7.4 distributor/cam damage

Bcrump1984 · Jul 14, 2024

Hi everyone. New here. Recently purchased a 96 2500 suburban with the 7.4. It was purchased with a crank no start. Guy said it had a hot start issue then quit running one day while driving. So far I have replaced the coil, crank shaft sensor, plugs, wires, cap/rotor and icm. I am currently in the middle of Bosch 4hole injector change and a fpr. Today when I pulled the distributor the gear is all tore up. What is the likelihood the cam gear is ruined as well? My father in law thinks the cam may be bad as well.

someotherguy · Jul 14, 2024

Welcome,

Replace the gear, be sure you only use a melonized (hardened) gear for the roller cam application. These early Vortec engines were known for improperly treated distributor gears; the roller cams are hardened and eat them up. The cam is almost surely just fine.

Richard

Bcrump1984 · Jul 14, 2024

someotherguy said:
Welcome,

Replace the gear, be sure you only use a melonized (hardened) gear for the roller cam application. These early Vortec engines were known for improperly treated distributor gears; the roller cams are hardened and eat them up. The cam is almost surely just fine.

Richard

I have ordered a cheap scope to try and inspect it. Have a new distributor on the way. Just replacing the whole thing because I have no idea if the old one is any good or if it was just the gear that’s bad. Hoping the cam is fine. Really don’t want to dive that deep into it as I am no mechanic and only have basic tools. Just trying to venture out and do a little more on my own than I have in the past. Probably gonna have father in law help with a timing chain. Based off my findings to this point I don’t think much has ever been touched on it

someotherguy · Jul 14, 2024

The scope may turn out to be a useful tool for other purposes, but I can assure you this is a somewhat common failure on the early Vortecs, and it's the distributor gear that gives its life while the cam is 100% fine.

You're wise to go ahead and replace the whole distributor, providing you bought a good brand. Honestly my advice would have been better had I recommended you do that instead of just replacing the gear. These distributors do wear at the top bushing and cause cam/crank correlation errors (P1345) that get the timing out of whack.

You will find it takes a scanner that can read the cam retard angle in order to properly set the distributor. There's discussion about that here in the groups if you spend some time searching. I'm not sure what the current good choices are for a DIY'er. You can't set these engines with a timing light.

Once you've got the distributor handled, and the injectors and regulator - that 7.4 'Burb should be a beast.

Curious, how many miles on it?

Richard

Bcrump1984 · Jul 15, 2024

It’s got 284k miles. How much do those type scanners usually run? Most likely I will just try and get the timing close enough to drive it to a shop and have the timing set. I don’t know much of anything in the way of advanced mechanical work or what a lot of the data those scanners give you on stuff like timing, fuel to air, and others. Just trying to get it running.

Schurkey · Jul 15, 2024

Bcrump1984 said:
I will just try and get the timing close enough to drive it to a shop and have the timing set.

The ignition timing is NOT ADJUSTABLE. You cannot "set the timing".

Turning the distributor housing adjusts the cam sensor signal/crank sensor signal alignment/synchronization. The sensor signals must be aligned within + or - 2 degrees at ~1100 rpm.

454cid · Jul 15, 2024

Schurkey said:
The ignition timing is NOT ADJUSTABLE. You cannot "set the timing".

Turning the distributor housing adjusts the cam sensor signal/crank sensor signal alignment/synchronization. The sensor signals must be aligned within + or - 2 degrees at ~1100 rpm.

This, and it's not hard to do, although it's best, in my experience, to have someone else on the key. I used a little screwdriver to wedge the throttle to an appropriate rpm.

Bcrump1984 · Jul 15, 2024

hopefully the obd2 scanner I have available can read it. If not then I may just have to have it towed to a shop that has the right tools. Trying to do it on a budget and do some myself. Getting a bit frustrated and feeling like I made a bad purchase. Only bought it cuz all my reading prior to buying it were simple fixes going off what I was told the issues were before I got it. Starting to get a little more involved to get running then I care to do myself.

Deancr11 · Jul 15, 2024

It will be alright man someone around here will help you out. It's not as hard as it seems. Line everything up drop the distributor in and tighten the bolt. You'll be closer to done.

7.4 distributor/cam damage

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