Why do modern car engines have different types of bolt type heads like Torx etc?

Why do car manufacturers use many different types of bolts and screws: there’s hex bolts, double hex, torx screws, XZN,  star shaped etc? Wouldn’t it be easier just to use a standard traditional bolt head?

Edited By Simon Robinson 4 on 26/07/2023 17:10:39

No, not when you are a robot.

Maybe desktop engineers needs more space savers as the cramp in things more and more, it looks so easy to maintain on a computer screen.

The robot can handle anything it’s tooled up for

My thoughts are its the car makers way of trying to stop the average man fix his own car by making the cost of specialist tools to expensive.

Martin P

Martin has it ! BMW gearbox held on by normal bolts - EXCEPT the two at the top, there torx ! Just to F--- You up ! It didn't work, I had a set of torx keys ! JCB turbo doost diaphram, 5point torx security( pin in middle), but WHY ? Noel.

My guess is there's more than one reason, such as:

• Different Preload requirements - For example Torx can go tighter than hex head without damaging the head, but hex are cheaper whe n that doesn't matter..
• When the bolt head has to fit into a small space - too small for a hex head
• To identify groups of bolts used for a common purpose, so that mechanics don't undo timing cover bolts when they're meant to be replacing the water pump.
• Making sure that different grades of bolts don't get mixed up during manufacture and maintenance. (The bolts holding the head down are a much higher grade than those that stop the sump falling off.)
• Encouraging garages to pay for the full manual.

Space saving may be the main reason: I'm amazed how tightly packed modern engines are, almost to the point it's necessary to take an engine out to change the oil filter. My guess is the needs of home mechanics aren't considered at all because most owners have their cars to serviced by fully equipped garages full of diagnostic gear, socket sets, and special tools.

Dave

They’ve caught the idea from model engineers, no doubt. Imperial, metric, BA (mixed systems?) thread form, large and smaller nuts/bolts (to look better) - and so it goes on. Get used to it.🙂 It’s not confined to just car engines!

Sorry SOD but that’s a load of tosh it’s what they can get at the right price.

It’s not a recent thing either when I worked on 6.7 v8 RR were bi-hex!.And that was nearly 50 years ago!

Edited By bernard towers on 26/07/2023 21:39:07

I like that, NDIY! My steam-wagon is getting like that because I have been building it over such an obscenely long time with any number of changes of parts and mind. Some fastenings are not very accessible either. I started the project in a larger scale, and for that was going to use UNF for all the structural fastenings because they and the A/F spanners were easy to obtain, and they looked neat as the hexagons are a little smaller than BSF/BSW ones.

Well, it is a vehicle... So at least I am in professional company.

.

Vehicles are not only cramped by having to pack more and more stuff in less and less space, (like my workshop but at least that is not hampered by the stylists and "value-engineers" but probably also designed for assembling not servicing.

.

The first plague lock-down's enforced idleness was too much for my car's battery, which seemed to have been the one installed from new. The two clips were held by Torx screws, one out in the open, the other hiding in a narrow canyon of full battery depth. I had to make an extension handle to hold the driver, of right-angle bent form. Nothing special, just a bit of pipe with a slot sawn in one end, and a load of insulating tape.

And as for the "cabin air filter"... I have never managed to find where Renault has hidden that!

My personal bugbear is not different styles of heads, because as SOD says they're usually selected to serve a functional purpose...

It's the fact that many manufacturers seem to mix standards.

On pretty much every modern vehicle I have worked on, there has been a nonsensical mix of ISO and DIN, or DIN and JIS preferred sizes, with a few vehicles using all three, sometimes on the same sub-assembly.

Which defeats the point of preferred sizes altogether and forces you to have (and if working away from your workshop, carry) significantly more tools than should be required.

.

Having worked on lots of industrial projects where maintaining standards and designing for maintainability was a big deal, it really feels like sloppy engineering to mix and match like that, especially as there have been no instances I have seen where the size difference between a 12 or 13mm headed M8 bolt (JIS or ISO/DIN), or a 16 or 17mm M10 bolt (ISO or DIN) would make a blind bit of difference to the packaging of the overall assembly.

.

And don't get me started on reduced head sizes on bleed screws... When you put a 9mm AF external hex on an M12×1 thread with about 20mm of engagement you're just asking for that head to get rounded off the second there's a whiff of corrosion...

Also, despite it being a part which is both essential to vehicle functioning and an obvious failure point, you've made it so bizzare that it's nearly unobtainable to the extent that as the vehicle manufacturer you're air-freighting them from the OEM in the far east whenever one is ordered.

Not that I'm bitter or anything, honest.

I'm shocked to hear Rolls Royce did that, but if you worked for them Bernard it must be true. Dreadful news, my next car won't be a Roller!

Surprising too, hard to imagine a production line switching bolt heads on engines mid-stream just to save a few bob.

Dave

Not just for assembly but for manufacturing in a more general sense.

With a FWD vehicle it would be very possible to put the clutch and housing outboard of the gearbox (rather than between gearbox and engine) using a hollow shaft, this would hugely reduce the expense and difficulty of the most significant wear-part replacement most cars ever receive, without much increase in mechanical complexity.

But, you couldn't use that design on a RWD/AWD/4WD vehicle, so suddenly you have to produce two variants of that particular engine if you want to offer those as options...

So it's No Bueno, because you're giving up a significant efficiency saving in being able to reuse the same engine in as many models as possible.

On some engines (Triumph Toledo I seem to remember) the clutch was in its normal position, but the input to the gearbox was via a quill to a hollow main shaft. You took off a cover over the top half of the clutch, took off a cover at the back of the gearbox, withdraw the quill, then you can unbolt the clutch a bit at a time, turning the engine slightly as you go, and lift the clutch assembly out upwards. All very nice, but it didn't seem to catch on, probably because it cost more. I'm not sure what held the gearbox to the engine.

However, my last 3 cars all were still going strong on the original clutch at over 150,000 miles, so it's a bit academic.

How about Metric bolt heads on Imperial threads?

How about Metric bolt heads on Imperial threads?

I recall reading about a vehicle or a motorbike that used only one or two sizes of nut +.bolt to facilitate disassembly

Military stuff can sometimes be like that

I've actuately got some of them on my J&S 1400 surface grinder. Mainly because the only 5/16" BSW screws I had that firred the need with the right sort of head, had 5mm allen key heads. Not a problem, it's only me that needs to remember.

Even nowadays you'll get a metric hex and an imperial thread on some Lidl stuff

I think the Chinese make a lot for the USA market so the design will be a 1/4" thread hex bolt but the hex head depends on whether it's destined for the USA(1/4" or Europe (6mm)