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How to tell if I have through bolts in my case

lr172

Well Known Member
I am pulling my cylinders this week for new pin plugs and new rings (engine started making more aluminum again - it had tapered off, but is back again). I looked at the parts diagram for my O-320B1A and it shows through studs that thread into the right case half. However, I have read that there is a mix of those that thread into the block and those that don't. It is a different procedure for tightening the nuts on the through bolt, so would like to know. I don't rememeber paying attention to this on the overhaul.

I am guessing that I will be able to see if the case is threaded when I pull the #3 cylinder, but not sure.

I would appreciate any tips or advice on this. For those following my oil temp issue, I have determined that I am getting at least moderate blow-by, which may be contributing to my temps. Compressions were all around 70 and the oil from my last change 3 hours ago is already turning brown.

I was able to get everything striped off the engine today and will pull the jugs when the new rings get here on Wed.

Larry
 
All Lycoming engines that I am familiar with have through bolts. (6 on a 4-cylinder engine)

ONLY loosen nuts and remove one cylinder at a time. The install sequence is documented in Lycoming Service Instruction 1029.
 
If you have an A as the last digit on the s/n, then I believe it will be a wide deck engine with through studs. You will also see 1/2" spacers on the front set of studs, across from #1 cylinder. Also there will be both mounted (threaded) and through studs on each cylinder, you can look from the top down and identify the through studs as it will pass compleatly through the engine and appear on an opposite side cylinder flange. These are to be torqued simultaneously from both sides, and you may notice when torquing the cylinders back that these studs will take a lot more turns to reach torque, this due the much longer length.
Tim Andres
 
Mine is a narrow deck and I know they all have through bolts; I used poor wording in my initial post. Apparently some of these bolts use an interference fit with the case and some use a thread engagement with the case. I am trying to figure out a way to identify which I have.

SI 1029 has two methods for tightening depending upon which type of through bolt.

Larry
 
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Wide deck crankcases were built in both the thru bolt and thru stud configuration.

Is there a way to tell which is which from the exterior with the jug off? Were the narrow decks the same or were they always threaded?

Larry
 
Ok, I just found an article outlining the details. Apparently the narrow decks all had the threaded "Case bolt" (i.e. stud threaded into the case) and the wide decks used the "Body fit" (i.e. interference or close tolerance) bolts not threaded into the case.

Thanks for the help.

Larry
 
Is your intention to just put new rings and pin plugs in and put it back together? If so, you're just wasting time and parts.
 
Thru bolts

My wide deck o 320 has a crankcase of unknown history as far as manufacturing date. There are no thru bolts between the cylinders. What I call the thru studs screw into one half of the case and go thru the other half of the case and the cylinder flange.
The thru bolts go thru both halves of the case and thru a cylinder flange on each side.
A well known engine builder told me either type is fine.
 
Is your intention to just put new rings and pin plugs in and put it back together? If so, you're just wasting time and parts.

why would you say that? It is 120 hrs. SMOH. It is eating the pin plugs, so they have to go (aluminum specs and flakes in the oil filter-it had tapered off, but they are back again). Replacing with the pins w/ integral caps. I do plan to hone the cylinders for the new rings. What else could I be doing/what am I missing here?

Larry
 
The hone is what I was thinking of. You didn't mention it in your first post. What kind of hone are you going to use?
 
The hone is what I was thinking of. You didn't mention it in your first post. What kind of hone are you going to use?

I thought that may have been the case, as new rings without honing is pointless, I agree.

I was just going to use a three arm hone with 240 grit stones. I had thought about hitting it lightly with a 400 grit after the 240. I have a sunnen, but I don't think it will go past 5"

Larry
 
Ok, I just found an article outlining the details. Apparently the narrow decks all had the threaded "Case bolt" (i.e. stud threaded into the case) and the wide decks used the "Body fit" (i.e. interference or close tolerance) bolts not threaded into the case.

