[Ironswede]

I have a Chevy 350 in my 72 nova.
My issue is I have the most extreme sounding backfire that I’ve ever heard. It’s as loud as a gunshot. Let me tell you what I did and see if you can help me figure out how to get back to when it was working fine.

So my car was running just fine until 2 weeks ago when I decided to convert from a th350 transmission over to a 700 R4. I was told when you pull the transmission that the engine may lean back and damage the distributor. So I took the cap off, hoping that that may, keep me safe from that issue. When I put the cap back on, it didn’t really seem to sit in the same place that it had before. But I snapped it back on anyway. HEI by the way.

I really tried to limit what I changed during the process so that if there were any issues, I would know where to look. But I definitely have a problem.

The car seem to start just fine. But I noticed originally when I started it that the passenger side headers seem to get significantly hotter than the driver side headers. And then I fired up a second time and the extreme back fire started it was so loud that it scared me that it sounded like it would be doing damage and I turned the car off immediately. So I haven’t really got a chance to let it run for more than 15 to 20 seconds.

1. do you think that I somehow messed up the timing? in my very limited experience that’s all I can come up with. And or is it possible that maybe I also messed up the distributor itself. Or something that I don’t know about because I really don’t know much about any of this. And just wanted to get your guys thoughts. I’ll try to make this is short as possible in the hopes that you are still reading and you all might be able to help. Thank you so much.

When I did the swap, I really tried to isolate what I did to adjust the transmission. Because I don’t know anything about timing and all that so I tried to not mess with it. So I thought just taking the cap off and putting it right back on wouldn’t be a big deal. But maybe it is.

I will monitor this thread closely. If you have additional questions, they can help me troubleshoot this I would really appreciate it. I was just trying to go to this really cool car show next month. It’s at an airport and it has planes and cars. And I thought I would have time to do this transmission swap. But now I’m very worried that I either won’t be able to finish it or that I did damage.

thank you

ryan

 

[doerf]

figure out why the cap did not go back on, cap can only sit down correctly in one place, rotation wise
if the distributor itself did not get moved or damaged, then with cap back on correctly and it should run as it did before

you should be able to pull cap and reinstall without any changes to how engine runs

 

[Peewee0413]

Have you checked the timing?

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[Ironswede]

Have you checked the timing?

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I would love to both learn how to check timing and to actually check timing. But I cannot let the car run for more than a couple seconds because of this backfire. It sounds brutal.

it looks as though the cap is on where it was. Are there any special notches or anything where those J hooks are supposed to go into? Here’s a couple pictures of how it sits right now.

 

[lwlevens]

Sounds like the timing is off.There is a notch on the distributor housing and cap that need to line up. Sounds like you didn't put the cap on where it belongs ,or when the engine leaned back when you removed the trans it might've broke the rotor. Next time use a jack with a piece of wood under the oil pan to support the engine.

 

[Bob's 65 Post]

Yes there are little indentations where these spring loaded Jhooks lock in to. Take the cap off, feel with your hand where those groves are and mark them on the side of the distributor and reinstall assuring you’re in them. The cap being off may be causing your backfire. Also make sure all the plug wire caps are seated firmly in the distributor cap.

 

[J Mark]

Before anything I don't believe the cap is on correctly. The cap should be notched, don't
rely on the hold down hooks. If you know it's on correct then see below.

Do you know or not if the distributor base did come into contact with the fire wall. If it did and the distributor wasn't tight it may have rotated a bit. Especially since you noted you have excessive heat on the headers. Sounds like it may be retarded. I cant explain why one side is hotter than the other.

In a situation where you can't run it I would do the eyeball check. Rotate the engine to top dead center, ID which plug wire is number one, then draw a line on the distributor base that lines up with the number one plug wire terminal. Pull the cap off and see where the rotor is pointing. If the rotor contact is to the left of the line you drew it is advanced, if to the right it is retarded. If the rotor contact is 180 degrees out of whack you need to rotate the engine on full turn and line up with top dead center again so it is on #1 compression stroke. Rotate the distributor so the rotor contact is at least lined up with your line or a tad to the left of the line. It should start with that setting without all the backfiring. This should now allow you to get a timing light on it. The cap not fitting correctly is concerning hopefully nothing is bent. Hopefully this is not to wordy.

