Fly Wheel Bolts

[Allen Payne]

Can they be re-used or should they be replaced?

 

On a K-Series.

 

Thanks

Allen

[xflow7]

Anyone is welcome to correct me, but I'm pretty sure accepted wisdom is to replace them. Relatively cheap insurance against potentially disasterous consequences if they fail.

 

Dave

 

Edited by - xflow7 on 5 Mar 2005 20:23:25

[V7 SLR]

They can be reused as long as there's no scuffing on the threads. That would indicate the flywheel had been straining against them and may have weakened them.

 

Make sure you apply blue threadlock when you reuse.

 

I had new ones but a friend gave them to me. New ones come with threadlock already aplied. I might have reused my old ones otherwise. Mind you, new ones are only about 75p each unless you buy the silly-priced ones I've seen somewhere at about a fiver each.

[Rob Walker]

Uprated ones are recomended for engines with high output. I had three standard ones fail on my K. QED can supply the uprated bolts at about £6 each ouch!

[Tony C]

"They can be reused as long as there's no scuffing on the threads. That would indicate the flywheel had been straining against them and may have weakened them."

 

Cobblers!!!

 

Bolts and/or nuts in critical locations such as this should only be used once - ask any engineer.

 

Sure you MAY be lucky, but do you want to take the chance.

 

It REALLY gets up my nose when advice such as this is given on an open forum.

 

I'm sorry if you are upset by my comments V7, but visual condition in this context is completely meaningless - maybe you have x-ray vision

 

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[old captain slow]

Just checked the good old Haynes manual and it says new bolts must be used on re-fitting the flywheel.

 

C7 CDW

[V7 SLR]

Tony, that advice came from a Rover parts counter.

 

And why would I care what you write on an open forum?

[Englishmaninwales]

I'm not sure I would trust the average person behind a Rover Parts counter. They seem to have enough trouble with oil filters/fuel filters/cambelts and so on

For the cost of the bolts and considering what they do, surely one just uses new bolts.

Malcolm

[Bare]

Hehhh.. I dunno If i would trust to anything 'Rover' if it came to that :-)

Most engines, certainly any that I've ever worked on have no requirement to replace Flywheel Bolts as a matter of course.

IF I was doing that..and I was suspicious of longevity, I'd Buy a set of ARP fasteners.. which would without doubt then be be the strongest part of that engine

[SLR No.77]

When I rebuilt my engine I decided to replace them. First Rover dealer had none, second had 5. Maybe that sums up the attitude of the dealers to replacing them They'd probably charge the customer and not replace them anyway - wouldn't the job would already be costed based on the schedule to be worked?

 

AFAIK the bolts are replaced due to being "pre-loctited" if that makes sense? Many bolts are the same in the Rover engine - the manual states to change the cam-carrier bolts, but they're only M6 and will go on for donkey's years. Again, the new ones are pre-loctited. I suspect that Rover does not trust the monkeys to apply the loctite correctly 😬 Rover's biggest problems are in the dealer network and I'm sure they recognise that.

 

I'm sure there are many professional engine builders who would not use new bolts - my guess is that they'd take the view that it's a sizeable bolt for the application and is not over-torqued for the bolt size.

 

Stu.

[Jason Plato]

Replace . You would be daft not to .

 

But also be sure to do them up properly using dummy bolts in 3 holes then new bolts in the other 3 . You need to ensure that you dont get any threadlocking compound between the faces of the flywheel and crank . This will cause fretting and failier of the flywheel bolts .

 

Also make sure that the dowel is a realy good fit in the hole and in the flywheel .

 

 

[Luke Beaumont]

I'd vote for replace as well. They are about £6 a set, which is far less a burden than willy nilly replacing the head bolts at £40 a set.

 

The flywheel bolts are assembled with a reasonable amount of torque (65ftlb?), and as far as my limited knowledge allows I suspect this falls into the method of torquing a fastener close to its elastic limit, which if I understand it correctly means once used it is weakened. Given my doubts over this, the criticality of the application and the cost of new bolts, I decided to always chuck the old ones. Hope that helps. Oh, and chill out Tony.

[AMMO]

I always replace. I like to sleep at night.

 

AMMO

[Allen Payne]

I think I'll be replacing them - assuming I can get them out. I've managed to break three 1/2" sockets today and still have four bolts to removed.

 

Thanks for the advice.

[oldbutnotslow]

Allen are you using chocolate sockets? 😬

They are reasonably tight but with a good breaker bar they should pop off quite easily. I’ve just taken mine off and for the cost I will be replacing them. Don’t care if the old ones are perfectly OK, its just not worth the hassle of having to pull the engine out again should one fail. Having said that I never bothered to replace them on rally cars I built in the 1970's but then again I knew no different back then! Loctite was something new and not used very often!

 

 

Grant

 

Black and stone chip and currently not going ☹️

here

[Alex Wong1697456877]

Tony C, can I quote someone who probably knows more about this than the average engineer?

 

Flywheel and rod bolts are the most highly stressed fasteners on an engine and therefore deserve special attention.

 

Providing that flywheel bolts are installed to the correct procedure, using the right lubricant and calibrated torque wrenches, then the bolt will typically only see shear loads.

 

Flywheel bolts are not installed using stretch principles because the thread minor diameter is the smallest diameter on the bolt and therefore applied stretch would be achieved through the threads, with a focus on the last exposed non-mating threads –definitely not good practice. It is not therefore usual to see permanent set or stretch in a flywheel bolt.

 

During use the bolt tends to suffer “nicks and scuffs ” through the applied shear loads of the application. Nicks and scuffs are stress concentrators and race engine building at the highest level has each bolt measured for a consistent surface finish prior to a once only installation.

 

When a flywheel bolt is installed for a second time, new nicks and scuffs are introduced as the bolt will probably not be locked in exactly the same position as the initial application.

 

Some local damage/stress concentration can be experienced when the flywheel has burrs around the holes into which the plain shank of the bolt will be fitted. This can lead to point loading - again not good practice.

 

Evidence of frettage or damage on the plain shank is a sign that the joint was improperly assembled or maintained and that the bolt has seen a higher stress regime than expected. ‘Frettage fatigue’ needs much lower stresses to initiate and propagate than fatigue without frottage. ‘Frettage fatigue’ has no predictable fatigue limit.

 

Fasteners affected in this manner should be replaced as their life is compromised. Holes should also be checked for dimensional conformance.

 

Corrosion has a similar compromising affect on fatigue properties and the same advice is given, as for frettage.

 

Where apparently good bolts are to be re-used, it essential to check the threads for damage or distortion. Improperly tightened joints lead to premature failure.

 

In racing flywheel bolts have been known to undergo permanent deformation through extreme shear loads.

 

If you have not lost the will to live reading through the above take a look at www.boltscience.com. This is a small company within Lancashire University, one of the universities that give us technical support.

Tony Baker

Northbridge Motorsport

---

 

So what V7 said is correct I think, but I always use mine once only.

[Sheds Moderator]

Flywheel bolts are not installed using stretch principles because the thread minor diameter is the smallest diameter on the bolt and therefore applied stretch would be achieved through the threads, with a focus on the last exposed non-mating threads –definitely not good practice.

Ah, this explains why K series head bolts, which as we all know are stretch type, are waisted down for most of their diameter.