How to Evaluate Machine Shop Work

What to inspect when you get your block back. Red flags, measuring guide, questions to ask.

Time: 14 min

Step 1: Inspect block surfaces

Check the deck and main bore for scratches, gouges, or unfinished spots. Decks should be machined flat (verify with a precision straightedge and feeler gauges).

Step 2: Measure cylinder bores

Use a bore gauge to measure each cylinder at top, middle, and bottom. Bores should all be within 0.0005" of each other and round (no taper or out-of-round).

Step 3: Check main bore alignment

Mains should be align-honed straight within 0.0005" end to end. Lay a precision arbor in and rotate it — any binding means misalignment.

Step 4: Inspect head surface and valve work

Heads should be flat and clean. Valve seats should be 3-angle ground with no chatter marks. Test valve sealing with a vacuum tester or wet test.

Step 5: Walk away if you find red flags

Visible chatter marks, missed cuts, sloppy measurements, or 'good enough' attitudes are deal breakers. A bad rebuild costs more than a good one done right.