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Crankcase bolt type for O320-A2B

Robert M

Robert M

Well Known Member
Hi guys!

I am in the process of accumulating all the hardware necessary to put my engine back together again, specifically the crankcase. In the Lycoming Parts Catalog PC-103, in figure 1-5, Standard Crankcase, Crankcase Attaching Parts, Reference # 6, STD-1416. I can't seem to find that particular bolt at any of my favorite shopping locations based on the number given.

Since these bolts are covered by the oil sump and inaccessible from the outside, I'm guessing they are drilled shank bolts (doesn't say in catalog).

These STD-1416 bolts are 1/4" x 20 x 1 1/2". I believe a replacement for these would be AN4-14. Although the AN4-14 are 1/4" x 24 X 1 1/2", I believe they will work but would require a 24 thread castle nut.

Anybody know if the AN4-14 would be a correct replacement?

Thanks.
 
Robert M said:
Anybody know if the AN4-14 would be a correct replacement?
Click to expand...

Looks like part number LW25S1.50 has replaced the STD-1416 bolt. Try a search for that. Some in stock here:
http://www.cessnadirect.com/lw25s1-50.html

Superior has part number SL25S-1.50, which is a PMA approved replacement for both the LW25S1.50 and STD-1416:
http://www.superiorairparts.com/downloads/eligibilities/lycoming/SL25S-1.50.pdf

An AN4 bolt will have 1/4-28 fine threads. One reason you wouldn't want to use these here is the torque requirement. You would have a very different pre-load on the bolt if you torqued a fine-thread bolt/nut to the same value as a coarse thread bolt/nut. Another is the thread length and shank length dimensions. Without a drawing of the Lycoming bolt there's really no telling whether the dimensions of an AN bolt are even close. You may get the overall length right, but you may end up with threads taking a bearing load or other undesirable configuration.
 
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hardware kit

I just ordered in a couple of ECI hardware kits for the engine assembly. I have not used one to assemble yet but looks pretty complete.

Jesse
970-874-7575
 
Bolts

Dart Aircraft in Waco TX is very helpful in sorting out part number changes. They sell Superior, ECI and Lycoming parts. Excellent service.
I believe there is a change in the torque specs for the 1/4" case bolts, can't remember where I found that.
 
l'll bet ya....

When you get the right bolt from lycoming or other supplier, I bet you find that it is an SAE Grade 8 bolt.
Someone please tell me if I'm wrong.
 
scsmith said:
When you get the right bolt from lycoming or other supplier, I bet you find that it is an SAE Grade 8 bolt.
Someone please tell me if I'm wrong.
Click to expand...

You may be right, but are you willing to bet your engine (or at least the hassle of dropping the sump to fix) on it in order to save less than $20?
 
I just rebuilt my o-320. The case bolts are just standard bolts. They were not Grade 8 and not even Grade 5. The 1/4" perimeter bolt don't really hold the case together, just the edges for sealing and rigidity. In my case, the three bolts in the sump area were the same 1/4-20 standard bolts but were drilled and used castle nuts. I presume this is because loose bolts cannot be identified during inspections.

Larry

Robert M said:
Hi guys!

I am in the process of accumulating all the hardware necessary to put my engine back together again, specifically the crankcase. In the Lycoming Parts Catalog PC-103, in figure 1-5, Standard Crankcase, Crankcase Attaching Parts, Reference # 6, STD-1416. I can't seem to find that particular bolt at any of my favorite shopping locations based on the number given.

Since these bolts are covered by the oil sump and inaccessible from the outside, I'm guessing they are drilled shank bolts (doesn't say in catalog).

These STD-1416 bolts are 1/4" x 20 x 1 1/2". I believe a replacement for these would be AN4-14. Although the AN4-14 are 1/4" x 24 X 1 1/2", I believe they will work but would require a 24 thread castle nut.

Anybody know if the AN4-14 would be a correct replacement?

Thanks.
Click to expand...
 
Bolts

lr172 said:
I just rebuilt my o-320. The case bolts are just standard bolts. They were not Grade 8 and not even Grade 5. The 1/4" perimeter bolt don't really hold the case together, just the edges for sealing and rigidity. In my case, the three bolts in the sump area were the same 1/4-20 standard bolts but were drilled and used castle nuts. I presume this is because loose bolts cannot be identified during inspections.

Larry
Click to expand...

They may very well be the equivalent strength of "just standard bolts" which would imply hardware store bolts. Hardware store bolts are only available in 1/4" length increments. Some of the Lycoming bolts are 1/8" INCREMENTS. Lycoming bolts are cadmium plated, hardware store are usually not cadmium.
 
scsmith said:
When you get the right bolt from lycoming or other supplier, I bet you find that it is an SAE Grade 8 bolt.
Someone please tell me if I'm wrong.
Click to expand...

If you do as much research as I did when building mine you'd find the spec for Lycoming engine bolts is exactly what you suggest. A very experienced engine builder confirmed this and pointed me to the most economical source.

But, as also pointed out, the 1/8" increments mean you'll use a few longer ones but the difference between $2 and .20 times all the case bolts is substantial. It's one thing to be cautious when not knowing any better, a good idea, but with enough information there are options. Looks like your qualifications put you in the latter group!
 
perhaps not so much cost as availability

It may not even be a discussion about cost. If I need a handful of bolts and I have to order them from an engine builder/supplier, it is going to take a while, and cost shipping too. How often have you paid $10 shipping on a $7 purchase. (so I guess it still is about cost).

But when you can go to an auto parts store and get the right bolt, why not?
I don't remember mine being a length problem.
 
flyingriki said:
If you do as much research as I did when building mine you'd find the spec for Lycoming engine bolts is exactly what you suggest. A very experienced engine builder confirmed this and pointed me to the most economical source.

But, as also pointed out, the 1/8" increments mean you'll use a few longer ones but the difference between $2 and .20 times all the case bolts is substantial. It's one thing to be cautious when not knowing any better, a good idea, but with enough information there are options. Looks like your qualifications put you in the latter group!
Click to expand...

So are you saying that the "STD" bolts specified by Lycoming are Grade 8 bolts?

Larry
 
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