Thanks for the help.

Larry

Larry,
Not quite. I have a wide deck IO-360A1A (I realize my engine is completely different than yours). My engine was manufactured with 3 different thru-bolt designs, the threaded kind, the interference fit kind, and the floating kind. Give Lycoming a call and they will tell you exactly what you have based on the serial number on the case. I went through this a number of years ago, so I don't recall who I spoke with, but he was very helpful. If you have a case made by a different manufacturer (i.e., Superior or someone else) you will need to call them. If your the case was overhauled by CSI or Divco, you will need the yellow tag or other supporting documentation that has the original Lycoming serial no. because they might have filled and stamped over the original number. Ask me how I know!
 
New rings

I see nothing wrong with rings only on a 120 hr. engine. A&P # 1572130. Go to work.
 
body fit or anchored thru bolts on Lycoming crankcases can be easily identified.
If you look at the crankcase above the starter. you will see the back end of the thru bolts that go to the front cylinder on the opposite side of the engine. If you see two nuts with fat washers securing the starter side of the thru bolt then you have body fit thru studs . If you see the end of a stud that is flush with the outside of the case, with not nuts or washers, you have anchored thru studs. All Lycoming engines use thru studs, N/D cases always had anchored thru studs. W/D cases can have either anchored thru studs(earlier design) or Body fit thru studs( later design). The rear most thru studs are always anchored regardless of case vintage or style.
Hope this helps.
Good Luck,
Mahlon
 
body fit or anchored thru bolts on Lycoming crankcases can be easily identified.
If you look at the crankcase above the starter. you will see the back end of the thru bolts that go to the front cylinder on the opposite side of the engine. If you see two nuts with fat washers securing the starter side of the thru bolt then you have body fit thru studs . If you see the end of a stud that is flush with the outside of the case, with not nuts or washers, you have anchored thru studs. All Lycoming engines use thru studs, N/D cases always had anchored thru studs. W/D cases can have either anchored thru studs(earlier design) or Body fit thru studs( later design). The rear most thru studs are always anchored regardless of case vintage or style.
Hope this helps.
Good Luck,
Mahlon

Thanks Mahlon!
 
body fit or anchored thru bolts on Lycoming crankcases can be easily identified.
If you look at the crankcase above the starter. you will see the back end of the thru bolts that go to the front cylinder on the opposite side of the engine. If you see two nuts with fat washers securing the starter side of the thru bolt then you have body fit thru studs . If you see the end of a stud that is flush with the outside of the case, with not nuts or washers, you have anchored thru studs. All Lycoming engines use thru studs, N/D cases always had anchored thru studs. W/D cases can have either anchored thru studs(earlier design) or Body fit thru studs( later design). The rear most thru studs are always anchored regardless of case vintage or style.
Hope this helps.
Good Luck,
Mahlon

Mahlon,

I have a N/D case. Does the center through bolt thread into the right case half like the rear through bolt?

Larry
 
Is there a way to tell which is which from the exterior with the jug off? Were the narrow decks the same or were they always threaded?

Larry

Once you have the cylinders off, it is pretty easy to tell what is a through-stud and what is a through-bolt, the difference of course being that the former is anchored into the far side of the case from where it emerges.

Find a cylinder stud (1/2" dia) and trace it back into the case. There will be cast aluminum case "meat" there, and if you follow it across the breadth of the case and it does not pop out the other side, it's a through-stud and is anchored in the far case half. You can tell which are simply non-through-studs, because there is no case material behind them, they are obviously shorties and immediately anchored.

Positive identification of a wide deck case also helps, eg the absence of the hold-down cylinder base plates and the use of normal nuts instead of the allen-head caps.

A page like this from the illustrated parts manual is also incredibly helpful. This is from the "standard cylinder flange" IO-540 parts manual. If you know you have a wide-deck, there is a special manual for that, whether you have a 360 or 540.

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