many steps backwards

Well, it’s been a month since I posted and it’s time to let you all know that I’m still alive & kicking.   The broken bolt will hopefully be removed in a few weeks (more about that in a moment.)   For now, I’m here to report that the engine is off of the plane and enough accessories have been removed to gain access to the generator, which will have to be removed to get to the bolt in question.

Steve Beaver follows the AV8tors group and is in the hanger next to the Cardinal.  He graciously lent me an engine hoist which I trundled from F8 to C1.

Dave Rohlick, who had helped drive the plane from Westerville to DLZ, volunteered an afternoon to finish unhooking and actually pulling the engine off. All in all, it didn’t go too badly.   Of all of the connections, there was only 1 wire that needed to be divided.  (Specifically, the “easy start” wire from the key switch panel to the ignition modules.  I don’t have the tool to remove the pins from the connectors, and did not want to remove the ignition modules if I didn’t have to.  That wire was cut and will be re-connected with the spade/blade connecters used for the EGT probes.)

Alas, after we pulled the engine, the magnitude of the fractured bolt revealed itself to be of serious issue.  Recall its dimensions: M6x90.  That 90 refers to mm.  I estimate that the bolt broke at about 70 mm or so.  The water pump was removed, but it’s only about 20 mm thick.  In other words, the broken fragment is at the bottom of a 50 mm hole and is essentially unreachable.

At the bottom of my despair, I imagined that I would have to ship the engine to a distant shop for removal of the generator on the rear end.  (Removing the generator should expose the broken bolt for removal.)  As fortune would have it, Shane (proprietor of Shamrock Aviation) is rated Heavy Maintenance on the Rotax 912 family and is qualified to remove said generator here at DLZ.

He came over to the hanger last Friday and looked things over.  He’s got an engine in the shop now and will need to finish that up and make room for mine.  (He has a dedicated area for working on one engine at a time.)   I’ve got the 1st week of January off work and he quickly suggested that I come to the shop and watch/do much of the work involved in the project.  BTW, he estimates it to be a 1 day job—much better than my guess!

If all goes well, I will return to the project on Jan 4 to remove the generator, remove the bolt, reinstall the generator and get the engine back to the hanger.  From there, re-hang the engine, re-attach all of the connections & plumbing and get back to trying to be airworthy.

 

Major Surgery

ugly mess of an amputated engine

 

Well, damn. Fractured water pump bolt.

 

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-   -   can you substitute class 12.9 for 8.8 bolts? (http://www.vansairforce.com/community/showthread.php?t=131641)

 

dbhill916 11-16-2015 03:43 PM can you substitute class 12.9 for 8.8 bolts?   Hi all, Is it safe to use bolts that are stronger than specified by Rotax, or will there be an unintended consequence (e.g., damage to the internal threads, etc.)? I over torqued the metric bolts on my water pump housing and will be pulling the engine to remove & replace the affected bolts. Unfortunately, LEAF is quoting 6 weeks to get replacement M6x90 bolts. I have located a domestic source of M6x90 bolts, but they appear to be considerably stronger as they are Class 12.9, vs Class 8.8 as found on one of the ruined bolts in my possession.   A quick internet search shows that Class 8.8 has a yield strength of 660 MPa while Class 12.9's yield strength is 1100 MPa. Is it possible to do damage using bolts that are too strong? Will the torque specifications be the same? If not, is there a known conversion? If not, then I will not use them and will just wait for Christmas.  thanks in advance, -dbh

 

