Stripped flywheel bolt

[Ross F-1]

Doing some clutch/trans work, had the flywheel off. Putting it back on one of the bolts went soft at 45 ft-lbs. It was sketchy last time, guess this was the last straw. (it's not the bolt threads). I used a different bolt and can get 30 ft-lbs but I'm kind of reluctant to count on it, even with Loctite 271. With the pegs locating the FW, and the spigot on the crank, I could probably let it go, but I'm thinking a helicoil is the right way, and will never be easier.

Anyone had to do it before? Anything to watch out for? It looks like the next size up (just drilling and re-tapping, no helicoil) would be a metric 12mm, likely less material removal than using a helicoil.

BTW, is the sheet metal locking plate supposed to be bent up against the bolt heads? I have yet to find one that was.

Opinions, please!

[cmbrucew]

Ross
Would a longer bolt, or a stud reach good threads?
Bruce

[Ross F-1]

No, unfortunately.

[Charlie ny]

Ross,
I'd go with the 12mm if it was mine.
Charlie ny

[49fordv8f4]

I would probably use a Heli-Coil if it were mine. I've never seen the thin plate under the bolts bent to lock the bolt heads either. I'm not sure the purpose for it , unless the mild steel would give more "grip" to the bolt heads to help keep them torqued than the cast iron flywheel would
Mark.

[Ross F-1]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by Charlie ny

Ross,
I'd go with the 12mm if it was mine.
Charlie ny

Originally Posted by 49fordv8f4

I would probably use a Heli-Coil if it were mine. ..

I like the 12mm because I'd be using the parent metal directly, with little removed for new threads. But I hate to have one unique bolt. I need to check whether a 12mm will fit thru the flywheel hole without drilling it out too, in which case the flywheel would have to go a specific way.

I don't suppose anyone thinks I can get away with it as-is???

[V8COOPMAN]

You KNOW you don't want to leave it like it is. And if it makes you feel better, you could always do a second 12 mm bolt 180 degrees out from this one. DD

[Ross F-1]

I checked, 12mm doesn't fit thru flywheel without drilling it out.

[Mart]

I'd probably go the other way and helicoil it. The flywheel bolts are drilled for safety wire, there is no reason to bend the plate up. The bolts are a fine pitch. Unless you went for a fine pitch metric you might not get the loading you need. The flywheel bolts are a highly critical item, they need to be right. A helicoiled thread is no weaker than the original thread in the parent metal.

Ideally you wouldn't want to have to use either remedy, but my gut feeling is that a helicoiled repair and keeping the bolts and flywheel stock would be the preferred method.

Too thick a bolt head can cause problems with the clutch plate too.

Mart.

[Bob C]

Originally Posted by 49fordv8f4

I would probably use a Heli-Coil if it were mine. I've never seen the thin plate under the bolts bent to lock the bolt heads either. I'm not sure the purpose for it , unless the mild steel would give more "grip" to the bolt heads to help keep them torqued than the cast iron flywheel would
Mark.

The thin plate is called a flywheel dowel retainer, keeps the dowels
from working there way out.

Bob

[Ross F-1]

Originally Posted by Bob C

The thin plate is called a flywheel dowel retainer, keeps the dowels
from working there way out.

Bob

Well, that makes sense!

The thing with the Helicoil solution is that there is precious little metal between the OD of the crank flange and the OD of the stock bolt hole. Helicoil OD would be real close to the edge.

Out hunting for parts, believe it or not my local True Value has both 12mm x 1.5 (standard fine) and 12mm x 1.25 (extra fine) taps. But so far I haven't located 12mm x 1.5 or x 1.25 grade 10.9 bolts. I have a helicoil kit in hand. I'll see what I can dig up tomorrow.

I did try a bolt about 1/4" longer, which barely clears the back of the block. Got it to 45 ft-lbs before it felt squeamish. The threads are just shot.

Mart, none of the bolts I have are drilled for safety wire (all from 8BA's)

[B-O-B]

auto parts store for your bolts.

[Brian]

Helicoil it Ross, be a reliable repair.

[CA Victoria]

Ross, you might look into these.
I have not compared them to heli-coil but have heard they are superior.
Maybe more suited to your situation.
http://www.timesert.com

[Fibber Mcgee]

My 49 has had a helicoil in it for several years and I don't know how many miles with no problems. I think I used the OD size bolt but don't remember for sure.

[rich b]

I would rethink using "hardware store" bolts for retaining a flywheel. Use bolts designed for the application; either originals or aftermarket like ARP.

