Cannot tighten Ford Crankshaft Pulley bolt to spec

Jcorstorphine

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I have been rebuilding my Ford diesel engine and have at last got all of the Torque to Yield bolts with the exception of the M20 x 1.5 pitch on the crankshaft pulley. This bolt is torqued to 20 Nm then tightened through 120 degrees but try as I might, I cannot get anywhere near the 120 degrees. Best I can get is about 50 degrees at which point I am pulling 220 Nm on the torque wrench.

Is it possible that as the bolt has been used before, I can no longer stretch it to the desired amount as set out in the manual.

My concern is that the “main crankshaft timing gear” is only secured by the locking force produced by the bolt with only a 3 mm seloc pin to provide location. If the bolt were to slacken, the timing gear may slip causing untold damage to the engine.

One thought was to use a Schnorr or Bellvile washer to provide a permanent tension on the bolt. The washer I am looking at can produce 20,000 lbs of tension in the a 20 mm bolt when fully compressed but will this be similar to the tensile force created by stretching a 20 mm x 1.5 mm pitch bolt by 1/3 of a turn i.e. equal to 0.5 mm stretch.

I am reluactant to use Loctite in case i need to get the bolt off again to change the crankshaft seal as I nearly gave myself a hernia getting the dam thing off in the first place.

All suggestions or comments gratelfully received.

John
 

rotrax

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I have been rebuilding my Ford diesel engine and have at last got all of the Torque to Yield bolts with the exception of the M20 x 1.5 pitch on the crankshaft pulley. This bolt is torqued to 20 Nm then tightened through 120 degrees but try as I might, I cannot get anywhere near the 120 degrees. Best I can get is about 50 degrees at which point I am pulling 220 Nm on the torque wrench.

Is it possible that as the bolt has been used before, I can no longer stretch it to the desired amount as set out in the manual.

My concern is that the “main crankshaft timing gear” is only secured by the locking force produced by the bolt with only a 3 mm seloc pin to provide location. If the bolt were to slacken, the timing gear may slip causing untold damage to the engine.

One thought was to use a Schnorr or Bellvile washer to provide a permanent tension on the bolt. The washer I am looking at can produce 20,000 lbs of tension in the a 20 mm bolt when fully compressed but will this be similar to the tensile force created by stretching a 20 mm x 1.5 mm pitch bolt by 1/3 of a turn i.e. equal to 0.5 mm stretch.

I am reluactant to use Loctite in case i need to get the bolt off again to change the crankshaft seal as I nearly gave myself a hernia getting the dam thing off in the first place.

All suggestions or comments gratelfully received.

John[/QUOTE Hi, I have been in the same position as you when the correct one use only stretch bolts have not been available. This was on high RPM highly stressed motorcycle race engines where a failure would have been REALY expensive. I would use a small amount of locktite-just a dot-and never had a failure. If you cant get the new bolt dont be worried about locktite-it breaks down with modest heat.Your other suggestions have merit.whatever you decide,Good Luck!
 

Bilgediver

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I have been rebuilding my Ford diesel engine and have at last got all of the Torque to Yield bolts with the exception of the M20 x 1.5 pitch on the crankshaft pulley. This bolt is torqued to 20 Nm then tightened through 120 degrees but try as I might, I cannot get anywhere near the 120 degrees. Best I can get is about 50 degrees at which point I am pulling 220 Nm on the torque wrench.

Is it possible that as the bolt has been used before, I can no longer stretch it to the desired amount as set out in the manual.

My concern is that the “main crankshaft timing gear” is only secured by the locking force produced by the bolt with only a 3 mm seloc pin to provide location. If the bolt were to slacken, the timing gear may slip causing untold damage to the engine.

One thought was to use a Schnorr or Bellvile washer to provide a permanent tension on the bolt. The washer I am looking at can produce 20,000 lbs of tension in the a 20 mm bolt when fully compressed but will this be similar to the tensile force created by stretching a 20 mm x 1.5 mm pitch bolt by 1/3 of a turn i.e. equal to 0.5 mm stretch.

I am reluactant to use Loctite in case i need to get the bolt off again to change the crankshaft seal as I nearly gave myself a hernia getting the dam thing off in the first place.

All suggestions or comments gratelfully received.

John

This bolt will be at least grade 8 so you are a long way short of the required clamping force and loctite will not help.

Are you sure the bolt is not thread bound. IE free to run up and down the thread. Can you borrow a geared head type torque wrench.

Forget the bolt having been used. If this was the case you might see it reach the desired angle with LESS torque if stretched. Your target is in excess of 300 NM
http://www.lsuagcenter.com/en/lawn_...uipment/hand_tools/Bolt+Tightening+Torque.htm


Just an after thought John....Are you using the correct length bolt with spacers if shown in the assembly drawing. IE maybe a thick washer. If you are using a shorter bolt then the torque by turn figures you obtain will be wrong. On many Mechanical assemblies it can be necessary to use what appear to be longer than necessary bolts in order to obtain the required tension as well as elasticity. IE the bolt acts as a stiff spring.
 
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