head bolt tightening..Help! V230

[matteb63]

Im tightening a reconditioned head to my V class 230 111 engined block.They are new bolts but after torquing them down Ive found that in the 2nd and 3rd tightening sequence some of the bolts will not tighten any more without jerking..I did oil the bolts but maybe not enough.
Can I remove, oil and then tighten them up again or any suggestions?

 

[matteb63]

1st...55Nm
2nd..90 Degrees
3rd...90 Degrees

 

[keith100]

"I did oil the bolts but maybe not enough".

Hopefully someone more knowledgeable than me will answer you, but I was taught not to oil head bolts, since the factory torque is for a "dry" bolt and oiling can distort readings and result in over-torquing?

 

[television]

Not a word said on the instructions, about oiling

 

[Number_Cruncher]

As it's an angle tightening specification, whether the bolts are oiled or not doesn't make that much difference - the angle method is *much* more precise than pure torque specifications which are very sensitive to friction levels.

The way I approach this type of tightening sequence is to to the initial snug torque, and then, mark each bolt with a dab of white paint, pointing in the same direction (say the front of the car).

Then, as you go round the sequence doing the 90 degree turn, it's obvious which have been done. After the first angle stage, go and have a cup of tea, and allow the gasket to settle a bit.

Then, do the second stage, after which all the paint blobs point towards the back of the car.

I use the paint, because there's *no* way that you can check with a torque wrench.

I wouldn't worry too much about the bolts jerking a bit.

 

[matteb63]

So can I remove them and redo them without buggering them up? They are suppose to stretch but maybe not before running the engine? The bolt of the head is not visable so I am unable to use marking paint! ..In the instructions it suggests that you oil the threads and bolt head!

 

[Number_Cruncher]

I don't know about re-use.

MB sometimes specifies a lenght measurement for head bolts, and if the bolts are shorter than this measurement, they can be re-used.

On the other hand, why are you taking them out again. If you've applied the snug torque and the two stages of angle tightening, then, you're done!

 

[Gt Russell]

OMG you should never oil the head bolts !! this could cause hydraulic lock which means any oil in the bottom of the bolt hole gets compressed and can crack the block
I used to be an engine re conditioner BTW

 

[mikestrivens]

I agree the bolts and bolt holes should be absolutely clean and clear of any contaminants of any sort. A long long time ago when I was a student I cracked a head by having a small amount of oil in the bolt hole. I have also seem a Tornado airframe destroyed by a similar circumstance. Ideally you need a compressor with airgun to ensure holes are clean.

 

[Number_Cruncher]

>>you should never oil the head bolts !!

In this case, and in the case of my MB engine, MB tells you to oil the bolts and bolt heads.

Yes, cracking of blind holes might happen in some circumstances, but, if the manufacturer has tested this method, and specified it, then, it's the procedure which should be followed.

The logic of asking for it in this case is to minimise the twist between the head of the bolt and the threads - the angle tightening method relies upon the threads turning as far as the head of the bolt, and twist in the shank tends to equal relaxation of the bolt in service.

I agree that thick oils and greases would very likely likely cause a hydraulic lock, but, a reasonable amount of engine oil wiped into the threads of the bolt will not cause damage on these engines (as long as the bolts aren't buzzed in!)

Of course, any dirt or other contamination should be removed.

 

[television]

The bolt are 102mm when new, that is not very long to get an accurate measurement, on the prewar RR engines the shank diameter was reduced, so that any stretching took place on the shank and not the thread, but they were in the order of being 25cm long

 

[Number_Cruncher]

It's easy enough to measure quite accurately, using the tang on a vernier caliper - the amount that the bolts stretch is significant, and easily measured.

For example, the short cylinder head bolts on OM606s are 102mm long when new, and can be re-used if under 104mm. The long bolts are 115mm new, and 117mm is their upper limit.

Yes, 2% or so is significant plastic strain - these bolts operate a way beyond yield.