The Stovebolt Site Forums The Shop Area Engine Shop replacing distributor (261)

My engine is a 1959 261. It runs okay, especially at idle and when cruising. But step on the gas and it shudders and shakes, then cruises nicely even at 60 mph or faster. I've checked virtually everything it could be and my mechanic who is older than me wondered if the distributor might be the problem. He didn't look at it, I just told him the symptoms. So, I'm thinking if it needs to be replaced, why not go HEI? I did a search and found that a distributor from an early 80s V6 from an S10 would fit. They are available at my flaps, about $200. I could also check out the local wrecking yard. I am open to suggestions. Thanks.

Can you see the vacuum advance moving the distributor as you increase RPM?

Too bad you do not have a high-pressure 235 or 261 nearby.
I'd swap the distributors and see if the shudder/shake is from the distributor.

Might the jitter-bugging be due a problem with the carburetor?

Rather than shotgunning parts at the problem, which rarely works, why not try to diagnose what's actually wrong? A HEI distributor might be a good idea, but the one you're looking at isn't a drop-in fit. The 2.8 liter V6 distributor from the 81-82 S-10 needs some modifications to the shaft to drive the oil pump properly and fit into the stovebolt block at the right height, and the large diameter HEI from the 90 degree 3.8 liter V6 also needs some tweaking to fit right.

Start out by removing the original distributor and doing a complete disassembly, including the centrifugal advance system below the breaker plate. years of crud and congealed grease and sludge on the centrifugal weights and springs can definitely cause the symptoms you're experiencing. If necessary, find an old geezer mechanic who understands centrifugal/vacuum advance systems. Computer timing controls have dumbed down mechanics to the point that few "professionals" and almost no hobbyists are able to actually evaluate what's going on in a mechanical distributor.
Jerry

Had a friend with a similar problem a few years ago, it turned out to be old gas. It had only been in there a year but it was 10% ethanol, nuff said.
Aside from that I would be suspect too, the centrifugal advance in the distributor, the vacuum advance zeros out at full throttle so it wouldnt be that IMHO

The carb has been checked (Wrenchbender) so has the timing, fuel filter, vacuum lines, gas, ignition components, plugs are clean. The vacuum advance certainly does move the distributor as you rev it up.

Check the fuel pressure, then valve adjustment

Shudder/shake on acceleration is also a classic symptom of bad spark plugs and/or plug wires. Since plug "wires" are usually graphite-infused nylon string, a breakdown inside the insulation can cause a miss under acceleration load. That's a difficult problem to diagnose.
Jerry

Thanks for the replies. I think I will take the distributor out and have my mechanic look at it. I wouldn't know exactly what to look for. except for the obvious.

Is the accelerator pump in the carb working? With the engine stopped remove the air cleaner, look down the carb throat and move the throttle to wide open. Do you see a stream of gas shoot down the carb throat?

Its not all that uncommon for the mechanical advance in these distributors to be functioning poorly or not at all after 60 plus years. You can take the distributor apart to a pretty good degree (but not completely unless you remove the gear). Most of the obvious issues will usually turn up, excessive crud, broken pins, broken or missing springs, rust, frozen advance weights. So a good cleaning, lubrication where needed and reassembly many times will do the trick. That being said, the only real way to confirm whether you got it is to put the distributor on a Sun, or Allen or King distributor machine and test it out.

I just finished a rebuild a couple of weeks ago. Without taking it apart or cleaning, the mechanical advance was not coming in when it should have been about 1200 engine rpm late (Sun 404 machine). I took it apart, rust and crud and a lot of it, and one partially frozen weight that hardly moved. Once I had it clean and rebuilt, I put it back on the Sun distributor machine and discovered it was still not coming in correctly, still a little bit late. Swapped the springs from another distributor and finally got the mechanical advance to come in on time. But you need a distributor machine to really get this right. If your mechanic has one, you are all set.

Notwithstanding, you might very well consider the other advice you have received here and get a new set of wires on, and a fresh tune up, cap, rotor points and condenser. All low hanging fruit that will not hurt to do even if its not needed.

As for HEI, its a great ignition. Tom Langdon at Stovebolt Engine Co. sells the S-10 conversions all done and ready to install. You will need to do some wiring to get it to work properly. On the other hand, the points are reliable, easy to work on, and if any part of the ignition does let you down, its an easy fix. I run a points distributor in my very modified 261 motor, never misses a beat.

Okay, took out the distributor, I had Wayne the mechanic look at it. There is a very tiny bit of play in the shaft, he's seen them worse, he said. The insides, underneath are very clean, points are very good too. I'm thinking to look elsewhere for a problem.

Valves have been set a year ago or so, by truckernix. I can't check the fuel pressure without a tester, but the fuel pump is relatively new. Just checked the accelerator pump too, working good. Jerry, I haven't checked the wires. I put them in new and have likely 6000-8000 miles on them since. If the truck cruises fine at say, 3000 rpm, how could they fail by accelerating?

I also double checked all the spark plugs. I gapped them before putting them back in. I didn't need to alter them, they are all at .030 Still stumped, though...

