Menu

Shop

Garage

Cart

Account

Products to Compare (max of 3)
X
Compare These Parts

How to Check Piston to Valve Clearance

6/11/2020

Interference is never a good thing, whether it's in football, while watching tv, or listening to the radio. It's an inconvenience and is almost always unwanted. None is more important to a car enthusiast than piston-to-valve interference. A miscalculation can result in utter catastrophe, and nearly every car enthusiast can tell a story about someone whose piston has missed a valve. To help prevent this disaster of magnificent proportions, I’m going to walk through the steps on how to check your piston to valve clearance and show you some tools that Speedway Motors offers to make it easier.

Now, I’m going to go over a more dynamic way of checking. You can do a much more in-depth procedure for those who are so inclined, or those situations where every hundred-thousandth matters. However, for the nitty-gritty folks who just want to make sure the new cam they got clears or want to see what they have to work with currently, this is for you.

Firstly, let's go over some specs. Typically you want a minimum of .080 of an inch of clearance on the intake valve and a minimum of .100 of an inch of clearance on the exhaust. Since the exhaust runs hotter, there’s more thermal expansion and therefore needs more room. I would never suggest going below these specs as they could cause issues, especially at high RPM, as there is potential for the valve to float. This reiterates that selecting the correct valve spring is important for your engine's usage; that way, this will be avoided as much as possible.

Next, to get an accurate reading, you will need to make sure all your engine's components are in good shape: no sloppy timing chains, no worn valve guides, loose rockers, bent pushrods, everything needs to be in proper working order. If any of these components were bad, they could throw off the reading and potentially cause piston to valve interference, damaging the valves and ruining lots of hard work and money and causing some serious frustration. To make sure my reading was accurate, I purchase a new Timing Chain for my application. This kit also allows you to advance or retard the cam timing by 2 degrees. Sometimes a kit like this is necessary to move your cam timing back to spec.

The second tool I bought was a basic Degree Wheel Kit. These are very nice for the price and give you some springs to keep tension and allow the system to work like normal, but they can easily be collapsed. It also provides a head-mounted dial indicator, so you can track how far the valve is traveling, as well as your basic degree wheel and piston stop. Another important tool can be found at almost any store you venture into playdoh. Color isn’t too important, but black should be avoided if possible. The necessity of playdoh will be explained later. One could also use modeling clay if wanted. Lastly, I grabbed 2 Solid Lifters to use for the cylinder I was testing, as I want to avoid the possibility of the hydraulic lifters collapsing under pressure.

The first thing I did was install the camshaft into the block. The bottom end had been reassembled. I made sure to liberally apply some Lithium Grease onto the Camshaft , then I installed the cam thrust plate and put on the timing gears and chain.

I lined up my markers on the gears, keeping the crank gear at zero advance. After installing, I also greased up the 2 lifters and installed them into the lifter bores for cylinder 1. Now comes the odd part. I like using Playdoh, as it's cheap and easy to find. I take about a half-dollar sized ball of Playdoh and spread it around the top of the piston for cylinder 1, making sure to cover the side opposite the valves very thoroughly. I typically will rotate the engine around once to make sure that the Playdoh doesn’t drag on the cylinder wall or get caught and smear inside the cylinder. That’s just not a mess I want to clean up.

After rotating the engine back to TDC for cylinder 1, I get ready to install the head. I typically like to use the head gasket here, as cold compressing the gasket without any sort of heat cycle will not harm it, and it can be reused in this circumstance. I then liberally lube the valves in the head and install the weak springs included in the basic degree wheel kit. I then put the head on like normal and torque the head down using the manufacturer-specified torque specs, making sure to lube the underside of the head bolts, as well as the threads to get an accurate torque reading.

