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Post by bezzer on Apr 21, 2018 12:57:03 GMT 1
Chaps/Chapesses,
Can any of you learned people tell me : When retorqueing a Cylinder head after heat cycles, on a 250/350 4L1/0, do you back the head bolts off say half a turn before retightening?, or do you check/re torque them from their existing position?. Obviously with a ‘cold’ engine.
I know this may be obvious to some of you, but I have instances in my job as a Bentley technician, where we torque, relieve and re-torque applications, effectively pre-stretching the fixings so to speak.
As ever Many thanks for any input you may have.
Cheers bezzer
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phil38
Thrash Merchant
Posts: 426
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Post by phil38 on Apr 21, 2018 14:59:28 GMT 1
I would normally just tighten. The head bolts are multi use, not torque to yield I think and I wouldn’t thing taking the tension (pressure) off the gasket makes sense. I don’t remember any of the bolts moving when I checked mine after heat cycles.
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Post by bezzer on Apr 21, 2018 15:37:01 GMT 1
I would normally just tighten. The head bolts are multi use, not torque to yield I think and I wouldn’t thing taking the tension (pressure) off the gasket makes sense. I don’t remember any of the bolts moving when I checked mine after heat cycles. Hi Phil, I really wasn’t sure of the procedure, but it did make more sense to me to keep the clamping force on the gasket. Thanks for the advice mate 👍🏻. |
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seb
L plate rider.
Posts: 13
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Post by seb on Apr 21, 2018 16:32:17 GMT 1
I'm no guru but my first thought would be to only tighten them. Indeed to make sure that pressure stays on the head gasket.
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Post by bezzer on Apr 21, 2018 18:54:26 GMT 1
I'm no guru but my first thought would be to only tighten them. Indeed to make sure that pressure stays on the head gasket. Cheers seb, that would confirm the previous train of thought bud 👍🏻. |
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coose
Drag-strip hero
Posts: 270 
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Post by coose on Apr 21, 2018 19:44:34 GMT 1
Yep, retorque from where they are.
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Post by wallcraft on Apr 21, 2018 21:52:50 GMT 1
Tricky one as sometimes they can grab /stick when re-torquing without backing of 1/8 of a turn giving false values, however not sure myself which is the correct way just to confuse!😞
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Post by Mr Kipling on Apr 21, 2018 22:01:06 GMT 1
As others said no need to back off just re torque...
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Post by bezzer on Apr 21, 2018 22:37:28 GMT 1
As others said no need to back off just re torque... Cheers Mr Kipling - duly noted sir 👍🏻 |
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Post by bezzer on Apr 24, 2018 21:27:48 GMT 1
Tricky one as sometimes they can grab /stick when re-torquing without backing of 1/8 of a turn giving false values, however not sure myself which is the correct way just to confuse!😞 Bug**r!, just when I thought I’d got it straight in my head!!! 🤣 |
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Post by 4l04ever on Apr 24, 2018 21:34:36 GMT 1
You could put a bit of copper slip on the threads before the bolts are fitted and screw on by hand to make sure there are no tight spots on the threads. This should also make sure you get a good torque reading.
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Post by bezzer on Apr 24, 2018 21:59:46 GMT 1
I will do that on the next build Rob, the head bolts have been replated so will run a plug tap down them first & try them on the studs before copper slipping them 👍🏻.
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Post by Tobyjugs on Apr 25, 2018 11:23:40 GMT 1
I use engine oil and also make sure there is some between the head of the bolt/nut and the cylinder head
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Post by bezzer on Apr 25, 2018 12:06:18 GMT 1
I use engine oil and also make sure there is some between the head of the bolt/nut and the cylinder head You sometimes need to be careful when using oil in a ‘blind’ thread (head bolt onto a stud for example), you can get a hydraulic action/false torque value if excess oil is present. |
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Post by Tobyjugs on Apr 25, 2018 12:44:34 GMT 1
I use engine oil and also make sure there is some between the head of the bolt/nut and the cylinder head You sometimes need to be careful when using oil in a ‘blind’ thread (head bolt onto a stud for example), you can get a hydraulic action/false torque value if excess oil is present. Yes that is correct but which way up is your blind hole? Your not exactly filling it up with oil are you. |
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Post by bezzer on Apr 25, 2018 13:27:59 GMT 1
You sometimes need to be careful when using oil in a ‘blind’ thread (head bolt onto a stud for example), you can get a hydraulic action/false torque value if excess oil is present. Yes that is correct but which way up is your blind hole? Your not exactly filling it up with oil are you. Also correct Tony, but the thread, particularly if a fine pitch, can actually push the oil upwards as the bolt is turned. I wasn’t decrying your input/advice mate, just issuing a word of general caution if adopting this method. And, yes, you certainly wouldn’t be filling it up with oil. |
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Post by Tobyjugs on Apr 25, 2018 14:25:54 GMT 1
Hi Bezzer no offence taken
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