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Fly to Crank Bolts Stripped the Crank


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Engine_-_Fly_to_Crank_Strip_2_111305.jpg

 

There is the bolt with the ford part # and a ruler. I am doing a ford 302 swap and was putting the flywheel on. We got the bolts for a M/T from the ford dealer and were proceeding to torque them down to 80 ft-lbs. Three of them stripped at around I would say 40. One of them could not even be removed, although it would rotate freely both directions, It simply wouldn't let go. We finally got it out by using the crowbar + the channel locks. Anyway, someone screwed up and speced us the wrong bolts. After looking at it the bolts would of had only 1/4" max of bite into the crank. Turns out they gave us the bolts for an Automatic (their flywheel/flexplates are MUCH thinner). So we used the tap and die to fix the threads and were thinking of replacing the bolts with grade 8's with more length and using all of the threads the crank has left (minus the first 1/4" which is thrashed) which is equal to what the correct bolts would have been able to hold onto. What bothers me though is that it is such a crucial part. I know that the thread amount will be the same, but it just doesn't seem like it is a good place to cut corners at all. Tommorow my brother is calling up ford to tell them whats up, because this is unacceptable. Any thoughts? I am going to go mope about my destroyed crank, might as well be the whole block b/c we don't have the means or skills to replace the crank.

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To reach full strength, the length of remaining engaged threads needs to equal the diameter of the bolt, anything less than that and you will have problems I can almost guarantee it.

 

Measure the length of the remaining threads and compare that to the diameter of the bolt, go from there.

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To reach full strength' date=' the length of remaining engaged threads needs to equal the diameter of the bolt, anything less than that and you will have problems I can almost guarantee it.

 

Measure the length of the remaining threads and compare that to the diameter of the bolt, go from there.[/quote']

 

There is going to be about 5/8" of bite assuming each hole was stripped 1/4" in, which they wernt. But i personally don't feel comfortable driving such a stressed piece that has faulty threads (we needed the tap and die to rewrite the threads) or is missing threads at critical depths (the farther away the threads are the less torque they can apply). I simply don't want a 20 something pound flywheel cutting my leg off at 5,500 rpm....

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I think there is a misunderstanding. There is absolutely nothing wrong with the flywheel. The stripped threads are acctually the threads in the end of the crank :icon52: . Here is a CAD to better understand it.

 

flybolt.jpg

 

So basically from the head of the bolt back there is 3/8" of no thread (in flywheel) then 1/4" of stripped thread (also no thread, in crank) and then there is 5/8" of bite in the crank.

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Well, John has been under alot of pressure these days, you know, too much coffee and one too many krispy kremes.

 

The flywheel isn't something you want to have to come off. Better to check it as you have been advised, and if necessasary, replace the crank. Life is a beach and then you ______ one. You fill in the blank as you see fit, but that's life in the hotrod lane.

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Yah I am going to talk to ford for now and see what they say. I can't replace a crank, I don't have the money for the crank, and I don't have the speciality tools if there are any. I guess I could do it and it would be a good learning experience, but it is probably cheaper just to get a new JY motor in the same condition. Plus i would feel bad putting in a brand new crank while not overhauling everything else downthere... My main beef with it is that Ford sold me the wrong bolts, straight from the dealer!! Ugh.

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That sucks that they sold you the wrong length bolts, but seeing as you installed them (ie; not a ford tech) I think you'll be hard pressed to get any help from them... Judging from your diagram (assuming the scale is correct) i'd say you're ok. There is still plenty of good thread there, and if you get good quality proper length bolts, along with locktite in there, you should be fine. My .02$. :)

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Scale is not correct. There would be .625" of good thread and .25" of stripped followed by .375" of no threads (flywheel). 7/16" 20 bolts.

 

It seems all of the ford databases got the part numbers mixed. Ford makes auto and manual bolts for the fly to crank. The auto bolts should be shorter because the flexplate is only 1/8" thick, the flywheel is 3/8" thick and so the manual bolts should be longer. but in their parts database they ahve manual bolts listed at about .75" and auto bolts at 1.06" that is wrong. All of the dealers I have called have confirmed that these are the specs. All of the people and performance shops I have asked have said that that is crazy the manual bolt should be longer. At kragen they even brought out a flexplate and a flywheel to compare. The manual bolts for sure should be longer.... I guess ill badger ford some.

