Issues with using 12.9 turbo mounting bolts ? Anyone ?
04-30-2012, 12:54 AM
#1
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Issues with using 12.9 turbo mounting bolts ? Anyone ?
I replaced my perfectly good stock turbo mounting bolts ( 8.8) when I replace the stock turbo, with the Vitesse (Garrett) turbo. At the time, I thought it might be a good idea to replace the stock allen head bolts with McMaster Carr bolts I bought
Now that I have it all together, it occurred to me that because the hardness of the bolts are different, so would the torque values would be different. Very different! Like 33 ft max torque different.... My plan was to go to something like 28 ft lbs OR just replace with the stock bolts
of course that would require me lowering the drivers side steering rack, to get the long 130mm bolt out and replace it with the stock 125mm one...
I would obviously like to just torque it up to 28 ft lbs and forget it, but I don't want this to bite me in the *** later .... Has anyone had problems using these bolts and do you think 28 ft lbs is enough for it to stay put ?? I also don't want to run the risk of crackling the turbo's mounting area with the higher torque values !!
Would love to hear experienced input on this issue....
Thanks in advance
Ed
Now that I have it all together, it occurred to me that because the hardness of the bolts are different, so would the torque values would be different. Very different! Like 33 ft max torque different.... My plan was to go to something like 28 ft lbs OR just replace with the stock bolts
of course that would require me lowering the drivers side steering rack, to get the long 130mm bolt out and replace it with the stock 125mm one... I would obviously like to just torque it up to 28 ft lbs and forget it, but I don't want this to bite me in the *** later .... Has anyone had problems using these bolts and do you think 28 ft lbs is enough for it to stay put ?? I also don't want to run the risk of crackling the turbo's mounting area with the higher torque values !!
Would love to hear experienced input on this issue....
Thanks in advance
Ed
04-30-2012, 01:07 AM
#3
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04-30-2012, 01:14 AM
#4
Nordschleife Master
The turbo mounting bolts are not torque to yield, so the torque value does not change regardless of bolt grade.
Also its been a long time since i did my turbo but if i remember right there is no specific torque spec for those bolts in the manual, so by default all M8 bolts should be torqued to about 15ft-lbs.
Also its been a long time since i did my turbo but if i remember right there is no specific torque spec for those bolts in the manual, so by default all M8 bolts should be torqued to about 15ft-lbs.
04-30-2012, 02:13 AM
#5
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The turbo mounting bolts are not torque to yield, so the torque value does not change regardless of bolt grade.
Also its been a long time since i did my turbo but if i remember right there is no specific torque spec for those bolts in the manual, so by default all M8 bolts should be torqued to about 15ft-lbs.
Also its been a long time since i did my turbo but if i remember right there is no specific torque spec for those bolts in the manual, so by default all M8 bolts should be torqued to about 15ft-lbs.
When I did the front crank pulley, I torqued it to only 7 ft lbs and those bolts are 10.9 Well, they started to back out !!! I damn near crapped in my pants when I saw the bolts backing out, as I was pulling everything off to do the oil pan ( they were only in for 500 miles). Then I looked and saw this chart on the web http://www.cncexpo.com/MetricBoltTorque.aspx
04-30-2012, 07:06 PM
#7
That torque table notes that the values are derived from "75% of proof load", that's why they change with the grade. In structural applications bolts are usually torqued to 50 or 75% of their yield strength.
As Technoduck said, as long as you aren't yielding the bolt, an 8.8 fastener will generate the same compressive force in the joint as a 10.9 fastener, at the same torque. It is mostly a function of the thread pitch, angle, and friction.
Use the stock values for torque on these and you will be fine. Use lock washers if you want. I don't think Loctite would help much as it softens at 350-400F IIRC.
As Technoduck said, as long as you aren't yielding the bolt, an 8.8 fastener will generate the same compressive force in the joint as a 10.9 fastener, at the same torque. It is mostly a function of the thread pitch, angle, and friction.
Use the stock values for torque on these and you will be fine. Use lock washers if you want. I don't think Loctite would help much as it softens at 350-400F IIRC.
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04-30-2012, 08:22 PM
#8
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That torque table notes that the values are derived from "75% of proof load", that's why they change with the grade. In structural applications bolts are usually torqued to 50 or 75% of their yield strength.
As Technoduck said, as long as you aren't yielding the bolt, an 8.8 fastener will generate the same compressive force in the joint as a 10.9 fastener, at the same torque. It is mostly a function of the thread pitch, angle, and friction.
Use the stock values for torque on these and you will be fine. Use lock washers if you want. I don't think Loctite would help much as it softens at 350-400F IIRC.
As Technoduck said, as long as you aren't yielding the bolt, an 8.8 fastener will generate the same compressive force in the joint as a 10.9 fastener, at the same torque. It is mostly a function of the thread pitch, angle, and friction.
Use the stock values for torque on these and you will be fine. Use lock washers if you want. I don't think Loctite would help much as it softens at 350-400F IIRC.
Thanks very much for your input ....
OK the bolts were already in and were treated with anti-seize, as the last thing I wanted was to have them strip when I try to remove them That's why I went with a 12.9 bolt ( In hindsight) I wish I just stuck with the stock bolts as I removed mine and they were in pristine shape. I did torque to a higher value (did it already before I read this ). I only went to about 20ft lbs ... I do have a little different set up when it comes to the turbo mount itself ( the Garret I have, uses an O ring and a thick paper gasket piled on top of one another, so there may be more of a squish factor..?
After 500 miles, the bolts did have a 1/2 and a 1/4 turn added to them respectively to the 15 ft lb setting... So, I was concerned they might loosen up again
Best regards
Ed
05-01-2012, 08:09 PM
#9
Yes, I think the gasket may be working against you at first until it compresses to a final thickness from all of the heat cycles. There are two different metals with much different expansion rates at this joint as well. The anti-seize is probably the icing on the cake, as it can greatly lower the friction coefficient between the threads, depending on the type used.
05-02-2012, 12:57 AM
#10
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Yes, I think the gasket may be working against you at first until it compresses to a final thickness from all of the heat cycles. There are two different metals with much different expansion rates at this joint as well. The anti-seize is probably the icing on the cake, as it can greatly lower the friction coefficient between the threads, depending on the type used.
I saw that. It seems if you use oil ( lubricant ) it can increase the torque valve by as much as 10% ..so you need to take that into account and lower the setting on your wrench. I used this stuff called Copaslip ...
Thanks again for your advice
Regards
Ed
05-03-2012, 09:48 PM
#12
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I just thought it was outrageous, to pay 20 bucks for one bolt....
05-04-2012, 02:06 PM
#14
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