R26 Head Bolt - Grade of Bolt

Begonnen von Kurt in S.A., 25 September 2010, 18:03:18

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Kurt in S.A.

Just wondering about something...I saw a post on a another forum where it appears the person sheared off one of the head bolts on his R26.  Apparently he got the broken piece out but then wanted to know what grade of bolt he could use as a replacement.  He suggested things like 10K or 10,9.  I suggested he get a bolt from a BMW supplier, but I get the feeling that's not an option or he's trying to do something locally at least to get going again.  I've done some checking and even asked at my dealer today, but no one really has any ideas.  I think it would be important to get a bolt that was designed for the application - some stretch while torquing, low compression motor, but not so brittle as to break.

Anyone know what the bolt grade is?  Does anyone know what the markings on the head of the bolt...that tells what the bolt grade is.

BTW...he mentioned that he used 25 pounds, 11kg, 111 newtons on the bolt.  That may have been his problem if he used a torque wrench that was longer than 12 inches and he put 25 pounds on it.  I told him it needed to be 25 ft-lbs or 33 newton-meters.

Kurt in S.A.
Kurt in S.A.

Kurt in S.A.

Kurt in S.A.

Rütz

#1
Zitatlike 10K or 10,9
"10K" is the old labelling of "10.9", which is shown on the original bolts from the 60's.
It is a european specification Norm:
1. digit indicates the force the bolt can handle without tearing.
"10" means 1.000 N/mm²

2. digit indicates the percentage of the above force, at which the bolt will start stretching.
"9" means 90%.

So "10.9" means: The bolt will start stretching at 900 N/mm² and tear beyond 1.000 N/mm².


Hope my english is not too pidgin...
Ruetz
I never dared to be radical when young.
For fear it would make me conservative when old. (Robert Frost)

Kurt in S.A.

Thanks...that's a good explanation.  I'm not much of a bolt guy, but there are other engineers at work who are.

I had heard somewhere else that the 10K and 10,9 were essentially the same.  So, 10,9 is basically the grade of bolt for a replacement?

If you're interested, he posted a picture of two original bolts (one sheared off) and a replacement bolt he's thinking of using.

http://www.freeimagehosting.net/image.php?97bd655015.jpg

I think what he wants to use is going to be too long.

Kurt in S.A.
Kurt in S.A.

sprint150

Dear Kurt,
obviously the alternate bolt showed in your picture has less tensile strength than the original bolts- do you know the index on the bolt head (which seems to be larger)?
Further, there is a difference regarding hardening process. For me, the original bolt was just overtorqued as you also assumed before.
Off topic: S.A.= San Antonio, TX- home of a part of my former company Fairchild/Dornier. They used to manufacture the wing of the D0 328 Commuter Aircraft....They went bankrupt in 2002... Are they still in SAT?

Greetings

Wolfgang

Kurt in S.A.

Zitat von: sprint150 am 26 September 2010, 11:15:12
Off topic: S.A.= San Antonio, TX- home of a part of my former company Fairchild/Dornier. They used to manufacture the wing of the D0 328 Commuter Aircraft....They went bankrupt in 2002... Are they still in SAT?

Wolfgang -

I don't think so...haven't heard about them in quite some time.  One website says that M7 Aerospace acquired their assets and now someone else as taken over M7's assets.

I recall going out to visit the facility about 10 years ago.  We were asked to consider performing a full-scale test of the wing.  Got a tour of the facility.  As I recall, they decided to do things in-house.  I believe not long after that things began to change within the company.

Kurt in S.A.
Kurt in S.A.

Rütz

Hi Kurt,
if it has the same grade (10.9), i think, this bolt will do "at a pinch". Shortening should be no problem.
Perhaps critical: The original bolt is a "Fit Screw" ("Close-Tolerance-Bolt"?), we say "Paßschraube", that means, the stem of the bolt is exact as thick as the outer diameter of the thread.
In the particular case this is important to transmit the torque from the head to the thread without to much torsion... :-\\

Ruetz
I never dared to be radical when young.
For fear it would make me conservative when old. (Robert Frost)

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