Help finding torque value for idler gear shaft

[stringfellow]

Lyc gurus: I am reassembling a 540. I could not find a specific torque value in the overhaul manual for the 5/16-18 x .87 bolts that fasten the idler gear shaft flange to the case.

The standard torque value listed in the overhaul manual for 5/16 bolts is 204 in-lbs. That seems awfully high for this application.

Am I missing anything? Thanks.

[az_gila]

Doesn't sound too high if there is a helicoil insert in the case.

As a second opinion I checked my Superior Vantage manual (4 cylinders but a similar accessory case) and found 200 in-lbs, essentially the same number.

[stringfellow]

Originally Posted by az_gila

Doesn't sound too high if there is a helicoil insert in the case.

As a second opinion I check my Superior Vantage manual (4 cylinders but a similar accessory case) and found 200 in-lbs, essentially the same number.

I'm not sure there is a helicoil. I'll have to take a closer look. Thanks.

[jrs14855]

no helicoil. Standard torque. I believe the parts catalog calls for a washer under the bolt head.

[stringfellow]

Originally Posted by jrs14855

no helicoil. Standard torque. I believe the parts catalog calls for a washer under the bolt head.

Standard torque for coarse thread bolts in tension from AC43.13? Or standard torque from the Lyc overhaul manual that doesn't even specify thread pitch?

Why the discrepancy? Is the engine hardware...harder? Less elastic?

[az_gila]

Originally Posted by stringfellow

Standard torque for coarse thread bolts in tension from AC43.13? Or standard torque from the Lyc overhaul manual that doesn't even specify thread pitch?

Why the discrepancy? Is the engine hardware...harder? Less elastic?

Torque standards per the manufacturer's service manual.

Perhaps no thread pitch is specified since Lycoming basically standardizes on a coarse pitch thread rather than the usual fine pitch of our airframe nuts and bolts? Every bolt and stud call out in the Lycoming parts manual specifies the thread diam and pitch, you can see how they are mostly (all?) coarse pitch.

That location in my O-360 manual does not specify a washer, though the older narrow deck manual does specify a dual tab locking device that locks both bolts with one part rather than safety wire.

[az_gila]

Originally Posted by stringfellow

....

Just noticed that the right hand bolt seems to have no head markings.

Don't all Lycoming bolts have the grade 6 "three ticks" marking like the bolt on the left?

[stringfellow]

Originally Posted by az_gila

Just noticed that the right hand bolt seems to have no head markings.

Don't all Lycoming bolts have the grade 6 "three ticks" marking like the bolt on the left?

Good question. I sent a lot of hardware to the cad plater for finishing. When I got my batch back, there were only (3) 5/16-18 x .75" bolts with the heads drilled for wire. I purchased an extra thinking I had misplaced the 4th. However, the spec says x .87", so that's what I bought.

I assume these were the original bolts used in 1976 for the first run. Was the three tick convention active back then? Also, they are only drilled in one axis on the head. The new bolt was drilled in several.

[BillL]

Originally Posted by stringfellow

Good question. I sent a lot of hardware to the cad plater for finishing. When I got my batch back, there were only (3) 5/16-18 x .75" bolts with the heads drilled for wire. I purchased an extra thinking I had misplaced the 4th. However, the spec says x .87", so that's what I bought.

I assume these were the original bolts used in 1976 for the first run. Was the three tick convention active back then? Also, they are only drilled in one axis on the head. The new bolt was drilled in several.

Gil means grade 5, not six ref

And yes SAE j429 bolt spec was published before '76.

BTW - did you get any assurance on the strength of the bolts returned from the cad plater? If they are pickled for cleaning, hydrogen embrittlement can leave the bolts weak in fatigue, not good for a cycling application on engines. You might want to check with the plater for quality assurance. I have seen too any broken bolts in production due to this.

Personally, I would not use a replated bolt inside an engine. Outside you can replace them, inside they can get ground up.

[az_gila]

Originally Posted by BillL

Gil means grade 5, not six ref

And yes SAE j429 bolt spec was published before '76.

BTW - did you get any assurance on the strength of the bolts returned from the cad plater? If they are pickled for cleaning, hydrogen embrittlement can leave the bolts weak in fatigue, not good for a cycling application on engines. You might want to check with the plater for quality assurance. I have seen too any broken bolts in production due to this.

Personally, I would not use a replated bolt inside an engine. Outside you can replace them, inside they can get ground up.

Thanks for the grade correction Bill, I forgot what number to add to the 'ticks'.

But, for the OP, there are only a few internal bolts in the Lycomings and since they are not accessible after assembly using the correct, and new, hardware is definitely a good idea.

These are probably the bolts in question -

http://www.aircraft-specialties.com/...dr-lw-31h0-88/

If the IO-540 case is like the O-360 case, then there is probably an internal row of hidden case bolts -

http://www.aircraft-specialties.com/...en-lw-25s1-50/

The cost for new internal hardware is cheap insurance.


When I was buying parts for my O-360 I found Aircraft Specialties Services (in the links above) had pretty good prices, and easy to search web site, and good service. Just a satisfied customer.