GT 2 litre cylinder head bolts.

[Roland]

Am in process of replacing a head gasket on above and have bought the gasket kit and head bolts off e-bay.
Problem is the new bolts do not look much like the old ones, being half a cm longer, and threaded through most of their length - the old ones had only a 1-2 inches of inches of thread. The bolt heads are male torx rather than a female hex. and not supplied with the thick washers under the head that were on the old bolts. The thread sizes are the same.
I've contacted the supplier who has checked his catalogues and assures me that the ones supplied are indeed correct, but I'm dubious about using them, particularly because of the different lengths and the possibility they will bottom in the block.

Has anyone had occasion to change head bolts and come across this, and am I being unduly cautious ?

[JohnB]

Hi just checked the length of some i purchase for my last 2l they are 110mm long the make are scan tech and are also male headed
And threaded through most of their length

[Roland]

Thanks for response Harriet,
Presume that measurement is from head flange - which corresponds to length of my old bolt.
Unfortunately I took the new bolts back to the supplier, who is not too far away. He found some other bolts which he said "belonged to a larger engine" but looked very similar to the ones that came off.
However, on trying them in my block, I found that the thread pitch was different ..
Haynes manual states there is no requirement by Volvo to replace the head bolts after removing the cylinder head, implying that they are not stretch bolts. However, my supplier reckons they are.
Who to believe ?
I realise using the old bolts is not good practise, but I need to get on with my life.

[Ade]

Hi,
I am a mechanical engineer by trade (hopefully you are reassured by this!) and i believe that the form of the head will not make a blind bit of difference. The thing to check is that the grade of bolt is the same. Bolt grades should be annotated by two numbers on the head somewhere i.e. 8.8, 10.9, 12.9. These numbers denote the tensile strength of the bolt and the percentage of the U.T. load that can be taken by the bolt whilst still remaining within the material's elastic limit.

eg. an 8.8 (general use) bolt has a material strength of 8kg/mm squared (based on CSA) an will be able to take 80% of that ultimate load and still return to normal. (all bolts stretch under load, its just by how much that varies)

Certain special fasteners do not always have this ISO notation on them so if your old head bolts haven't got this (or your new ones for that matter) then you have no hard and fast means of comparing the bolts.

as for the washers, i would be inclined to re-use the original volvo ones on the new bolts but make sure you flatten the faces (smooth file and some patience unless you have the facility to make some new ones or have access to a surface grinder) and get them parallel before using them again. Having said that certain torx and socket type cap head bolts (ie possibly your new ones) have a 'thrust face' which negates the need for a washer. If the bottom of the bolt head is quite large, ie the size of an equivalent washer for that size of thread and very flat then you may well not need the washers.

The only way of comparing the bolts without a metallurgical analysis (and this is very much the 'pikey' way of doing it, but somewhat effective if you have the feel for it) is to take a stroke with a file over the head of each bolt and get a 'feel' for the hardness of either steel. They should feel identical if they are the same material and therefore the same grade of bolt. The only other way to do it is a destructive test with a very big torque wrench and compare the shear torques of each one respectively. Again should be identical give or take 3-4lbs/ft but that way entails fucking up one of your new bolts which i'm guessing you don't want to do!

As for the extra length, try screwing one into the block without the head on and bottom it out and measure the distance between the top of the block and the thrust face. compare this to your measurement from the cylinder head mating face to the spot face for the bolt head. As long as you will have maybe 0.080" or more of clearance at the bottom of the hole, you're good to go! If not no harm ever came from trimming a bolt down, just don't roll the end of the thread when you de-burr it or you will have difficulty screwing it in and it may compromise the thread in the block. With the right technique there is no reason you cannot chop a bolt/stud and have it glide in just as smooth as it did before you took the hacksaw to it!

Whether volvo recommend changing the bolts or not, do it anyway- ALWAYS!!!!!!!!!!!

