The Stovebolt Site Forums The Shop Area Engine Shop Small Hole in Block Behind Exhaust Pipe Flange on 261

I was filling the cooling system of my rebuilt 261 tonight when the coolant started flowing out a small hole in the block just behind the exhaust pipe flange.

It's too dark and cold on the driveway to investigate further tonight but what the heck is that hole doing there? A block petcock is at the rear of the block and low for good drainage. I'm going to put a threaded plug in there tomorrow but what's the purpose of that hole?

Thanks!!!

That hole is where the throttle pivot goes in some applications. It should be threaded 5/16" coarse.

Wrap a 5/16" stainless steel bolt with some teflon tape or teflon thread sealer and screw it into the hole, unless you are using that hole for you throttle linkage bell crank. Seems kind of strange that a bolt hole will go through into the water jacket, but it does. I guess it's an emergency coolant drain.

This is a very small hole like the one on the distributor side of the head that has the square-head plug in it. That one was drilled to provide an oil passage to the middle of the head and the oil connector. You can't even see it when the exhaust pipe is connected to the manifold. My throttle pivot is on a raised surface so it wasn't drilled all the way through.

Is there some kind of water passage on a 261 that was needed inside the block? Could this be related to the extra water holes between the block and the head of a 261?

I'm going to get a plug for it but it is smaller than 1/8" pipe thread which I tried last night.

Thanks!

Wally, up to 1959 there were two spots for throttle pivots, one 9 1/2" from rear of block and one at 12 9/16" from rear. The front hole is not raised very much and is drilled through to the water jacket. Both spots are threaded 5/16" corse thread.

Dave is the resident hole expert.

Wally, my 261 came out of a school bus, it had the throttle pivot in the hole. I didn't put it back in and when I filled it up with water to start it, it came running out.Maybe the engines in the larger trucks used that position for the pivot.? Did your engine come out of a large truck or bus?

Tommy, Laissez le bon temps rouler!!! (Pardon my French.) We went to one of your Metairie Mardi Gras parades a few years back! Those step ladders modified to hold 2-3 kids on a shelf to watch the parade were great. Some had wheels and were used like a cart to haul an ice cooler around.

Thanks, guys. The engine man had the 261 so I don't know its source. It is indeed a 5/16" 18-thread hole. I had a hard enough time with my throttle pivot. I don't know how they could have used that hole.

Thanks, again, especially pre-68 Dave!

Wally,FYI,the 216 only had the front hole. If you are using the rear hole your linkage has been modified

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