The Stovebolt Site Forums The Shop Area General Truck Talk Inline durability?

I have no idea how many miles are on the 261 sitting in my garage so I'm going to rebuild it. Assuming I maintain it properly and don't run it for extended periods over 2500 RPM how many miles should I expect it to last before it needs another rebuild?

I'm not the complete expert on this, but I have heard from others around here that about 60k is a reasonable number of miles for most of the older inline 6's.

I'm sure someone will correct me on that. I'm deciding to rebuild or simply fix at this point myself.

I have 160,000 miles on my 250. It has never been messed with other than regular services and a new carb. I'm planning on rebuilding it this summer because it leaks in about 5 places and its coming with me to college next fall.

In the days when these 261s were new, 60 to 70k seemed to be a reasonable figure. I have a feeling that today's oils will change that figure to something much greater. We had a 1960 Pontiac from new with a 261 and it started smoking at about 70k. We has a "ring job" done and it was good as new. Oh, I forgot to mention that we didn't have an oil filter on it, imagine that!

I would think that with todays modern lubricants,and much better steel,alloys in the rings,etc.and better bearings they would at least double the old 60,000 mile figures.Just my opinion.

If you change the oil regularly, and don't flog the engine to death (i.e. just take it easy) those old engines should go a lot farther than 60 to 70k.

I would do a compression check first...If You
have no knocking, or smoking, I would drive it...
Bill B

Been running my stock late 235 daily for 11-1/2 years now and about 90K miles, mostly under 3000rpm.
I got it when it was already 10 years past the last rebuilt, so probably 150K and over 20 years daily on the road.

I just replaced the head. Oil pressure is to spec and compression is very high and even and it doesn't burn oil.

I'm having a late 261 built for me right now.
Mostly stock, but with 254 cam (very mild) and electronic ignition.
Building for performance gives very little gains under 3500 rpm. The later 235/261 engines run practically forever if you keep it mostly under 3000 rpm with regular oil and filter changes.

Keep the oil changed & you should get way north of 100K.

The other best thing you can do is keep the carburator well tuned. Rich running is very bad for piston rings- it washes the oil off the cylinder walls and wears them. If you keep the carburator well tuned or switch over to fuel injection you will get a clean burn and a long life from the rings.

The 235 in my truck has 58k original miles. It sat in a garage for about 15 years and was used very infrequently until I got it in 2003. It has a few oil leaks, but runs terrific. Nothing has been done to the engine except for regular maintainence. I have added HEI and dual exhaust if that counts. I'm not sure if any work was done to the head before I got it, but it seems to run just fine on unleaded. It doesn't smoke or burn oil and I can get up to 20mpg if I'm easy on the pedal(I usually get 16 - 17mpg). Even so, I'm replacing it with a warmed up and righteously built 261 in the coming months. I'm betting it will last longer than I.

One point that should be remembered is that the 261 uses babbit bearings. I don't know how much difference that makes; I can just remember my adventures as a brash youth and the two 261s I had that threw rods. I got tired of grinding the caps...If it were me I would sneak a 235 in there. My .02

big chevy 3600,I think you are referring to a 216 and not the 261 engine .

Mine had 236000 on it when I got it, it had never even had the head off. It did need a rebuild, though. Burnt valve on #5, and several of the rings were broken. I think if the maintainance is kept up, they'll go as long or longer than any modern "throw away" engine in todays cars.
BTW-It is the 216, not the 261 that has the babbit bearings, though I do beleive that the early low pressure 235 had the babbits also.

The stock 261 had more provisions for durability than the 235, and were designed so to run the large 2 ton work trucks. Stellite hardened valves w/ rotaters, large radiator, the bypass thermostat, and the head with the "steam" holes mainly.

my 216 has 93000 original miles or so, and best to my knowledge it has never been rebuilt(i know the previous owners, and the trucks life history pretty well), it purrs like a sewing machine. i have done little thinks to it for its own good- a carb rebuild, valve cover gasket, new plugs every 2 years, about every to 2-3 tanks of fuel i put a little lead additive into gas, i run regular oil in it and change oil every year (thats about every 1500 miles) i try not to run high rpms, because it has the babbit bearings

I have depended on both 216 and 235 ci sixes all ny truck driving life-about fifty years so far- and found them to be the most durable and dependable engines ever built!! Expect at least 150 thousand miles before some wear begins to show up in oil use and loss of compression. It all depends on how you drive and service them. I change the oil and filter every 3,000 miles and drive a decent speed. Also regular tuneups and filter changes for air and gas is required. I think GM stopped making the 235 engines in in 62 because the lasted too long..the same for the 261 a very close kin of the 235...

I got to stop this speed reading... :hammering:

My gmc 270... roughly equal to the 261... went 270,000 miles without a rebuild. I changed the oil once every 60,000 miles or so... It was leaking a quart of oil between every 2 fillups, so I just kept adding oil to it. Purred like a kitten and started right up till I finally decided to tackle that oil leak and rebuild the engine.

I had a 1949 chevrolet 1 ton( 9ft box)WITH A 250 that read 392xxx or so before the odo & speedo went kaput in 1999. i parket it 2 1\2 years ago due to rear end failure.

NOT FOR SALE

NO PICS

IT WAS MY GRANDFATHERS

NO IT WILL NOT SET AND RUST

Until my first new car in 1987 I never owend anything with less than 100K and mostly we would get them at 150-200k.

Ran 250 sixes for years. 425k on my 67 Biscayne, needed a rebuild at 250k and we just kept drivin her. Oil change every 3k and kept tuned up. When it went to the J yard (broke in half) it had 8:1 in #5, 2:1 in #3, and the rest were 5:1.

My 1982 P/u is on its 2nd motor at 52k. 1st gear in cow poop and an oil change every now and then.

Be nice, keep oil changed and carb adjusted, and lotsa miles are there.