SBM 340 Rear Main Cap
Here are four rear main caps from different size LA engines. Bottom to top: 1965 273, late 80’s 318, 19?? 340, X- block 340 with 360 oil pan configuration. I lined up the block surfaces and the web thickness, bolt bosses, and oil pump surfaces are nearly identical. As far as I’m concerned, there isn’t a lick of difference between any of them. And from a strength strand point, the front and rear mains don’t carry nearly the load that the middle three do. That’s why when they put four bolt mains on the XNR blocks it’s only the middle three to get them. Supposedly the 340 has thicker web on the middle three than the 318. Maybe tomorrow I’ll pull out the rest of the middle mains and compare them to one another and take some measurements. I did that a couple years ago, and it didn’t seem to me that the differences were very significant at that time.
Here are four rear main caps from different size LA engines. Bottom to top: 1965 273, late 80’s 318, 19?? 340, X- block 340 with 360 oil pan configuration. I lined up the block surfaces and the web thickness, bolt bosses, and oil pump surfaces are nearly identical. As far as I’m concerned, there isn’t a lick of difference between any of them. And from a strength strand point, the front and rear mains don’t carry nearly the load that the middle three do. That’s why when they put four bolt mains on the XNR blocks it’s only the middle three to get them. Supposedly the 340 has thicker web on the middle three than the 318. Maybe tomorrow I’ll pull out the rest of the middle mains and compare them to one another and take some measurements. I did that a couple years ago, and it didn’t seem to me that the differences were very significant at that time.