Flywheel Bolts - Want To Know Why You Should Replace Them?

[philbey]

Have a look at these pictures - I was just reading THIS THREAD and there was some dispute over whether or not to replace flywheel bolts. Personally, I've always been a fan of replacing, and the one time I didn't, the damn flywheel fell off.

 

Today I had to get some longer flywheel bolts, so I whacked a thread gauge on the old one to check the pitch. While not paying much attention to what I was doing, I couldn't seem to get a thread to match. On closer inspection I found.....

 

 

Here's another picture, it actually sticks out like dogs balls!

 

 

In the second photo, you can see the necking of the bolt, where elongation has made the bolt thinner. The reason its only the top half of the bolt is because that's the flywheel side, where there's no threads to engage the bolt, so it can stretch.

 

This bolt has undergone Plastic deformation - the strain put on the bolt has permanently changed its shape. This occurs when the stress on the Bolt material passes the Yield Strength. (See Irokin's post in the other thread)

 

To put this bolt back in and retorque it would more than likely bring the material very close to its Tensile strength (ie BREAKAGE) - If it didn't break on torque up, it could very likely break mid operation and it's gearbox out time!

 

It cost me about 10 bucks for a new set of High Tensile bolts from Coventry, well worth the money I say.

 

Incidentally, these were off an Automatic flexplate, I would dare say a Manual would see higher loads on the flywheel bolts.

 

Good Times. TP.

Edited November 19, 2008 by philbey

[parrot]

Holy shit! You have convinced me

[irokin]

Fantastic demonstration! Well done :jamie:

[furryfrog]

Yeh ive always been a fan of replacing them, can't say ive come across ones like yours though someone went to town on them.

 

funny thing is i went to coventry a few days ago to get some for my motor and they don't have the correct pitch I'm after, i think its 1.00 which is heaps fine, looks like its off to nissan.

 

I remember seeing a photo of a vlt where the flywheel came flying through the passenger side of the transmission tunnel scary stuff.

[Rolla Boy]

I've never seen anything like them...

 

Thats crazy...

[philbey]

Yeh, like I mentioned I had a flywheel come loose once. Looking back we were lucky the damn thing didn't go through the tunnel. It dropped down onto the spigot while spinning and the ring gear dug a 3/4 inch groove through all the ribs on the inside of the bell housing.

 

I've heard some horror stories about them coming through the floor too.

 

Spend the 12 bucks!

[Trev]

They don't even look like flywheel bolts, They look like cheap everyday bolts.

[philbey]

Haha, you'd probably look cheap and everyday if you'd been in there for a good few decades.

 

You make a good point though Trev, they could be standard bolts, not high tensiles, which would explain the excessive stretch. They did have a number on them, but it could just be random factory numbering with no real meaning. I'll check later.

 

High tensile or not, if your bolts get any plastic deformation then you're best to just replace them.

[Teddy]

Insane !

 

Its amazing what things you can find if you look hard enough!

 

Touch wood that my head bolts on the Daily Driver are OK.. 4 headgaskets down +...

 

heheh

[Trev]

The reason i say it is that every flyheel/flexplate bolt i have seen (and i have seen alot working at a mechanics) are a shanked bolt with a flanged short head whereas they are squaring straight onto the plate.

[TE278U]

philbey, you raise some valid points,

 

however,

 

use genuine parts!!!

 

just any high tensile bolts aren't necessarily going to cut it. (some aftermarket ones will suffice, but check all specs carefully)

 

you need to know the tension/torque that is to be applied to them as per the factory settings, and many 8.8 high tensile bolts are not up to the task.

 

i agree with the idea of replacing them if they are in the state shown,

 

but be very careful when giving advice out on a forum where it could be misinterpreted.

 

as far as flex plate bolts being under more or less strain??? what is your evidence to support this?

 

i can appreciate you trying to make people's car's safer, but please be careful when you give advice that is unfounded.

 

the bolts that you have shown are highly fatigued and should be replaced, but i don't necessarily agree with just going down to Coventry's and buying high tensile bolts.

 

I sell the same bolts at my work that they do, and we refuse to sell any bolts for flywheel applications, as the manufactureres specs are very specific, and we won't risk people's safety or a lawsuit for the sake of a few bucks.

 

and Trev, i agree with the use of plain shanked bolts. they are stronger through the plain shank area as there is no reduction in diameter for the thread.

 

 

in all modifications please take care.

 

 

sorry to rant on, but this is very important, and anybody is free to give an opinion or tell me i'm wrong, but i want to see evidence.

 

that's my 2c.

 

-dave

[philbey]

Dave, I hear you man, but I've rang a lot of toyota people over the last few days and they're all telling me they don't have any. ARP apparently don't make the aftermarket 4AGE items that fit K motors anymore.

 

I thought was all a bit odd, but if anyone knows where to get some of the damn things please let me know.

 

I'll do some calculations on these based on the torque setting, that will give me a good idea if the high tensiles are up to the task.

 

As for the Auto/Manual loading, I don't have evidence, that call is based on simple deduction. Manuals will have some axial bolt loading via the clutch springs being engaged/disengaged, while autos don't. The manual can also see greater shear loading if the driver is a brute (ie clutch dropping)

 

As for the bolts being fatigued I greatly doubt that, they haven't snapped, and a fatigue failure with that sort of deformation should snap fairly quickly.

 

I had another look at the flywheel assembly after Trevs comments, I agree that they are not the correct bolts. I don't know what the standard length is, but these don't have a straight shank because they are only 15mm bolts, the flexplate is quite thin. As for whether these are high tensile or not, I'm hedging my bets with no.

 

I'll do some numbers and see what I come up with. If anyone knows where I can get OEM bolts though, please let me know!

[Damon550]

haha that bolt looks like the stretchy guy of fantastic four

 

looked at my flywheel bolts the other day when i replaced the spigot bearing and they were 17mm

 

talking about things you should replace when you do something just yesterday we couldnt get the gearbox off a bush basher because the spigot bearing had seized to the spigot so in the end the gear box faced the seldge hammer and it came off in lots of peices

Edited November 22, 2008 by Damon550

[Taz_Rx]

+1 for not the correct bolts. They look like 14mm's? and K FW bolts are 17mm.

 

I've got a few sets (beit used) of genuine FW bolts for a K if you want some Philbey?

 

FYI I had a hell of a time getting some ARP head studs. Ended up coming from the states, via NZ!!!

[philbey]

They are a 14mm Hex, you sure 17mm Hex's fit, the PCD is quite small? Like Trev said, most other flywheel bolts I've seen are flared heads.

 

I'll see what I can drag up new part wise first and I might get back to you!