Catastrophic Failure
Turbo Mini Forums

So why do the both of you think loctite is a bad idea on rod cap bolts ???

I've done it for the last 30 plus years (apart from on designs that use locktabs) with no issues - and no bolts ever coming loose.....

EDIT - for bolts also read nuts where applicable to avoid any confusion.

Edited by Rod S on 5th Apr, 2009.

Schrödinger's cat - so which one am I ???

Because as the bolt is torqued up the loctite sets therefore the preload on the bolt will be less that desired.

Add to that, when cyclic load is applied to the bolt, the loctite will break up relieving what preload is there.

Ouch!

I reckon a bit of JB weld and the conrod will be as good as new.

nah, wood glue, if it makes the broken part of the wood even stronger, imagine what its like on metal!

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

In all seriousness, the hole in the gearbox wouild make a neat oil return from the turbo.

Schrödinger's cat - so which one am I ???

sorry to see you suffered that loss gary ,well done for having a positive attitude .


thanks for sharing it with us and sorry bout all the neggo whinging !!!


im with rod on the loctite front , i allways put it on anything i really dont want to come undone ...ny last long distance engine ,1300 astra went 325k miles revving regularly to 7200, following this system.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Nasty mess there!

fasteners and torque - before I retire I will write an article on this as its often a very mis understood subject. Rod you are correct in that any bolted joint should be designed around the "clamp load" required to keep the joint intact at its operating loads. To achieve sufficient clamp load you must have sifficient number of fasteners AND they must be torqued to circa 75% of their yield strength. For example - a recent thread on mains bolts - if you replace a bolt in a joint which was designed to use 2 10.9 grade bolts torqued to 75% of yield without friction with 2 12.9 grade bolts - do you use the same torque figures as the 10.9 grade bolts? No of course not - chances are a 12.9 grade bolt with a 10.9 grade torque would only be at - guessing 40% of yield - not enough stretch means the bolt can come loose under cycle loading. So you decide to torque the now 12.9 - ususally cap head bolts to the required 75% of yield for a 12.9 grade - happy? - have you checked the under head stress generated by this larger torque is sustainable by the parent material you are clamping? - I hope this is a little illustration that there is more to bolts than meets the eye!

lubricant be it loctite/ oil or water basically reduces the friction in the threads/ under bolt head area - a good thing? sometimes yes - reducing the friction in a bolted joint in these areas means more applied torque - by you is transmitted into clamp load on the joint by means of stretching the bolt more (yes towards the yield limit!) so loctited joints may appear to perform better in this way beacuse the bolts are stretched further into the recoverable elastic zone - don't try this with 12.9's!, there are exceptions of course such as when bolting into alloy where you will sometimes never stretch the bolt anywhere near yield without stripping the threads - hence locking measures are needed like loctite to ensure the joint stays permanently clamped.

I'm very happy with the fact I rid the new Lotus Evora of all chassis bound "locking aids" like loctite or lock washers - I designed the joints/bolts properly, whe nthey appear in the shops have a look underneath! I wanted to do the same with the S2 but it carried all the bodges from the S1 with it which couldn't be corrected without starting again!

JK

If Carling made Mini engines
it would probably be like this one!

god that must have been knocking its bollox off big time to get the crank that blue!!!

blue bollox's makes me wince..

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

haha in other words this is just total descruction!!

i would never ever use loctite on rod bolts or mains for that, just use some arp moly lube... perfection!!

that was with one rebore at 225k james ,oh and big end shells at 90k and 225 k .

it only stopped cos it was nicked and involved in a police chase,and the crims went into a roundabout and floored it in the wet and wheel spun straight ahead inot the kerb and stuck the strut through the bonnet .

i dont think they were expecting 98 bhp from a 75 bhp 1300 sohc astra van !!!

that my theft deterant ,make it too powerfull for numpty car thieves to drive it!lol

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Jk very good lesson for all to pay attention to. But I will always maintane that criticaly bolted joints require mechanical locking and should not be designed to rely on just physics to keep them together.

When I went to change my crank I found all the mains bolts loose or under torqued. Paranoid does not even come close. I re checked the torque three times over two days before I was happy to finish rebuilding the motor.

Does anyone have a bottom end that is posatively locked or like the above are they all friction locked?

Own the day

The problem with any method of locking device is that you introduce more "friction" into the clamp load equation, with washers its extra friction faces, with lube you have to have a clear understanding of its repeatabile properties - like ARP's have - hence more chance of varying friction causing loss of clamp load, a bolted joint hsould need no more than the preload on the bolt to hold it together - otherwise its not designed properly

JK

If Carling made Mini engines
it would probably be like this one!

The standard A+ mains bolt shouldnt need any locking device as the head of the bolt is designed in such a way to resist loosening, it has its own built in spring. Any one will know that these bolts go with a crack when breaking them loose.

JK its always a breath of fresh air to read an artical which has been wrote by someone with a true understanding of a subject Fair play for sharing the info,
regards,
Paul.

My fault for starting the "loctite" debate.

Schrödinger's cat - so which one am I ???

In my line of work any bolt which could possibly work loose let alone work its way free is posatively locked after being torqued down usually with locking wire. Some departments even have a tol that applies the correct tension on the wire before the final terminating action is completed.

these engines were not put together with what we have done with them in mind.

I have found the big end studs streched on 3 out of four rods before on top of finding the mains bolts loose on another motor,

earlier motors had lock tabs fitted why were these excluded from later engines?

Own the day

Schrödinger's cat - so which one am I ???

point taken, but mains bolts worked their way in

I go along with John K, there should be enough pre load on the fastener to prevent cyclic loading of the fastener, which otherwise then leads to loosening or complete failure at worst.

On 14th Apr, 2009 Sprocket said:
point taken, but mains bolts worked their way in

I go along with John K, there should be enough pre load on the fastener to prevent cyclic loading of the fastener, which otherwise then leads to loosening or complete failure at worst.

Schrödinger's cat - so which one am I ???

YES he could have put oil in the dam thing

On 14th Apr, 2009 Rod S said:

On 14th Apr, 2009 Sprocket said:
point taken, but mains bolts worked their way in

I go along with John K, there should be enough pre load on the fastener to prevent cyclic loading of the fastener, which otherwise then leads to loosening or complete failure at worst.

Sprocket,

I don't disagree with you - the basic design should be right in the first place - but the basic design is over 50 years old and people are putting the loads way beyond that level anyway.

Working with what we have, my personal choice is to use loctite as added security against unexpected loads esp. cyclic or under fault conditions ("beyond design base" is just a phrase I use from my previous industry).

Going back to how I caused all this debate..... Gary's big end bolts came undone and (4th photo) were in the sump.

Whether they came undone causing the failure, or whether they came undone after the bearing failed and were subject to excessive vibration loads so just unscrewed....... begs the question : -

Could it have been avoided ???