47-55.1 Eliminate draft tube options

[TX3100Guy]

Originally Posted by geezer#99

Hei is big and tall.
You gonna have room for it?

I guess I'll find out for sure tomorrow.

Here is a pic of the engine with the ill-fated magneto before it shorted out.

[dsraven]

Hei requires a 10ga power wire so run a relay driven by the regular ign coil power wire. Use a good relay and know that during normal run, not normal starting, the coil gets less than 12v due to the ballast resistor.

[TX3100Guy]

Originally Posted by dsraven

Hei requires a 10ga power wire so run a relay driven by the regular ign coil power wire. Use a good relay and know that during normal run, not normal starting, the coil gets less than 12v due to the ballast resistor.

No problem on using 10 gauge wire with a 20amp fuse inline. My plan was to connect it directly to the ignition wire off of the ignition switch (which is also 10 gauge wire). I wasn't planning on running a relay since none are showing on both the American Autowire wiring harness for a GM HEI, nor or the wiring diagram with the distributor. The same goes for the ballast resistor, none is showing for an HEI type distributor, just for a traditional distributor with an external coil.

[TX3100Guy]

No need to fret any further on how to wire and attach a GM HEI distributor. It won't fit.

It seems that the bottom of the distributor, given its width, hits the pushrod cover and won't seat fully to the cam gear and oil pump drive. I need it to seat another 1/2" further, but that is no bueno.

[geezer#99]

I see Tom has a small cap dizzy.


https://www.12bolt.com/store/p584/Di...6-235-261.html

[leegreen]

some prior art here
https://67-72chevytrucks.com/vboard/...d.php?t=586186
and
https://www.chevytalk.org/fusionbb/s...php?tid/75735/

One guy on last link describes how to DIY a 250 HEI + a SBC HEI shaft to work

Help figure this out for me, the 261 in my driveway wants a HEI

[TX3100Guy]

Originally Posted by leegreen

Help figure this out for me, the 261 in my driveway wants a HEI

So far, no joy on finding an HEI unit that 1) will fit and 2) has the correct oil pump shaft. I may forced to 1) wait for my magneto to be corrected or 2) go the traditional distributor/coil setup.

[dsraven]

pretty sure I seen an hei from an inline 6 used in a 235. just can't remember where I seen that. would likely need a recurve and max advance check. getting the magneto back in would be the coolest and more period correct of course. finding a good used old dizzy would get you running till the mag gets back though. by the time you find one, get t checked and set up with new parts, wire it, and get it all working properly your nag may be back.

[TX3100Guy]

Originally Posted by dsraven

pretty sure I seen an hei from an inline 6 used in a 235. just can't remember where I seen that. would likely need a recurve and max advance check. getting the magneto back in would be the coolest and more period correct of course. finding a good used old dizzy would get you running till the mag gets back though. by the time you find one, get t checked and set up with new parts, wire it, and get it all working properly your nag may be back.

Funny, I've been thinking the same thing. Now I have to drive back to Arlington, TX (about an hour away) and return the ill fated HEI and plug wires. I found another HEI online, but asked the vendor to get me some dimensions before I click on "BUY". Other than this particular one, every HEI that I see online has way to big of a distributor to fit, or it has the same collar as the repaired magneto had that prevented it from fully seating into the oil pump drive.

I thought about just biting the bullet and putting a traditional distributor and coil in, but with all the rewiring and finding a home for the coil, I gave up. I'm going to beg the folks a Joe Hunt to move my mag to the front of the line, since I already had to wait nearly a month for the initial repair.

[leegreen]

Here is a article I failed to re-find yesterday: 250 HEI, cut off the flange and use the flange from a 235. 'looks' easy.
https://www.jalopyjournal.com/forum/...ersion.189074/

also some good points about vacuum advance. Which raises some questions for your application

[TX3100Guy]

Originally Posted by leegreen

Here is a article I failed to re-find yesterday: 250 HEI, cut off the flange and use the flange from a 235. 'looks' easy.
https://www.jalopyjournal.com/forum/...ersion.189074/

also some good points about vacuum advance. Which raises some questions for your application

Wow, that's a bit like heart surgery on a distributor...... Great article and great DIY.

