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Old 17th May 2018, 15:32   #21
kaiser
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Quote:
Originally Posted by p2roverman View Post
Certainly a conflict of opinion over camshaft bolts in the elastic range or beyond.

However, my original question concerned the quality of the currently supplied new Indian-made bolts. If I want to re-use the original English bolts, previously used once, suggestions on what to torque them up to? Because they have been used and stretched as a result of use, I feel that the low torque plus angle turn method is no longer applicable, so my question to the guys that re-use camshaft bolts is "what do you torque them to?"
You torque them exactly as prescribed.
They have not stretched permanently. A quarter turn (90 degrees), if the pitch is 1mm, will be a stretch of 0.25mm, in the absolute max!!. As soon as they are taken off, they revert back to the original size. They behave exactly like a spring that you pull. You would not dream of discarding that after having used it once, would you? The bolt is EXACTLY the same when you use it again.
So you torque the bolts exactly like they tell you to, it is really very simple!.
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Old 21st May 2018, 11:29   #22
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Originally Posted by kaiser View Post
You torque them exactly as prescribed.
They have not stretched permanently. A quarter turn (90 degrees), if the pitch is 1mm, will be a stretch of 0.25mm, in the absolute max!!. As soon as they are taken off, they revert back to the original size. They behave exactly like a spring that you pull. You would not dream of discarding that after having used it once, would you? The bolt is EXACTLY the same when you use it again.
So you torque the bolts exactly like they tell you to, it is really very simple!.
Thanks Kaiser. I'm more than happy with the engineering analysis and will prefer to reuse known good UK-made bolts.

If I do at some times use the new Indian-made bolts I will grind off the lip on the washers where this is on the side that abuts the wheels; some of my earlier comments refer.
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Old 21st May 2018, 11:57   #23
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I worked at Rover when "stretch" bolts were first introduced and the machinery used for production does not always use the Service method of tightening (ie Torque plus angle) .Often they are torqued to yield condition, as the sensors can sense the drop off in torque as the yield point is reached . I raised the question of reuse when the manual states replace and was advised that bolts could be reused but only a few times and as there was no knowing if that was the case it was safer for the company to advise replace as default position.
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Old 21st May 2018, 13:24   #24
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I worked at Rover when "stretch" bolts were first introduced and the machinery used for production does not always use the Service method of tightening (ie Torque plus angle) .Often they are torqued to yield condition, as the sensors can sense the drop off in torque as the yield point is reached . I raised the question of reuse when the manual states replace and was advised that bolts could be reused but only a few times and as there was no knowing if that was the case it was safer for the company to advise replace as default position.
They don't know what they are talking about. There is no bolt on the rover engine that is torqued to yield. There is a video of a Rover engineer talking about torquing the cylinder head bolts to yield, and that is clearly nonsense, as the bolts when taken off are the prescribed length. Had they been taken to yield, they would have been permanently stretched, thus longer, and they would then have a section with a narrower diameter, and a visible deformation.
The main bolts on the K4 are torqued to 20NM and one full turn. That is a stretch of 1mm on a long bolt of about 400mm (estimate), after the torque That will be well inside the elastic range.

Note in this video how much you can stretch the bolt before it yields!
You are nowhere near that anywhere in the Rover engines!!

https://www.youtube.com/watch?v=D8U4G5kcpcM
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Old 21st May 2018, 15:35   #25
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Originally Posted by p2roverman View Post
If I want to re-use the original English bolts, previously used once, suggestions on what to torque them up to?
Mike,

I have just fitted new bolts. I found that applying the specified 90 degree turn was virtually impossible to achieve with any degree of accuracy since a tool with a handle length of about 50 cm is required and there are so many obstructions. I tried a torque angle gauge but securing the restraining bar was problematic. In the end I had to use the ratchet on a torque wrench to estimate the 90 degree turn. When I checked afterwards this approximated to 110 Nm in total (i.e. including the initial 27 Nm). Is that helpful to you?

Simon
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Old 21st May 2018, 15:58   #26
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Mike,

I have just fitted new bolts. I found that applying the specified 90 degree turn was virtually impossible to achieve with any degree of accuracy since a tool with a handle length of about 50 cm is required and there are so many obstructions. I tried a torque angle gauge but securing the restraining bar was problematic. In the end I had to use the ratchet on a torque wrench to estimate the 90 degree turn. When I checked afterwards this approximated to 110 Nm in total (i.e. including the initial 27 Nm). Is that helpful to you?

Simon
Thank you Simon and Kaiser.
I also had to turn the exta 90 dergrees in estimated segments of 30 degrees. The estimated figure of 110Nm (74 ft-lb) seems reasonable for the bolt size, I'll perhaps go to 70 at the same time checking how far past the initial 20 ft-lb the wrench has turned in degrees.

However, the first engine is sucessfully done and I'll now turn to another. So much fas been written about this job that many will have been put off. I actually found it quite straight-forward once the concept of the cam drive principle was understood.
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Old 21st May 2018, 17:33   #27
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Paint pens come in handy here - torque the bolts down then mark the heads with a vertical or horizontal line and you can accurately see it turn 90 degrees.
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Old 21st May 2018, 19:35   #28
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It is a bit like the argument i had with the chief mechanic where I worked. One of our lorries, not in Birmingham, lost a rear axle wheel going round an island. This in turn hit a woman who unfortunately lost her life. (Big panick by company) we were being instructed how we were to ‘re- torque the wheels on our lorries’. We were told that each night we had to borrow the torque wrench from the garage and retorque all wheels on whichever lorry you were driving. When I asked how to retorque the wheel nuts, I was told to ‘ place the proper socket on the extension of the torque wrench,set the wrench to the correct poundage and proceed to tighten until the wrench “broke”. Questioning if that was the correct way to ‘re-torque’. I was laughed at. This was just after the days of lorry drivers having a 6foot tube which was used on wheel bolts to tighten them after a puncture. When the laughter had died down, I said I would prove how wrong the instructions were. I asked for five minutes alone in the yard. I then went out and on one of the old lorries that was used for spares, got a 6ft piece of scaffold pole and tightened up the rear wheel by jumping up and down on it. Asked the chief mechanic to show us how to tighten the wheel nuts up with the torque wrench. He did it the way he told us to. I then suggested that he undo them and have the threads checked for stretching. He asked why. I said when you have undone them, I will show you why. He could not undo them. Asked me what I had done, and I told him. He said it was ridiculous to do that. I then explained that to re- torque a wheel, first you must undo a nut one flat before torquing a nut or bolt up otherwise how tight do you know it is. This was taught to me as an apprentice at the GEC at Witton, Birmingham, when I was an apprentice. He took the one stud from the hub that I had over tightened, and had the thread checked. He later phoned me up and said he had learned something he had never thought about. The stud was scrap. I can not remember how much it had stretched, but it was scrap by a considerable degree. He said he had carried out tests on it in the workshop, and said that although when tightened to the correct poundage, you could undo it very easily with ‘almost half the pressure’. Totally dangerous assumption just to ‘retorque’ a nut/bolt without first undoing it one flat.

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