Tech Tip: How to Check Piston Ring Groove Back Clearance

Tech Tip: How to Check Piston Ring Groove Back Clearance

It is extremely important to check rings for sufficient back clearance to verify correct ring set application for the engine. 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.

It is extremely important to check rings for sufficient back clearance to verify correct ring set application for the engine.
Figure 1
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.



The sketch in Figure 1 illustrates groove depths of a piston.



It is 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.



Oil rings are more difficult to check. However, 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 15˝.


Figure 2
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 designed 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

MEYLE Expands Electronics, Sensor Product Portfolio

The focus is on assistance systems and engine and transmission management, with more than 300 new part numbers.

Hamburg-based manufacturer MEYLE announced it is expanding its portfolio of electronic and sensor spare parts by more than 300 references "to meet the demand from independent repair shops for high-quality and precisely fitting parts." The focus is on assistance systems and engine and transmission management, with more than 300 new part numbers in the pipeline, as well as the expansion of its product range specifically for electric vehicles, the company said.

FCS Introduces 42 New Numbers in May

Complete strut assemblies, shock absorbers, shock absorber assembly kits and suspension struts for popular VIO applications are included.

Philips Ultinon Drive 5000 LED Lightbar Line Expands

Lumileds has expanded the Philips Ultinon Drive 5000 series to include eight models.

DMA Adds New BrakeMaster Coverage

New coverage for Ford and Chevy includes popular pickup trucks and SUVs.

Akebono Expands Severe Duty Disc Brake Pad Kits

Akebono said it expanded its severe-duty ultra-premium disc brake pad line by 14 new part numbers.

Other Posts
GSP Releases New CV Axle Part Numbers

GSP said 14 new CV axle part numbers are in stock and ready to ship.

BCA Bearings Unveils 2024 Endless Summer Promotion

The Endless Summer promotion runs from May 1 through June 30, 2024.

PRT Launches 30 New Complete Strut Assemblies

The new items represent more than 10 million vehicles in new coverage, PRT said.

RNR Tire Express Hosts Mother’s Day Giveaway

The eighth-annual event promises $100,000 in prizes, as well as a brand new 2024 Buick Encore for one select nominee.