The Stovebolt Site Forums The Shop Area Engine Shop Which 261 to build and balancing musings

My rebuilt 235 with only 40K on it sounds like it threw a rod. Still has oil pressure but has a horendous noise that is not in the valve train. Let go with a racket at betweeen 3 and 4 grand, 4 being my self imposed red line. I do like to wind it out on a regular basis. Anyhow, the silver lining here is that I have a reason to build one of two 261's I have in my garage. One is a 55 Pontiac and the other is 63, yes the date code is 63, Chevy. Patrick say's he thinks some 261's were used in 63 4x4's, or perhaps could be a replacement block. The 63 already has full flo oiling and I know I can change the 55 to the same so this is not an issue. Other than that does anyone know of any differences that might make one better than the other? Both are drilled for hydrualics if I decide to go that way.

My other question is about what the machine shop I'm looking at tells me about balancing. They grind to get the weights of rotaing parts the same and then send just the crank out to be balanced. I thought everything has to be spun to balance the assy. Does this sound like half a job or am I missing something here?

Thanks, Grant

Hey Grant,sorry about the engine. If the full flow oiling is not an issue to you, any year 261 should be fine.I remember the early 261 has a different style of main bearing shell locating tang.I think it was changed around 1955.63 4x4's used the 261 in its last appearance. The later style main bearings are slightly less expensive.Check you blocks out carefully around the cylinder bores. I have seen a few with cracks running vertically on the thrust face of the cylinders. Have the rods resized, the ones on both my 261's were not done right from the factory.Balancing is a good idea.Inline six cylinder cranks are balanced seperately from the rods and pistons.If possible, try to deal directly with the man who balances the engine,less chance for a problem.If using stock style pistons, you may want to check the deck height carefully. Replacement pistons fall as much as .040 below the block deck.Try to keep the pistons no more than 20 thou below the the deck, heps promote turbulence and a faster burn.Running mild cams, I had absolutely no intake to piston clearance problem with .040 cut off the block deck, but check it for sure.We gonna line up the 261's at Wendall for a race of honor? lol

Hey Grant sorry to hear of your engine woes, I can relate. I hope you get your truck underway in less time than it's taking me.

I am probably gonna get some flak on this but I am dubious about the value of balancing an inline 6. Equalize the piston and rod weights, yes. Balance the crank - no. The Inline 6 is inherently balanced by virtue of the crank design, and any slight imbalance won't be a problem at the RPM turned by a street 261. I have built engines both balanced and not, and can honestly tell no difference in smoothness or power. Of course it won't hurt anything, and if it gives you a little peace of mind (especially after hammering a rod) then go for it. But if the budget is tight, having the crank balanced would be the first thing I would forego.

No flack here, sixpak,

However, since these old 6s have a longer crank, and only 4 main bearings, it is more susceptable to twist and vibration. Having a crank balanced is good insurance, to make sure the crank isn't WAY off balance to start with. Plus balancing is done with the rings, rod bearings, damper and flywheel in mind, so it corrects for those tolerances as well.

Trust me, bad crank bearings pull major vacuum.
My rebuild is 7 months and counting. Bad main bearing killed my 235.

chip