Captain Avgas 11-16-2015 06:40 PM Stick with 8.8   Quote: Originally Posted by dbhill916 (Post 1029996) Hi all, Is it safe to use bolts that are stronger than specified by Rotax, or will there be an unintended consequence (e.g., damage to the internal threads, etc.)? I over torqued the metric bolts on my water pump housing and will be pulling the engine to remove & replace the affected bolts. Unfortunately, LEAF is quoting 6 weeks to get replacement M6x90 bolts. I have located a domestic source of M6x90 bolts, but they appear to be considerably stronger as they are Class 12.9, vs Class 8.8 as found on one of the ruined bolts in my possession.   A quick internet search shows that Class 8.8 has a yield strength of 660 MPa while Class 12.9's yield strength is 1100 MPa. Is it possible to do damage using bolts that are too strong? Will the torque specifications be the same? If not, is there a known conversion? If not, then I will not use them and will just wait for Christmas.  thanks in advance, -dbh The long answer to this requires a thesis on bolts. The short answer is to replace the 8.8 bolts with the same grade as specified by the engine manufacturer. This is not a moment for backyard intuitive engineering on your engine which is, after all, your life support system. 12.9 bolts have a high ultimate tensile strength but a low ductility (they're more brittle). If they're plated they're also much more prone to hydrogen embrittlement. That could be crucial in this instance. They also need to be torqued up to a much higher proof load than 8.8s. In engineering, more is sometimes less. Play it safe and stick with 8.8.

 

RFSchaller 11-16-2015 11:56 PM Bob, I agree with your observation, but look at the application. I wouldn't lose any sleep over more brittle bolts in the application of water pump pressure boundary retention. Landing gear would be a different story. Rich

 

Jesse 11-17-2015 07:23 AM Have you tried contacting Lockwood in FL? They may have what you need in stock.

 

Captain Avgas 11-17-2015 08:28 AM Quote: Originally Posted by RFSchaller (Post 1030143) Bob, I agree with your observation, but look at the application. I wouldn't lose any sleep over more brittle bolts in the application of water pump pressure boundary retention. Landing gear would be a different story. Rich Rich, put it this way. If the OP uses the specified fasteners he will be 100% safe. If he does not then there could be ramifications that the layman cannot understand. For instance the depth of female thread available may be specifically engineered for an 8.8 bolt and may be insufficient for the higher torque required for a 12.9 bolt. Consequently he may strip the female thread or damage it such that it fails down the track in flight. Neither scenario would good. Alternatively there are other dangers in not torquing a 12.9 fastener to its specified torque. The fact that the OP is asking this question on this forum suggest to me that he is not an engineer and therefore my recommendation to him is to use the Rotax specified fasteners at the Rotax specified torque.  My other concern would be whether when the OP overtorqued the original bolts he damaged the female threads at that time.

 

GaryK 11-17-2015 09:34 AM Try McMaster Carr   Dave, Did you try McMaster Carr. They usually have most in stock Gary

 

David Paule 11-17-2015 10:33 AM Don't Change the Torque   There's no change to the assembly torque if you go with a higher-strength bolt, provided - The thread form hasn't changed, The material remains steel, the head type is the same, the thread engagement is the same, the same washers or nuts are used, and the same lubrication or lack of it is used upon assembly. If all these are true, then the torque to preload relationship is unchanged, and you should use the original assembly torque to obtain the bolt preload, the clamping force, which the designers wanted. A higher-strength bolt DOES NOT need higher torque in this type of a replacement situation. It might well be damaging.  You'd use a higher torque in a wholly new design that fully uses the higher strength of the new bolt, but not for a replacement bolt. Dave

 

DanH 11-17-2015 11:20 AM May I request some clarification please? Here's my understanding, and I would appreciate the education if I'm misinformed. The clamping force applied by a bolt is fundamentally a function of its elastic modulus, and all steels have roughly the same modulus of elasticity, about 3.0^7 psi. The mechanical difference between the 12.9 and 8.8 is yield strength (roughly 90% of 1200 MPa vs 80% of 800 MPa). That means the 12.9 can be stretched further (i.e. torqued to some higher value) before it yields, which of course increases the clamp force. If an 8.8 and a 12.9 have the same modulus, then stretching them equally (same torque, assuming same thread pitch, form, and friction) should result in the same clamp force. There's no reason why a 12.9 mustbe torqued to a higher level. The required clamp force is usually dictated by the anticipated cyclical stress; we want the clamp force to be higher than the cyclical stress which tries to pull the clamped joint apart. If an 8.8 was adequate in this regard, a 12.9 should be fine.  Lower ductility for a 12.9 has no bearing on this discussion. It merely indicates a short plastic region on the stress-strain plot. The stress applied here, using the torque specified for the 8.8, would not put a 12.9 anywhere near that plastic region. So what am I missing? POSTSCRIPT....just posted to find Dave has already covered the question.

