So, what I have is a fully rebuilt 261, which I have already done the 20mins @ 2K RPM break-in run. Following this, I had trouble starting it, as I found a vacuum leak after I removed the vac gauge I had on it. Now I want to readjust the timing and the carb as well.
Since I have a flywheel off of a 216, I don't want to go by the markings on it and instead use the vac gauge to tell me where it needs to be. I found that max vac of 24lbs was WAY before the ball bearing(to the right of it), which I believe means retarded? I played with the throttle adjustment and fuel/air needle (which I honestly can't tell where it sounds best) and this is what it sounded like:
I turned it off to try starting again and it wouldn't fire at all. I adjusted the distributer clock-wise to where it should be 5 degrees before the ball-bearing and it will start and run, but it's around 20lbs of vacuum. Should I ignore the highest vac and just keep it in this general timing? Also, what should I be looking for with the fuel/air adjustment and what is a realistic RPM, as I believe the manual for this engine (1960) says 450RPM. Thanks!
Vac gauge for idle mixture screw and curb idle speed is a pretty universally accepted method.
You will get far less consensus on this message board regarding TIMING with a vac gauge. Some like it, some don’t. However, I would say that even those who use vac gauge for timing would say that max vacuum is a reference point, but then you have to back it off “a bit.”
I can’t get your videos to play sound, but if timing was causing a no start, it’s obviously too much. Should be able to hear/ feel it kicking back against the starter if it’s that far advanced.
The ball itself represents 5 degrees BTDC on many of these flywheels, but I can’t say that’s the case for you. My engine likes quite a bit more timing than the 5 degree ball.
Around 20in vacuum at idle is fine...very good in fact. 18 is fine also. Did you check the 216 flywheel with top dead center of the 261? Idle speed ought to be around 450~550 with 500 being a nice medium. Sounds like yours is running too fast. At a certain rpm point you'll transition from your idle circuit to the "off-idle" circuit and it sounds like you're at that point.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
It wouldn't be that hard to find TDC then mark the balancer and timing cover, a paint pen would work. Maximum vacuum isn't worth anything if it won't start. Set it were it fires right up, runs smooth and shut's back off without any problems. Till you get some drive miles on it, you won't know what timing it's going to like.
So I pulled the plug and rotated to TDC, according to the piston and the rotor position. I labelled the flywheel with Deve's suggestion, so you can see the "1", which is just to the left of the ball-bearing.
The guy who dreamed up the "time it with a vacuum gauge" myth should have a 3 pound hammer applied to all his fingers the next time he gets within arms' reach of a keyboard! 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!
Waiting for them to come in to local FLAPS, then I will do the 'static' timing that Deve suggests. It looks like TDC is accurate on the flywheel, based on my previous pic, so that would make the ball 5 degrees advanced ('5' is labelled on flywheel beside it. I supposed I will shoot for that for now and then adjust the carb. I don't really get the 'advanced until it pings under load and then retard until it doesn't'. I was trying to get 'optimal', but I will settle for 'spec'
You can still tinker with the timing once you get it set to stock specifications. So get the timing set to 5 degrees, set your idle speed to the proper specification, then adjust your idle mixture screw to get your best lean idle, then readjust idle speed. Once you have that set, now you have your base line. If you want to move your timing a bit, try 2 degrees to start and see if it makes any difference. How? Well that is the thing. Usually, a stop watch and two fixed points, or the race track. Or, you could just keep advancing it until the motor pings and back off a couple degrees. I am not so sure that is "optimal". On the other hand, lets say you drag another couple of horsepower out of the motor, so 148 instead of 145. I dont know that you would ever be able to quantify those kinds of numbers in a low HP motor. So me, with a nice running stock moor that starts and shuts off without any issues, I think I would be like Ron Popeil and just set it and forget it.