The fact that they are threaded all the way along does not make any difference to the U.T.S. (sorry, engineering jargon, ultimate tensile strength) of the bolt. A bolt is only as strong as its smallest cross sectional area (ie its thread).

Hope this helps, any questions, just shout!

adey

[Ade]

Just a quick thought, though the shoulder of a bolt does not increase its UTS, it's stretch rate may be different to one that is threaded all the way so any torque settings you use should be supplied with the new bolts and may well be different to the volvo specs. Not 100% sure on that though, speak to the bolt manufacturer if poss. They aren't going to be drastically different i would think, but another point worth bearing in mind.

Bloody hell, never realised i knew so much about bolts!!!

Obviously sequence will be the same.

Another little tip, when you go through the torque stages, it doesn't hurt to add a couple of your own increments. Makes the clamping force more even still.

ie if it says go through the sequence to 40lbs/ft then again to 80lbs/ft then angle of 45 for instance (i dont know that engine) it will do you no harm whatsoever to go through the sequence at say 25 then 40 then 60 then 80 then 20 degrees a further 25 degrees.

But thats just me being pedantic, in reality it probably doesn't make much difference as long as you follow the manufacturers specs.

[Roland]

Phew - thanks Ade that's great !
I returned to the supplier this pm and retrieved my original bolts with a view to chopping the excess length off, and you've now confirmed that should be OK, but I'll check the hole depth in the block first to see whether it's necessary. The tensile number on the new bolt head is 10.9 but nothing visible on the old ones.
The head flange (ie thrust face) on the new bolt is the same diameter as the old one so I'm going to use the old washers after cleaning up as you suggest.
Only other problem (I hope) is finding a torx socket to fit the bolt head. Why do manufacturers do this ? What was wrong with the hex head ?

If this all seems a bit pedantic to anyone else reading this thread, it possibly is. But there is so much work involved in stripping this engine, with limited access, to get at the cylinder head and put it all back together again, that I don't want to have to repeat the exercise.

I note your comments re increasing the torque stages and will do that - which reminds me I also need to procure an angle torque gauge for the final stage.

[JohnB]

If you want you can have the ones i have for free just cover the postage

[Roland]

Thanks Harriet - I'll pm you.

[Ade]

glad my advice helped, a 10.9 bolt is perfectly fine for a head bolt whatever the old ones were. As for why manufacturers use torx heads, its anyones guess but i was always led to believe that they were introduced as an anti tamper fitting so the masses cant go taking things they dont understand to bits willy nilly. Obviously they've been around long enough now for the tools to have become readily available. You notice a lot of spline fitting cap head bolts on the german machinery these days for the same purpose, of course the spline drivers are becoming more readily available too now. First time i lifted a spanner to an audi i realised that a driver bit set was goint to be a good investment!

i say bin the fuckin lot and stick to hex heads and hex socket cap heads!

Whatever you do don't even attempt to use shit quality driver bits. A good set made in something like S2 tool steel will set you back about 50 quid if you shop around and will be the best 50 quid you have ever spent. For your money you should get a full complement of long and short bits in hex, torx and spline with 1/2" and 3/8" bit holders.

Worth its weight in gold, SERIOUSLY!

All you will get from trying to do a cylinder head bolt with poor quality tools is one big fuck off headache.

I know from personal experience, did a peugeot XUD turbo engine once, dropped my bit because it slipped, spent half hour trying to find it, found it then on the next bolt it snapped! Never bought a crap one ever again!

peugeots, torx bolts and crap tools

[Ade]

I noticed your general distaste for the idea of having to strip it again, which is absolutely right. Do it once and do it right! So........... probably goes without saying but you have had the head skimmed and checked for flatness haven't you? and checked the block for flatness. Do yourself a favour and check it, then check it again, then drink some tea and check it again, then scratch your head/bollocks and check it one last time. Plunger clock is most ideal but a GOOD (and i emphasise good) straight edge and a fag paper will do just fine with a bit of skill, or a piece of glass as a flat surface (modern glass is kept within very tight tolerances of flatness) and apply some engineering blue (marking out ink) to the block/head then GENTLY rub the piece of glass over the surfaces. In theory it should abraid the ink evenly all over. If it takes it off in certain spots only then you know you have valleys/high spots which need rectifying. There will normally be a flatness tolerance on these surfaces of around 0.0015"-0.0025" over the area, however if flatter can be achieved then it's always better.

