PSA - Check your Boxer Distributor Advance Spring Pins

Good day All,

Just a brief PSA to have your Boxer's distributor advance pins/springs checked, as it could save you a lot of work chasing down a very odd and intermittent running issue.

On my 512BB, I had a ongoing issue where my car would experience random fouling of a cylinder/plug after driving for about 15-20 mins. Up and until the fouling started, the car ran like a Swiss clock. I checked, checked, everything and I could not find the cause. I cleaned everything, rechecked the carbs, etc and the car would again run like a top, but only after the fouled plugs were cleaned or replaced. The Distributor advance looked OK, when checking it on the car and so no real smoking gun as to cause. Having ruled out anything to do with Fuel, I focused on ignition... checked the module, replaced the module, tested the distributor pickup... and nothing. I opened up my distributor and found that the advance springs did not look stock, as some clearly were modified via wire snips. As a long shot, I tried to find replacement parts... but they are NLA. The shops that do service these distributors are all located in the US and none would sell me parts. All wanted me to ship my distributor to them. The cost was OK, but the greater concern was the potential of the distributors being lost/damaged during transport to/from the US, as I am in Canada. So... I was left on my own and so armed with the Sun 504 Distributor machine I had to reverse engineer both the 504 and how the distributor advance worked and its relation to the springs, etc. Having done this I noted that the machine would periodically display an oddity in the smoothness in the advance. Since my machine dates back to the late 60's I had to upgrade it, replace some old parts, and double check the machine along with creating some resourceful calibration items/processes... and the machine checked out (Kudos to the original 504 designers for such a simple and elegant design). I kept testing and reviewing the distributor and finally found the cause. The reason for the periodic oddity in the advance was do to worn portion/divot located on the inside of the distributor advance "cup" The primary advance spring pushes against a pin that contacts this cup. The spring that someone installed was too strong and so more force was placed on the pin and so caused accelerated wear in this area. The result was that the advance would be smooth before and after the divot, but at the divot would affect the movement of the advance mechanism causing inconsistent advance. Measuring everything and correlating to engine/dist RPM (who says trigonometry is useless ), I found that the advance issue would occur around 3000 to 3500 RPM... which is my typical cruising RPM... and so explains the plug fouling.

Repairing this was not very straightforward given that parts are NLA and the cup's various inner obstacles. So my machinist buddy fabricated an appropriate tool to use on the CNC lathe. To remove the divots (one for each advance weight) 0.014" had to be removed, then polished, etc. We ensured not remove material all the way to the bottom of the cup, so that weight's bottom could still contact the cup when at max advance (which is a physical limit given the advance weight movement arc and the size of the inner centre plastic bushing). After all this the advance was completely smooth.

The next step was to determine the replacement springs. I used my existing ones to determine the spring parameters and characteristics and then worked backwards as to what spring parameters I would need. I sourced some from McMaster Carr, but they had only one that was in the ball park. I also found that Hill Engineering does sell a new replacement weight/spring/pins/cups kit (DIS-85F-RBK01), but the springs are nowhere close to what I needed. However, all of the other HE parts are direct replacements to the original Marelli parts, which is good to know. I did find two other spring manufacturers (Lee Spring and Spring store) and ordered a number of them in the sizes and spring rates I estimated/calculated. This worked great and I was able to adjust my distributor advance appropriately. I will also add that the little washers that may be needed were ordered from Asia in the sizes and thicknesses I needed for minimal $... like a few $ for 100 washers in various thicknesses all in Stainless Steel.

So... ensure to have your Boxer (and other) Distributor periodically taken apart and checked for this type of wear, as it can be a real bear to sort out given that the affects will happen over time, which simply makes it even harder to diagnose.

Going forward... given this issue and that there is little info on the part parameters needed, I have started working on a retro-fittable solution to provide a totally programmable electronic advance mini module. I will start a thread on this project once it matures a bit. If the design proves out, then it would effectively negate the need for the entire mechanical advance setup, their maintenance, and the need to send out the distributors for service/calibration. Best of all the design would require no permanent changes to the distributor, etc and would look totally OEM.

Cheers,

Sam




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Good day Robert,

Understood.

As mentioned in my earlier post, the Hill Engineering kit includes all new parts and so if there was a need for these parts, then this would be the kit to get (see pic)... less the included springs. It is worth nothing that the HE weight spring pocket depths are different than they were on m,y Boxer and so if one does use the HE kit, then there is a good chance that new springs will be required.

