So, I have this B&M Torque converter (#20412) that has hole spacing smaller than my stock flex plate. A board member is looking into whether or not he has a dual pattern plate for me. In the meantime, I have been mulling it over, and think I can accurately drill these 3 holes into the plate myself. :idea2: I would mount the flex plate on the engine, hold the new converter up tight against the plate with the pilot nose in the crank to center it. Then mark the placement of the converter pads by spraying the areas with contrasting paint. Find the center of the area the pads touch, center punch and drill on a drill press. (The pads on the converter are round, so finding the center of them should be pretty easy.) I've considered if this would screw up the balance of the plate, but am thinking that all things being equal, if I am removing equal amounts of material from 3 exactly spaced areas the balance won't be affected. Right? I am really hoping to get this engine back into the car this weekend while the wife is in Iowa visiting her Mother. (No interruptions) :laugh: I could still use my stock converter since the cam I am using (TA 212) doesn't require a higher stall converter, but would like to get this in now while it is easy. I may upgrade to a bigger cam down the road. o No:
I wouldn't advise drilling your flex plate there is no room for error. Even if you didn't feel any viberation your tranny might . It could shorten the life of your tranny. Bob H.
Dale, If you need a dual pattern flexplate, bring that converter out so we can double check it, and I have plenty of flexplates with both bolt hole patterns. I will be in the shop till about 8PM all week, except Weds.. JW
My vote is go for it. Measure as accurately as possible, make the holes slightly larger than the thread OD of the bolts...it's the crank's job to center the converter, not the flexplate. Deburr the holes and you're set. Devon
Thanks Jim! I may stop out tonight. Or maybe this afternoon since it has been so slow here at work. If all else fails, I think I may go for it.
I've never drilled one, but you may need a carbide drill bit.....isn't that matal hardened? One more thing you may try, if you have a good set of dial calipers and are good with math, just for accuracy you could measure a distance from the existing holes and scribe the the spot to drill using the sharp edge of the calipers. That's how we used to do it at the machine shop I used to work for when we had to drill a bolt circle. We used to spray ink onto the surface to make the marks easier to see before hitting them with a center punch where the lines intersected. Do you understand what I'm trying to say? If you take 1/2 the size of the center hole in the flexplate, then subtract that from half the bolt circle, that would be the exact distance from the edge of the center hole to make the mark. Then make 3 of marks, each of them 1/3 of the way around. You can do that by referencing the 3 existing holes. You could make the new holes about 1" away from them but along the new line from the correct bolt circle. Phew.....sometimes I'm so smart I amaze myself! LOL :Smarty:
Break out the Dycum Blue! Yeah, I know what your getting at. I'll see what Jim can do for me 1st though.
Unless someone goes hog-wild with drilling in the wrong spots, such an endeavor won't even come close to affecting the factory balance. To put it bluntly, there was a lot of tolerance there. Devon
Coat all 3 torque convertor mounting pads with lipstick, then press the convertor up to the flexplate. All 3 pads should leave a perfect painted image on the flexplate. Punch and drill your holes.
Yardley has lipstick in his toolbox? uzzled: Do you keep that in the same drwaer as the petroleum jelly? uzzled: uzzled: ou: :laugh: :laugh:
I'm going to remember that tip for the future! :TU: Yeah, but she will be out of town this weekend. she would never know. :idea2: Hmmm, what parts can I run through the dishwasher this weekend...:laugh: Thanks to all for the input. I met with JW last night at his shop, and he had just what I needed in his stash of plates. Thanks again Jim! :beers2:
Since when is there tolerance spinning something heavy as a torque converter People spend good money to get their engines balanced including the flywheel/flexplate front damper and crank pulley and yet the torque converter has tolerance?????????o No: That is wierd Bob H.
IMO I dont think drilling three holes in the flexplate is going to affect the balance that drastically. Your removing metal in three equal places on the plate. It would be a different story if you drilled three holes right next to one another. The converter does get centered on the crank, not the flexplate mounts. I have replaced flexplates on balanced engines with no ill effects. What are you supposed to do when you have to replace a flywheel on an externally balanced engine?
Bob, no offense, but it comes down to an understanding of rotational dynamics and how acceleration & mass has it's effect. In a nutshell, pistons/rods are balanced to within a gram or so depending on how much someone wants to spend. That part of the reciprocating assembly needs to be right on because of the huge loads seen at higher rpm. The balancer & flexplate/flywheel have a somewhat smaller role to play in the balance game, though for sure it's important. My point was that the factory balance job was pretty loose compared to what you'd get paying for a true balanced assembly at an aftermarket machine shop. I've had no problems drilling flexplate holes, and neither should anyone else if they're willing to do it right. Devon
If there are any little fluctuations in density or thickness where you drill or if the area around one hole that you drill has a slightly different density or thickness than any of the other holes that could be enough to throw the balance off, although it wouldn't be by much as long as the holes are 120 apart.
Done it LOTS of times, never been a problem (including to the BBC in my suburban, with many many miles put on it since), sometimes you guys really make simple things way to complicated! ou:
