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Continental stud may have pulled out

bob turner

Registered User
Not sure, but my buddy may have a through stud that pulled out during light cylinder torquing. My manual is at the airport.
Are Helicoils an approved repair for these critical studs, or is it off to Divco?
 
I am sure it is - is it a legal field fix?

C-85 that has been mistreated with too many top overhauls. Last entry before prop strike was "rebuilt" and they even got the crankshaft wrong. One hour on "rebuilt" cylinders, and no hone marks?

This is a disassembly, magnaflux, mike, and re- assemble. Crank is beautiful, bearings brand new, but a lot of other anomalies, especially logbook ones.
 
How does a helicoil fix a through stud?
Also my question. Through studs don’t thread into anything other than the nuts on opposite cylinders or am I mistaken? I’m not an A&P but I just watched and handed wrenches to one doing a top on an IO 520BB

Edit: Unless they thread into a boss on the opposite case half.

Rich
 
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I may have the nomenclature wrong. On the 85 there are long studs that are seated in one case half and are used to hold the cylinder on the opposite side. They are threaded into the soft case aluminum near the main bearing seats. Those threads have pulled out.
 
I may have the nomenclature wrong. On the 85 there are long studs that are seated in one case half and are used to hold the cylinder on the opposite side. They are threaded into the soft case aluminum near the main bearing seats. Those threads have pulled out.

Happened recently to an 0-200 we had here in our shop... did a top and when torquing down pulled one of the Case studs... we wound up sending it to Divco because the case half’s were fretted.. They put a helicoil in it after doing a full overhaul on the case...

Brian


Sent from my iPhone using Tapatalk
 
Magical things happen at Divco, we’ll worth a stop if you’re even in Tulsa.
 
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I assumed that he meant a stud threaded into a boss in the opposing case half.

A helicoil is a good fix for a pulled stud. I'm not going to look up the reference, but it's a common repair (and I have used that repair on O-200 cases). However, DIVCO will tell you these cases do fatigue from the studs being torqued multiple times and after a number of overhauls, should be retired rather than continuing to add helicoils and inserts to replace pulled threads in a fatigued case. So the owner (or his mechanic) will have to make a decision about whether this pulled stud is a one off incident that would be appropriate to repair with a helicoil, or whether it is a fatigued case that needs to be replaced. If I remember correctly (which I may not as it's been a number of years), the guys at DIVCO told me they really didn't want to overhaul a case more than 3 times, which could be loosely interpreted to say they recommend scrapping it after about 7000 hours.

He will have to split the case anyway to tap and insert the helicoil as the helicoil insert is larger than the stud hole in the opposite case half hole. If it's a really fatigued case, he may have other studs start pulling when he puts the case back together again and starts torquing down the cylinders. Been there. Ended up replacing the case.

-Cub Builder
 
I may have the nomenclature wrong. On the 85 there are long studs that are seated in one case half and are used to hold the cylinder on the opposite side. They are threaded into the soft case aluminum near the main bearing seats. Those threads have pulled out.

A cylinder was replaced the year before I bought my C85 powered Cub. One of these studs was overtorqued and ended up cracking around the main journal in the case, which I noticed 400 hrs later while replacing seals. Divco rejected the case, ended up with a C85 stroker when it was all said and done.
 
I got my manual. Page 55 is the authority for the Helicoil. Then I went to inspect the engine. It was not the stud I expected, and it had been Helicoiled before. It now needs a larger insert.

I have had Divco do work. They can weld up broken bearing bosses, so inserts would be childs play for them. I did not know that new cases were available.

I pulled all cylinders today, and there are several suspicious studs. Thanks for your input - I will let you know of the outcome. This has never happened to me before.
 
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