Broken flywheel teeth and pinging

[nameiztaken]

Timeline of what happened:

- Bought 1991 Ford Explorer 4.0 ohv / 5spd in January 2021 in good condition.

- Starter gives out a couple months later, seemingly just due to age. Replaced it with a napa reman. All is fine for a few months.

- Engine starts having a pinging issue under load, Replaced every potential cause, maf sensor, intake gaskets, decarbon treatment, etc etc. none of which solved the issue.

- Replaced spark plugs (autolite) with Motorcrafts, engine immediately stops pinging, but on the first start with new plugs something sounds like its not meshing right. A couple days later, flywheel teeth have broken off. I checked the firing order/wires many many times.

- Replaced flywheel, replaced starter, all is fine for a couple days then it starts making bad noises again. A month later, the flywheel teeth are broken off again. Thats where we are now.


What I think may be the problem and why — this is why I’m posting, please tell me what you think about this:

I’m suspect of the timing chain. I think it may have jumped, causing the pinging/detonation problem.
I think the advanced timing may have caused the engine to kick back onto the starter, breaking and grinding flywheel teeth. Another symptom that leads me to the timing chain is excessive oil usage, with no obvious leaks or smoke from the exhaust.

I’m basically waiting and deciding whether I truly want to keep dumping money into thsi truck. Not much else is wrong with it aside from the repeated flywheel destruction.

Tell me what you think, I’m looking for any possible ideas.

 

[franklin2]

Are you the one driving it? Did it sound like it was kicking back against the starter when you were driving it?

 

[nameiztaken]

Are you the one driving it? Did it sound like it was kicking back against the starter when you were driving it?

Not while driving, only when starting. I was the only driver.

heres a video of the sound, listen for the random impacts while cranking:

Watch kf2k57 | Streamable

Watch this video on Streamable.

streamable.com

 

[RonD]

Up to 1996 Explorers had the 4.0l OHV engine, and no timing chain issues, that was the 4.0l SOHC a different engine

I would say you got the wrong starter motor from Napa for a manual transmission, most Explorers would have an automatic
A starter motor's gear is suppose to be slightly softer metal than the Ring Gear, so the start gear wears out not the ring gear

On your video is the Spark or Fuel disabled?


Spark plug wires on the 4.0l OHV coil pack are
3 4
2 6
1 5
front

the 5 6 4 side often gets mis-wired, follow each wire to driver's side cylinder


Pinging would not be related to the flywheel ring gear issue
Best guess would the the heat range of the original spark plugs were wrong since changing them stopped the pinging
Spark plug tips have to dissipate heat fast enough so they don't stay hot enough to ignite lower octane fuel(87)
But they need to stay hot to work well, so spark plugs have heat ranges
Carbon build up on the tips also cause them to retain heat longer

 

[nameiztaken]

Up to 1996 Explorers had the 4.0l OHV engine, and no timing chain issues, that was the 4.0l SOHC a different engine

I would say you got the wrong starter motor from Napa for a manual transmission, most Explorers would have an automatic
A starter motor's gear is suppose to be slightly softer metal than the Ring Gear, so the start gear wears out not the ring gear

On your video is the Spark or Fuel disabled?


Spark plug wires on the 4.0l OHV coil pack are
3 4
2 6
1 5
front

the 5 6 4 side often gets mis-wired, follow each wire to driver's side cylinder


Pinging would not be related to the flywheel ring gear issue
Best guess would the the heat range of the original spark plugs were wrong since changing them stopped the pinging
Spark plug tips have to dissipate heat fast enough so they don't stay hot enough to ignite lower octane fuel(87)
But they need to stay hot to work well, so spark plugs have heat ranges
Carbon build up on the tips also cause them to retain heat longer

I checked on both starters that the part numbers on the starter were correct for the 5spd but I could have been sold the wrong part and was not able to put two of them side by side. Still odd that the napa starter I bought first worked for a few months with no issues… then again who knows.

Probably right about the pinging problem and plugs.

 

[RonD]

What about the video?
Was fuel or spark disabled?

 

[nameiztaken]

What about the video?
Was fuel or spark disabled?

Yes sorry, fuel and spark disabled. Makes the same noise with both enabled.

 

[RonD]

So definitely an issue with the starter/ring gear meshing/matchup, not caused by a back fire or hydro-lock in a cylinder

Hydro-lock is when a fluid(gasoline or coolant) gets into a cylinder in enough volume to prevent that cylinder's piston from easily going passed TDC when both valves are closed, causes a noticeable hesitation in cranking engine over, and puts ALOT of stress on starter gear and ring gear

Backfire, in this case, usually only happens after engine is warmed up, a cylinder "fires" early when piston is on the way up, and halts/slows down the piston causing the hesitation and stress on starter gear and ring gear


More likely is that the starter gear and ring gear are not a match
This can work if engine starts up right away
But longer cranking time cause the skipping and higher wear

Also there is a Block plate between transmission and engine used to line up the starter motor with ring gear
Just a thin metal plate
If new clutch is installed you or shop can forget to put it back in and starter WILL shift around causing mis-alignment with ring gear

 

[nameiztaken]

So definitely an issue with the starter/ring gear meshing/matchup, not caused by a back fire or hydro-lock in a cylinder

Hydro-lock is when a fluid(gasoline or coolant) gets into a cylinder in enough volume to prevent that cylinder's piston from easily going passed TDC when both valves are closed, causes a noticeable hesitation in cranking engine over, and puts ALOT of stress on starter gear and ring gear

Backfire, in this case, usually only happens after engine is warmed up, a cylinder "fires" early when piston is on the way up, and halts/slows down the piston causing the hesitation and stress on starter gear and ring gear


More likely is that the starter gear and ring gear are not a match
This can work if engine starts up right away
But longer cranking time cause the skipping and higher wear

Also there is a Block plate between transmission and engine used to line up the starter motor with ring gear
Just a thin metal plate
If new clutch is installed you or shop can forget to put it back in and starter WILL shift around causing mis-alignment with ring gear

Plate between the block and the transmission was reinstalled after any work, so rules that out.
I might try one last time replacing the flywheel and ensuring I get the right starter.

I’m fairly confident the starters I’ve been using are correct but I’ve been sold trash parts before.

I’m almost concerned of a slightly bent crankshaft or worn main bearing…

 

[Shran]

If the crank was bent the engine would destroy itself in very short order. Worn main bearings would be a low/no oil pressure/knock scenario with lots of metal in the oil.

Problem with starters these days is that they are really all the same junk rebuilds, no matter where you buy them. NAPA sells the same crap that O'Reilly, AutoZone, Advance, etc all sell...just at a higher price.

I would suspect that you have a defective starter (very likely) or the wrong starter or your starter mounting bolts/alignment hole are so grossly oversize and loose that the starter is hitting the flywheel while the engine is running.

 

[nameiztaken]

Ok, so I’ve examined the photos I have of both starters I installed. Both look correct and are not the longer one for automatics.

I think its safe to say the starters I used were correct and should not have caused repeated flywheel teeth loss.

 

[nameiztaken]

heres an automatic starter for comparison

 

[RonD]

The starter teeth also look OK
Or is that one never been used?

Starter would have been the most common issue so not really sure what to say????