rodgling
|
| posted on 28/5/12 at 12:52 PM |
|
|
flywheel bolts
Turns out my lightweight flywheel needs some shorter bolts than standard. I've turned up some suitable-looking bolts at work - they are the
right grade (12.9) and size, but socket (allen-key) head rather than normal hex bolts like the stock BMW bolts. Is there any reason these
shouldn't be OK? The extra height of the socket head won't be an issue, just wondered if there are any other special requirements for
flywheel bolts I've not thought of.
|
|
|
|
|
JAMSTER
|
| posted on 28/5/12 at 12:57 PM |
|
|
why not just buy the right ones as a flywheel is not something you want to fall of . could result in serious injury just imho
|
|
|
rodgling
|
| posted on 28/5/12 at 01:02 PM |
|
|
It's an after-market flywheel, getting hold of the bolts from the USA will be slow/tricky/expensive. Whereas I have some bolts in front of me
that (as far as I can see) are the right spec, so it seems silly not to use them if they're OK?
|
|
|
FuryRebuild
|
| posted on 28/5/12 at 01:06 PM |
|
|
kevlar plate to line your transmission tunnel?
I admire your skill to turn up the bolts, but take a look at ARPs site to see what they put into a bolt. They roll rather than cut the threads, and
apply several treatments to the metal before they ship them. Probably why they cost 10x as much and ARP have a reputation for excellence.
As an example, the stud kit that replaces my cylinder head bolts can be reused again and again. So it means i have to choke back the £100+ cost of the
bolts, but worth it. You never ever want a flywheel letting loose.
I prefer socket-headded blots myself - better in confined spaces, and the material around the allen hole reduces the chances of rounding.
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
|
|
|
rodgling
|
| posted on 28/5/12 at 01:16 PM |
|
|
Sorry, by "turn up" I mean "obtained" not "made"  . I'm not planning to use homemade flywheel bolts :-) I
know a lot of people use ARP on zetecs, but I don't think it's commonly done on BMWs, presumably not a weak point on these engines.
[Edited on 28/5/12 by rodgling]
|
|
|
coyoteboy
|
| posted on 28/5/12 at 01:21 PM |
|
|
From an initial thought process I can't see any reason why generic 12.9 bolts won't suffice, there's no fatigue to worry about, the
bolts don't resist the torque of the engine, that's down to the friction against the crank end. I'd love to be proved wrong but many
of the bolt manufacturers blab on about how their cold rolled bolts are super strong and awesome but is any of it actually needed? When did you last
hear of a flywheel falling off? Do you think stock flywheel bolts are cold rolled titanium coated £10 per bolt?
Bit of loctite, ensure they're long enough and not too long, away I'd go.
[Edited on 28/5/12 by coyoteboy]
|
|
|
MikeRJ
|
| posted on 28/5/12 at 01:30 PM |
|
|
quote:
Originally posted by coyoteboy
When did you last hear of a flywheel falling off?
It happens. I've seen the result in a FWD car and that was nasty; in a 7 style car it would be horrific.
|
|
|
emwmarine
|
| posted on 28/5/12 at 02:53 PM |
|
|
Others have used the original bolts and put washers in. I think the aftermarket flywheels only need a 1 mm or 2mm shorter bolts.
Building a Dax Rush.
|
|
|
perksy
|
| posted on 28/5/12 at 02:54 PM |
|
|
Yep, saw a Caterham once that had lost its flywheel on the rolling road somewhere
The flywheel ripped out the side of the car and tried to bed itself into the wall
Also heard about another that had come loose on a Westy, Luckily the RR operator heard it start to loosen off and stopped the run before it made a
break for freedom
[Edited on 28/5/12 by perksy]
|
|
|
coyoteboy
|
| posted on 28/5/12 at 03:23 PM |
|
|
quote:
It happens. I've seen the result in a FWD car and that was nasty; in a 7 style car it would be horrific.
Yes, but /why/ is the question to ask, not does it happen. Incorrectly tightened bolts? No loctite? Poor assembly?
Certainly seen a lightened civic one let go at 8Krpm, not fun. But I'm fairly certain it's rare the bolts actually *fail*, poor assembly
and/or them working loose is far more likely.
|
|
|
rodgling
|
| posted on 28/5/12 at 03:55 PM |
|
|
In my case the standard bolts are 20 mm too long so washers aren't going to cut it. I could shorten the standard bolts but that doesn't
seem ideal to me.
My feeling is that generic bolts of the correct grade, with locktite (medium strength OK? or should I use red?), should be safe.
|
|
|
MikeRJ
|
| posted on 28/5/12 at 04:29 PM |
|
|
quote:
Originally posted by coyoteboy
Certainly seen a lightened civic one let go at 8Krpm, not fun. But I'm fairly certain it's rare the bolts actually *fail*, poor assembly
and/or them working loose is far more likely.
Pinto flywheel bolts are known to fail in highly tuned engines, so the cranks either get machined for extra dowels or the YB Cosworth crank and
special flywheel is used which has 9 bolts instead of 6.
|
|
|
coyoteboy
|
| posted on 28/5/12 at 04:41 PM |
|
|
Fair enough, but what's the cause of the failures?
|
|
|
A1
|
| posted on 28/5/12 at 06:15 PM |
|
|
chinese (not to point any fingers) bolts made of cheese?
|
|
|
rodgling
|
| posted on 31/5/12 at 08:25 PM |
|
|
Change of plan. I've just tried some BMW flywheel bolts (from an older engine with a thinner flywheel) which are 2 mm too short for my
application. I ended up with 5 engaged threads where the standard flywheel and bolt combo would give 8 engaged threads. I don't think
that's enough?
So new plan is to take a set of standard bolts to a machine shop and get them to cut them to exactly 30 mm, which will give me exactly the right
amount of thread engagement on (shortened) OEM flywheel bolts. Sensible?
|
|
|
cliftyhanger
|
| posted on 31/5/12 at 08:31 PM |
|
|
Sounds very good plan to me. Assuming there are still enough threads and the shouldered section is not too long.
|
|
|
nilocp
|
| posted on 1/6/12 at 06:10 PM |
|
|
FWIW, the bolt spec is fine, but make sure they are shouldered. Do not use fully threaded bolts, as they do not have enough 'purchase'
where they go through the flywheel.
The bolt in effect should act as a dowel.
CP
|
|
|
daviep
|
| posted on 1/6/12 at 06:17 PM |
|
|
quote:
Originally posted by nilocp
FWIW, the bolt spec is fine, but make sure they are shouldered. Do not use fully threaded bolts, as they do not have enough 'purchase'
where they go through the flywheel.
The bolt in effect should act as a dowel.
CP
Fully threaded bolts, they would be called "set screws" 
Cheers
Davie
“A truly great library contains something in it to offend everyone.”
|
|
|
nilocp
|
| posted on 1/6/12 at 07:03 PM |
|
|
Fully threaded bolts, they would be called "set screws"
Cheers
Davie
Now I know that, I was just trying to be specific for those that might not know
|
|
|
rodgling
|
| posted on 1/6/12 at 09:03 PM |
|
|
The OEM bolts that I got cut down to length are not shouldered (well, maybe 1 mm) so I don't think there's a problem. After all the
flywheel is held by the clamping force, not by pressing against the side of the bolt. Plus there is a locating dowel and central hub to locate it.
Anyway the gearbox is on now... it's too late to go back :-)
|
|
|
MikeRJ
|
| posted on 2/6/12 at 08:07 AM |
|
|
quote:
Originally posted by coyoteboy
Fair enough, but what's the cause of the failures?
Torsional vibration.
|
|
|
