Cbarnes Posted June 10, 2022 Share Posted June 10, 2022 Well, it appears that I have busted the center out of my flex plate. I am looking to buy a beefier/stronger Flex plate to replace it. But I am getting confused. I searched Jegs and Summit, both have SFI rated flex plates, but some are for internal balanced engines, and some are for external balanced engines, most are 164 tooth, but have seen a couple that said they were 184 tooth. Can someone please help me out as to what flex plate I should buy? Thanks, Carl 1984 F250 XLT Supercab, 7.5L/460, Automatic, 4X4. Link to comment Share on other sites More sharing options...
Littlebeefy Posted June 10, 2022 Share Posted June 10, 2022 I'm sure Gary will jump in with all of the correct info, but... If you have the stock 84 engine and crank, it is externally balanced. You need to by an imbalanced/weighted flexplate. I have a 460 in an 84 Bronco with internal balance and my flywheel is 180 teeth. That's a manual, though, so don't use that as the basis. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 10, 2022 Share Posted June 10, 2022 Hi Carl The 460 went to external balance in 1979 (D9TE cast into the block by the starter) I have never seen anything but a 164 tooth flywheel between a 460 and a C6. The one you want should cross to D9TZ-6375-A Link to comment Share on other sites More sharing options...
ratdude747 Posted June 11, 2022 Share Posted June 11, 2022 From what I've seen on various engine building shows, look by the crank pulley... supposedly if it's externally balanced, there's a big balance weight there that fits on the crank snout. At least on the 460's they were tearing down. Most aftermarket cranks are internally balanced... so if your engine isn't stock, it could be internally balanced despite the engine's factory build date. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 11, 2022 Share Posted June 11, 2022 From what I've seen on various engine building shows, look by the crank pulley... supposedly if it's externally balanced, there's a big balance weight there that fits on the crank snout. At least on the 460's they were tearing down. Most aftermarket cranks are internally balanced... so if your engine isn't stock, it could be internally balanced despite the engine's factory build date. The crank throws of an internal balance crank won't fit inside a D9TE block. So no Bullnose ever came with a front sump internal balance engine.(that has the dipstick in the timing cover) Yes. If you don't know what year the engine is you can tell if there is a cylindrical spacer behind the harmonic balancer or a tomahawk (hatchet) style external weight. The most sure way is to look for that casting number right behind the starter motor. Link to comment Share on other sites More sharing options...
Cbarnes Posted June 11, 2022 Author Share Posted June 11, 2022 The crank throws of an internal balance crank won't fit inside a D9TE block. So no Bullnose ever came with a front sump internal balance engine.(that has the dipstick in the timing cover) Yes. If you don't know what year the engine is you can tell if there is a cylindrical spacer behind the harmonic balancer or a tomahawk (hatchet) style external weight. The most sure way is to look for that casting number right behind the starter motor. From what I know about this truck it is bone stock. I haven’t had a chance to check the casting number or the crank snout. But will do that first thing in the morning. I would really like to go back with something other than factory original. According to carfax this truck only had 44,000 miles. Can’t figure out why the flexplate would fail. I don’t drive mine like it was stolen, and the truck doesn’t give any indications that is was abused previously. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 11, 2022 Share Posted June 11, 2022 From what I know about this truck it is bone stock. I haven’t had a chance to check the casting number or the crank snout. But will do that first thing in the morning. I would really like to go back with something other than factory original. According to carfax this truck only had 44,000 miles. Can’t figure out why the flexplate would fail. I don’t drive mine like it was stolen, and the truck doesn’t give any indications that is was abused previously. That really is odd that a flexplate would tear the center out in 44k miles. Hopefully you will find the cause when you take it apart. I don't see any issue using an SFI flexplate. Specification 21.9 mandates they can withstand ~13,000 rpm for an hour. But that still doesn't mean they are any better balanced for your truck engine turning 4,000. Link to comment Share on other sites More sharing options...
mat in tn Posted June 11, 2022 Share Posted June 11, 2022 That really is odd that a flexplate would tear the center out in 44k miles. Hopefully you will find the cause when you take it apart. I don't see any issue using an SFI flexplate. Specification 21.9 mandates they can withstand ~13,000 rpm for an hour. But that still doesn't mean they are any better balanced for your truck engine turning 4,000. the only reason i can imagine for the center to fail is alignment. causing over working of the metal flexing out of phase. look for leaking at the rear main seal while it is exposed. a c6 is full hydrostatic. it does not have a locking torque converter and the torque converter is more likely to fail than the flex plate. what does this sound like when the engine is running? is it just not moving or is it grinding? Link to comment Share on other sites More sharing options...
Cbarnes Posted June 11, 2022 Author Share Posted June 11, 2022 the only reason i can imagine for the center to fail is alignment. causing over working of the metal flexing out of phase. look for leaking at the rear main seal while it is exposed. a c6 is full hydrostatic. it does not have a locking torque converter and the torque converter is more likely to fail than the flex plate. what does this sound like when the engine is running? is it just not moving or is it grinding? Well, I went and bought a digital inspection camera. It is still hard to see, but I am pretty sure the center of the flexplate busted out. Here are a few pics that I took of the image on the screen of the inspection camera. Link to comment Share on other sites More sharing options...
mat in tn Posted June 13, 2022 Share Posted June 13, 2022 Well, I went and bought a digital inspection camera. It is still hard to see, but I am pretty sure the center of the flexplate busted out. Here are a few pics that I took of the image on the screen of the inspection camera. on the plus side. you may not need to remove the four torque converter nuts while under the truck. Link to comment Share on other sites More sharing options...
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