vauxhall astra crankbolt

[pj11]

Hi replaced 02 Astra G 1.6 16v camshaft belt kit. Crankshaft bolt supplied has a different thread to old one, Vauxhall say its the correct bolt The old bolt is 12mm x65mm x 150 pitch the new bolt is 12mm x65x 175 pitch and it don`t fit as anyone come across this problem before ?.

Many thanks

Paul

 

[MrTinker]

I'm not to sure if i've had that problem on that engine, but i've had loads of bolts supplied that where wrong, and the parts lad swearing blind it's the right one! All too often its been labelled wrongly in the factory, so its the right part No. but the wrong part.(this happens a lot more than you might think)
In this case I really wouldn't think twice about putting a good blob of thread lock on the old one and putting it back in.

 

[Whitworth]

Check if it's a stretch bolt before reusing. If it is get a new one.

Explanation of a stretch bolt blagged from another website:-

The replacement bolts your dealer supplied are referred to as s-t-r-e-t-c-h bolts, because they are PERMANENTLY stretched when properly installed. When stretched they actually "neck down" or have a reduced diameter and area where the metal has been stretched. This reduced area has experienced Plastic Deformation, and will not hold the same torque (tension) if applied again, it will in fact stretch more, (loosing tension) and often fracture. This is why stretch bolts must ALWAYS be replaced, and never reused.

 

[Burnerman]

Interesting posts! I can fully understand why stretch bolts are used in cylinder head applications as they continue to pull down onto a slightly compressible gasket material - but I've never come across them on a crank pulley bolt.
I just put loctite on them and bung them back in......maybe I should revise my technique!
John

 

[Whitworth]

What made me think it might be is the size. 12mm quite small compared to 'traditional' monster crank bolt, plus they give you one in the kit (albeit the wrong one!)
Might be worth asking on a Vauxhall forum just in case after all its only a few quid.
Is the belt on this one tensioned by the offset water pump pulley? Would it be worth changing this too?

 

[MrTinker]

This is why stretch bolts must ALWAYS be replaced, and never reused.

Not strictly true, some can be reused, for example Ford Zetec 1.8 head bolts can be reused 3 times.

In this case it depends, if the engine code is Z16XE reuse bolt, for the other engine codes it says replace bolt, but unless you have the special crank locking tool to hand, you are never going to be able to tighten the bolt properly!

 

[MrTinker]

I can fully understand why stretch bolts are used in cylinder head applications as they continue to pull down onto a slightly compressible gasket material

Ah thats not why stretch bolts are used, they are used because they provide a much more accurate means of determining clamping force.

When a bolt is torqued down there will be a tolerance on how much torque is applied to the bolt, namely, working tolerance of the torque wrench, manufacturing tolerance of the bolt, and what type and how much lubrication is used on the threads, so there will be a difference from one bolt to the next.
See graph below:
A non stretch bolt torqued down with a small tolerance between a & b will result in a large tolerance in clamping load x
When a bolt is tightened past it's yield point elongation of the bolt occurs(it stretches) so a similar tolerance in torque on the bolt between c & d results in a very tight tolerance in clamping load y

Untitled

• MrTinker
• 17 Apr 2011
• 1

 

[Burnerman]

I'd like to thank you for that post and I'm delighted to be corrected
As you said, some of the main factors must be the accuracy of the torque wrench (I haven't had mine checked for 10 years now) and the degree of lubrication used on the threads. This surely must play a part in the re-use of the Zetec bolts?
John

 

[MrTinker]

Well that is the thing, torquing a bolt down in the normal manner, the end result is very dependant on how it is done, when it's taken past it's yield point so long as you get it there or there about the end result will be very close to what it should be.

Regarding Zetec head bolts I should point out it is only some that can be reused, some should be replaced, it depends on the exact engine. The ones that can be reused must be made from a particular type of steel that can stretch a long way before any danger of snapping, unlike a high tensile bolt.

 

[Whitworth]

As an aside, 85% of bolt torque is absorbed through thread friction and bolt flange friction
So for every 100 lb/ft only 15 is actually stretching the bolt.
Very important to clean high torque threads and use proper lube if specified.


Anyway, PJ, got it sorted yet?

 

[pj11]

Many thanks for your replies, sorry i didn`t replie sooner.

Well it is recommened to repalce the stretch bolt when changing the

cambelt, not sure why one is not supplied with kit would make life easier.

( there are a few horror stories on vauxhall owners website)

Went back to my local vauxhall dealer, and the guy insisted that vauxhall

only listed that bolt for the reg for my vehicle, so he had ordered

another just incase it was package wrong.Well as we were discussing my

problem his collage who was on the phone over heard our conversation

pointed out that he had the same problem in the past. It turns out that

instead of inputting in their computer the vehicle reg (which only gives

you the option of one size of bolt) you needed to input the vehicle type

ie ASTRA G which then showed the different sizes of bolts avaliable so

we were able to order the correct size bolt. Hey presto job done

Many thanks

Paul

 

[Whitworth]

Bally good show
Another happy ending, I'm wellin' up