Small Block Chevy 350 Build Pt.3 | Filing rings and checking main clearances
This video covers filing piston rings to achieve the correct end gap and checking the main bearing clearances on a Small Block Chevy 350. The build includes measuring clearances (typically with plastigauge and micrometers), adjusting ring end gaps by filing, and documenting measurements before reassembly.
Build Sequence
1. Prepare block and components
Clean the block, journals, and parts thoroughly. Mount the block on an engine stand and lay out pistons, rings, bearings, and tools so measurements and filing go smoothly.
2. Check crank journal sizes (optional)
Measure crank journal diameters with a micrometer to know target bearing clearances. Record measurements to compare against bearing shell sizes.
3. Install main bearings and caps dry for trial fit
Install bearing shells in block and caps. Lightly oil or use assembly lube if required by the method. Torque main cap bolts to spec to seat the caps for clearance checks.
4. Measure main clearances with plastigauge
Place a strip of plastigauge on each journal, install and torque the cap, then remove the cap and compare the flattened plastigauge width to the scale to determine clearance. Record results for each journal.
5. Evaluate bearing clearance results
Compare measured clearances to target specs for SBC 350 mains. Decide if different bearing thicknesses or undersize bearings are needed if clearances are out of spec.
6. Check piston ring end gaps in bore
Insert each ring into the correct cylinder bore (square ring on a piston or use a ring expander and push it down with a piston to ring seating depth) and measure the ring end gap with feeler gauges to see how much material must be removed.
7. File ring ends to achieve target end gap
Clamp the ring in a filer or use a guided hand file and gently file the ring ends, removing small amounts at a time. Recheck the gap frequently until the specified end gap is reached for each ring and cylinder.
8. Final check and document measurements
After filing, re-measure ring gaps and main clearances. Ensure all readings are within specified tolerances and document values for future reference before final assembly.
9. Clean and prepare for reassembly
Thoroughly clean any filings, debris, and surfaces. Lightly lubricate bearings with assembly lube and proceed with reassembly steps (piston installation, torque to spec) as the next video covers.
Frequently Asked Questions
Why do you file piston rings instead of buying pre-gapped rings?
Many rings must be filed to match the specific bore diameter and application to achieve correct end gap at operating temperature. Pre-gapped rings may not match your precise bore size or intended oil control/boost conditions, so filing allows custom fit to spec.
VIEW FULL ARTICLE →How much end gap should I aim for on a SBC 350?
Typical end gaps for a small block Chevy 350 depend on bore size and application; common values are around 0.015"–0.025" for standard applications. Always check the ring manufacturer's recommended gap and increase gap for higher cylinder pressures or nitrous applications.
VIEW FULL ARTICLE →How much material should I remove when filing a ring?
Remove very small amounts and recheck frequently. It's safer to file a little and re-measure than to over-file. Typically you remove only a few thousandths of an inch per iteration until the desired gap is reached.
VIEW FULL ARTICLE →What if my main clearances are out of spec?
If clearances are too tight or too loose, you can change to a different bearing thickness (undersize or oversize shells where applicable) or machine journals/replace bearings as required. Excessive out-of-spec clearances may require machining the crank or selecting alternate bearings.
VIEW FULL ARTICLE →Is plastigauge accurate enough for checking main clearances?
Plastigauge is accurate enough for quick checks and verification, but it's not as precise as micrometer and bore gauge measurements. For final bearing clearance confirmation on performance builds, more precise measuring methods are recommended.
VIEW FULL ARTICLE →Related Builds
Small Block Chevy 350 Build Pt. 6 | This Is How It's Actually Supposed To Be Done
Small Block Chevy 350 Build Pt.5 | Continued frustrations with rod clearances
Small Block Chevy 350 Build Pt. 11 | Installing the intake manifold and figuring out sbc nuisances
Small Block Chevy 350 Build Pt. 7 | Checking Crank Clearance and installing the rods.
Small Block Chevy 350 Build Pt. 8 | Installing Camshaft and timing components
Small Block Chevy 350 Build Pt.1 | Lifting This Engine Without Breaking ItParts Used (4)
Complete main bearing set for the crank; used when checking and correcting main clearances.