55 Roadmaster Engine Timing/Tuning

[buickbrothers]

I've gone back to try and get my engine running as it should be since I've put more break-in hours on the engine. It's getting closer to expected performance, but I know it's not dialed-in to the optimized level. Here's what bothers me the most, I can't get the car to run a 350 rpm to set the timing as the book states. Why is that? Things to know about that have been done beside the engine rebuild:

 

1. I rebuilt the carter carb. Used same original metering rods. I went back through the carb step-by-step and made some adjustments per documentation I found on Mikes Carburetor Part's website. I have the WCFB Climatic Control carburetor. These changes helped but I still could not get down to 350 rpm. I can essentially get to around 480 rpm with points being used in my distributor. I was getting a lot of fluctuation showing on my vacuum gauge at this rpm level. I'm not sure if I have a carb or distributor issue (or something else) preventing me from getting to 350 rpm. My dwell reading was 30.   

2.  I decided to swap the distributor. Now, don't shoot me as I know this is a sensitive topic in the forum and I don't want to start that debate. This distributor has the 1181LS pertronix vs. points. After the swap, I still couldn't get down to 350 rpm. However, the fluctuation showing on my vacuum gauge flattened out. Needle is barely moving from its' position. What is also interesting is that my dwell is reading 41. I can also get the rpm down to around 430 - still can't get to the 350 rpm.

 

My questions:

1. What are things to check that are preventing me from getting to 350 rpm?

2. What could have caused the vacuum gage fluctuation when running points vs. it going away when I swapped distributors?

3. Why the dwell change from 30 on points to 41 on pertronix?

 

I've consider putting the points on the swapped/installed distributor to see if it was a mechanical issue with the first distributor vs. the points/pertronix obvious difference. So you all know, I did wire the pertronix to keep the ballast resistor in the path (I left my same original coil in as well and didn't install the flame thrower coil):

 

         

[JohnD1956]

Have you scrutinized the carb linkage set up when you have tried to get the RPM down?  Specifically, is the idle adjustment screw still bottomod out on it's boss when you are turning it down,, or is there a gap between the base of the screw and its boss?  

[old-tank]

Measuring dwell with electronic ignition is meaningless.

The vacuum gauge fluctuations are probably due to unequal lobes in the distributor.

Idle down?  Engine dies before the idle gets down to that RPM or physically cannot turn screws to get it down to that RPM.

Return spring location incorrect?

[buickbrothers]

To make sure we are in sync, are you referring to the fast idle cam screw that touches that boss? If so, it's backed completely off the cam - doesn't touch. Then I attempt to back out the throttle adjustment screw which does starts to lower the rpm. However, I can only go so far and then the car starts to die.   

[buickbrothers]

I'm beginning to think I need to contact a priest and have an exorcism done on this car. It just seems to be fighting back on every single thing you try to get working right! Sorry - just needed to vent! 

[buickbrothers]

Engine dies before the idle gets down to that RPM - not a physically cannot turn screws to get it down to that RPM. Please clarify "return spring"? Are you indicating linkage return spring or something else? It's correct per photo's before tear down. 

 

[NTX5467]

I'll start by admitting I do NOT know all of the intricacies of the earlier Carter 4bbls and how they relate to Buicks.  Or know where the timing marks might be, whether on the lower pulley, damper, of viewed through a hole in the bellhousing.  BTAIM

 

Also, if you desire to exactly match tuning in the manual to what the car/engine does, you'll need to find some low octane leaded race gas, rather than even non-ethanol fuel.  I'm presuming some of the instructions you  found on the carburetor service website might have had some alterations for ethanol'd unleaded fuel?

 

For those of us who grew up with engine hot base idle speeds, in gear, of 550rpm, 350rpm seems a bit unusual.  The ONLY reason to use that low of an idle speed is to ensure the mechanical advance weights in the distributor are in their "Zero advance" position and/or low enough manifold vacuum such that manifold vacuum level is below when the vac advance mechanism starts to advance things.  These specs were configured in a time when gas had lead in it and few people had something like a then-high tech timing light.  Vac gauges, yes.  So, set the idle speed down to where the engine is barely running to set the timing.   Plain

and simple.

 

I'm presuming you have a timing light.  So if the timing mark is in the bellhousing, when you get it set, you might consider putting a mark on a pulley and the engine block.  Basically making an easier-to-access mark for where the timing should be set when all is right.  Be aware, too, that dwell can affect ignition timing, degree for degree, as to variance from the desired 30 degrees.  

