2010 at the Hammond Barn

[Phil Waterman]

Originally Posted by Bob Carriere

Encountered a slight technical difficulty on SUnday while driving my C15a chassis.

AS you know Rob and I have had our stock Rochester B carburators rebuilt and flow tested by the Oak brothers in TO. Both our vehicles now run so ever much better...... and they look brand new.

Well I was driving mine in the back field using just a fast idle setting when I decided to see if it would climb the steep...45 degree... pile of wood chip located in a corner of the back field. Amazing.... in low gear.....few times and noticed that at a steep angle the carb was flowing raw gas ...literaly dripping gas...... not a good thing if all those fumes could collect inside the engine compartment......did not seem to affect engine performance...

I raised my problem on the Stove bolt site and CarbKing confirmed that I may have exceeded the design of the civilian Rochester B carb which is intended for flat street driving. .... He recommended sourcing a military carburator that would have been original on a GMC 270 engine.

Phil have you had any similar experience with your new 261/Rochester combo?

...
Bob

Hi Bob

Interesting issue, maximum angle of operation for Rochester B Carb. First I'll have to do some checking in Chev parts book remember seeing that 261 engine was fitted in heavy 4x4 Chev trucks. I'll look to see if a different carb or float setting is listed.

I have another NOS B Carb on the shelf I'll hook it up to the electric fuel pump and see what happens at various angles. Problem may be something stupid like that the current electric fuel pumps put out a little more pressure than the stock manual pumps as originally equipped. I'll check numbers but I think it is putting out 2-3 PSI more than needed.

Did discover something that you may want to take into consideration if you are going to operate your 261 at extreme angle, keep an eye on the oil pressure. Discovered recently that my 261 at full song going down the highway is pumping so much oil up into the engine that if you hit the brakes going into a sweeping left hand turn the oil pressure will suddenly drop from 42 PSI to under 5 PSI momentarily.

I have the 261 4x4 sump oil pan but it doesn't have the lower baffle found on the military 216. My surmise is that when you hit the brakes and turn left the oil sloshes forward away from the oil pickup allowing it to suck air for a moment. This doesn’t show up on the normal instrument panel gage which are slow reading due to their small tube size on my CMP with the standard 216 oil gage that reads 0-30 SI it is pegged almost all the time. I installed a second fast reading pressure gage which reads 0-80 PSI this one shows the pressure fluctuations. Got to do some more research on this issue.

I have done some studies on what grade and side angles the original 216 systems could work at, I’ll have to put the pictures and notes together and post them.

[gjamo]

This fuel starvation issue at extreme angles is why Dodge came up with their concentric bowl carby.
Graeme

[Bob Carriere]

Hi Graeme....

Tell me more about this egocentric carb..... what model - year-application are we talking about...??

Strange thing about the Rochester....while leaking at that funny angle the engine never missed a beat amd kept running at the same RPM..... I would have expected it to flood or starve....

Bob C.

[Alex Blair (RIP)]

Originally Posted by Bob Carriere

Hi Graeme....

Tell me more about this egocentric carb..... what model - year-application are we talking about...??

Strange thing about the Rochester....while leaking at that funny angle the engine never missed a beat amd kept running at the same RPM..... I would have expected it to flood or starve....

Bob C.

Bob..They are similar to the ones on the Volvo's you have sitting in your back fourty..
I used to repair..clean and tune my dads '63 Volvo wagon when I was just home on leave from the Air Force..
Leaned about them from an old Dutchman that was the only resident expert on them for Volvo's in Halifax in the early '60's..
Here is the carb we are taking about(Not exactly like the Volvo ,but similar,,.)

http://www.ingfatrygg.se/amal.html

[Bob Carriere]

Alex

Those were SOB sidedraft carbs...... how does it compare to the Dodge carb Graeme is referring to...?

Now you are going to tell me that all those Volvo carbs/cars that we sent to the junk dealer were priceless.... !!!!

Bob

[Bob Carriere]

Interesting comments about the oil pressure..... I was so busy staying in the seat and watching the raw gas leak out I never checked the gauges. As you know I have extra mechanical guages for the test runs. The strange part is that even at high angle the engine never faltered.....same steady fast idle.... and I repeated going up the stack of wood chips at least 3 or 4 times....rear end of the frame was almost dragging on the ground.

Will try a repeat performance this weekend if the weather cooperate and I can get a Rob to video the event.