As for the MSD units with programmable advance... indeed, I am aware of these. However, what I have in mind is different, smaller, and can be used with the original setup or any of the MSD and other electronic modules. Plus the programming of the curve could be done remotely using one's smart phone, etc.
Given my experience with going through the Boxer's (and no doubt other older F-car distributors)... and that the number of shops that correctly service these distributors is limited, I thought that having a fully retrofit solution for relatively low $... and removing the service aspect of the advance mechanism would make f-car owner's experience much easier. Who knows, perhaps the design will not pan out...but I am thinking it is worth a try.

Cheers,

Sam

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Good day Dave,

Indeed, I felt a heads up was in order, as I never really gave much thought to periodic disassembly, inspection, and re-lubing the the distributor advance mechanism. Kind of like...it is out of sight and it works and so was off my radar. Given my experience I thought it would highlight this often overlooked (at least to me) maintenance area. All in all the advance mechanism is quite straightforward and elegant at the same time. The real "magic" are the springs and how they combine to create the overall advance curve. For the most part the springs should not need changing, but if people much with them... like someone did on mine, then problems result. Good for you that you had a shop check and refresh the distributor, as obviously you were ahead of the curve. As for the Dinoplex, they can work fine until they don't, as its internal components are 40 years old. Some parts do not degrade too much with time, but others do quite dramatically with heat accelerating things... and the latter parts form the core of how the Dinoplex works. The good thing is that one can easily install a modern aftermarket unit for modest $, or find a ship that retrofits the old housing with new guts (which is what I have done for a number of Dinoplexes). That said just be aware that the Dinoplex is old and bit of a weak link and so plan your extended drives accordingly.

It would be great to meet up. Sadly, I do not make it to the Chicago area much these days. I really do miss living there, as it is really a very vibrant area and the people are outstanding.

Take care and enjoy your Car!

Cheers,

Sam

 

Good day Peter,

It should be a "fun" project. I have had the design rattling around in my noggin for a year now. It all started when I had to dig deeper into my Distributor... and finding no parts, info, or shops relatively close to me. As they say necessity is the mother of most inventions, and what I have in mind is included in this statement. Also, since there are several other older f-car and other marques in my area... and have or will have similar issues, I suspect they will be interested too. My 365 (GT4 2+2) has dual distributor setup, but the overall operation is a bit funky as compared to the dual 308 distributor arrangement. So, my design will take the 365 setup into account. The end goal is for the solution to be unnoticeable/hidden without any permanent mods... allowing one to revert back to the original setup if ever wanted. The core tech is quite straightforward and I think most will be surprised at the overall size... about the size of a watch, but a bit taller. The real effort is finding a bit of time to work on this... especially now, as it is Summer and my car is running well (just finished a 45min drive )and so it is hard to stay inside. So... progress will be sporadic.

Cheers,

Sam

 

Good day 2Dinos,

Thanks for your posts.

Surprisingly, the old tech used by the Sun machines works very well all things considered. As a double check, I created a created and added an electronic feedback mechanism and then compared the results to my high end electronic test equipment and the accuracy was excellent. Not perfect, but then again the distributor itself is not perfect... but certainly well within what I would consider accurate. Going forward, I could certainly add more advanced tech to the Sun machine, but I question why?... as getting more decimal point accuracy will not truly result in any improvements that will be seen while driving the car.

As for the springs... I did not have any real baseline except for the hand modded springs and so I did my best to apply the scientific/engineering method to calculate the various spring characteristics needed to be. I did try to formally create the formula for the distributor advance setup...but I gave up realizing that I was out of practice with rotational kinematic calculations... and that I really just needed a base line. As a result I bought an inexpensive spring force gauge, designed and created a 3D spring holder, and physically measured the parameters of the altered springs and distributor's advance mechanism. From this I arrived at 4 or 5 spring types and ordered them to try. It turned out that the 2nd spring out of the 5 ordered was extremely close and so I used it and all has been fine. I could certainly improve things further, but thought it is best for me to focus on a full electronic retrofittable advance mechanism add-on that will negate the need for springs ... and will result in a fully programmable advance curve.

With all that said... although I have a plethora of tech at my disposal, I am always in awe of what was done many years ago with the tech at the time which was not anywhere close to what is available or as inexpensive as today. Truly those that created these devices and without access to the advanced computers, simulation software, and current manufacturing technologies is a testament to the ingenuity, resourcefulness, and skills of all those who participated in these designs. Kudos to all of these people!

Cheers,

Sam

 

Good day Rifledriver,

Indeed, thank you as well for your comments, insight, and experience!

Cheers,

Sam