The Stovebolt Site Forums The Shop Area Engine Shop How can I tell if my 350 is a 4 bolt main?

Hello!

Engine in question is a '70 350/300HP out of a Kingswood station wagon.

Any way I can tell if it's a 4 bolt main without pulling the pan?

Thanks...

Chris

Get the casting # off the left rear corner of the block.

That's not 100% proof, though. GM built plenty of 2 bolt main engines using the same block as the 4 bolt main. The casting number is a good start, though, and the serial number stamped on the front of the block will help, too, by identifying the original aplication. Other than that, you really need to pull to pan to know for sure.

Fiber optic camera through the drain plug will also do it. Some shops have them around these days for sound diagnostics without disassembly. If the engine is in a car where you can't pull the pan this could be an inexpensive option.

All of the fiber optic borescopes I’ve looked at are in the $300 range, add a camera to that and your looking at a grand. That seems like an expensive way to look inside the crankcase, unless of course you happen to have one in your tool box. I’d go along with Jerry on this one, if it’s out of the vehicle I’d just roll it up on the bell housing and unscrew the pan before I spent that kind of money.

DG

Just for your info, I had a 1970 Chevelle with a 350/300hp. It was a 2 bolt main. If memory serves correctly, most 350/300hp motors were 2 bolt mains.
don

As mentioned 350's with the casting numbers ending in "010" come in either 2 bolt main or 4 bolt main. From my experience the 4 bolt main blocks came in LT-1 motors and in heavy duty 3/4 ton and above trucks.

I am not not suggesting buying one of these inspection cameras from Harbor Freight but the $89 one looks interesting. It looks like it uses LEDs instead of fiber-optics for illumination.

I have one of those HF cameras. The camera end is too large to fit down the dipstick tube, as it's just a tad over 1/2" in diameter.

I doubt a 1970 engine in a station wagon has 4-bolt mains. Usually, the 4-bolt mains were used in the ultra (not that 300hp is not high performance in the day) high performance engines (i.e LT-1) and all truck engines.

The stock 350 CID engine in my 1971 RS Camero was a 2-bolt main that was rated at around 270 HP (I think). I ended up building my own LT-1 from the GM parts department and salvaged truck block and 2.02 angle plug heads.

The stamped ID number on the front of the block ahead of the passenger's side head will have a "T" in the suffix following the numbers on 4-bolt engines. I used to identify them that way when we were searching salvage yards for engines to build for the round track.
Jerry