Reminds me of fiat twin cam flywheel bolts. Can't be sure they are 1.5mm
pitch though and I haven't got one to hand at the moment to check. I may
be able to in a day or so. You might try some part places and see as
flywheel bolts are that sort of spec in my experience.
These are indeed for a flywheel application, on a BMW M10 engine where I
want to install a racing flywheel that is a lot thinner than the stock
flywheel, so the stock bolts won't work. Good tip on looking at other
flywheel bolts, though.
In my limited eperience they are only threaded the amount needed as they
are specials for the manufacturer. Cutting extra thread with the likes
of a die won't produced the quality of thread in this critical application.
jim rozen wrote:
Correct. That plan only works if they are fully threaded to start with.
If they are high strength waisted fasteners then threading extra
along the shank is of course impossible anyway. Die cut threads
will not work in that application.
What *do* the flywheel bolts actually look like?
please reply to:
OK, you are *not* going to find a regular fastener house
to sell you those bolts. The car manufacturer makes them
up special and I'd be willing to bet a coke there's
no off-the shelf solution, which is what you're looking
You might possibly call Metric and Multistandard
Components in Elmsford, NY and ask them to quote to
make some of them. Be prepared to supply a sketch
of the exact part you want and be prepared to supply
If you could find a fully threaded fastener you could
of course machine the waist in it yourself.
please reply to:
Jim, you really honestly think that if that was even remotely possible, I
wouldn't have already done that?
Stock bolt is threaded only at the end, somewhat like a NAS or MS bolt. It
can't be usefully shortened.
If you can't find the shorter bolts what about using the standard and
having the flywheel modifed so the central boss is thicker. The extra
mass in the centre will have negligable effect on the performance unlike
the mass at the periphery.
Basically, the idea here is to use a light steel flywheel that I already
have rather than making one up. The bolts have to fit under the clutch
plate, and the thickness of a hex head bolt is basically what the flywheel
was designed for. It's a PITA. I have ordered a bunch of 10.9 spec bolts,
I figure that I can loctite them in and toss them after one use. the bolts
are basically in tension only, the flywheel is located on a center spigot
and a dowel. The race flywheel/clutch combo is about 1/3 the weight of the
stock setup, and that will raise any torsional vibration frequencies and
lower their amplitude reducing the overall stress on the bolts, although I
don't know how to predict that.
I phone the Tacoma guys, they don't have them. I now believe that the 12.9
spec is only for SHCS.
Thanks, all. I appreciate the help.
I just had a look at the fiat bolts from a Lancia Beta 2L and they are
M12 x 1.25 unforetunately. Marking on the head were as follows
Thats 4 lines one above the other sort of forming a pine tree shape with
R12 beneath it. Not sure what the R12 is but it doesn't really matter
for you now anyway.
I just did a quick check of my reference books (e.g., Industrial
Fasteners Institute Metric Standards Book) and supplier catalogs and it
appears that your assumption is correct: 12.9 is for SHCS only and 10.9
is the highest grade of hex head cap screw (aka bolt).
If you really want the 12.9 grade with a lower head height, you could
try looking for a socket BUTTON head cap screw; a button head looks like
a pan or round head but has a hex recess like a socket head. The M12
socket button head has a head height of 6.24 - 6.60mm, which is much
lower than a M12 SHCS and even a little lower than a M12 hex cap screw
(7.24 - 7.76mm). However, I don't know how readily available the M12
SBHCS is with 1.50 pitch.
Let me know if you need further assistance with this.
On Thu, 14 Oct 2004 09:02:10 -0300, "jtaylor"
||> These are indeed for a flywheel application, on a BMW M10 engine where I||> want to install a racing flywheel that is a lot thinner than the stock||> flywheel, so the stock bolts won't work. Good tip on looking at other||> flywheel bolts, though.
||Spacer under the heads?
The heads are recessed to just below the surface, and the clutch disc covers
that surface, so he cannot space the heads higher.
What about cutting the heads off the bolts to make studs out of them, then
threading them from the backside of the flywheel and using nuts to retain the
Texas Parts Guy
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