Hi there have to replace my flexplate, it`s got a crack between two holes in it. 1) I reseached on the board. Is the Hays 15-075 Sfi Flexplate still the way to go in 2024? I`m swapping from my stock plate. 2)Do I have to take any special steps(e.g. balancing) or can I just bolt it in an be done? Engine sees no more than 5500 rpm Thanks in advance Jens
I got my SFI flex plate from Jim Weise. I believe TA sells it. It's a nice piece. Pretty sure you can just bolt it on unless the one there now was modified for balance.
I just bought the TA flex plate...https://www.taperformance.com/proddetail.asp?prod=TA_2033A-EXT Looks just the one above in the picture.
The important thing about the one pictured is that it has the correct offset. The one it replaced on my engine was flat, and the flex plate teeth were too close to the starter pinion gear. It eventually ruined two mini starters I used. Had to get the Robb Mc starter so I could adjust the clearance with shims. When I replaced the flat flex plate, I was able to remove the shims and clearance was fine.
Not likely. The engines were rough-balanced internally. Buick punched holes in the flexplate to final-balance the rear of the engine. New flexplate would need to be match-balanced to the original to retain factory balance. Find five Buick flexplates, you'll almost certainly find five different patterns of drilled/punched balancing holes. They did about the same up front, cramming steel pins into the torsional damper which would otherwise be neutral-balanced. Replacing the damper requires removing the pin(s) from the original damper, and putting them into the replacement damper in the same relative location. These front-and-rear final-balancing operations were done AFTER the engine was assembled including the oil pan, (so they couldn't do the balance corrections on the crankshaft, where it belongs) and--I think--running under it's own power. The factory balance wasn't all that great. But it's also hard to improve upon due to the screwy center-of-mass balancing on the OEM connecting rods. Note all the lightening holes at the top, (next to the two torque-converter bolt holes, some of the balancing holes are double-punched) because for this particular engine the standard offset weight at the bottom wasn't enough. Unlike this particular engine, where the standard offset weight was just a bit too much. A single hole punched through the sheetmetal got it into spec.
Hey Schurkey...that`s what I reseached too...but seems not everybody is as worried, some say it`s not too much of a problem for a non-all-out-race engine. Mine has been build 11 years ago, I bet it`s been much more internally balanced than a 1970ties stocker at GM, so a "neutral" flexplate might be not too much of a problem...but then...I don`t know, just guessing. Jens
I know Jim Weise has a Master flex plate that he match balances to on all his engines. When I bought the flex plate, he has to remove just a bit of metal on mine IIRC.
That's an interesting deal... I had always assumed that they added weight pins to a balancer, or knocked holes in a flexplate, when they were qualifying the parts for use on the assembly line. Not sure exactly the process that would be used to determine balance by knocking holes or install pins with an assembled engine. They were hot run before about 73, and after that they were air motored with compressed air thru the plug holes, but I'm pretty sure that was simply to verify oil pressure and a leak check. I will ask long time BMD engineer Dennis Manner about it at the nats this spring. And there is no such thing as a neutral balance harmonic balancer or flexplate for the BBB from the factory. JW
It's touched-on in the SAE paper from when the engine was introduced. Specifically, page 8. https://www.diyauto.com/manufacture...nference-bb-handout-booklet-scan-by-jim-weise He's still alive? I thought he passed. You are completely correct. My mistake on the damper. (Somewhat corrected in my previous post.) Only if you paid for aftermarket balancing, and as said--that's really tough on a Buick using OEM rods. If your engine doesn't shake excessively now...I wouldn't change flexplates without at least making an attempt to match the punched balance holes.
I don't see a balance weight on this one. Only one drilled balance hole, probably to correct manufacturing anomalies. See post #2
The weight might be on the other side..... I got one from TA. It only has the 6 TC bolt holes and the 6 large weight reduction holes .