 

Captain Avgas 11-17-2015 09:05 PM My guess is that the original 8.8 bolt will be a mil spec product with cad plating. Cad plating is very lubricious and has a lower coefficient of friction compared to unplated steel. 12.9 fasteners are normally black steel due to the quality control problems associated with plating such a high strength alloy. Of course using a black bolt has it own shortcomings in terms of corrosion. But all other things being equal, the black 12.9 will have to be torqued to a higher level than the cad plated 8.8 to achieve the same clamping force. Now one could go to Milspec-HDBK-60 to get a detailed formula for calculating the torque based on various friction co-efficients. But I don't think the OP is going to do that. So under the circumstances I still think that the conservative approach for the OP to take would be to obtain the engine manufacturer's specified bolts with the same plating and use the engine manufacturer's specified torque.

 

BillL 11-17-2015 09:24 PM Quote: Originally Posted by David Paule (Post 1030215) There's no change to the assembly torque if you go with a higher-strength bolt, provided - The thread form hasn't changed, The material remains steel, the head type is the same, the thread engagement is the same, the same washers or nuts are used, and the same lubrication or lack of it is used upon assembly. If all these are true, then the torque to preload relationship is unchanged, and you should use the original assembly torque to obtain the bolt preload, the clamping force, which the designers wanted. A higher-strength bolt DOES NOT need higher torque in this type of a replacement situation. It might well be damaging.  You'd use a higher torque in a wholly new design that fully uses the higher strength of the new bolt, but not for a replacement bolt. Dave Yep, my thoughts exactly. And- I have never seen an engine bolt installed with dry torque. Preload, pre stretched, and torqued to length, but not dry.

 

RFSchaller 11-17-2015 10:36 PM Bob, As an engineer you know we make our bread and butter answering the questions about what should be done when the OEM specs aren't met. I would not disagree with your statements, but I do think you are being overly conservative in this application. Maybe it's just my experience as a home builder seeing other applications, but I would still be comfortable with his suggested substitution. There are only a few critical applications like landing gear, cylinder head retention and prop bolts that raise the hairs on the back of my neck. Even if one bolt did fail on the water pump (and why would it since preload is most of the stress) you'd just get a leak you could address. I think the probability and consequences in this application result in low risk. Rich

 

tjo 11-18-2015 12:33 AM You guys are way over thinking this. The substitution is fine unless we are talking about cylinder bolts, or case bolts, or rod bolts, but if that were true, they wouldn't be grade 8.8, which is the SAE grade 5 equivalent. It sounds like they used the low strength bolts to save the case and make it so the bolt would fail if over torqued. I think the only risk with a higher strength bolt is overtorquing and damaging the engine case (or whatever the bolt is threading into). Tim

 

Captain Avgas 11-18-2015 04:58 AM Quote: Originally Posted by RFSchaller (Post 1030394) Bob, I would not disagree with your statements, but I do think you are being overly conservative in this application.   Rich Rich, you are right, in this particular case I have been extremely conservative, maybe too conservative. But in my defence I have had one eye on the original question and the other eye on the VansAirforce general audience, the bulk of whom do not come from a scientific background. We owe it to them to stress that changing out structural fasteners with those in any way different from that specified by the design engineer is not an option to be taken lightly by the uninitiated. At least the original poster had the common sense to ask the question and he should receive credit for that.  I have been impressed with the technical calibre of posts made by all the contributors to this thread and I'm confident the OP can now make an informed decision.

