Most Chevy 350 small-block engines use two 3/8-16 starter mounting bolts. Variations exist by model and year, including some that use 7/16-14 or metric bolts; confirm with your manual or by inspecting the bolts.
Common sizes you might encounter
The mounting bolts that attach the starter to the engine block and bell housing can vary across 350 engines. The two most common sizes you’re likely to encounter are 3/8-16 UNC and 7/16-14 UNC. The exact length of the bolts depends on your block thickness, flywheel or flexplate spacing, and the starter model.
- 3/8-16 UNC bolts (two bolts) — the standard size for many Chevrolet 350 small-blocks.
- 7/16-14 UNC bolts — used on some non-chevrolet 350s or aftermarket/upgraded starters.
Note: The fastener length can range from about 1 in to 1-1/2 in, and some setups may require washers or spacers. Always verify with the service manual or by measuring the current bolts.
How to identify the correct size for your 350
To ensure you use the correct bolts, measure the existing hardware or consult official documentation. The steps below help you determine the exact size and grade needed.
- Inspect the current bolts: measure the diameter with calipers and count thread pitch per inch or per millimeter to identify UNC, SAE, or metric threads.
- Check the starter and engine block clearance: ensure the bolt length allows full thread engagement without bottoming out or hitting internal components.
- Consult the service manual or manufacturer specs for your specific 350 model and year.
- Choose bolts of appropriate grade (e.g., Grade 5 or Grade 8 for strength) and with corrosion-resistant finishes if needed.
If in doubt, bring a sample bolt to an auto parts store or use a starter mounting hardware kit that lists compatible models.
Practical tips for replacement
When replacing starter bolts, use fresh fasteners rather than reused ones if the threads are damaged or worn. Apply a light coat of anti-seize compound on the threads to facilitate future removal, and avoid overtightening to prevent damaging the starter or block threads.
Choosing the right grade and material
For most street use, standard grades (like Grade 5 or Grade 8 steel) are sufficient. If you operate in a marine or highly corrosive environment, consider corrosion-resistant options or stainless alternatives, but ensure the material does not promote binding or galling with the starter-mounting surfaces.
Summary
In practice, the typical starter bolts for a Chevrolet 350 engine are 3/8-16 UNC, but variations exist by model and year. Always verify size and length against the specific engine installation, service manual, or by measuring the existing bolts. Using the correct size and grade helps ensure proper alignment and secure mounting, reducing the risk of starter misalignment or failure.