Update on 216 to 261 engine switch

[Phil Waterman]

Hi All

Been working on the 261 engine which has the large full flow oil filter, while the 235 is running on the test stand to warm the shop.

In the picture at the top of this tread you can see the original full flow oil filter unit as used on the later 261 chevy truck engine. As I'm preparing the engine to start running it in I was working on the oil filter unit, comparing the original with the replacement spin-on type filter unit I plan to use. Couple of things I noticed one the original has a bypass valve if the the filter becomes plugged. It would seem a good idea as the new spin-on filter unit doesn't have this feature. So figured I'd find out at what point does the bypass open and discovered that basically always flowing oil and never really closing completely. With this in mind I guess the spin-on with no bypass is a more positive way of filtering the oil. It also means that if any of you are going to reused the original 261 filter units be sure to clean and check the filter bypass.

As to the 235 on the test stand this particular engine has the hydraulic valve lifters and valve rotators on the exhaust valves. While the engine sounds pretty good and getting better all the time, when you let the engine sit for a couple of days and the lifters all have a chance to leak-down all the way it sounds like a cement mixer full of rocks when you first start it until the oil pressure comes back up.