 

dbhill916 11-18-2015 05:53 AM thank you   Quote: Originally Posted by Captain Avgas (Post 1030427) ...At least the original poster had the common sense to ask the question and he should receive credit for that.  I have been impressed with the technical calibre of posts made by all the contributors to this thread and I'm confident the OP can now make an informed decision. Gentlemen all, I thank you all for the wealth of information and opinion. Many decades ago I was an engineer, but I think that only makes it dangerous for me to rely on my own analyses; thus the reason I asked the question here. The responses were exactly the kind of engineering discussion that is so informative on what might be perceived as an apparently trivial topic (nothing is trivial in aviation engineering!).   Jesse gets the credit for the optimal solution:) : Lockwood's web site shows that not only are they in stock, but they're much cheaper than LEAF's (except for the shipping fees.) Hopefully, I will have the best of both worlds: original specifications and timely availability. In the event that they aren't shipped any time soon, I will wait until I find the original spec 8.8's. thanks again for a lively discussion, -dbh :)

All times are GMT -5. The time now is 05:54 AM.

 

----------------

Update 11/16/15, notice posted on Van’s Air Force:

Hi all,

Is it safe to use bolts that are stronger than specified by Rotax, or will there be an unintended consequence (e.g., damage to the internal threads, etc.)?
I over torqued the metric bolts on my water pump housing and will be pulling the engine to remove & replace the affected bolts. Unfortunately, LEAF is quoting 6 weeks to get replacement M6x90 bolts. I have located a domestic source of M6x90 bolts, but they appear to be considerably stronger as they are Class 12.9, vs Class 8.8 as found on one of the ruined bolts in my possession. 

A quick internet search shows that Class 8.8 has a yield strength of 660 MPa while Class 12.9's yield strength is 1100 MPa. Is it possible to do damage using bolts that are too strong? Will the torque specifications be the same? If not, is there a known conversion? If not, then I will not use them and will just wait for Christmas. 

thanks in advance,

-dbh

---------------------------------------------------- 

I spent a few hours at the local A&P trying to get the carbs balanced, but we never got the engine to run smoothly.  That’s the good news.  When we were standing around trying to figure out what we were missing, I noted that the front gear strut was wet.  Following the moisture trail upwards led to the discovery that one of the bolts holding the water pump to the engine case was ‘loose’.  Loose, as in “slides out with no resistance.”  I had a sinking feeling and fished it out completely.  Yep, it’s fractured right though the threads.

 If you go back to http://n76012.blogspot.com/2015/02/46-06-engine-mount.html, you’ll see that I had to remove the water pump housing to get the engine mount on.  Thinking back, I remember being amazed at how high the torque settings were to seat those bolts back onto the water pump.  In retrospect, I’m guessing I used ft-lbs instead of in-lbs and probably overtorqued these guys by a factor of 12.  Damn.

This discovery was last Wednesday.  I’m looking for some time to go through the various manuals and catalogs to order the correct replacement bolts from LEAF.  I expect it will take two days of labor to remove the engine.  A friend has offered to help back out the remnants of the bolt from the engine, and hopefully we won’t find any more broken bolts to deal with.   With any luck, I’ll have Thursday & Friday of next week to tackle this setback.

 

