O/T Torque setting on a polo why turn 90 deg after torque settings

[Bilbo]

I helped my son change his head gasket this weekend on his 12 year old Polo

 

The head bolts are torque down twice first 20 then 40 m KN in the manual ok fair enough

 

Then all bolts are turned 90 deg twice

 

Why

 

Why not give 4 torque setting 🤔

 

Some of the other bolts are the same but only turned 90 deg once

 

Its not a problem I just wondered why it seemed a little imprecise, the engine is alloy head with cast block

 

Any ideas

 

'Can you hear me running' ......... OH YES and its music to my ears 😬 😬 😬

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? engineered by Roger King, on Weber's with Brooklands and Clamshell wings, Freestyle Motorsport suspension.

[Big Brother]

I think this is because most head bolts on modern engines are "stretch" bolts.

Tightening them through 90 degrees allows the bolts to stretch by a specific amount. I don't think this can be accurately measured by the torque of the bolt.

 

Steve

 

 

SE7EN-UP!

-----_{Build a man a fire, and he'll be warm for a day.}

Set a man on fire, and he'll be warm for the rest of his life!-----

 

[Bilbo]

Hi Se7en-Up

 

Well I thought that but its not stated in the Haynes Manual. So we ordered new bolts and only 8 instead of 10 arrived. So currently has 2 old ones in the last to be tightened holes.

 

The engines not been started yet

 

Why did we use the old ones well volkspares asked why we wanted them Oily Rag said well they are stretch bolts and should they not be replaced volkspares.... what are stretch bolts 🤔

 

So rather the reason I asked. Think another phone calls in order to the main dealer

 

'Can you hear me running' ......... OH YES and its music to my ears 😬 😬 😬

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? engineered by Roger King, on Weber's with Brooklands and Clamshell wings, Freestyle Motorsport suspension.

 

Edited by - Bilbo on 26 Nov 2007 20:02:26

[oilyhands]

All bolts stretch when tightened, the idea of 'snugging' the bolt and then applying the stretch by a certain number of degrees allows a higher level of clamping consitency to be acheived when the bolt is fully tightened. Torque readings can be skewed by lubricants on the thread, lubricants under the head, the surface finish under the bolt head and on the clamping surface. An angle turn will give apply a known amount of stretch and provided the material is consistently manufactured will give a measured amount of clamping force.

 

Oily

[j passfield]

Most engines now have these "stretch " bolts fitted, some manufacturers will give you a maximum length, so you can re-use upto that length, others specify that the bolts are renewed each time. If you don't have an angle gauge, mark reference points on the bolt head and the cylinder head surface, remember that if they are hex. head bolts 1 flat is equal to 60 degrees.

[Bilbo]

Hi Oily

 

That does make things clearer and they are supplied with grease read that as copperslip for the threads and under the heads.

 

Now I think we need a view on stay as installed or swap the bolts I think leave as currently installed.

 

I do not think the heads been off before and surprisingly for the mileage there no lip at the top of the bore and had minimal carbon

 

Read on

 

j passfield

 

Well we used a T square aligned/attached to achieve the 90 deg (that took ages for me with each bolt to be happy) and I doubt any is more than 0-3 degrees in error.

 

The only point is to get it running around town till the end of January then dump it in part exchange for something a lot newer.

 

Ok we should have had a angle gauge but I was only asked to assist……. later

 

 

'Can you hear me running' ......... OH YES and its music to my ears 😬 😬 😬

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? engineered by Roger King, on Weber's with Brooklands and Clamshell wings, Freestyle Motorsport suspension.

[Sheds Moderator]

I would stick with your reused stretch bolts if all seems well so far. I reused mine in the K (I didn't know at the time but you can measure the bolts before tightening to check they aren't already overstretched) on the basis that I knew they were only once used.

 

The HG I swapped is still OK 5 years on, so I must have got something right.

[Bilbo]

Hi batteredoldsupersport

 

Well that is rather what I thought hence fitting them but its nice to get a little reassurance

 

'Can you hear me running' ......... OH YES and its music to my ears 😬 😬 😬

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? engineered by Roger King, on Weber's with Brooklands and Clamshell wings, Freestyle Motorsport suspension.