 

As to the electronic ign dwell reading, to me, it is an accurate number, but it is usually considered "not significant" as there is no way to change or adjust it.  It's still the same situation as with points, just done with transistors and such.  Of course, when you change distributors, you always check/set the timing anyway, so no way to test the two settings against each other with respect to base timing.  So, don't worry about it.

 

The observed 41 degrees electronic dwell reading is similar to what the old dual-point distributors ran, for better coil saturation and a hotter spark.  So, it should work better than single points ever could in that respect.  How much difference it would make?  Probably only above 3500rpm or so and when the engine is under full load, as in WOT acceleration.  The more stable vac readings with the electronics in control probably could be the result of the longer dwell, I suspect.

 

Remember, too, that when the factory idle speed specs were written, they were using a new carburetor with NO deposits in it.  You might have kitted the carb and looked to see that all was clean, but IF there might be any "hard" deposits in hidden passages (air or fuel), the cleaner will not touch them.  Such things have to be removed mechanically with twist drill bits, by observation.  I doubt the '55-era fuels used any additives which would leave such hard deposits, too.  Yet modern fuels seem to, otherwise the fuel injection-rated metal fuel filters would not need to be changed every so often, lest they resist the electric fuel pumps enough to melt the wiring harnesses going to them (observed on '90s Chevy/GMC Suburbans when the fuel filters had not been changed, usually happening after 70K miles).

 

If you want to use the 350rpm level, yet the engine will not do it in "P", if you start at 500 or so rpm and then put the transmission in "D", will it go that low then?  With a foot firmly planted on the brake pedal?  If it will do that, then with an assistant holding the brake, set the timing that way.  When done, it's done.  Doesn't matter how you got there, just that you got there.

 

All of the little holes and slots locations near the carb throttle plates are calibrated around the slower idle speeds for "idle speed setting", so getting as close to them as possible is necessary for best results.  After getting the idle and dwell set (with the points), then optimize the idle mixture and speed around the factory specs.

 

The idle mixture screws should have sensitivity to turning them in and out at the base idle speed.  If not, increase the idle speed 25rpm or so and re-check.  

 

In using your points distributor, set the dwell FIRST, then the ignition timing.  With the electronic distributor, just set the timing as the dwell is non-adjustable and electronic.  Then optimize the hot base idle speed and mixture.

 

Sorry for the length.  I hope this might explain why some of the settings were done as they were, in a time when many people had a vac gauge and had to borrow high-tech instruments like timing lights and dwell-tachs from others (who needed them for their work).

 

Enjoy!

NTX5467

[NTX5467]

With the electronic ignition distributor, you can probably widen the spark plug gap to .040" with the recommended ign coil for the distributor.  On a normal ignition, you can do that too.   The stock coil should have enough guts to produce that much spark, I suspect.  If it does not, head back toward .035" gap.

 

I know we are all used to seeing the normal plugs which are not "extended gap", but the extended gap plugs put the spark out in the chamber for an easier initiation of ignition with its spark.  In one Petersen Publications book I bought back in the late 1960s, it likened the effect of being like advancing timing by 2 degrees from using a non-extended gap plug.  Using an AC 45TS instead of the spec AC 45 plug, for example.

 

That book also mentioned a "J-gap" plug which Champion had back then for "racing".  The difference in this plug was that the ground electrode extended only 1/2 of the way across the center electrode.  Exposing more of the spark kernel to the air/fuel mix.  After reading that, I got out my point file (remember them?) and filed the ground electrodes of the J-14Y Champions in our car to the J-gap specs.  Throttle response off-idle was a bit cleaner and more energetic.  Maybe a slight bit better at WOT, too, but I did no timed tests, just how things felt.

 

In the 1990s, when the "quality of the spark" came under scrutiny, the ACDelco Rapidfire plugs had such a J-gap orientation and a few other "tricks" for a more-exposed spark kernel.  NGK V-Power plugs took things a bit further with their center electrode having a "V" cut into it, to force the spark to the edges of the ground electrode, plus the J-gap, too.  Toyota used them OEM, but with a normal NGK part number.  From my experiences, they DO allow the use of leaner mixtures reliably (which is what happens with E10 fuels compared to E0 fuels), so they can be a somewhat inexpensive way to get to what I did with all of my electrode filing decades ago.  They also seem to have more affect with a more-open combustion chamber than a wedge chamber, but they work with all of them, from my experiences.  I could usually get about 25K miles between re-gappings.