 

[AllyMcReal]

Let us know what ends up working. I had a similar problem that was a loose electrical connection to a Pertronix system I installed. Car would crank and not start, but then the loose connection would intermittently connect and explode raw fuel/air mixture in the exhaust. Blew apart a muffler. So if the answer isn't timing, check for loose connections.

 

[67 canso sd]

. Blew apart a muffler.

This reminds me of how we initiated new young guys into the shop. Empty 4l jug of whatever, drill a hole in the cap that would fit your blower nozzle, zap strap the handle wide open, tuck it up under the car. Get the kid to crank from inside, the whole time talking about how the last guy blew a muffler because he pumped the gas…. Then hit the ball valve for air. Ahhh memories… ok back to topic at hand.

 

[Ironswede]

I cant tell you all how much I appreciate your help and advice. It can be a helpless feeling when you dont know what youre doing. But I appreciate you guys helping me through it.

Ok so I went out just now and felt those little notches in the base. Looks like I wasnt quite in them with the hooks. To get the hooks and notches lined up I needed to turn the cap about 1/4 to 1/2" counter clockwise. Dont know how much difference that will make being such a small turn. But Im hesitant to fire the car up right now. Its dark and I dont want my neighbors thinking there is gun fire next door if I didnt fix the issue.

I will fire it up in the morning. I would love for it to be that easy. Usually isnt for me.

NOTE: My engine is from blueprint. I went to their site to see what kind of distributor came wth the car. Their site mentions that it typically doesnt fit NOVAs...

Notes: This is a "Large Cap" HEI distributor with an in cap coil. It primarily fits trucks, and full size vehicles. It does not Typically fit Camaro's, Novas, Corvettes, etc. If your vehicle did not originally come with an HEI distributor of this style, please see our BPP3503RD or BPP3501BK (Paired with an external BPP8252BK or BPP82021BK type coils).

There is little to no room for the distributor by the firewall. It wouldnt surprise me if it did come in contact with the firewall when the motor leaned back. Though it does seem pretty tight still. I cant turn it by hand.

After we figure this out, do you guys recommend me getting a smaller distributor? Like one of the skinnier ones that requires a separate coil?

And thank you J MArk. Thats great info. I will try to set top dead center if the above didnt work. Its something Ive always wanted to learn anyway.

 

[lwlevens]

In the second pic it looks like the J hook is off from the indentation on the distributor. (But it might just be in the pic.)

 

[lwlevens]

Just go fire it up now. I'm sure it'll be ok since you lined up the notches.

 

[J Mark]

I cant tell you all how much I appreciate your help and advice. It can be a helpless feeling when you dont know what youre doing. But I appreciate you guys helping me through it.

Ok so I went out just now and felt those little notches in the base. Looks like I wasnt quite in them with the hooks. To get the hooks and notches lined up I needed to turn the cap about 1/4 to 1/2" counter clockwise. Dont know how much difference that will make being such a small turn. But Im hesitant to fire the car up right now. Its dark and I dont want my neighbors thinking there is gun fire next door if I didnt fix the issue.

I will fire it up in the morning. I would love for it to be that easy. Usually isnt for me.

NOTE: My engine is from blueprint. I went to their site to see what kind of distributor came wth the car. Their site mentions that it typically doesnt fit NOVAs...

Notes: This is a "Large Cap" HEI distributor with an in cap coil. It primarily fits trucks, and full size vehicles. It does not Typically fit Camaro's, Novas, Corvettes, etc. If your vehicle did not originally come with an HEI distributor of this style, please see our BPP3503RD or BPP3501BK (Paired with an external BPP8252BK or BPP82021BK type coils).

There is little to no room for the distributor by the firewall. It wouldnt surprise me if it did come in contact with the firewall when the motor leaned back. Though it does seem pretty tight still. I cant turn it by hand.

After we figure this out, do you guys recommend me getting a smaller distributor? Like one of the skinnier ones that requires a separate coil?

And thank you J MArk. Thats great info. I will try to set top dead center if the above didnt work. Its something Ive always wanted to learn anyway.

I too learned the hard way and had the benefit of getting help from somebody when I was very young.

 

[lwlevens]

I would install a ready to run distributor uses an external coil, a lot smaller than those hei distributors.

