My son and I are restoring a 1956 6400 with a 261 engine. (I have a journal in the "Project Journal" section. In any event, we are strongly considering upgrading this to a spin on full flow oil filter. It currently has a by-pass filter on it. This engine in a replacement, made in March 1958. I believe it was a dealer installed engine, but in any case, the engine has no serial numbers stamped on the deck by the dist, so I do know it came from GM parts. It has the dowel in the side and the 1/2" oil outlet and inlet ports. It also has a 1/8" port at the outlet. Someone at some time, probably when the engine was replaced, brazed a "T" in the return like from the filter and connected the oil pressure capillary tube to it. Thus the pressure on the oil pressure gauge is reading from the filter. These are both pretty small lines, so I am fairly certain it is by-pass. I was looking at another site, and there was a photo of a dowel in the side of the block that is almost flush. As I understand, this dowel in this position is for by-pass, and if it is pushed in, the large oil outlet and return ports can be used for a full flow filter. Can someone who knows these chime in and let me know if I am on the right track. How is the dowel moved. Do I just push it in?
Also, can you post a few more pictures of the entire right side of the manifold side of the block? You posted a good picture, but, a little closer look at “details” might be helpful. There are a couple “plugs” on the full-flow-capable block.
This should help us determine if the block can be configured for a full-flow oil lubrication system.
Yes your engine is full flow capable, however as you said it is in the bypass mode. I left mine in the bypass mode because I was unsure of the ramifications of pushing the pin in. Once it is in there is no going back. How far does it go in to get into the full flow mode, I have heard about 1/2" but cant say for sure. Thinking you could use a suitable 40oz hammer and correct size punch. Interesting to know my 62 year 261 was delivered in a cab front truck and delivered in the bypass mode from the factory.
Last edited by sstock; 03/07/20212:46 PM.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Getting that dowel to move after it's been in one position for 60-something years can be a challenge. Pounding on a stubborn dowel pin could drack an otherwise serviceable block. I'd suggest using a good penetrating oil like KROIL (www.kanolabs.com) with the engine rolled onto its side for a couple of days so the oil can puddle over the plug, followed by moderate heat applied to the block near the dowel with a torch, before trying to drive it into the "full flow" position. I'd also suggest drilling and tapping the dowel for a bolt thread, so a slide hammer puller can be used to reverse the procedure if necessary. If I ever decide to run a full flow filter on the 261 I have with the dual capability, I'm going to pull the dowel out, thread the block for a fine thread bolt, and fabricate a dowel from an Allen head bolt so I can screw the plug in and out, with a jam nut to keep it secure.
That covers the "how"- - - -let's examine the "why" behind the procedure. Full flow oil filtering is far less efficient at keeping oil clean than flowing a small volume of oil through a tightly woven filter medium and removing contaminants that will pass through a full flow filter. In order to flow enough volume to keep the engine lubricated it's necessary to flow a large volume of oil through the filter quickly, so the pores of the filter media must be fairly large. Smaller particles won't be filtered out. For really good cleanup of the oil, an engine should have two filters, a full flow for straining out chunks big enough to damage bearings and/or clog oil passages, and a bypass filter to catch the fine debris. There are some hydraulic fluid filters that can trap particles down to 1 micron in size, much smaller than even a normal bypass filter can catch. Ditto for Diesel fuel filters.
Some carburetors have a fine mesh brass strainer screen at the inlet fitting. Training material from Carter carburetor company used to claim that the screen was there to catch "rocks, marbles, and bowling balls". A full flow filter serves the same purpose for motor oil. For really efficient oil filtering, rum BOTH types of filters. Jerry
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