 

As for the Iridium fine-wire electrode spark plugs, what makes them better is that the "fine wire" of their electrodes puts any spark they produce right out into the mixture, no shrouding of the spark kernel at all, for a more substantial POW when the spark happens.  There are a few YouTube videos on this on a lawn mower engine.  Longer run time on a tank of fuel plus less deposits on the cyl head.  Of course, with over 100K change intervals, plus the better combustion, they can be "forever" spark plugs.  For a price.  For most people, the NGK V-Power plugs can be the best value, though.  Considering how many miles the vehicles get driven is a factor too, plus ease of getting to the plugs in the car.

 

Y'all enjoy!

NTX5467

[old-tank]

1 hour ago, buickbrothers said:

Engine dies before the idle gets down to that RPM - not a physically cannot turn screws to get it down to that RPM. Please clarify "return spring"? Are you indicating linkage return spring or something else? It's correct per photo's before tear down. 

 

Linkage return spring.  May have to lengthen throttle rod.  Pic of spring connection?

[buickbrothers]

Here's a pic of the return spring:

 

 

[buickbrothers]

Thank you for the response NTX5467 and insights. I'm especially interested in the spark plug information and desire a better clean burn of the fuel. The 4 barrel carter carb seems a bit finicky to me and a bit fuel heavy. Probably just goes with these old classic cars - that constant smell of gas. Since I have pulled the 1st plug a few times when setting the timing, I'm already seeing the deposits build up and want a cleaner burn if possible. Even Mike's Carb Parts video's comments are that this carb can be complicated. Since I knew nothing about a Buick when I got this car, I've had to rely on the books, video's and forum to sort fact from fiction. Agree, 1955 vs. 2024 fuels and other fluids are different and need to be taken into consideration. It's does seem like I am supposed to be able to get to 350 rpm to disengage vacuum advance on the distributor to set the timing for this Buick designed engine. If I can't, does that mean it's pointing me to a problem that needs to be resolved and what problem is it trying to point me too? I don't know - just trying to figure it out with help from the experts in the forum. I can try the option of putting it in drive, as you mentioned, to drop the rpm down. Thanks.           

[60FlatTop]

I have been reading this and thought the 350 RPM idle was low, only a hair above cranking speed.  Here is a tune up specification chart I clipped from the Team Buick site that pretty much standardizes 450. My 1960 401 is set for 450 in Drive.

 

Where did you get your specification?

 

[buickbrothers]

Thanks 60FlaTop. I have a similar chart that includes dwell. The shop manual calls out dropping to 350 rpm to set the timing and once that is set, you adjust up to 450 rpm for the idle. That may be why the chart shows 450 idle. The point of starting at 350 rpm, per the manual, is that it is supposed to guarantee the vacuum advance on the distributor is disengaged. My understanding is that just disconnecting the vacuum line from the distributor won't do it, which makes no sense to me. Just passing this on...   

[NTX5467]

I looked in the AMA Consolidated Specs document I downloaded a year or so ago.

 

Timing mark on damper, so easy to see, hopefully.

Centrifugal advance starts at about 600rpm.  Hot base idle speed is 450rpm.  Vac advance starts at about 6" Hg,  5 degrees BTDC base timing.  ONE distributor part number for all Buick V-8s in 1955.

 

When the ambient daytime temps get up to tine lower 70s, check the operation of the automatic choke BEFORE starting the engine for the first time.  It should just easily close, with the throttle set on full fast idle position (not started).  Losen the thermostat adjustment and rotate it leaner until it barely closes fully.  With time, the choke springs will tighten so using the service manual setting will make them too tight and the choke opens slower than it did when new.  Which can aggravate any "carboning-up" issues.  Test and re-check for best results.

 

Personally, I would not be concerned with the "350 rpm" situation.  If the vac advance has a metal tube going to it, just get a small wrench and unhook and plug it to set the timing at 450rpm.  When done, reconnect it.  And that should solve your low-rpm issue.

 

As to the base timing, for diagnostics, try a bit more advance and see if you get any part-throttle pinging on hills and such, with the fuel you are using.  See how far you can go before pinging happens, as to timing advance.  Might go 2 degrees at a time.  Perhaps @old-tank can advise of his experiences in what has worked for him?

 

Enjoy!

NTX5467

 

[JohnD1956]

2 hours ago, buickbrothers said:

The point of starting at 350 rpm, per the manual, is that it is supposed to guarantee the vacuum advance on the distributor is disengaged. My understanding is that just disconnecting the vacuum line from the distributor won't do it, which makes no sense to me.