Fractured water pump bolt

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VAF Forums > Model Specific > RV-12  can you substitute class 12.9 for 8.8 bolts? Welcome, dbhill916. You last visited: Today at 05:01 AM  Private Messages: Unread 0, Total 16. User CP FAQ Members List Calendar New Posts Search  Quick Links  Log Out  View First Unread   Thread Tools  Search this Thread  Rate Thread  Display Modes    #1       11-16-2015, 03:43 PM dbhill916    Join Date: May 2013 Location: Columbus, OH Posts: 77    can you substitute class 12.9 for 8.8 bolts? Hi all, Is it safe to use bolts that are stronger than specified by Rotax, or will there be an unintended consequence (e.g., damage to the internal threads, etc.)? I over torqued the metric bolts on my water pump housing and will be pulling the engine to remove & replace the affected bolts. Unfortunately, LEAF is quoting 6 weeks to get replacement M6x90 bolts. I have located a domestic source of M6x90 bolts, but they appear to be considerably stronger as they are Class 12.9, vs Class 8.8 as found on one of the ruined bolts in my possession.   A quick internet search shows that Class 8.8 has a yield strength of 660 MPa while Class 12.9's yield strength is 1100 MPa. Is it possible to do damage using bolts that are too strong? Will the torque specifications be the same? If not, is there a known conversion? If not, then I will not use them and will just wait for Christmas.  thanks in advance, -dbh __________________ ------------- David B. Hill RV-12-0760 N76012  http://n76012.blogspot.com Dues paid through 6-2016       #2       11-16-2015, 06:40 PM Captain Avgas    Join Date: Oct 2005 Location: Melbourne, Australia Posts: 1,469    Stick with 8.8 Quote: Originally Posted by dbhill916  Hi all, Is it safe to use bolts that are stronger than specified by Rotax, or will there be an unintended consequence (e.g., damage to the internal threads, etc.)? I over torqued the metric bolts on my water pump housing and will be pulling the engine to remove & replace the affected bolts. Unfortunately, LEAF is quoting 6 weeks to get replacement M6x90 bolts. I have located a domestic source of M6x90 bolts, but they appear to be considerably stronger as they are Class 12.9, vs Class 8.8 as found on one of the ruined bolts in my possession.   A quick internet search shows that Class 8.8 has a yield strength of 660 MPa while Class 12.9's yield strength is 1100 MPa. Is it possible to do damage using bolts that are too strong? Will the torque specifications be the same? If not, is there a known conversion? If not, then I will not use them and will just wait for Christmas.  thanks in advance, -dbh The long answer to this requires a thesis on bolts. The short answer is to replace the 8.8 bolts with the same grade as specified by the engine manufacturer. This is not a moment for backyard intuitive engineering on your engine which is, after all, your life support system. 12.9 bolts have a high ultimate tensile strength but a low ductility (they're more brittle). If they're plated they're also much more prone to hydrogen embrittlement. That could be crucial in this instance. They also need to be torqued up to a much higher proof load than 8.8s. In engineering, more is sometimes less. Play it safe and stick with 8.8. __________________ Regards Bob Barrow RV7A      #3       11-16-2015, 11:56 PM RFSchaller    Join Date: Oct 2010 Location: Phoenix, AZ Posts: 1,509   Bob, I agree with your observation, but look at the application. I wouldn't lose any sleep over more brittle bolts in the application of water pump pressure boundary retention. Landing gear would be a different story. Rich      #4       Yesterday, 07:23 AM Jesse    Join Date: May 2005 Location: Dunnellon, FL Posts: 1,649   Have you tried contacting Lockwood in FL? They may have what you need in stock. __________________ Jesse Saint (Saint Aviation, Inc. - VAF Advertiser) 352-427-0285 jesse@saintaviation.com RV Hotel (hangar, room, car) at X35 in north FL Commercial ASEL/S A&P/IA EAA Technical Counselor RV-10 N256H 1,300+ hrs Dynamic Prop Balancing, Prebuy Inspections, Condition Inspections, Repairs and Mods, Airframe, Engine, Avionics and Ferrying      #5       Yesterday, 08:28 AM Captain Avgas    Join Date: Oct 2005 Location: Melbourne, Australia Posts: 1,469   Quote: Originally Posted by RFSchaller  Bob, I agree with your observation, but look at the application. I wouldn't lose any sleep over more brittle bolts in the application of water pump pressure boundary retention. Landing gear would be a different story. Rich Rich, put it this way. If the OP uses the specified fasteners he will be 100% safe. If he does not then there could be ramifications that the layman cannot understand. For instance the depth of female thread available may be specifically engineered for an 8.8 bolt and may be insufficient for the higher torque required for a 12.9 bolt. Consequently he may strip the female thread or damage it such that it fails down the track in flight. Neither scenario would good. Alternatively there are other dangers in not torquing a 12.9 fastener to its specified torque. The fact that the OP is asking this question on this forum suggest to me that he is not an engineer and therefore my recommendation to him is to use the Rotax specified fasteners at the Rotax specified torque.  