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The mkiv Supra Owners Club

Snapping small bolts


Ian C

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This must be an age thing. It looks like all the 10mm and 12mm bolts in my engine bay are having end-of-life issues. During 11 years of ownership I've never snapped a bolt on it, despite going single, swapping the engine, and doing loads of other stuff. In the last 6 months I've had SIX bolts snap:

 

2* PAS reservoir 10mm mounting bolts

1* 10mm bolt on suspension turret holding on a GReddy master cylinder stopper

2* 10mm bolts holding on the radiator clamps

1* 12mm bolt holding on the front subframe bolt spreader plate

 

Every one of them bolt into the chassis. I've had all the cam caps off a couple of times recently and they are ok, just seems to be non-load bearing stuff that goes into the chassis. Very peculiar. The master cylinder stopper one is ever odder, as it's a bolt from my spares pile and was only installed a couple of years ago, yet it's snapped the same way, the head just twisted off the shank when trying to undo it. The car is and always has been garaged, so it shouldn't be weather effects or anything.

 

I've got a plan to pull the engine bay apart and clean things up in general, so during this I'll undo every 10mm and 12mm bolt I can spot and get at. Any that break will get drilled out and retapped and replaced.

 

Questions:

1) Does anyone know of any decent bolts that don't look crap, in 10mm and 12mm, varying shank length and probably that funny thread pitch Toyota use :)

2) Has anyone else experienced this phenomenon?

3) Anyone got any theories on why it's happening?

4) Black powdercoating of TB's, plenums, PAS reserviours etc - good idea in a red engine bay? I think so :D Any details about this process would be handy.

 

-Ian

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Reson its happening is most likely as you Said you have been unscrewing them before all bolts used is mostly 8:8 durability and they strech easy. One should probebly replace when unscrewing em.

 

I bought a bulk set in Sweden and paid for how much it weighted spent around 100 quid on various length and size.

 

Usually its standard thred IIRC to M10 then they use finer thred usually 1 size under like M10 is usually 1.5 and Toyota use 1.25

 

 

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I am here: http://maps.google.com/maps?ll=57.729198,11.786096

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I've taken the rad clamps off a few times over the years, but both of them broke at the same time, that's the weird thing. Can't believe the price of bolts. If I just went for the boggo stainless hex heads and separate washers it'd be pretty cheap, but I just think it'd look really rubbish :shrug:

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It depends where the screws are. A lot of them are screwed into captive nuts in the shell, so the exposed end of the thread rusts, then when you try to unscrew it...

 

Not much you can do except remove them all and copper grease them before they corrode too much, or, if you can be bothered, get at the underside and clean and lubricate the exposed threads before applying the spanner.

 

Oh, and buy some proper penetrating fluid like Plus Gas, WD-40 is no use for freeing properly rusted threads.

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The Plus Gas tip is a good one, I'd still replace the bolt afterwards, but if it saves me drilling it out, then hurrah. All the snapped ones so far are in chassis captive nuts.

 

I don't think I've been overtightening things, maybe I have and over the years it's taken a toll. Funny they are all going at once :shrug: Who uses a torque wrench for the radiator clamps :D

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Thats exactly the point, no one uses torque wrenches unless its on engine bolts, how do you know

what say 20 ft lbs is which is easily reached with a spanner or 1/4 drive ratchet ?

 

Most wheel studs break because they've been over tightened either with an air gun or 2ft breaker bar

which will easy double 75-80 ft lbs which is approx the torque for the nuts.

 

Using some copper slip will definitely help and should up the torque the bolt can take along with

preventing corrosion

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If someone wants to put a list together of sizes requiered i can go and see a local fastners supplier and

see what deal is available.

 

Much better and cheaper to buy in bulk if you can, buying a kit someone else has put together is always

going to cost more.

