Stripped flywheel bolt

Ross F-1

Ross F-1

Well-known member
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!
 
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.
 
Charlie ny said:
Ross,
I'd go with the 12mm if it was mine.
Charlie ny
Click to expand...

49fordv8f4 said:
I would probably use a Heli-Coil if it were mine. ..
Click to expand...

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???
 
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
 
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.
 
49fordv8f4 said:
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.
Click to expand...

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

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

Bob
Click to expand...

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