 

[J Mark]

I would install a ready to run distributor uses an external coil, a lot smaller than those hei distributors.

Amen!

 

[RifRaf]

I believe others have already given some instructions on how to properly install your HEI distributor cap. I just wanted to add some photos (with some notes) that might also help.

Remove your distributor cap. Look at the inside of the distributor cap. There is a small, square peg that has been molded into the bottom of the distributor cap (yellow arrows in images below).

This square peg needs to line up with a square slot that is machined into the base of the distributor body where the cap is installed (red arrows in images below). As you place the cap on the distributor body, you will need to twist/rotate the cap until you feel the square peg (within the cap) drop into the square slot on the body of the distributor base. When the peg drops into the slot, you will feel it... and should not be able to twist/rotate the distributor cap on the body of the distributor.

• Note: Before installing the cap onto the distributor base, be sure that all 4 hold down J-hooks are turned to the outside of the distributor cap (green circles in image above). Sometimes these hold-down hooks can move/turn while you are installing the distributor cap... and get hung up on the base of the distributor causing a improper fit of the cap to the body of the distributor.

Once you feel the cap "lock into place" (as described above), keep pressing the cap down on the distributor base and use a long, thin screwdriver to "push-down" and turn the cap's hold down J-hooks so they lock into the grooves on the underside of the distributor base. These HEI caps are a tight fit against the firewalls of our Novas, so be sure to visually verify that all of the hold-down hooks are securely fastened to the base of the distributor.

• Note: If you are not able to turn one or more of the distributor cap's hold-down J-hooks in a clockwise direction (to lock the cap into place), try turning the hold-down hook(s) in a counter-clockwise direction.
• Also, be sure that there are not any wires that are getting caught between the bottom of the cap and the body of the distributor.

 

[Ironswede]

OK. Great news. Me moving the cap to where those hook grooves were made a big difference. I do not hear any of that backfiring or knocking sounds. It smells like it’s running really rich though. Also, I guess yesterday when I was trying to turn those hooks, I may have had a Shrek moment. I broke one of all the little hooks off. One of the ones that I couldn’t see in the back. So at the very least, I’m going to need a new cap. But this could be an opportunity to go with one of those ready to run distributors that you guys mentioned.

My concern is that I won’t know which one to get. The distributor that’s in my car now says it has some sort of melon I used steel. So I guess I need to find one that has that similar metal tape. At least that’s what I’m finding in my research. Most of the ones I found say they were iron though. And then I guess I would need a coil as well. And then figure out how to connect the wires that run to my HEI distributor and convert them to whatever hook up is on the coil? I don’t know I’m skipping here. I think by now you realized I don’t really know what I’m talking about. But I sure like to learn.

 

[Ironswede]

Also, just want to double check. But are the ready to run distributors smaller in diameter than a traditional HEI distributor?

I also realized that that square notch probably is not sitting in the groove. Because the distributor is now touching the firewall. I wonder if putting the transmission in place just did not allow for as much room as I had before. So I don’t think I can set that distributor cap in the right spot as it is. So do I hammer the firewall? Or is there a better option?

 

[RifRaf]

Most "Ready to Run" distributors (MSD, Pertronix, Allstar, etc) are smaller then the HEI and use a smaller diameter cap. Most of these "Ready to Run" distributors also run on full battery voltage to the + side of the coil. Depending on what type of cam you have in the car, you may need a "melonized" distributor gear. Some of the "Ready to Run" distributors come with a "melonized" distributor gear... so you need to pay close attention to the product's description.

If you decide to stay with the HEI, you may have to hammer in my firewallI to gain clearance for the large cap. I had to hammer in my firewall in my 74 Nova so the HEI cap would fit.
Another thing that you could do to gain some clearance between the HEI cap and the firewall would be to add some shims/spacers underneath the transmission mount to raise the back of the transmission. This will also tilt the back of the engine up... and may gain the clearance that is needed for the HEI cap to fit.

• Note: When you raise the back of the transmission, you will also be changing the U-joint working angles... and this could affect your "overall" driveline angles (possibly causing a vibration while driving).

 

[67 canso sd]

If you have to hammer firewall to fit a HEI, what is your engine sitting at degrees down? No hammer used on my 2nd gen with HEI. Engine at 3 deg down.