Now I am concerned about dropping oil pressure..... it may be that with such a short duration at high angle and with the two large spin on oil filters it akes a while for the air to travel in the line by the sensor for the gauge.

In any event it seems I need to find the kind of carburator that may have been installed on the GMC 270..... but.... from my 1955-59 civvy GM manuals they show and list the same Rochester B as the 261.

CarbKing from Stovebolt recommended the YF879S as an alternative.... foundout they were used in Internationals 6 in the 261 to 282 c.i. size.

So far no such carb is for sale with any of the carb places I checked on the web.

This weekend I will dig out a spare intake manifold and design a jig that will allow me to test various carburators at different angles.... basically an oversize protractor..... load up the carb bowl with red diesel ... less danger... and have a one gallon tank piped in above the carb to simulate some line pressure......tilt by hand an record finding. Will photo for the record.

I will try out a proverbial W-1 for base line followed by various Rochesters and YF that are the wrong size but basically same configuration. I even have a nos military 235 mid 70 Rochester that I can try....

While rummaging in the various boxes of spare carbs I found one I had squirrelled away back in the mid 70s....NOS taken from a 6 cylinder military engine stored in old plywood box.... it is the waterproof type....Holley I beleive and double barrell..... possibly an early 2 1/2 deuce.... will show to Grant he should recognize it.....According to pictures in an old motor truck manual circa 1953...Carb is a Holley 885ffg from a large international engine....or a GMC 270 or 288 c.i.

The other more dangerous but more fun plan is to run the engine at fast idle and lift the front end gradually with the front loader of the tractor and record oil pressure and leaks at various angle..... than lift the rearend and repeat the tests.....

The oil pressure issue maybe easier to solve with baffles, a in-line pressure tank with a gallon capacity like the extreme 4x4 rock crawler use to maintain oil pressure...... or a dry sump hihihi.

I am more concerned with raw gas leaking around a hot manifold within an enclosed engine compartment.....

There as to be a way as original 216 with Carter W-1 were tested in very steep hills just outisde Ottawa at the DND proving grounds.... they have various hill sizes.... the interesting ones are at 45 and the steep one at 50+degrees...... or may be it is just my imagination.... but the last one still visible from the road way would be hard to walkup on foot.....

So stay tuned and if one finds a YF 879 let me know.

Bob

[Phil Waterman]

Hi Bob

Can not remember are your filters mounted open end up or down? Reason I ask is that on my 261 in Beauty the filter is mounted open or screw-on end up and I always fill it with oil when I change it. In that position any air in the filter is immediately pushed through by the oil coming in. So as long as the engine is pumping oil it should flow through OK.

I tried an experiment with the 235 engine on the test stand mounting spin on filter closed end up screw-on end down. This leaves an air bubble trapped in the top of the filter. No evident effect on the oil pressure accept when the engine stops the oil pressure bleed down is considerably longer. Mounting the filter this way though makes changing them a mess.

Going up the hill should not be a problem as the pump and pick up should be in the deep end of the oil pan. It would be going down that the oil could flow away from the pickup. I retried my truck on steep down grade low RPM no noticeable pressure change. My oil pressure drop may only occur at full song on the engine 2800-3000 rpm. So I suspect that it just the amount of oil these pumps are pushing up into the engine.

As we discussed before the big spin on filters and the 1/2" lines running to them do act as an oil cooler. Takes a long time to get the oil up to operating temp.

Keep us posted on your carb angle experiments. Good idea using diesel fuel I was just going to use gas, but your way is safer, but how much more or less viscus is diesel and will that change how it goes past the float valve?

[Grant Bowker]

Originally Posted by Bob Carriere

In any event it seems I need to find the kind of carburator that may have been installed on the GMC 270..... but.... from my 1955-59 civvy GM manuals they show and list the same Rochester B as the 261.
Bob

TM 9-801 lists the CCKW as using Zenith carbs, type 28AV11 on early vehicles an type 30 BW 11GM on late vehicles. I have not checked the various TM10s to see if any very early vehicles used something else.

The C60X used a Zenith 28AVII (according to the maintenance manual)

The C15TA used a Zenith carb for the first jobs and a Carter Dustproof carb for the after jobs according to the parts book but the maintenance manual only lists the Zenith 28AVII.

Although the American and Canadian listings describe the Zenith carb differently 28AV11 as opposed to 28AVII (eleven as opposed to eye-eye) I suspect they are the same thing.