VALVE SPRING BROKEN

I was in the Garage this lunch time and they showed me the parts they changed. Two similar things (ive not idea of mechanichs) they were 2 small things like 3 or 4 cm. Diameter and 2 cm lengh , metal. like a small disc... they told me that one of them was bad and the other one was starting to be bad so they changed both, I could see that they were curved in one part, inside like a small hole was curved....

The car was running ok in speed but not at low Revs...

What an explanation.. hope somebody have understood!!!

Which part of "at the very worst" didn't you understand?

THey weren't stretch bolts....

Went through that with my 1.4 Citroen, trying to change the valve stem seals without removing the head. In the end it was burning a lot of oil and leaking oil from the oilway area. So I pulled the head off and did the seals, that cured it (130 ish thousand miles). Total cost about £20 well worth it :O)

Which arent stretch bolts? Were talking about TU series engines here. I've got one sat on drive (My girlfriends) in a peugeot 106 and that has the so called 'stretch bolts' on it

Almudena Soria ( snipped-for-privacy@eurocom.co.uk) gurgled happily, sounding much like they were saying :

Well, it ain't a valve spring, then...

Guy King ( snipped-for-privacy@zetnet.co.uk) gurgled happily, sounding much like they were saying :

Yep, and I had a Hillman Wimp Sport that had 'em. I'm not saying that *no* engines have 'em, I'm disagreeing that *most* do.

Actually if your news client threaded conversations properly you'd find we were on about Vauxhalls.

Duncanwood:

However, as with old Vauxhauls if you're careful you don't disturb the headgasket & you can get away with it.

You then wittered something about needing them to which he replied that they were reusable.

The message from Adrian contains these words:

I'd say very few do.

If you payed attention to the full thread you'll find I was talking about TU engines..........

Ray Bentos ( snipped-for-privacy@blueyonder.co.uk) gurgled happily, sounding much like they were saying :

I was in at a Cit specialist friend of mine's workshop the other week, and he was just putting the finishing touches to a head gasket on an AX. Started it, not running quite right, compression down on one - a valve had got slightly bent. Off came the head, new gasket straight in the bin, new head bolts straight in the bin.

I can see the point of the gasket as it will have been slightly crushed but the headbolts? Thats just plain wasteful.

stretch bolts are usually supposed to be one shot use only, but in practice many are reused. some give a stretch length beyond which they should not be reused.

mrcheerful

Tightening any bolt by any means stretches it, only if you stretch it past it's elastic limit does it need replacing.

If people did them up to a normal torque setting rather than a stretch setting they could be reused indefinitely. There's no intrinsic difference between a stretch bolt and any other bolt and the additional tightening past the yield point achieves nothing other than to permanently stretch and weaken the bolt. It adds no clamping force (it actually reduces this as the bolt weakens) and serves only to ensure that the bolt has been tightened at least to yield rather than to 90% of yield which is normal bolt practice.

Of course to do this you have to know enough about bolt theory to be able to calculate the correct torque setting taking into account the thread form, lubrication on the threads and the k factor for friction. I do this routinely on engines such as the CVH and Peugeot 205s but most people will just follow the HBOL and buy new bolts every time.

Furthermore, if you buy quality bolts such as ARP ones for race engines you'll find they all use a torque value (or a measured elongation value) and are never stretched past yield regardless of the OE type of bolt they are replacing. Stretching a bolt past yield is a BAD thing n'kay. In fact ARP specify that any bolt which has permanently deformed past its manufactured length is scrap and should be thrown away. A tad harsh maybe but they are covering their corporate arses and perhaps can't be blamed for this in a litigious world such as that in which we now live.

Up until about 25 years ago there was no such thing as a 'stretch' bolt and then all the OE manufacturers suddenly thought 'hey, brand new source of revenue for non reusable service parts' and jumped onto the bandwagon simultaneously. In other words it's just a con.

As to the OP. You're a cretin. You post something omitting the type of car or engine which is obviously crucial to any constructive answer and then admit it probably wasn't a valve spring in the first place because you didn't listen properly to what you were told. If you know FA about engines, which is clearly the case, it surely isn't rocket science to think to ask the mechanic to write down the fault for you so you can at least pass the correct info on to those who might be able to advise you further.

-- Dave Baker - Puma Race Engines

I thought the reasoning was that retorquing after some use was no longer required, which would improve reliability and servicing costs? Since the bolt is in stretch tension it is always trying harder to pull the head down.

mrcheerful

Conor ( snipped-for-privacy@gmail.com) gurgled happily, sounding much like they were saying :

Stretch bolts which are specified as single-use only.

Less wasteful than having to do the head gasket yet again because the stretch bolts had been re-used.

Stretch bolts on TU engines So if you would renew a gasket after only 5 or so minutes use, so therefore.........

Surely you wouldn't want to use a gasket again which had been in place indefinetely

'ANY' and every bolt is in stretch tension after being tightened. Tightening past the yield point doesn't change or add to this, it just weakens the bolt and reduces the clamping force. Try and understand what non elastic deformation means. It means that the bolt has now permanently stretched and will not return to its original length and this extra length is not adding to the force pulling the head down.

The maximum possible clamping force obtainable from a bolt is when the bolt is tightened exactly to its elastic limit. Prior to this point and more torque could usefully be applied. Past this point and the bolt has permanently elongated and is now weakened. Continue stretching anything, a bolt or otherwise, past its elastic limit and it will stretch, thin out and eventually break.

By definition any stretch bolt is not applying the maximum potential clamping force it could be generating because it has been tensioned past its optimum point. They aren't a superior type of fitting. They are just a con to get people to buy new bolts. They aren't used in state of the art systems.

Google for 'bolt clamping force' or 'bolt torque'.

-- Dave Baker - Puma Race Engines