversize OD guides.
|Modifying Guides to Accept Oversize Valve Stems
|Recommended method when you will be replacing the valves anyway. Can be performed using a reamer or a valve guide hone. Honing gives precise control of clearances.
|May need different stem seals for positive seal. Leads to other operations such as seat refacing. Not all shops are equipped to service these modified heads. Special tooling will be required.
|Replace Integral Guides with False (Repair) Guides
|Uses less tooling than liners. Operation is performed on a seat and guide machine so you can set up one time and do all guides. Faster removal and installation than Thin-Wall Liners Available in cast iron and bronze alloy. Self-supporting chimney. Serviceability – can be replaced more readily in future.
|Large mass of the guide transfers heat more evenly to the head. Set up time can be prohibitive if you’re only repairing one or two guides in a head. On the bench methods are usually quicker in these cases.
Choose a system that best fits your needs. The on the bench methods usually are used by do-it-yourselfers and low volume shops. Shops with a large volume can justify the expense of a guide and seat machine for guide replacement as well as other cylinder head machining operations. There are, of course, exceptions to every rule so use this as a road map not a rulebook.
You may also want to check out a couple of books with great explanations of techniques and step-by-step instructions on most of these procedures. The first is Sunnen’s Complete Cylinder Head and Engine Building Handbook by John G. Edwards. Unfortunately, this book is no longer in print, but you may be able to pick up a used copy on E-Bay or Amazon. The second book we recommend is Engine Service Automotive Machining & Engine Repair by Gary Lewis and published by AERA.
If you’re confused or have more questions, contact the tech department.