Depending on the machine shop that has done your head they may have used a big vertical mill with a dirty great slab mill cutter on it. This is ideal as the cutter can make a pass without the head going anywhere near the back edge of the cutter so no tilting of the machine spindle is necessary to avoid the 'back cut' (which ruins the 'lay' of the surface finish, which is important) achieving a more or less perfectly flat surface.

If a smaller toolroom type universal mill has been used, it will have been done with a fly cutter and the spindle of the mill will have been offset by a fraction of a degree to avoid the 'back cut'. This method is ok but it depends on a skilled operator to set the machine as an excessive tilt will lead to 'dishing' of the head, meaning anything but flat. The key is to keep the dishing (which will occur if the spindle is tilted) within the flatness tolerance but you will always get it.

Of course a big enough surface grinder kicks the shit out of both of these methods, however grinding aluminium is quite a skilled process insofar as selecting the correct grinding wheel compound, coolant and correct feed and traverse speeds. It is doable whatever you may have heard, but very expensive because of the skill of operator required and the size of grinder. Most toolroom surface grinders are just a little bit too small for a cyliner head off a 4 pot 2l.

Just thought i'd share the knowledge! hope it's of interest/use. Might be informaive to anyone else reding this thread as well hopefully.

[Roland]

Thanks for that Ade - you are a mine of useful information !

Errr .... I haven't had the head skimmed, my defence being that Volvo categorically state (according to Haynes) that the heads on these cars should not be re-surfaced.
However, I have used the straight edge, and feeler guage technique and can detect no discernible warpage. I was close to home (within a mile) when the gasket blew and limped back on three cylinders with clouds of steam coming from the exhaust. The engine did not overheat that I noticed and the coolant level was not overly low.
I also got my next door neighbour, who builds GT40's for a hobby, to give the head and block the once over. He reckoned there was minimal damage. The gasket was intact and it was difficult to see where it had blown.

So, fingers crossed, I'll re-assemble and if it all goes pear shaped there will be another scrap car on here for sale as spares. I can't face re-doing the thing again.
As it is - I'm also debating with myself whether to change the timing belt, idlers, ancilliary belts and water pump - which are now mainly dis-assembled and/or accesssible - and due for change - until I know whether the gasket repair is successful.

Decisions, decisions !

On a more positive note, thank you Harriet for the head bolts. They are the right length and branded (Scan Tech who are Swedish suppliers of Volvo & Saab parts) so should be a better bet than my anonymous e-bay items.

[Roland]

For anyone interested, when I came to measure the depth of the hole in the block, which the head bolts locate in, it seems there is plenty of depth, even for the longest bolts in my collection .

The depth of the hole in the block face, having cleared out all the crud (of which there was plenty) is 43mm.
The original bolts had a depth of 29.25 mm protruding below the cylinder head and with the thick washer in place on the thrust face of the bolt.
The Scan Soft bolts showed 30mm protruding and the bolts off e-bay showed 33.4 mm.

So it appears, even with the longest bolt, there is nearly a centimetre of clearance at the base of the hole. And this is of course before the head gasket is fitted, which would probably occupy another 1-2mm.

So hope this info is helpful to anyone else contemplating this job. It's reassuring to know that even if some debris finds it's way into those bolt holes, there is still a good margin for clearance.

[Ade]

That will be because of the design of the head, its a flatty with a bowl in piston combustion chamber isn't it? You would be able to skim it but you would also have to re-cut the valve seats and readjust the valve clearances to keep the valve protrusion the same as when you started. Pain in the arse or what!!

Or do it the pikey way and stick a thicker head gasket in there!!