From what I understand is that these stocker flexplates get cracks and have to be replaced, right? So, in real world experiences, if you guys just swapped in the new SFI plate, would you experience hefty rocking and shaking afterwards, out of balance experiences, or does it go rather smoothly? No problem hole-matching the new plate to the old stock one, but above this? Engine stays in the car for now, and how could it possibly be balanced without further detection tools to do so?
In In general, it goes smoothly. You just replace the flex plate. I don't think most shops would even concern themselves with balance. Like I said, I bought my replacement flex plate from my engine builder Jim Weise. He has a Master flex plate he uses for his engines, or engines like mine. He match balances the replacement flex plate to that Master. If your engine was built by AM&P, maybe Mike Phillips would know something about that. I would e mail him and ask. His E mail is ampmike@aol.com.
Interesting Schurkey, been a long time since I read that SAE book.. Still going to ask Dennis how exactly this was done on a running engine. How would you measure imbalance, quantify weight addition or removal, and locate weight addition/removal locations. I understand how a crank balancer works, but how could one separate all the vibrations cause by everything spinning, from actual rotating assembly imbalance? I can tell you, not everything in that book is the truth.. some of it is "the company line".. Cliff Studaker, the BMD Engineer who was the lead designer of the engine, and wrote that book sat in my office and told me all about it. Specifically when it comes to increasing the crankshaft main dia from 3 to 3.25 inches. Cliff gave me a brand new 50 year old copy of that book when he visited me.. He happened to be the uncle of the wife of one of my customers. Was a great guy, answered many of the "why did they do it that way" questions I had, I only regret I did not get him to autograph that book for me. He passed away several years ago. Dennis is alive and well. I will bring that book with me, and have a chat with him about it. One thing is for sure.. We, as a community have been replacing worn out/broken flexplates on vehicles in service for decades, and I don't ever recall having anyone complain of a vibration afterword.. as long as they replaced it with the OEM type replacement part.. the aftermarket stuff is another matter all together, had been for 40 years, right up until the latest SFI flexplate was introduced about 4-5 years ago. That one matches my oem "master" flexplate perfectly when balance checked on a rotating assembly.. and I find it hard to believe that is a coincidence, after my factory flexplate was subject to some random material removal on the assembly line. It was produced from the original Buick blueprints for that flexplate. JW
Clearly, this was done with technology available in the mid-1960s or earlier. There would be a lot of "noise" in the engine shake to be sifted-through and ignored to get to the actual imbalance correction. I imagine there were pressure pads front and rear that synchronized to a degree-wheel internal to the balance machine; so that the pin(s) could be driven in, and holes punched/drilled in the correct locations. This was no-doubt a high-speed, automated procedure. ALSO kinda guessing that it was not enormously accurate, even by industry standards for balance. Buick clearly didn't do a proper job of balancing the connecting rods except by overall weight; where most other manufacturers at least attempted to balance big-end--small-end separately even if the tolerances were fairly loose. Pontiac also rough-balanced engines before assembly, then final-balanced after assembly; but with the oil pan off, and the short-block spun by a machine rather than run under their own power like Buick. The final-balance correction could be done on the crankshaft where it belongs, instead of custom-balancing the external parts. The promotional film by Pontiac says that they're balanced to "within one-half inch-ounce" which sounds wonderful to the Great Unwashed but pales in comparison to a proper aftermarket balance job accurate to a few grams. Guessing that's 1/2 inch-ounce front, and 1/2 inch-ounce rear, rather than 1/2 inch-ounce combined--but the video is not that specific. (1/2 oz = 14 grams.) Here's that Pontiac video, the audio is faulty--it's silent for awhile. The final-balance info is given directly after the audio comes back at approx. 9:40 of the 11-minute segment of the multi-part video. The full video was longer, but the later part isn't on Youtube that I can find.
Here is another reference to balancing the engine after its assembled. The last line says "The engine is balanced dynamically front and rear, oil pressure is checked and final adjustments made to the engine timing." I would like to hear details about how this balancing was performed in such a fast-paced production environment. This is a photo from the Buick engine plant and was dated 1972. The text is on the rear of the photo.
