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The mkiv Supra Owners Club

broken bolt on crankshaft


jza800

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the worst is almost happened to me, have an engine which has broken one off the bolts on the crankshaft to the flywheel, can i Mount the flywheel without that one bolt, because there are 7 other bolts????

 

Was this doing it up and if so what bolts and flywheel are you using.

 

If stock don't worry but if not, Make sure they havnt bottomed out on the block.

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Place nut on the top of the broken bolt and weld it inside.

 

Take the spanner and undo the nut with bolt.

 

Job done!

That's probably what I would try first.

 

The thing that would worry me, is if it had an effect on balance - as mentioned above.

 

Any crank vibrations at what could be 7k rpm plus, could be very nasty

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previously owner have tried to get i out, and then came to me for help.. and it stuck, so therefore I must send the work on to a workshop .. but is it possible to do this without taking the crankshaft out, as it seems in my eyes to be posible to do without taking it off

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Have you tried drilling it and use a tap to get it out? Dont know what it's called, but like this:

 

http://www.atoy.fi/kuva-data/119-014300011.jpg

 

 

It's just me, but if you cant get it out without pulling the crank, I'd just leave it out. The bolt is so near the middle of the crank and in the end, I doubt it will cause any severe unbalance and after all it's only the end of the nut that is missing, which what, 5-10grams in a 15kg crank.

Edited by Krister (see edit history)
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I have tried with that, with no luck, so the last i tried was with a torx, but as you can see the broke too :( so i think the last solution is to drill it out, and remake the thread in the crank Again.. i really dont hope they will have the crank out for the small a Work.. i think if they are a little carefull they can do it without getting metal shavings in the engine..

 

 

I had the same thought that 7 bolts would be ok, unless I could get the drill out and put 8 new in, have allready 8 nye bolts.

Edited by jza800 (see edit history)
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If your doing this by hand the first thing i'd do is make a ring to bolt to the end of the crank, say 10 mm thick

 

Drill 5 holes in it using the same PCD that's in the crank, use 4 of them to bolt the ring to the crank, you use

the 5th as a guide hole to keep you centralised over the hole with the broken bolt in it

 

I'd make a drill bush to go in the 5th hole and make it 20 mm long which will keep the drill online and square

with the hole.

 

Find out the tapping drill size of the holes in the crank and drill out using a slightly smaller diameter drill

 

Excuse my dodgy sketch but this is what i'd make easily in 30 mins and should let you get the bolt

out with no damage to the thread

drill ring.JPG

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If your doing this by hand the first thing i'd do is make a ring to bolt to the end of the crank, say 10 mm thick

 

Drill 5 holes in it using the same PCD that's in the crank, use 4 of them to bolt the ring to the crank, you use

the 5th as a guide hole to keep you centralised over the hole with the broken bolt in it

 

I'd make a drill bush to go in the 5th hole and make it 20 mm long which will keep the drill online and square

with the hole.

 

Find out the tapping drill size of the holes in the crank and drill out using a slightly smaller diameter drill

 

Excuse my dodgy sketch but this is what i'd make easily in 30 mins and should let you get the bolt

out with no damage to the thread

 

That is alright, but will let the machine shop to the rest as they probely have the more right Tool than i have, but is it a easy fix for the machineshop?? and can they do it with the crank in the engine, as i dont feel like taking it out, as thet will result in new bearings :(

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What will he need to drill tool-hard material though?

 

I'm assuming a torx bit is considerably harder than the crankshaft material.

 

Carbide drill bit?

 

Yes a carbide drill bit will be required if there's broken off torx bits etc in the bolt.

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