After a long hunt, I finally found me a 261 about 70 miles from home the other day. Yesterday did some dirt rubbing and cleaning and here is what it is: Block number 3769717, Casting date C 1 2, Engine serial F0313LB Any info would be appreciated. I know it was a big truck because it had the big vacuum port on the side of the intake for the 2 speed rear end vacuum source. A couple head scratchers is it has a oil filter canister that was hooked up just like my 235 in the bypass mode. The big tapped oil ports had factory plugs on them and the dowel is remained flush with the block, I believe in bypass mode. So didnt all these engines from the factory have the dowel punched in for full oil filtration? Why was this engine in the bypass mode? Engine spins easy and is stock bore.
Another interesting note is this odd looking thermostat I found in the housing, looks like it says 160 on it, anyone have anything to say just what is the purpose of this? The water pump looked like a stock automobile one.
Carburetor looks like a bigger venturi and correct for the 261.
Head was casting 3836850 , C16 9. Exhaust valve on number 5 was stuck and the pushrod was bent.
Any input and comments will be appreciated, was thinking of getting it ready to go into my 53 3100
Steve
Last edited by sstock; 04/04/20192:16 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
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
Engine serial F0313LB F = Flint, MI plant 03 = March 13 = 3th LB = (in 1961) = base engine on the CLS60 truck
Head casting: 3836850 = 1954-1963 261 head Head casting date: C 16 9 C = March 16 = 16th 9 = 1959
That would be a real nice engine in your 1953 truck. - use your 1953 clutch assembly and u-joint cover/assembly - use your 1953 generator - use Pre '68 Dave's water pump re-locator (and your 1953 water pump) - if your 1953 truck has the 3/8" fan belt groove, it should match up OK with the 261's harmonic balancer's belt-groove.
You can use the by-pass oil filter.
The 261s usually had a different design/style thermostat. You can use the thermostat housing and thermostat from your 1953 engine.
Others will correct the above, and/or, provide additional information.
The dowel in the side of the block would need to be driven inward about 1/2" below the surface to put the oil system into the "full flow" mode. If you do that, you'll either need to install the correct canister filter and run 1/2" diameter lines, or run a 1/2" diameter bypass hose from one port to the other. With the current setup, you'll need to use a regular bypass filter and 1/4" diameter oil lines. That thermostat is a "bellows" type original equipment item. There was also a specially designed thermostat that allowed coolant to circulate through the engine but not the radiator during warmup on the big rigs, but it's no longer in production. The simplest way to assure proper thermostat operation is to use a 235-type housing without the big bypass hose system. Otherwise, some of the hot coolant can return to the engine without going to the radiator first.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thanks for the info Tim. I am 6 volt but this engine cam with a 12V flywheel big clutch arrangement that looks fairly fresh, so dont know if I will make the change. Are the balancers interchangeable and both cranks internally balanced? With the dowel in the flush position, I suppose I do not need to connect the big oil ports together with a large hose, is there really any advantage to running it in the full filtering mode. Did GM leave all there trucks leaving the assembly line in bypass mode?
Steve
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
I am about complete with an install of a 55-57 261 in my '53 3100, and here are a few things I have encountered. Please correct me if I word something incorrectly:
1. Use the Pre-68 Dave adaptor plate and 216 water pump to allow for proper fan placement. The machine shop can drill the needed holes for adaptor plate installment. But make sure the harmonic balancer accepts a 3/8" belt. 2. The 261 will not have the front motor mount holes drilled behind the thermostat housing. These will need to be drilled prior to installment so that the 216 front motor mount can be used. 3. A Delco 10-SI alternator can be used if the truck is converted fully to 12 volts. 4. The 216 bellhousing will need to be used, or else the 261 bellhousing will need to be modified for the rear motor mounts. 5. Thermostat housing from the 216 can be used with 180 degree thermostat. 6. The 216 fuel pump can be used.
This is what came to mind initially...I'll think of more later.
