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Help finding torque value for idler gear shaft

stringfellow

stringfellow

Active Member
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.

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

no helicoil. Standard torque. I believe the parts catalog calls for a washer under the bolt head.
 
jrs14855 said:
no helicoil. Standard torque. I believe the parts catalog calls for a washer under the bolt head.
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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?
 
stringfellow said:
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?
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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 said:
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?
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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.
 
stringfellow said:
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.
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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.
 
BillL said:
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.
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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/bolt-3125-18-x-88-long-hex-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/bolt-250-20-x-1-50-long-dr-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.
 
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@stringfellow I saw your nick and immediately the Airwolf theme popped into my head, thanks for the memory :D
 
The bolt should never have been replated as then they are not spec bolts that were in the engine. If one was worried about the plating new bolts are not that expensive in the long run if one fails and at the least trashes the engine. Also noticed they are not the same like the other poster said, two different safety wire hole counts. Inside an engine there is no room for anything that is questionable.
 
Bolts

Bolts from former ECI, Superior and Lycoming may not look the same or have the same plating. I got new bolts- some were silver, some had the yellow dichromate dip that is done after the cad plating.
Nothing wrong with re plating if it is done by an approved shop.
 
I use Precision Metal Finishing in Canby, Oregon. They do primarily aircraft hardware I think and are used by many engine shops to the best of my knowledge.

Thus far the only hardware that's been plated and reused is the case perimeter bolts. I purchased new nuts and star washers, however.

It is probably a good idea to replace the other three 5/16-18 bolts for the idler shafts, as they likely do receive a serious amount of force (it is indeed LW-31H0.88, which supersedes STD-2167.) So, I've just ordered some. I wish I could solve the mystery of why I only have x.75" bolts instead of .88". This engine is a first run and this is its first overhaul. I plunged those holes with the calipers an their depth is approx 1", save for one which is much deeper or open to the crankcase.

Case perimeter bolts, and even the spine that's open to the sump I am not as concerned about. I did replace the STD-1409s with STD-2249s per SI 1509.

It would be nice to replace all engine hardware with new, but it adds up.
 
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