The point of that low idle is to negate BOTH the mechanical and vacuum advance.  The metal line to the vac advance unit should not have to be disconnected if you can get the engine speed that low.  If you cannot get it that low it might be because of vacuum leaks.  You might want to set to 450 RPM and then spray the carb and its base to check for leaks.  Also you may want to disconnect the power brake line (if so equipped) and cap it off.  And same at the wiper motor, and then see if you can get to the 350.  If I recall you are also supposed to be doing this with the engine fully warmed up.  So make sure the choke plate is wide open.  And do not forget to check the short rubber vacuum hoses on the lower side of the vacuum pump.  Make sure they are proper sized and tight. .  

[old-tank]

18 hours ago, NTX5467 said:

Centrifugal advance starts at about 600rpm.

An old Chiltons manual says 375rpm.  Anyhow, apply the parking brake, chock the wheels, carb off the fast idle cam, put it in drive and you will be close enough.  (just don't forget and rev the engine at this point)

[NTX5467]

The A.M.A. Specs list it as 300 distributor rpm, which would be 600 engine rpm.  With the hot base idle rpm of 450rpm.  That's what I based my comments on.

 

Take care,

NTX5467

[buickbrothers]

I got a start on this today and will do more tomorrow. Feedback welcome on things to try. No vacuum leaks identified today. Disconnected everything as JohnD1956 indicated except one line to my vacuum gage. Fast idle screw is gapped from boss - not touching. I set the rpm level using the throttle stop screw. I can't attempt the test to drop the rpm to 350/375 by putting it in drive until my brother is here tomorrow to work the brake.  I was able to get to low 400 rpm's and the car just doesn't like this level. I made two videos - one at 400ish rpm's and the second at 600ish rpm's. You will see the erratic vacuum gage movement on the first video and the rpm's going up after I rev the engine and slowly dropping down while idling. The erratic vacuum gage swings seem to settle down if I set the idle around 600. I have run the new engine through one full tank of gas in terms of breaking in time. Been using marvel oil to loosen valves (machine shop did these). I did switch to a double roller timing chain when I rebuilt the engine and 4.25 pistons if that makes a difference in things. I am at 5 degree's on my timing mark setting. Maybe my valves are still tight not broken in? Am I missing something on the carb that won't allow me to go to the 350/375 rpm's? 

 

Video one at 400ish rpm idle:  https://youtu.be/H2VbPlosrzM

Video two at 600ish rpm idle: https://youtu.be/6v3FZRRJh1I

[JohnD1956]

In the 400 RPM it sounds to me like it will easily go down another 100 RPM.  Don't expect it to run smoothly at the 350 RPM.  It will just about run but it will run that slowly for the few seconds it takes to adjust the timing.  

[old-tank]

Set it at 5-7 and call it good.  And move on to other projects.

[buickbrothers]

Final update on this subject. Got the rpm down to about 375 with it shifted in drive. Made a few small adjustments but it was pretty well dialed in. Set idle around 475. Tested and re-adjusted the brakes so we could safely use the manual brakes (my power booster is out and waiting on parts). Finally took that car out for it's very first drive on the road. Wow, the engine is running great! Very smooth. Drove it around in a school parking lot that is across the street from my house. The parking lot has some inclines entering and existing the parking lot and the transmission operated great with no issues. No slips or hesitation on engine or transmission on flats or inclines. I was expecting that I may need to make linkage adjustments on the transmission, but it performed perfectly. I can't say how blessed I felt after this drive since I've had many setbacks, since last year, on this engine due to a snapped rocker arm as a result of new after-market rods causing a clearance problem. I also had to pull the drive shaft back out to repair a major transmission link in the torque ball to drive shaft area. I give all the glory to God that this first drive was a blessing and that years of work, and over-coming many setbacks, is showing that this car will come back to life. Thanks for all the advice gents! Appreciate the feedback and keeping me on course! Here's a video on the last leg of the drive pulling the car back into the driveway and under the car port. 

 

https://youtu.be/_Oe2gicfIWI

       

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[JohnD1956]

Wonderful, and a beautiful Buick too! Looks like you are doing a superb job restoring it. 

[buickbrothers]

Thank you JohnD1956. I’ve done things and learned things I’ve never done before on this car. I’m on year seven and hoping to complete this year, if possible, this year. Without the help of the forum, I don’t thought I could get there. Thank you and everyone for your help. Watch for more posts, I still have some big items left to go to get over the finish line!