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View Full Version : Engine: V8 Flywheel & Crank Redrilling For SBC Bolts



3x2stude
02-09-2017, 08:40 PM
Several years ago when I first started getting parts machined for a 289 build I had the flywheel drilled and the crank drilled and tapped to put SBC flywheel bolts it from the outside. I am finally going to assemble the short block soon and I wanted to review the info I got but I cannot find it. Anyone else ever done this? I know I did not dream this up myself:)

JK

Jerry Forrester
02-09-2017, 11:04 PM
Several years ago when I first started getting parts machined for a 289 build I had the flywheel drilled and the crank drilled and tapped to put SBC flywheel bolts it from the outside. I am finally going to assemble the short block soon and I wanted to review the info I got but I cannot find it. Anyone else ever done this? I know I did not dream this up myself:)

JK

Ted Harbit is your man. He's the only one I know of that has done it. If I remember correctly.

DieselJim
02-10-2017, 07:53 AM
If the crank was tap to 7/16-20, use Moroso bolt # 38760 for auto or 38755 for manual. This info supplied to me by Deepinhock.

bezhawk
02-10-2017, 09:40 AM
I just did this with a Fidanza aluminum flywheel. Also chamfer the holes through the flywheel to reduce stress risers. The flywheel is countersunk to fit off the crank flange, so it self centers. Got ARP bolts from my local speed shop.

karterfred88
02-10-2017, 11:18 AM
Just a quick question. How thick is the flange on the crank? How many threads at 7/16-20 tapping will be there to hold the bolts? I was considering making 2 nut plates to slide in behind the flange to avoid pan removal, but if tapping the flange will supply enough holding power it certainly would be easier than making nut plates.

PackardV8
02-10-2017, 02:04 PM
Ted Harbit is your man. He's the only one I know of that has done it. If I remember correctly.
Just a quick question. How thick is the flange on the crank? How many threads at 7/16-20 tapping will be there to hold the bolts? I was considering making 2 nut plates to slide in behind the flange to avoid pan removal, but if tapping the flange will supply enough holding power it certainly would be easier than making nut plates.

Been done many times by many of us over many years. If the flywheel is ground, if flywheel and pressure plate are balanced, if shift points are <6,000, if correct ARP bolts are used, if the pilot drill and tap are used correctly, I've never had any problems just tapping the flange.

jack vines

karterfred88
02-10-2017, 06:46 PM
Been done many times by many of us over many years. If the flywheel is ground, if flywheel and pressure plate are balanced, if shift points are <6,000, if correct ARP bolts are used, if the pilot drill and tap are used correctly, I've never had any problems just tapping the flange.

jack vines
Thanks Jack!!
Since it will be an everyday driver---sort of, and since my pan and rear main don't currently leak, that's the way I'll do it! Do you know the correct ARP bolts for a manual trans? I'm using a Fidanza/Fairborn Aluminum flywheel in my 5 speed conversion. Now just to grind off the A/T bolt heads without touching the flange!!

3x2stude
02-11-2017, 10:29 PM
Karterfred88,

To do this modification the crank should be removed from the motor and the alteration should be done at a machine shop. The fact that your current pan seal does not leak is irrelevant. You would need to drop the pan to get the old bolts out at a minimum. Someone correct me if I am wrong?

JK

DieselJim
02-11-2017, 10:55 PM
Karterfred88,

To do this modification the crank should be removed from the motor and the alteration should be done at a machine shop. The fact that your current pan seal does not leak is irrelevant. You would need to drop the pan to get the old bolts out at a minimum. Someone correct me if I am wrong?

JK Use a cut off wheel in a die grinder. Cut the head off the bolt. Been there. Done that.

3x2stude
02-11-2017, 11:11 PM
DJ

The crank needs drilled and tapped, "accurately". You're going to do that with the crank in the block in the car?

JK

karterfred88
02-11-2017, 11:20 PM
Karterfred88,

To do this modification the crank should be removed from the motor and the alteration should be done at a machine shop. The fact that your current pan seal does not leak is irrelevant. You would need to drop the pan to get the old bolts out at a minimum. Someone correct me if I am wrong?

JK

You can grind the head of the bolts off being careful, from under the car with the trans and covers out of the way, one at a time, rotate grind, rotate. Of course you can't insert a new bolt that way, then you need to pull the rear main cap to insert them. Once out, tapping is pretty straight forward if done carefully. My concern was if the threads would have sufficient length (depth), since the flange is only so thick. I was going to create two half circle nut plates drilled and tapped to match the offset mounting holes in the crank, and slipped up the backside of the flange from below. But if it's been done satisfactorily without that I'm all in for grinding. The crank holes are, or should be .37525 (24/64) as drilled, the 7/16-20 drill size for tapping is recommended at .3830- .390625 {25/64(-)}. Carefully using brand new adjustable hand reamer, taper, plug and bottoming taps should make it doable in the car.
I have used this company's adjustable reamers to fit larger shouldered lug bolts into wheel hubs and work very well.
https://drillsandcutters.com/4-a-hss-adjustable-reamer-3-8-13-32/?utm_medium=googleshopping&utm_source=bc&gclid=CPmImM7iidICFc9LDQod4Y0HFQ

https://drillsandcutters.com/7-16-20-carbon-steel-hand-tap-set/?utm_medium=googleshopping&utm_source=bc&gclid=CMm5sPbcidICFYuLswodV44NGQ

DEEPNHOCK
02-12-2017, 08:14 AM
While a machine shop would help ensure the bolt holes are drilled and tapped accurately....(or would it?)

You can get square with a drill guide. (and use it as a tap starter, too)

http://toolmonger.com/wp-content/uploads/2008/12/drill-guide-action.jpeg http://cdn3.craftsy.com/blog/wp-content/uploads/2015/04/IMG_3649_edited-2.jpg

You will have to finagle and clamp the guide on there, but that's not impossible.
If the crank is in the block, you will need to use a bottoming tap (after the tapered tap) to ensure the threads are all the way through.