Optimal would be "advanced until just below when it pings under load." It is a seat-of-the-pants determination. Drive it up a hill under load and listen. Make an adjustment. Drive it up a hill. Wash, rinse, repeat until it pings them retard the timing and drive it up the hill again and listen. These engines were designed back when you never knew what exact octane you would end up with at a gas station. This issue was so prevalent that GM included an "Octane Selector" on the distributor so that the driver could compensate for the various octane gas one would run into. The octane selector allowed for changing the timing to keep the engine from pinging without losing ones place so they could reset it back to normal by using the marks on the octane selector. No timing light needed.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
Waiting for them to come in to local FLAPS, then I will do the 'static' timing that Deve suggests. It looks like TDC is accurate on the flywheel, based on my previous pic, so that would make the ball 5 degrees advanced ('5' is labelled on flywheel beside it. I supposed I will shoot for that for now and then adjust the carb. I don't really get the 'advanced until it pings under load and then retard until it doesn't'. I was trying to get 'optimal', but I will settle for 'spec'
And there’s a fair chance your $25 points will be garbage.
Guess where that static timing procedure actually came from? 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!
I told Deve about it, and he included the information in his blog as if it was his own idea. It was originally used as a method of setting the ignition timing on 1928-31 Model A Ford engines by inserting a "timing pin" into a notch in the the camshaft gear through a hole in the timing cover, and adjusting the distribitor to fire the #1 spark plug. 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!
All great info, thanks. Would the octane selector be used in the road test? Or is it too limited in rotation?
My octane selector adjusts +- 10 degrees. Once you get the timing set "on the ball" with the octane selector set at zero, tThe octane selector works great for this because you can make the adjustment without using a timing light. And you can put it back where it came from if you don't like it. That's how I did mine.
Last edited by Bill Hanlon; 05/11/20222:57 AM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
One degree of movement of the distributor changes the ignition timing at the crankshaft two degrees, since the crank turns twice as fast as the distributor. It doesn't take much adjustment at the octane selector to make a big difference at the flywheel. Also, one degree of ignition timing over-advance once the best torque point under load is reached robs as much power as 5 degrees of retarded timing from the ideal setting. I've proved that repeatedly on dyno runs. Over advance is trying to make the engine run backwards. ALWAYS err on the side of "not enough" timing advance. That's why monitoring vacuum at idle while changing timing makes no sense at all. 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!
Tried again yesterday, static timed to the ball-bearing's 5degrees. Started but ran really rough, advanced it quite a bit and it ran better, but again, wouldn't start unless I put it all back again. Plus smoked out the garage. I think I might try timing it to actual TDC and see what that does. Just to be clear, as the rotor turns clockwise, the cam 'peak' should pass and just as the points close, this position should be slightly BEFORE the position of the #1 plug wire?
Just an FYI, a 261's point gap is .019" for new, not .022" that the 216 manual states, so that might also make a difference. I marked the 216 flywheel at TDC, so I won't be relying on the ball-bearing and we'll see how it goes...
Tried at TDC and won't fire at all. The rotor always seems to be right in between the plug wires. Do I have the distributor out one tooth? Should I pull it and give the oil pump one small tweak?
No need to pull the distributor. Just get the number 1 cylinder at top dead center on the compression stroke and turn the distributor until the rotor lines up with a cap wire post. That will now be your new number one wire. Tighten the distributor clamp. Put the #1 plug wire in that post and move the rest of the wires on the cap according to the firing order. Once you do this, take a look where the timing mark on the flywheel is. If it is not in the neighborhood of ball bearing, you may have a bad timing gear or a bad gear where the distributor meets the cam shaft.
Last edited by 52Carl; 05/13/202212:24 AM.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
Tried at TDC and won't fire at all. The rotor always seems to be right in between the plug wires. Do I have the distributor out one tooth? Should I pull it and give the oil pump one small tweak?
Are you certain you are TDC on COMPRESSION stroke?
Just asking here but how did you determine TDC? As for the rotor, something is amiss. If you are confident, really confident, that you have the flywheel marked at TDC for the motor, then bring the motor to TDC for No. 1 cylinder (the compresson stroke). Take a piece of chalk and put a vertical line directly under the middle of the No. 1 plug wire tower on the cap. You are putting this mark on the body of the distributor. Double check that you have the firing order right with the plug wires. Once you have confirmed the firing order on the cap is corect, remove the cap. The rotor should be pointed directly at your chalk mark. If its not, loosen the screw on the clamp, not the bolt for the octane selector, and turn the distributor until the rotor is pointing directly at your chalk mark. If your TDC determination is corect, you should now be very very close to, if not exactly on, TDC.
