Ford 8N Fan blade hit shroud/engine quit

GManBart · Jan 3, 2013

1948 Ford 8N, pretty much in original configuration. I was skidding some trees out of the woods, and ran the tractor for about an hour, with no problems. Heading down my driveway I opened the throttle a bit, heard a metal clicking come from the fan blade/shroud area a couple of times, and before I could cut the throttle, the fan blades hit the shroud pretty hard, saw a couple of sparks, and the engine quit. The shroud had cracked all the way through in one spot, causing the contact (there are a couple of other small cracks. I checked all the wiring, and everything looks the way it should (just had the hood off last month). I can't find any obvious damage, but it won't start...turns over fine, but that's it. I haven't pulled a plug wire to see if it's getting spark yet (it was really cold, getting dark, and I had to pull it out of the driveway).

I'm wondering if the fan blade strike could have thrown the timing off? I'm a novice at flathead engines, so I'm not even sure if that can happen the way it could with OHV engines with camshafts running off a timing chain. Thoughts, guesses? R,

Bart

Egon · Jan 3, 2013

Any idea why the fan hit the shroud?

GManBart · Jan 3, 2013

The shroud has several cracks in it, and it looks like that crack just got big enough that when I increased the throttle, the change in vibration caused it to get in the way of the fan blades...probably just hit the right RPM to cause a harmonic vibration problem. I had the hood off, and front axle separated a few weeks ago, and it's possible that the shroud got dinged or pushed out of shape then, and it finally caused a problem (haven't used it a whole lot since getting then).

The more I think about it, I'm not so sure it would be easy to throw the timing off on anything with the front distributor, because of how it connects to the camshaft, but that's just a guess. I'm going to go over the wiring again, to see if I missed something getting cut, and then see if it has spark. R,

GManBart · Jan 4, 2013

Reviewed the wiring diagram, then went over all the wires visually, and everything looks okay. I'll check for spark tomorrow.

GManBart · Jan 4, 2013

Eureka, an easy fix! Hats off to my local Ford repair and restoration guy, Skip, at Skip's Repair in Whitmore Lake, Michigan, Skip's Repair. I called up to ask about a new shroud, and see if he had any ideas on the problem. As soon as I asked about the shroud he said he has a pile of used ones, and that they only reinstall them on exact restorations because, "they cause problems". I told him what mine did, and he said "reach in, and see if you can pull forward on the coil, even a tiny bit". Sure enough, I grabbed it, and it moved forward something small, like a 16th of an inch. I didn't think it would make any difference....wrong, it started on the first try! Skip rocks! :thumbsup: He didn't make a penny from me today, but I've given him a fair amount of business before, and you can guarantee he's the first guy I call when I need to buy parts!

SDT · Jan 5, 2013

Egon said:
Any idea why the fan hit the shroud?

Wear of the front axle pin and/or bushing is the most common cause of fan/shroud interference. Failure to use the proper rubber spacer pads between the radiator and the axle support can also cause fan shroud interference.

SDT

GManBart · Jan 5, 2013

SDT said:
Wear of the front axle pin and/or bushing is the most common cause of fan/shroud interference. Failure to use the proper rubber spacer pads between the radiator and the axle support can also cause fan shroud interference.

SDT

Thanks. I know the rubber spacer pads are there, and appear to be correct. I had the front axle separated last month, and the front pin and bushing seemed to be okay. The shroud had something like 4-5 cracks that went from front to back. The one that the blade caught looks like it was the biggest of the bunch, and the blade only caught a very small amount of it going by the marks on the blade, and on the shroud. My best guess is that it just got big enough to flex when it got to the right RPM for a harmonic vibration. Either way, it appears no harm, no foul....cut off the bottom of the shroud since it was already completely broken, and made sure there's no way the rest of it can get to the fan blades.

imgone52 · Jan 5, 2013

Thumbs up to all the "Skips" out there. We gotta hope they share their knowledge with the next generation so the tractors keep working:thumbsup:

Soundguy · Jan 5, 2013

ps.. there is no timing chain on that engine.. it's gear driven.. and dizzy is hard timed to cam.

just a FYI...

GManBart · Jan 5, 2013

Soundguy said:
ps.. there is no timing chain on that engine.. it's gear driven.. and dizzy is hard timed to cam.

just a FYI...

I knew it didn't have a chain, but did a poor job of saying that...clarified it somewhat in the later post. I wasn't sure if the shaft that connects to the camshaft gear, and goes through the breaker plate, could be sheared off, or knocked out of alignment. Luckily, that didn't happen either way!