-Patrick 1953 Chevrolet 3100 261 / 4-speed / 4:11 / Commercial Red
Full flow filters really don't do as good a job of cleaning up the oil as a bypass filter. It's possible to run both types, with a VERY tight-weave filter element in the bypass canister, but a plain old Fram or AC bypass filter will do the job quite well by itself without going to the trouble and expense of adding a full flow.
It would be a very good idea to use the water pump adapter plate, as using the low-mounted pump in your truck will create fan position issues and poor cooling. A 216 or 235 harmonic balancer is a direct swap. Use whichever balancer, water pump and charging system that will have the correct belt width for all the components. If you decide to keep the 12V flywheel, you'll also need to go with a 12V starter. It will have a shaft diameter of 1/2" instead of the 5/8" shaft of the 6 volt unit. Of course, that will also require converting the whole truck to 12V.
The 850 casting number cylinder head is correct for a 261. If you choose to use an 848 head, read the tech tip on how to drill the "steam" holes for correct coolant flow. It will increase the compression and result in a little more power and torque. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Panel Fan - the '848 head will work fine on the 261, but it will need to be drilled for the 3 pairs of "steam holes" that are in the block and '850 head, to assure proper cooling. Use a 261 head gasket as a template, and note that the holes are slightly angled toward the driver's side of the head to assure they meet the water jacket in the head. Scroll down in this post, and you will see a diagram showing the angle of the holes drilled in the head: 848 "Steam Hole" Drilling Angle
Congrats on the engine. re. thermostat. It's an old bellows type thermostat from back in the day. I've been running the one that came in my 216 for 6 years without any problems. It is a 160. I tried a 180 for a short time and went back to the 160. The 49 3100 was parked in 69 so that thermostat I'm still running is atleast 50 yrs old...... and still works...... Good luck. Pic Pic 2
There might have been a bypass oil filter RPO. RPOs are not shown in that Specifications Manual. Or (clutching at straws with this statement): you might have a replacement engine that came setup fo bypass filter, but was able to go either way..
Good point Tim, I'm sure it had to have an available rpo for the bypass oil filter. once those rods are pushed in, I doubt they could get them back out without a whole host of issues. Thanks all for your comments and input all. Even got the water pump adapter ordered from super pre68 Dave. Knocked about 57 years of dirt of the old boy today, sitting on the engine stand waiting for the next step.
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
Drill and tap that dowel, and you can push it in and pull it out at will, but I can't see a good reason to do so. Of the three 261's I've got on hand, only one has the full flow plumbing, and right now it's in the bypass mode. When I build it up, I'll probably set it up for full flow to strain out the rocks, marbles, and bowling balls, and also use a Frantz type toilet paper filter to really clean up the oil in bypass mode. The Cummins 855 cubic inch inline engines used both full flow and bypass filters at the same time, so the concept is at least 60 years old. Wix has bypass type spin-on filters that go down to 1 micron filtration for people who don't like changing a cartridge type filter. A roll of cheap toilet paper gets down way below even that level of filtration. Most full flow filters are at the 10-15 micron level or larger because they have to flow enough volume to keep all the bearings lubricated. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
To do that Jerry , would a standard oil pump suffice or would a high volume be required? I have been schooled by Pre68 Dave that the top ends did not need a lot of oil, he points out the change in design on the groove in the rocker in 1958 was to limit amount of oil in the rocker cover. Planning a few upgrades on this engine, entertaining the idea of machining a one piece rear main, as well as drilling the snout of the crank for a retainer bolt.
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
There's no such thing as a "high volume" pump for a 235/261, at least until I get through making an adapter to use a small block V8 oil pump on a stovebolt six. That project is in progress right now. The Melling M45 pump is as good as it gets right now, and one of them on John's 261 was making 70-something PSI during the initial run-in. That should be enough volume to handle all the oil filtration that even I could dream up, IMHO!
While you're drilling and tapping, also thread the camshaft snout and use the same push tool that you use on the harmonic balancer to install the timing gear. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