Just for grins- - - -try another set of spark plugs. If the wires are that new, no problem. Sometimes wires get neglected during an otherwise good tune up just because they don't show any external damage. At 3,000 RPM each plug wire is carrying a minimum of 10,000 volts- - - -25 times a second. The greatest challenge a spark plug or a wire ever faces is acceleration- - - -I've seen firing voltage jump from 10-15K volts at cruise to 30K or more on a hard pull when monitoring oscilloscope patterns during dyno runs. It doesn't take much fouling to make a plug miss under load, especially if it's EVER been flooded enough to get the porcelain tips wet with gasoline. I've seen "clean" looking plugs that absolutely would not let an engine run- - - -swapped plugs and it fired right up!
Jerry

I like this one... Wich is very true.
I learned to always go back and referred to your bases. ALMOST ALL of them do not and just play the parts changing game.
I did learn at a very young age, grandpa told me... There is two kinds of mechanics, the real mechanics and the parts changer... You decide which one you want to be, but parts changers don't fly here....
The sad thing is, like most hands-on trade, it's a dying art.

To come back to the original subject, I would also suspect bad fire. Sometime the plugs might look good and have a nice fire OUTSIDE the engine, but do not fire good under compression. Remember, air is an insulator. 6-7:1 compression ratio is much more harder to spark. A good ol plug tester test plugs under pressure.
By the way, plugs are a good place to start if you want to play the parts changing game, there are cheap, and not always a bad thing to change, specially in an old engine causing problem.

J. F.

Since no one else has mentioned it............... New parts these days are not always GOOD parts. Quality is sub-par on all but NOS. So, just because you put new plugs, wires, points, condenser, rotor, cap on don't mean one or all isn't bad. Just saying!

I have 6 new plugs on order, hopefully be here this afternoon. Autolite 303s.

Champion RJ12YC, J12YC, RJ14YC or J14YC (R for Resistor), or the older equivalent RJ12Y, J12Y, RJ14y and J14Y, will also do the trick and are usually in stock at local auto parts place.

Replaced the spark plugs, no change. I know of a person nearby who might have a correct spare distributor. I'll try the swap, not sure when I can get to it. Thanks for all the suggestions.

If you go to an HEI the late 70's 250 inline 6 cylinder one is almost a straight drop in. Most will actually turn the oil pump but the tang on the distributor shaft is just barely in the groove of the oil pump shaft so some needs to be turned off the hold down shoulder. Speedway makes a hold down clamp just for this application. Early on they used a coil that was remotely mounted but I think all the replacement ones are coil-in-cap. A really good distributor.

Did you check the dwell. You might have a week coil, maybe to test, close the points gap a little, gives more time to the coil to charge.
Do test and go by elimination. Test, don't replace. It's free, and help you understand how things work, more you do, better you become at it, plus it's fun...

I used to love it when a vehicle would come into the shop with half a dozen new parts- - - -and the same symptoms as before the "mechanic's" repairs got started. We called those guys "wheelbarrow mechanics"- - - -roll a wheelbarrow full of new parts up to the job and keep swapping bits and pieces until something fixed the problem- - - -and NEVER take anything off. "It was bad anyway". Sun had a slogan on all their test equipment- - - -"We test- - -not guess!"

Shortly after I started teaching at a state trade school in Tennessee the retired former chief administrator of the tech school brought his truck in for repair. It was a 1955 International pickup with a 6 volt electrical system. The lead instructor had warned me about this one- - - -"It won't start when it's hot, and he won't let me put an 8 volt battery in it!" Sure enough, the vehicle had a new 6 volt battery, coil, rebuilt carburetor, rebuilt generator, voltage regulator, starter, big battery cables, etc., and a BUNCH of ground wires between the frame and the engine. It took me 15 minutes to fix it. While cranking, the starter had 5.3 volts applied to it (excellent)- - - -and the voltage at the coil primary terminal was 4.2 volts! When I reached under the dash and touched the back of the ignition switch, I burned my fingers on the loose, corroded primary wire terminal from the switch to the coil. One lug terminal and about 2 inches cut back to eliminate the charred insulation on that wire, and the problem was solved forever!
Jerry

I found the champion plugs you buy lately are crap. The one with black writing a I believe are a cheap imported. The older one with the red writing seems to hold Better. I pull all kinds of antique tractors, and the black writing ones are absolutely crap. I switched about 5 years ago to Autolite or Delco with better luck.
Might just be an idea but it also seems like the plated ones are easier to fool than the black one...

I have had others say the same thing to me about the champion plugs. I have not had any trouble or failures, even with the new manufactured plugs. That’s just my experience with them. I have been running them a long time, 40 years, so I will probably keep using them and the auto parts place always has them in stock.

I hope ACDelco doesn't fall in the category of "cheap imported ones".

Today I purchased 6, genuine ACDelco spark plugs, R45S.
Listed on the box.....Made in China.

Looked at my other set of genuine ACDelco spark plugs, R43S...
Listed on the box.....Made in Mexico.