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replacing distributor (261)
#1269784 Thu Jun 21 2018 01:33 PM
Joined: Mar 2007
Posts: 4,992
Leo Online OP
'Bolter


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.

Re: replacing distributor (261)
Leo #1269791 Thu Jun 21 2018 02:35 PM
Joined: Sep 2001
Posts: 31,392
Bubba
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?



Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: replacing distributor (261)
Leo #1269797 Thu Jun 21 2018 03:01 PM
Joined: Feb 2004
Posts: 23,638
H
Kettle Custodian (pot stirrer)
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


"Freedom's just another word for nothing left to lose"
Kris Kristofferson

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!

WAG MORE- - - - - -BARK LESS!
Re: replacing distributor (261)
Leo #1269798 Thu Jun 21 2018 03:04 PM
Joined: Jan 2013
Posts: 1,677
S
'Bolter
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

Last edited by sstock; Thu Jun 21 2018 03:09 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
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: replacing distributor (261)
Leo #1269799 Thu Jun 21 2018 03:08 PM
Joined: Mar 2007
Posts: 4,992
Leo Online OP
'Bolter


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.


Re: replacing distributor (261)
Leo #1269801 Thu Jun 21 2018 03:11 PM
Joined: Jan 2013
Posts: 1,677
S
'Bolter
Check the fuel pressure, then valve adjustment

Last edited by sstock; Thu Jun 21 2018 03:11 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
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: replacing distributor (261)
Leo #1269802 Thu Jun 21 2018 03:12 PM
Joined: Feb 2004
Posts: 23,638
H
Kettle Custodian (pot stirrer)
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


"Freedom's just another word for nothing left to lose"
Kris Kristofferson

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!

WAG MORE- - - - - -BARK LESS!
Re: replacing distributor (261)
Leo #1269806 Thu Jun 21 2018 04:09 PM
Joined: Mar 2007
Posts: 4,992
Leo Online OP
'Bolter


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.

Re: replacing distributor (261)
Leo #1269813 Thu Jun 21 2018 05:18 PM
Joined: Nov 2004
Posts: 270
S
Custom Title
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?


49 Chevy 3600
48 International KB-1 Service Truck
55 Willys CJ5 - Chevy 331 powered
26 Model T Roadster Rat Rod
70 Tucker Sno-Cat 442-A
96 Dodge 3500 Cummins dually flatbed x-cab 4x4
06 Jeep Wrangler LJ rock crawler
If you can't fix it with a hammer, it's an electrical problem
Re: replacing distributor (261)
Leo #1269816 Thu Jun 21 2018 07:01 PM
Joined: Dec 2017
Posts: 1,036
D
'Bolter
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.

Last edited by Dragsix; Thu Jun 21 2018 07:07 PM.

Mike
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