[TX3100Guy]

Originally Posted by leegreen

also some good points about vacuum advance. Which raises some questions for your application

The mag doesn't have a vacuum advance and the tag that Joe Hunt put on it suggests that it needs to be set at 24 degrees before TDC

[dsraven]

LG, thats like the write up I seen but not the exact one. there is another one out there somewhere nut that one is pretty self explanatory if somebody were so inclined.

[1project2many]

I don't believe I would have a problem using an original distributor and an aftermarket electronic ignition. HEI is a readily available form of electronic ignition but it is not the only one. Pertronix may sell a sensor that can be installed in the distributor to replace the points if you'd like to trade points for a completely electronic system.

One consideration for this setup is based on the challenges you've already faced. Magneto service takes time and specialized knowledge. Spending time to design your wiring harness and ignition system for a relatively easy magneto to distributor swap allows you to keep a backup ignition system on the shelf.

For street use, either ignition system will be completely acceptable.

[TX3100Guy]

Originally Posted by 1project2many

I don't believe I would have a problem using an original distributor and an aftermarket electronic ignition. HEI is a readily available form of electronic ignition but it is not the only one. Pertronix may sell a sensor that can be installed in the distributor to replace the points if you'd like to trade points for a completely electronic system.

One consideration for this setup is based on the challenges you've already faced. Magneto service takes time and specialized knowledge. Spending time to design your wiring harness and ignition system for a relatively easy magneto to distributor swap allows you to keep a backup ignition system on the shelf.

For street use, either ignition system will be completely acceptable.

I completely agree. The fact is that I don't have an OEM distributor to work with and rather than spend the money on it an the kit to either add an HEI to it (Deve Tech has a DIY on that task) or add a Pertronix module, I have been pursuing another HEI distributor. I've reached out to the company to give me some dimensions so I can compare them to the Summit HEI I had to return. IF the head unit is just a shade smaller in circumference and/or the shaft is 1/2" taller, it will work.

Given the unexpected demise of the magneto the second time I started the rebuilt engine, having a backup HEI on the shelf is a no brainer. I'm pretty sure I can have the wiring in place for both the magneto and the HEI unit and be able to switch them out fairly easy. The magneto only needs a wire to ground it out and I've already wired in a relay on the ignition circuit to cause it to ground out when the ignition switch is turned off. The HEI unit needs a wire from the ignition circuit and a wire to the electronic tach.

[TX3100Guy]

Can't find an HEI distributor that won't interfere with the pushrod cover and/or has a flange on the shaft that prevents the oil pump shaft and cam gear from fully engaging.

As a result, I ordered a normal distributor, but one with optical sensors instead of points and condenser. I have already begun the wiring task to support both the magneto and the distributor. It should be here Thursday and my plans are to get it installed as soon as I can.

Now the challenge is to get the engine to TDC on the #1 cylinder. With the radiator on, its a challenge to get the engine lined up properly. The "BB" marking on the flywheel is a challenge to get lined up bumping the starter. The last time I tried that, I was 180 degree out.

[leegreen]

pull the plugs then put a strap wrench on either the nose of water pump or the rim of supercharger pulley - the crank pulley is fairly well hidden with the addition of PS and supercharger. Or drop the bellhousing dust shield and grab the flywheel with some gloves.

[TX3100Guy]

Originally Posted by leegreen

pull the plugs then put a strap wrench on either the nose of water pump or the rim of supercharger pulley - the crank pulley is fairly well hidden with the addition of PS and supercharger. Or drop the bellhousing dust shield and grab the flywheel with some gloves.