My other concern would be whether when the OP overtorqued the original bolts he damaged the female threads at that time. __________________ Regards Bob Barrow RV7A Last edited by Captain Avgas : Yesterday at 08:34 AM.      #6       Yesterday, 09:34 AM GaryK    Join Date: Nov 2005 Location: Zeeland, Michigan Posts: 211    Try McMaster Carr Dave, Did you try McMaster Carr. They usually have most in stock Gary      #7       Yesterday, 10:33 AM David Paule    Join Date: Dec 2009 Location: Boulder, CO Posts: 2,319    Don't Change the Torque There's no change to the assembly torque if you go with a higher-strength bolt, provided - The thread form hasn't changed, The material remains steel, the head type is the same, the thread engagement is the same, the same washers or nuts are used, and the same lubrication or lack of it is used upon assembly. If all these are true, then the torque to preload relationship is unchanged, and you should use the original assembly torque to obtain the bolt preload, the clamping force, which the designers wanted. A higher-strength bolt DOES NOT need higher torque in this type of a replacement situation. It might well be damaging.  You'd use a higher torque in a wholly new design that fully uses the higher strength of the new bolt, but not for a replacement bolt. Dave Last edited by David Paule : Yesterday at 10:37 AM.      #8       Yesterday, 11:20 AM DanH    Join Date: Oct 2005 Location: 08A Posts: 5,549   May I request some clarification please? Here's my understanding, and I would appreciate the education if I'm misinformed. The clamping force applied by a bolt is fundamentally a function of its elastic modulus, and all steels have roughly the same modulus of elasticity, about 3.0^7 psi. The mechanical difference between the 12.9 and 8.8 is yield strength (roughly 90% of 1200 MPa vs 80% of 800 MPa). That means the 12.9 can be stretched further (i.e. torqued to some higher value) before it yields, which of course increases the clamp force. If an 8.8 and a 12.9 have the same modulus, then stretching them equally (same torque, assuming same thread pitch, form, and friction) should result in the same clamp force. There's no reason why a 12.9 mustbe torqued to a higher level. The required clamp force is usually dictated by the anticipated cyclical stress; we want the clamp force to be higher than the cyclical stress which tries to pull the clamped joint apart. If an 8.8 was adequate in this regard, a 12.9 should be fine.  Lower ductility for a 12.9 has no bearing on this discussion. It merely indicates a short plastic region on the stress-strain plot. The stress applied here, using the torque specified for the 8.8, would not put a 12.9 anywhere near that plastic region. So what am I missing? POSTSCRIPT....just posted to find Dave has already covered the question. __________________ Dan Horton  RV-8 SS Barrett IO-390 Last edited by DanH : Yesterday at 11:24 AM.      #9       Yesterday, 09:05 PM Captain Avgas    Join Date: Oct 2005 Location: Melbourne, Australia Posts: 1,469   My guess is that the original 8.8 bolt will be a mil spec product with cad plating. Cad plating is very lubricious and has a lower coefficient of friction compared to unplated steel. 12.9 fasteners are normally black steel due to the quality control problems associated with plating such a high strength alloy. Of course using a black bolt has it own shortcomings in terms of corrosion. But all other things being equal, the black 12.9 will have to be torqued to a higher level than the cad plated 8.8 to achieve the same clamping force. Now one could go to Milspec-HDBK-60 to get a detailed formula for calculating the torque based on various friction co-efficients. But I don't think the OP is going to do that. So under the circumstances I still think that the conservative approach for the OP to take would be to obtain the engine manufacturer's specified bolts with the same plating and use the engine manufacturer's specified torque. __________________ Regards Bob Barrow RV7A Last edited by Captain Avgas : Yesterday at 09:55 PM.      #10       Yesterday, 09:24 PM BillL    Join Date: Sep 2007 Location: Chillicothe, IL Posts: 2,287   Quote: Originally Posted by David Paule  There's no change to the assembly torque if you go with a higher-strength bolt, provided - The thread form hasn't changed, The material remains steel, the head type is the same, the thread engagement is the same, the same washers or nuts are used, and the same lubrication or lack of it is used upon assembly. If all these are true, then the torque to preload relationship is unchanged, and you should use the original assembly torque to obtain the bolt preload, the clamping force, which the designers wanted. A higher-strength bolt DOES NOT need higher torque in this type of a replacement situation. It might well be damaging.  