Not all machine shops do equal work. Some are excellent. Some will take your money, do substandard work, and hand it back in a box. Here's how to inspect what you got and catch problems before you button up an engine that will fail at 5,000 miles.
What to do when you pick up your block
Don't just take the bag of parts and leave. Spend 15 minutes at the shop asking for a walkthrough of what was done and the measurements taken. A good shop will have documentation and will be glad to talk you through it. A bad shop will be defensive.
Bring the measurements home written down. They are the baseline you will check every clearance against during assembly, and they are your evidence if something has to go back.
Inspecting the block
| Check | What good looks like |
|---|---|
| Bore surface finish | Uniform crosshatch at roughly 45°, visible but fine. NO longitudinal scratches running up and down the bore. Smooth shiny spots mean the hone didn't cut evenly. |
| Bore size measurement | Ask for the measurement sheet. All bores within 0.0002" of each other; taper (top to bottom) under 0.0001". If they can't provide measurements, that's a problem. |
| Deck surface finish | Perfectly flat with a fine, uniform machine finish. No waves, high spots or rough patches. Against a straight edge there should be zero light gap anywhere. |
| Oil passages | Thoroughly cleaned. Run a bent wire into every gallery and blow compressed air through. One casting chip left in a gallery can destroy a bearing within the first hour. |
| Main bearing bores | Perfectly smooth and round. Any fretting, scoring or debris indicates a problem. |
Inspecting the cylinder heads
| Check | What good looks like |
|---|---|
| Valve seating | Blue Dykem on the seat, install the valve, rotate 45° — the Dykem should wipe uniformly all the way around. Any gap means the seat isn't concentric or the valve face isn't flat. |
| Deck flatness | Straight edge and feeler gauges. Maximum allowable warp for most applications is 0.002"; a properly surfaced head should be 0.001" or better. A warped deck blows head gaskets. |
| Guide clearance | Wiggle each valve stem side to side. Minimal movement — 0.001"–0.003" intake, 0.002"–0.004" exhaust, application dependent. Excessive slop means worn guides that weren't repaired. |
| Combustion chamber volume | For a performance build, chambers cc'd and matched within 0.5 cc. Volume differences change compression ratio and unbalance power output cylinder to cylinder. |
Red flags — walk away or get it redone
- Shop can't provide measurements — "we set it to spec" without documentation
- Block returned with visible casting flash or debris in the bore
- Deck or bore shows witness marks from previous machining that weren't cleaned up
- Head gasket surface shows waviness against a straight edge
- No crosshatch pattern visible in the bores (under-honed means the rings won't seat)
- Oil passages not thoroughly cleaned — look for discoloration and debris
- Work was done faster than it physically takes (a proper bore and hone takes time)
- No torque plates used when honing for performance applications
- Price dramatically below market rates — cheap machining is expensive in the long run
Questions to ask every machine shop
- "Do you use a torque plate when honing?" Essential for performance builds — it simulates head bolt stress on the bore.
- "What is your bore-to-bore consistency spec?" The answer should be within 0.0002".
- "Do you provide a written measurement sheet?" If no, that is a warning sign.
- "What equipment do you use for boring and honing?" CNC equipment is a good sign.
- "How do you clean the block after machining?" The answer should be hot tank or jet wash, not a spray with the garden hose.
- "What is your normal turnaround time?" Rushed work cuts corners.