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Sorry, my mistake. Buy another crank... :-)

 

Just chase the holes with a tap, buy the correct bolts, and if you can get them torqued to spec you should be fine. Might also use some blue Loctite. If you can't get them torqued, then you'll need to drill the hole(s) out and install an insert.

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Unfortunately it's a critical joint there, tough luck, you could ignore it if you have enough engagement and it will hold the torque, just check it after 1kmi if you are nervous. But replacing the crank is easier than you'd think all you have to do is replace the main bearings and the crank (measure thenm accurately, the main bearings are split and will press in pretty easily, get a good book about rebuilding ford engines and follow it) and while you're at it replace the front and rear seals and of course a new oil pan gasket. Also check to be sure your oil pickup is on there real good. It's no biggie. If your engine is internally balanced, have it balanced, otherwise you can just externally balance it as you would have normally, everything else is bolt and torque. Not a biggie IMO In my opinion, I'd rather replace a crank than replace a camshaft. I think it's easier.

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Unfortunately it's a critical joint there, tough luck, you could ignore it if you have enough engagement and it will hold the torque, just check it after 1kmi if you are nervous. But replacing the crank is easier than you'd think all you have to do is replace the main bearings and the crank (measure thenm accurately, the main bearings are split and will press in pretty easily, get a good book about rebuilding ford engines and follow it) and while you're at it replace the front and rear seals and of course a new oil pan gasket. Also check to be sure your oil pickup is on there real good. It's no biggie. If your engine is internally balanced, have it balanced, otherwise you can just externally balance it as you would have normally, everything else is bolt and torque. Not a biggie IMO In my opinion, I'd rather replace a crank than replace a camshaft. I think it's easier.

 

$$$$$$$$$$$$$

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I dont really think its Fords fault. You couldnt tell that they werent long enough? A flex plate is much thinner than a flywheel. I think your going to be screwed as far as Ford helping with the repairs. If one of their techs would have installed the wrong bolts sure but they probably would have noticed that they were too short.

 

 

Guy

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I dont really think its Fords fault. You couldnt tell that they werent long enough? A flex plate is much thinner than a flywheel. I think your going to be screwed as far as Ford helping with the repairs. If one of their techs would have installed the wrong bolts sure but they probably would have noticed that they were too short.

 

 

Guy

 

That is a possibility. But I dont see it as my responsibility to make sure the part fits if that is what every ford dealer specifies then I believe that it is indeed the correct bolt. Having no prior experience with this part of the engine, I simply assumed it was normal. We will see what happens, for now I am researching helicoils.

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Is there room behind the crank flange to put a nut, perhapse you could get some longer bolts and counter tighten a nut behind? That'd be reasonable IMO. As I recall from the Chevy, there was enough room to put nuts back there. You could use super high strength loctite.

 

You're worried about cutting your feet off, but you're putting an engine with 2X original torque in a 35 year-old car? Come on here weigh the odds. If you throw a rod on some JY engine and it rcochets back I doubt your firewall will stop it.

 

It's a sad state of affairs though, I had a similar experiance with the crank pulley bolt I was given one that was too long and before I could even tighten it down to 30ft-lbs it stopped turning and the crank was still 1/4" spaced, so I started backing it out and it took over 50ft-lbs to walk it out, when I got it out it was so mangled on the tip I thought for sure the threads inside the crank were trash, turns out the bolt was 3/8 too long and all the threads gummed up. I ran a magnet in to take out the shavings which were were minimal and chased the threads which were luckily allright and took the torque witht he correct bolt. But what a nightmare.

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You're worried about cutting your feet off, but you're putting an engine with 2X original torque in a 35 year-old car? Come on here weigh the odds. If you throw a rod on some JY engine and it rcochets back I doubt your firewall will stop it.

 

What type of rod? Push rod or connecting rod? Also, it is a salvage 94 engine that my brother used for about 3 years in his capri, it is sound. I wouldn't worry about the doubling of torque in the Z, as almost the entire driveline will be new. The rod through the firewall I guess is a concern, but it is going to be a stock engine that wont be abused. It is for the street, I dont plan to push it hard enough to throw anything. But if there is a weak flywheel bolt or two I am not sure how hard I would have to push. It just makes me uneasy that is all.

 

I am lucky though that the last bolt stripped, we got almost all of the bolts to 80 ft/lb with only 1/4" bite, if we had acctually run the engine with that much, I think the flywheel would of come off for sure.

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