Thanks Lee, I was thinking of grabbing the flywheel as you suggested. My issue is that when I rotate the flywheel, through any means, when the "BB" shows in the sight window of the starter, I can't tell if I'm at TDC on the compression stroke or TDC at the exhaust stroke, since the flywheel/crank has to rotate twice to get to #1 TDC. Right?

[dsraven]

if you do that and arent sure if youre at TDC, remove number 1 spark plug and blow some air down the hole. if you hear air coming from intake or exhaust then give it one more turn.
I have taken an old spark plug, broken out the porcelain, cleaned it up, removed the ground electrode and then threaded the inside part for a pipe thread. that way I can screw in a short whip hose witha shut off valve and an air connection quick connect and screw that into the spark plug hole to check for TDC, leaking valves etc. beware that if at TDC and you blast air in the cylinder the result can be that the engine quickly turns over so use caution and a little bit of air flow, just enough to check whether air flows through the intake or exhaust valves. you will hear air coming through the exhaust pipe or through the carb, so remove the air filter and listen carefully (or have a helper listen for you)

[dsraven]

that tool is sorta the same thing as a leak down tester but the old engines have that big spark plug thread so some testers don't come with the adapter for that. besides, making the tool is quicker than sourcing a leak down tester and then either waiting for delivery or driving across town to pick one up.

[TX3100Guy]

Originally Posted by dsraven

that tool is sorta the same thing as a leak down tester but the old engines have that big spark plug thread so some testers don't come with the adapter for that. besides, making the tool is quicker than sourcing a leak down tester and then either waiting for delivery or driving across town to pick one up.

You gave me an idea. I have a compression tester. If I connect the fitting to the #1 cylinder and move the flywheel, won't the gauge show that the cylinder is under compression at TDC on the compression stroke and not on the 180 degree out stroke?

[dsraven]

it should at least show a blip on the gauge I would think. worth a try, right?

[TX3100Guy]

Originally Posted by dsraven

it should at least show a blip on the gauge I would think. worth a try, right?

A friend suggested that I put a cork or stopper in the other spark plug openings and keep track of which ones pop out as they reach their compression stroke.

[1project2many]

I started this reply earlier but was sidetracked. If the resources below are not helpful for your truck, maybe someone else can make use of them.


Coil in cap HEI distributors are large. The cap alone is at least 5" X 5". Later GM distributors as used on the 4.3 TBI trucks returned to a divorced coil design and the caps are significantly smaller in diameter. Those later distributors are intended to work with an ECM controlling timing and do not have mechanical or vacuum advance. There is an RPM based advance function built into the ignition module in case the ECM fails. It may be possible to locate the specs. In thinking about this, adapting a TBI 4.3 distributor to your engine may produce performance and driveability similar to running the mag.

Just looking at pictures of your engine I find it hard to believe an actual HEI distributor would fit. Folks market all sorts of electronic ignition conversions as HEI so it can be confusing. There are a number of vendors selling a version of the small cap electronic distributor linked to previously. Pertronix sells an all new distributor using their ignition and what appears to be a stock cap. https://www.cjponyparts.com/pertroni...261/p/DIST138/ There is a clean used one on Ebay: https://www.ebay.com/itm/314748272414 . There is also a Mallory electronic system: https://www.summitracing.com/parts/maa-4518001 . These are not really copies of HEI systems, but different versions of electronic ignition.

If the goal is to get the truck running with a minimal amount of lost time and expense, something like that used Pertronix distributor might be a great choice. For a period correct replacement, maybe something like this Mallory Dual Point Distributor would look as cool as the mag? https://www.ebay.com/itm/235602933529 and here: https://www.ebay.com/itm/256675182001

I am sure this is extremely frustrating. The end result will be worth the effort. Your truck is unique and very interesting.

---------------

Yes, a cork in #1 should pop out on compression stroke. Just make sure to do the engine work before finishing off what was corked.

[geezer#99]

If you use a factory side cover then an hei fits. They’re indented compared to your ribbed cover.


https://www.ebay.com/itm/324321238128