Remove all of the plugs and make sure they are clan, no soot. Reinstall. Now try to start the motor. It should start. If its not, then something else is going on here. With adequate cranking compression, spark, clean plugs and fuel, you should be running.
Mike - I have had it running already, did the 20 min break-in. I was just looking to adjust timing after fixing a vac leak. I will reset and clean the plugs again as you suggest and get it to go. It was running rough, so perhaps timing wasn't really all that needed attention.
It might not be. If you are running a Rodchester B, they can be really really pesky, particularily the power piston. Notorious for being stuck or frozen leading to over rich and poor running consditions.
Sorry it took me so long to respond to Jerry's comment below. Been out of town.
Originally Posted by Hotrod Lincoln
One degree of movement of the distributor changes the ignition timing at the crankshaft two degrees, since the crank turns twice as fast as the distributor. It doesn't take much adjustment at the octane selector to make a big difference at the flywheel. Also, one degree of ignition timing over-advance once the best torque point under load is reached robs as much power as 5 degrees of retarded timing from the ideal setting. I've proved that repeatedly on dyno runs. Over advance is trying to make the engine run backwards. ALWAYS err on the side of "not enough" timing advance. That's why monitoring vacuum at idle while changing timing makes no sense at all. Jerry
The radius from the center of the distributor shaft to the outer (curved) edge of the octane selector scale is 1.825”. So a circle with this radius would have a circumference of 11.467”. This circle has 360 one degree arcs, each being 0.0318 inches long. So twenty of them ( +10 to 0 to -10) on the octane selector scale should be either 0.318 inches long if displaying “crankshaft degrees” (2 crank rotations per distributor, each crank degree is ½ distributor degree — most spark timing specs are done this way) or 0.636 inches long if displaying camshaft/distributor degrees.
I suspect that the vacuum advance/octane selector shown below is an aftermarket knock off. The distance along the red curve from 10 degrees advanced to 10 degrees retarded measures 0.403 inches. If it were in “crankshaft” degrees the arc would be smaller at 0.318”. If it were in “distributor/camshaft” degrees it should be larger at 0.636”.
So the answer is “it measures closer to (but more than) crankshaft degrees than distributor degrees”.
Last edited by Bill Hanlon; 05/13/20228:37 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Ok, cleaned plugs, TDC - which is about 5-10 degrees retarded, probably got it to start around 5 degrees advanced (according to the ball on 216 flywheel) adjusted it to about 10 degrees advanced, which kept it running. Really rough though and lite popping sound out the muffler. I didn't want to mess with it anymore until I got some advice first 😉
Have you turned it in and out to see if it smooths out the idle and raises vacuum? 2.5 turns out is quite a bit. But every engine is different.
Depending how you unhooked the vac advance and how high your idle is set, that could create a vacuum leak. I don’t see any reason not to hook back up.
You should have enough timing now for it to run fairly smooth. If you’ve checked points gap, firing order, adjusted idle mix, etc᠁.I’d maybe start hunting for vacuum leaks. An unlit propane torch, or carb cleaner applied to manifold connections᠁carb base, etc. If you hear the idle change᠁you’ve found your leak.
(I also don’t recall if we’ve addressed valve adjustment, but my impression is that this thing ran ok in the past)
The guy who dreamed up the "time it with a vacuum gauge" myth should have a 3 pound hammer applied to all his fingers the next time he gets within arms' reach of a keyboard! Jerry
Yeah it is pretty funny stuff.
Kicking self for selling off my Taskforce trucks. Still looking for an LCF or conventional big bolt in decent shape.
As of 10-26-2022, A 55.2 Taskforce long bed now the work begins
Ok, cleaned plugs, TDC - which is about 5-10 degrees retarded, probably got it to start around 5 degrees advanced (according to the ball on 216 flywheel) adjusted it to about 10 degrees advanced, which kept it running. Really rough though and lite popping sound out the muffler. I didn't want to mess with it anymore until I got some advice first 😉
Didn't see this before, this engine has hydraulic lifters. Manual calls for 1.5 turns after lash is out. Deve calls for 1/4 turn... http://devestechnet.com/Home/ValveAdjust
I will reset and start again.