You'd use a higher torque in a wholly new design that fully uses the higher strength of the new bolt, but not for a replacement bolt. Dave Yep, my thoughts exactly. And- I have never seen an engine bolt installed with dry torque. Preload, pre stretched, and torqued to length, but not dry. __________________ Bill Lane Building 7 tipper. QB,Canopy : on hold G3X/GNS 650 Panel, Built by SteinAir: Installed IO-360 M1B, Hartzell CS Composite Wiring 98% sans FWF.   FWF:SJ Cowl & baffles fitted, air inlet diffusers, &  new BL plenum=DONE Refitting -0 to -1 tips. VAF Donation for 2014 w/ a little extra       #11       Yesterday, 10:36 PM RFSchaller    Join Date: Oct 2010 Location: Phoenix, AZ Posts: 1,509   Bob, As an engineer you know we make our bread and butter answering the questions about what should be done when the OEM specs aren't met. I would not disagree with your statements, but I do think you are being overly conservative in this application. Maybe it's just my experience as a home builder seeing other applications, but I would still be comfortable with his suggested substitution. There are only a few critical applications like landing gear, cylinder head retention and prop bolts that raise the hairs on the back of my neck. Even if one bolt did fail on the water pump (and why would it since preload is most of the stress) you'd just get a leak you could address. I think the probability and consequences in this application result in low risk. Rich      #12       Today, 12:33 AM tjo    Join Date: Dec 2009 Location: La Center,wa Posts: 161   You guys are way over thinking this. The substitution is fine unless we are talking about cylinder bolts, or case bolts, or rod bolts, but if that were true, they wouldn't be grade 8.8, which is the SAE grade 5 equivalent. It sounds like they used the low strength bolts to save the case and make it so the bolt would fail if over torqued. I think the only risk with a higher strength bolt is overtorquing and damaging the engine case (or whatever the bolt is threading into). Tim Last edited by tjo : Today at 12:37 AM.      #13       Today, 04:58 AM Captain Avgas    Join Date: Oct 2005 Location: Melbourne, Australia Posts: 1,469   Quote: Originally Posted by RFSchaller  Bob, I would not disagree with your statements, but I do think you are being overly conservative in this application.   Rich Rich, you are right, in this particular case I have been extremely conservative, maybe too conservative. But in my defence I have had one eye on the original question and the other eye on the VansAirforce general audience, the bulk of whom do not come from a scientific background. We owe it to them to stress that changing out structural fasteners with those in any way different from that specified by the design engineer is not an option to be taken lightly by the uninitiated. At least the original poster had the common sense to ask the question and he should receive credit for that.  I have been impressed with the technical calibre of posts made by all the contributors to this thread and I'm confident the OP can now make an informed decision. __________________ Regards Bob Barrow RV7A      #14       Today, 05:53 AM dbhill916    Join Date: May 2013 Location: Columbus, OH Posts: 77    thank you Quote: Originally Posted by Captain Avgas  ...At least the original poster had the common sense to ask the question and he should receive credit for that.  I have been impressed with the technical calibre of posts made by all the contributors to this thread and I'm confident the OP can now make an informed decision. Gentlemen all, I thank you all for the wealth of information and opinion. Many decades ago I was an engineer, but I think that only makes it dangerous for me to rely on my own analyses; thus the reason I asked the question here. The responses were exactly the kind of engineering discussion that is so informative on what might be perceived as an apparently trivial topic (nothing is trivial in aviation engineering!).   Jesse gets the credit for the optimal solution : Lockwood's web site shows that not only are they in stock, but they're much cheaper than LEAF's (except for the shipping fees.) Hopefully, I will have the best of both worlds: original specifications and timely availability. In the event that they aren't shipped any time soon, I will wait until I find the original spec 8.8's. thanks again for a lively discussion, -dbh __________________ ------------- David B. Hill RV-12-0760 N76012  http://n76012.blogspot.com Dues paid through 6-2016       « Previous Thread | Next Thread » Quick Reply Message: Options Show your signature Quote message in reply?     Posting Rules You may post new threads You may post replies You may not post attachments You may edit your posts vB code is On Smilies are On [IMG] code is On HTML code is Off Forum Jump     User Control Panel  Private Messages  Subscriptions  Who's Online  Search Forums  Forums Home       Main      Temp / Test / Misc. 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