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I'm not really after the dress-up bolt set thang, more just ones that look like this:

Completely agree - I'm more a function over form kinda guy, but if you're going to replace something you may as well keep it looking neat ;)

 

If someone wants to put a list together of sizes requiered i can go and see a local fastners supplier and

see what deal is available.

 

Much better and cheaper to buy in bulk if you can, buying a kit someone else has put together is always

going to cost more.

I'd certainly be interested in contributing to a bulk order - would genuine Toyota parts be significantly more expensive?

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If someone wants to put a list together of sizes requiered i can go and see a local fastners supplier and

see what deal is available.

 

Much better and cheaper to buy in bulk if you can, buying a kit someone else has put together is always

going to cost more.

 

Really I'd like a selection of shank lengths in:

M10 * 1.25pitch

M12 * 1.25pitch

 

Probably 15mm, 20mm, and 30mm shanks. Maybe 20 or 30 of each so I never need any again :)

 

As for torquing things up, I've always just had a feel for it - or so I thought :D I've used a torque wrench on cam caps and wheel nuts and all that, but I figured a non-critical bolt holding on a bracket just gets done up tight. Not "veins standing out" tight but kinda decently nipped up. What I should do, now that you mention it, is do something up as tight as I think it should be, and then actually check it with a torque wrench, see how wildly off I am :D

 

The copper slip tip is very handy, thank you, I'll do them all with this stuff so they are easier to undo in the future - I hate rusted up stuff.

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Thats exactly the point, no one uses torque wrenches unless its on engine bolts, how do you know

what say 20 ft lbs is which is easily reached with a spanner or 1/4 drive ratchet ?

 

I realised, while posting up pics in my subframe disaster thread, that I snapped the head off a 12mm bolt holding that bracket in place with very little force. I've never touched that bolt before in all my years of ownership, so this phenomenon can't just be me continually overtightening regularly-accessed bolts :) I was willing to believe it was until I realised that.

 

I probably haven't helped matters, though, admittedly :D

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[COOL][/COOL]

I realised, while posting up pics in my subframe disaster thread, that I snapped the head off a 12mm bolt holding that bracket in place with very little force. I've never touched that bolt before in all my years of ownership, so this phenomenon can't just be me continually overtightening regularly-accessed bolts :) I was willing to believe it was until I realised that.

 

I probably haven't helped matters, though, admittedly :D

 

Sorry i might have sounded like i was saying you were at fault which im not but just pointing

out that over tightening is one of the main reasons for bolt failure.

 

As well as they've probably not been touched for nearly 20 yrs or had any copper slip

etc when they were first fitted.

 

Its strange though that my old UK spec has only had issues with some of the eccentric

adjusters and all the other bolts inc the engine under tray bolts have come straight out.

 

 

Or could it be down to poor quality bolts, i remember how the japs used to use very soft

X head screws on the motorbikes just about everywhere which were utter crap !

Edited by Dnk (see edit history)
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If you really want the indented hex head bolts with built in washer flange in metric fine sizes you are pretty much limited to buying OE ones or something of similar size from another car maker. If the car had proper threads (Imperial) you could do what i do and use NAS bolts for anything critical. But it has silly metric *rap so you can't ;)

 

 

Oh, and try just TWO Weetabix for while...

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Not sure if im missing something but aren't most of the bolts in the engine bay normal

metric threads and not metric fine ?

 

If they are and your prepared to pay for them then flanged hex heads are available in aluminium, st/st

and titanium, not the cheepest place to buy from but Demon Tweeks sell them

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Not sure if im missing something but aren't most of the bolts in the engine bay normal

metric threads and not metric fine ?

 

If they are and your prepared to pay for them then flanged hex heads are available in aluminium, st/st

and titanium, not the cheepest place to buy from but Demon Tweeks sell them

 

As far as I know they are normal, I haven't noticed any fine thread ones. In fact most of the ones I have been replacing have been M6 & M8 iirc. Not sure if Ian is getting mixed up with the head size? (10mm socket and 12mm socket required for the most part).

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