[Walt Dupont--Me.]

Most of the 8BA engines don't have safety wire flywheel bolts. Walt

[Lawrie]

I would not use a heli coil in light of the OD of the coil,why not get a 12mm fine thread bolt,drill or ream out the hole it the flywheel.
I would feel a lot better if it were mine doing it this way.
Lawrie

[flathead4rd]

I like CA Victoria's solution.

[Ross F-1]

I looked into the Time Serts, but they require even more material removal than a helicoil. The engine is in the truck, I would not feel comfortable doing the countersink they require in place.

I wasn't planning to use a hardware store bolt, although the True Value has a hardened 10.9 line, but only in 12mm coarse. I'll get one at NAPA or a fastener store. I'll believe I'll be going back with a 12mm x 1.25, which has almost exactly the same pitch as a 20 thrds/inch.

Thanks for all the help!

[cmbrucew]

Ross F1
For peace of mind, remove the crank and have it drilled and tapped 45° around.
This would also give you fresh ring gear teeth for the starter
Bruce

[Ross F-1]

If I were going to pull it all apart, I'd just replace the crank. I have three others on the shelf. I don't think I'd want to add any more holes to the flange, and the dowels would be problematic.

Not sure how that would change the teeth? I use a mini-starter anyway.

[CT AV8]

Or just replace the flywheel. Easier than messing with the crank.
Has anyone here welded up a flywheel hole and retapped it?

[V8COOPMAN]

Originally Posted by CT AV8

Or just replace the flywheel. Easier than messing with the crank.
Has anyone here welded up a flywheel hole and retapped it?

Threaded hole in CRANKSHAFT flange........not flywheel! DD

[Mart]

I just did some calculations and if you can get some proper good quality bolts, it does sound like 12x1.25mm would be a good fix. If I were doing it this way I would do at least 2 bolts and might even do all 4. Don't drill out any holes in the crank as they are already above the minor diameter for 12x 1.25. You will have to drill the flywheel to 12mm.

Holding the tap square to the block might be a little tricky. Maybe drill the flywheel first then thap through. If doing it in vehicle it may be hard to ensure good alignment and removal of chips. They will just fall to the bottom of the bellhousing though, so no big deal.

You might be able to rig some sort of v block or something to hold the drill square.

Mart.

[Ross F-1]

Sponsored Links (Register now to hide all advertisements)

Mart, I am planning to make a drill guide to keep the bit square, and will go thru the flywheel. The tap drill for a 12mm x 1.25 is a 27/64, which is .422". The pitch diameter on the 7/16"-20 is .405", so I'm only removing about 8 thou all around.

This is an 8BA, so chips will just fall to the floor. I have the offending hole on the bottom.

[GOSFAST]

Hi Ross, fix it with the correct heli-coil thread. It's actually quite simple if you make a simple drill & tap guide. We've made dozens of these "guides" over the years. We have most "slotted" but you can do it by the center-to-center method on the bolt locations.

Thanks, Gary in N.Y.

P.S. Here's a couple shots of a few with one showing the tooling mounted. The same tool is used first as the drill guide then moved and used as the tap guide. The tools have all been tapped with the respective heli-coils taps.

[V8COOPMAN]

That there chingadero is geniusly simple! It don't get no slicker'n that. DD

[Ross F-1]

Got 'er done! Actually doing it once I had all the pieces in hand, fixture made, etc. took a lot less time than all the hand-wringing! Par for the course...

Gary's excellent drilling fixture inspired me to make one out of square tubing. Worked like a champ. The 27/64" tap drill leaves a little bit of the old thread, but since the 12mmx1.25 is almost exactly 20 TPI, it actually helps keep the tap going in the right way. There is almost no room behind the flange, so I rigged a piece of heavy sheet metal with a magnet to keep from drilling into the oil pan. The tap just barely made it thru to the full-size threaded part.

Thanks for all the help, glad to have this behind me!

[CA Victoria]

Looks good, I will need to store that in the memory banks. Good use of a metric bolt size.

[32phil]

Ya just GOTTA love this forum.....The wealth of information and willingness to help each other is unmatched.....anywhere.....I have no plans to drill a crank flange.... but.... the methods described will certainly come in handy in one of my upcoming disasters...I'm sure....

[Mart]

Ross, did you take a brave pill and do all 4? Just the one? Or two?

Mart.

[Ross F-1]

Just the one, Mart. I'll post a pic of how I will compensate for the heavier 12mm bolt, not that I think it's really an issue. Amazing how close the 12mm is to a 7/16".