Tech Tip: Getting Your (Piston) Groove Back

Tech Tip: Getting Your (Piston) Groove Back

The piston ring set and the piston must be engineered to complement each other from a standpoint of clearance between the back of the piston ring and the bottom of the piston groove. This clearance is referred to as back clearance. If the clearance is not sufficient, severe engine damage can result when the piston and rings are installed in the engine.

Getting Your Groove Back
The piston ring set and the piston must be engineered to complement each other from a standpoint of clearance between the back of the piston ring and the bottom of the piston groove. figure 1

This clearance is referred to as back clearance. If the clearance is not sufficient, severe engine damage can result when the piston and rings are installed in the engine.

Figure 1 illustrates groove depths of a piston.


Checking for Piston Ring Groove Back Clearance
It’s simple to check compression ring back clearance. Place the outer diameter (O.D.) of the piston ring fully into the piston groove as illustrated in Figure 2.

No portion of the inside diameter (I.D.) should protrude beyond the piston land.

Figure 2Oil rings, however, are more difficult to check. By placing the oil rails and expander together as they would be assembled and inserting as shown, it can determine if back clearance exists. Minimum clearance should be 0.015”.


Pistons are designed to have considerable more clearance in the ring land area than in the skirt area. Be sure the ring or ring assembly does not protrude beyond the groove lands.

The design in head clearance will ensure sufficient clearance behind the ring when the piston is installed in the cylinder.


In situations where piston grooves are deeper, the oil ring can be difficult to install because the oil ring assembly tends to “pop off” the piston.

Once the rings are installed, however, they will perform properly even though there is more than normal back clearance.

Some engine manufacturers have changed piston dimensions within an engine model making it necessary to catalog two piston ring sets — deep groove and shallow groove — within one engine model.

Source: Hastings Piston Rings.

You May Also Like

Impact Wrench Technology

Interchangeable anvils are a feature on some new impacts.

Technology is defined as the application of scientific knowledge for practical purposes, especially in industry. We often picture technology as something that has computers and electronics attached, and often it does. But, in the world of impacts, both in the realm of pneumatic and cordless, technology bears much deeper roots.

Brake Lathe Basics

Resurfacing drums and rotors is a machining process with its own specific guidelines.

Refrigerant Oil Has to Be Right

Oil type is just as important as oil capacity.

Three bottles of refrigerant oil
Top 5 Tools: Steve Coffell, Auto World, Hazelwood, MO

Steve Coffell, a technician at Auto World in Hazelwood, MO, says his Top 5 Favorite Tools are: Related Articles – Mayhew Introduces New 14-Piece Micro Hand Tool Set – New Small Stud Extractor Now Available from Mayhew Tools – Matco Debuts 5-Piece Purple Screwdriver Set   OTC Genisys Touch – Quick scan, bidirectional control Snap-on

Wheel Bearing Adjustment Tools & Equipment

A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. It’s important to adjust the wheel bearing endplay to the proper specifications. If the bearing set is adjusted too loose or too tight, it can cause the bearing to fail prematurely. There are a few types of assemblies, so using correct procedures and tools will ensure a comeback-free wheel bearing installation.

Other Posts

Tools in the Eye of the Beholder

We’re here to help you see all the tools, so you can invest wisely.

Multimeter Accuracy: How Important Is It?

Multimeter accuracy is critical for EV diagnostics.

multimeter
More Than A Scan Tool

Scan tools serve as indispensable diagnostic hubs, offering access to a wealth of resources, from OEM technical bulletins to community-documented repairs.

scan tool
Battling Stress and Burnout

Here are some quick tips for managing stress and avoiding burnout in the fast-paced automotive repair industry.

Nadine Battah