I installed the factory length pushrods, but this would be a great opportunity to easily find the correct length pushrods for your setup with a Pushrod Length Checker. I then installed the rockers and tighten down until there was roughly .016 of an inch of clearance between the rocker and the valve tip. These are Ford’s specs for a solid lifter application your manufacturer may vary. Then, all I did was rotate the engine around a full revolution and pull everything back apart and remove the head. (If you can’t fully rotate the engine around DO NOT FORCE IT! This could cause damage to any number of parts on your engine. Simply rotate the engine back and disassemble and thoroughly inspect as to where your interference is.)

You can see the indentations left by the valves in the Playdoh. This will show you your piston to valve clearance. It is usually suggested to cut the Playdoh with a razor blade in the deepest portion of the indentation. Then you can take a pair of calipers and get a reasonably accurate measurement of how much room you have.

Remember, you want to be within the specs given earlier if you are, then everything is good to go. Disassemble and thoroughly clean all the parts used and prep for the reassembly of your engine. Now, like I said, this is very nitty-gritty. It’s a simple, yet fairly accurate way of doing it, and for my particular rebuild, that’s all I needed. You can take it much further and get absolute pinpoint accuracy, and this would always be suggested given you have the time, money, and tools necessary. As always, if you do have any additional questions, you can always contact the wonder Tech Team here at Speedway Motors on our hotline. Or check out some more articles here in the Toolbox.

Products Featured in this Article

Related Articles

Adding a Water Bypass Kit to an Intake Manifold
by Kevin Webel - Posted in Tech
5/1/2020
Keep your rear cylinders running cool in a high performance engine by installing a water bypass kit to the intake manifold.
Micro Sprint Steering Maintenance
by Alex Owen - Posted in Tech
3/5/2020
Steering is one of the most important components of racing. Learn some tips on how to maintain the rack and pinion steering setup and how often the steering box should be serviced to prevent steering from locking up.
Disc Brake Conversion
by Tyler Wesely - Posted in Tech
5/24/2019
How to change brake pads, rotors and calipers using the Mustang II complete brake kit. Replace your drum brakes with disc brakes for performance and better braking ride. For use on Bobcat and Mustang II spindles.
Front Spring Choices for Traditional Straight Axle Hot Rods
by Mark Houlahan - Posted in Tech
6/15/2021
It may feel like a daunting task attempting to determine the best leaf spring for your traditional hot rod straight axle build, but our buyer's guide will surely help.
Solid Axle Choices for Your Traditional Hot Rod
by Eric McMillan - Posted in Tech
6/15/2021
When it comes to a traditional style build on an early hot rod it just has to be rolling on a solid front axle of some sort. In this buyer's guide we take you through I-beam and round tube solid axles, spindle choices, radius rod needs, and more.
How to Use a Stud Extractor Tool
by Steve Lewis - Posted in Tech
6/15/2021
Broken exhaust studs are a common problem. This article describes what you need and how to remove a broken stud from an exhaust manifold. Learn how simple it is to remove broken or stubborn studs with a Titan Tools stud extractor tool.
MSD Ignition Box: Ignition Controller Buyer's Guide
by Jason Lubken - Posted in Tech
6/15/2021
Looking for an easy performance upgrade to your ignition system? MSD's line of Ignition Control Boxes offer extreme improvements to drivability and high rpm applications. Here's a look at the differences between the 6 series line-up.
Pyrometers: Probe Vs. Infrared
by Longacre® - Posted in Tech
6/11/2021
When choosing a type of pyrometer, it's important to know the differences between prob and infrared. This article compares the two and when to use which kind.
Optimal Tire Pressure Setup for Quick Lap Times
by Longacre® - Posted in Tech
6/11/2021
Dirt Track Racing Tire pressure affects many variables when it comes to dirt track racing that can contribute to speed. Find out more on how the right amount of air can help you reach your dirt track lap time goals.
How to Choose a Racing Harness
by Charles Aman - Posted in Tech
6/11/2021
Having a difficult time deciding which racing harness to use? With many options to consider from size to closure type, this article will walk you through how to go about choosing the perfect one for you and your race car. Safety first!
Error
X
Note
X
Ok