Olddaddy Posted June 3, 2007 Report Posted June 3, 2007 The big adapter plate bolts to the engine and the crank hub sticks out behind the plate. You bolt the crank adapter to the hub, and the eight hole flex plate bolts to the crank adapter. Then it's like any other automatic setup, the flex plate bolts to the torque converter and the tranny bolts up to the back side of the adapter plate. Clear as mud, right? Quote
Fireball Posted June 3, 2007 Report Posted June 3, 2007 That is clear, even I understood this correctly. BUT, questions keep popping into my otherwise hollow head. You said 8 bolt flexplate, ummm, Smallblock Mopar LA series 273, 318, 340 and 360 all have 6 bolt flexplate to crank bolting. 8 bolts are special billet cranks for racing, and then 426 hemi. Like this So maybe you have old cast iron 727 behind wrinkle head 318 and thats the reason why 904 does not fit? If my memory only serves me correctly on this those early smallblocks had 8 bolt crank flanges Please don't get frustrated with me flooding these questions Olddaddy, I just want to make sure if this would be something to buy for my car. I have 904, converter and driveshaft waiting in my garage... Quote
Plymouthy Adams Posted June 3, 2007 Report Posted June 3, 2007 The special race crank flex plate as mentioned above carries Mopar part number 2466715 The book also states all flex plate on all A engines interchange..however one must be careful not to mix internal balanced flex plate with externaly balanced appliations..this applies to some 340's and all 360 engines.. Quote
Olddaddy Posted June 3, 2007 Report Posted June 3, 2007 The eight hole flex plates were used on Hemis, and probably others. They were used on all industrial applications with a 727/flathead six drivetrain. You can find them on ebay, complete with bolts for under $100. I bought mine for $40. Quote
Fireball Posted June 4, 2007 Report Posted June 4, 2007 Tim, the weights in external balanced engines are in the converter not the flexplate in the OEM applications. Olddaddy, if you will start "mass production" of this kit, I propose you could make both 8 bolt and 6 bolt versions? If you wonder why bother, my opinion is that the 6 bolt flexplates are so much more common, easily available all over the world, even for free, and whenever a word HEMI is included the prices and rarity raises. I think it's easier to drill a different pattern into adapter, than trying to locate an specific flexplate for it. That's ofcourse only my suggestion and you fabricate per your decisions. I'm just sure it is easier to sell a kit that adapts the most common available parts. For you the production cost is just the same with 6 or 8 holes tapped right? Quote
Plymouthy Adams Posted June 4, 2007 Report Posted June 4, 2007 With all due respect, Mopar built the engine, Mopar wrote the book...The statement I made is directly from their book part number P4452790 page 109... from the book All the "A" engine flywheels and torque converter flex plates are interchangable except for the engines with cast cranks. That is basically the 73 340 and all 360 engines...they are balanced externally and Mopar sell the kit for retrofit Pt # 4120241..but the line about the flex plate I quoted..it puzzles me as I also thought one flex plate for small blocks...just threw that in as written. Further they say later in the book they have one flex plate that works with all small block..Part number 2400885..so what makes this so special? May the two OEM unit compared in physical size/weight of unit? Just said what I did to prevent mix and match, and the convertor does not get the weight "in" as you said but rather "welded on" to the face of the convertor. Therefore the afore mentioned kit... There must be some truth to this as I went asking for a flex plate for my engine years ago..(well know Mopar performance shop) I was asked what small block engine as they are different. That is why I went to the book... As I don't know all from the top of my head..that is why I bought this engine book years ago... Quote
Fireball Posted June 4, 2007 Report Posted June 4, 2007 Oh I'm not saying you are wrong by any means Tim, and I don't know all out of my head either. I think your quotation from that book: " All the "A" engine flywheels and torque converter flex plates are interchangable except for the engines with cast cranks." causes the confusion here, because it is speaking of flywheels within the same sentence, and they are different story because they are weighted. Or, perhaps it is about poly engines, which are A series? I have done both removing the balancing weights from converter and adding them into another application, just for this internal/external reason. I'd still say the difference is in the converter bolt diameter and spacing, not the balancing of the flexplate. There are 5/16" and 7/16" applications. And when we add Magnum engines and aftermarket flexplates to this soup, the validity of your comment that they fit but are not all the same is even more true. I'm not being an smartass, this is good info sharing and if my poor way of impressing myself in English causes somebodys blood temperature to raise, forgive me. I still know my way around small block mopars, I have raced and build them a lot. Both internal and external balanced engines. Quote
Plymouthy Adams Posted June 4, 2007 Report Posted June 4, 2007 Agreed.....I read as much as I could on that last night...I even went forward to the big block and there was the same statement there in regard to their flexplate. It is confusing as can be, if could be just the authors use of words. The mere fact that the portion of the book I quote using reference to the "A" engine instead of "LA" could make one wonder as it came straight from the "LA" engine section. The book has a seperate section to cover the "A" engine. I went out to the shop and compared the three flex plates I had in one cabinet, identical..but I also know these are 318 pieces..and I do not have a spare 360 laying around at this time... I did find reference to the size of the bolts (5/16 and 3/8) so that may well be the OEM difference for internal/external applications, another gentle reminder to prevent mis-match as the warning to never bolt the 5/16 converter to the 3/8 flex plate. The introduction of the Magnum series of the small blocks further adds to the confusion in the mix. I basically stay away from these, I do have a Magnum 3.9 in the 51 Plymouth Suburban. When I purchased that book way back when at my local Direct Connection retailer, (remember that name?) They went through and stuck out the few errors and inked them in by hand. Maybe there are other changes to this book I am unaware of. One thing is for certian, and my main reason to post about the flex plate was to inform all about the different subtle changes Mopar made over the years and at mininum three cranks per engine application..the possibility of mis-match is quite high if you just grab a part from here or a part form there. And anyone retrofitting may do well to take the entire drivetrain from a donor and remember well the original year and application for future repairs. Quote
Plymouthy Adams Posted June 4, 2007 Report Posted June 4, 2007 Done a bit more searching, appears there are three available flex plates...OEM use per internal and exteral..still not settled but the following list show two different bolt patterns, two different bolt sizes and a combo flex plate with both bolt patterns..plus the special race forged crank with 8 bolt application. By looking it appears the issue is more in line with what size torque converter along with what performance level engine determined the application of the flex plate. The dual pattern explains the previous mention one size fits all. Chrysler Y T/F 904 '71 - '76 340 external dual bolt circle, 5/16" bolt, 6 hole cast crank 102340 Chrysler Y T/F 904 '71 - '92 360 external dual bolt circle, 5/16" bolt, 6 hole cast crank 102390 Chrysler Y T/F 727 '71 - '76 340 external dual bolt circle, 5/16" bolt, 6 hole cast crank 102350 Chrysler Y T/F 727 '71 - '92 360 external dual bolt circle, 5/16" bolt, 6 hole cast crank 102360 Chrysler Y T/F 727 '71 & up 383-440 external dual bolt circle, 5/16" bolt, 6 hole cast crank 102370 Chrysler Y All T/F 318-440 internal small bolt circle, 7/16" bolt, 6 hole forged crank 145200 Chrysler N All T/F 426 HEMI internal small bolt circle, 7/16" bolt, 8 hole forged crank 145300 Chrysler N All T/F 318-440 internal small bolt circle, 5/16" bolt, 6 hole forged crank 145600 Chrysler N All T/F 318-440 internal large bolt circle, 5/16" bolt, 6 hole forged crank 145700 Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.