Stretch bolts

Tempus Fugit · Oct 8, 2014

There's a very interesting debate going on elsewhere with regards the bolts which clamp the block, oil rail and head together on the 1.8k Series. It centres around whether the bolts are actually "stretch" bolts or not? If they are what makes them so, as all bolts are apparently stretch bolts?

Also following a replacement HG have folks replaced the bolts or have they used the original ones?

Ta

djb222 · Oct 8, 2014

have a read of this,

http://www.partinfo.co.uk/files/SB2165 - CYLINDER HEAD STRETCH BOLTS.pdf

I've replaced the hg on my freelancer and never considered not using new stretch bolts. So for around £20 - £40 is it worth the risk.

baptista · Oct 8, 2014

would you re-use a condom???

asp383 · Oct 8, 2014

Technically, they're not stretch bolts, but because of their length & having to bolt top to bottom, they may stretch. It's been quite a few years since I last played with a K-series, so can't remember the stretch length & not got my Haynes manual to hand to check it, but you measure the length of the bolts & replace if over a pre-specified length

htr · Oct 8, 2014

Tempus Fugit said:
There's a very interesting debate going on elsewhere with regards the bolts which clamp the block, oil rail and head together on the 1.8k Series. It centres around whether the bolts are actually "stretch" bolts or not? If they are what makes them so, as all bolts are apparently stretch bolts?

Also following a replacement HG have folks replaced the bolts or have they used the original ones?

Ta

Very topical! I'm in the exact process of replacing my 1.8's HG. I've received new st'd H'bolts and carefully compared them with the ones I removed. Those 'old' ones had less than three hours running! However, when I compared the new ones which arrived yesterday with the old ones, the old ones appear to be nearly 1mm longer. The new ones are all identical lengths.

I compared them by placing them side by side but the head of one is beside the tip of the other. With the new bolts the tips touch the underside of their opposite's head. New with old and there's a gap of nearly 1mm.

htr · Oct 8, 2014

baptista said:
would you re-use a condom???

Only if its measurements were still good!

freelance · Oct 8, 2014

those foregotten teenage years, two lads, one girl and one condom, just had to share it, and the girl.

Tempus Fugit · Oct 8, 2014

asp383 said:
Technically, they're not stretch bolts, but because of their length & having to bolt top to bottom, they may stretch. It's been quite a few years since I last played with a K-series, so can't remember the stretch length & not got my Haynes manual to hand to check it, but you measure the length of the bolts & replace if over a pre-specified length

Why are they not stretch bolts? The industry seem to think they are?

htr · Oct 9, 2014

Tempus Fugit said:
Why are they not stretch bolts? The industry seem to think they are?

I think that they are. The w'shop manual [possibly the Haynes manual too] show how to measure them to check if they are still serviceable [useable]. That and my own observations seem to confirm that they are stretch bolts.

Optimus Prime · Oct 9, 2014

they stretch when you torque them up, not when you run the engine.

was always taught that once they were torqued up, that was it and they shouldn't be re-used if undone.

htr · Oct 9, 2014

Optimus Prime said:
they stretch when you torque them up, not when you run the engine.

was always taught that once they were torqued up, that was it and they shouldn't be re-used if undone.

I agree, it's cheap insurance to fit new bolts when taking the head off.

Nodge68 · Oct 10, 2014

asp383 said:
Technically, they're not stretch bolts, but because of their length & having to bolt top to bottom, they may stretch. It's been quite a few years since I last played with a K-series, so can't remember the stretch length & not got my Haynes manual to hand to check it, but you measure the length of the bolts & replace if over a pre-specified length

They are stretch bolts. They stretch by 1.5mm once final torque is applied. If they are the removed and the length checked, the bolts will have a measurable increase in length.

Safeman23 · Oct 10, 2014

That is correct Optimus. TTY bolts are a one off application only.

Tempus Fugit · Oct 10, 2014

Thanks chaps, now another question.

Because of the different characteristics of the aluminium block and the bolts, one will expand at a different rate from the other. So will the bolts stretch then contract with the block so that the block expands in line with the bolts, vertically would that be? So the bolts stretch, contract, stretch, contract in line with the engine getting hot then cooling down. Or does the block expand horizontally as it is held in check by the bolts?

Stretch bolts

Tempus Fugit

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djb222

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