Flywheel bolts

[CJH]

I may be replacing my gearbox soon, so I want to replace the spigot bearing at the same time, which means the flywheel has to come off. I know it's considered acceptable to reuse the old flywheel bolts, but Bentley says to "always replace", and since I don't know the history of the ones on my flywheel it seems sensible. There's also that "44 ft lb plus an additional quarter turn", which suggests a bit of stretch maybe.

So anyway, I have a set which I was going to use on my new engine - got them from Brickwerks for a very reasonable price. They are M12 x 20 x 1.5P (fine pitch), 12.9 high tensile cap head bolts. If I use them in my existing engine then I'll need a new set for the new engine. Brickwerks still have them for a good price, but I'm a tight git and, I thought, they're only bolts - I've bought loads off ebay and they're usually really cheap.

It turns out the 1.5mm fine pitch cuts down the field a lot, and then the 20mm length makes them really hard to find. The shortest I found (at a reasonable price) are 25mm. But surprise surprise - the threaded receiving hole in the end of the crank shaft is about 8-9mm longer than it needs to be for 20mm bolts, so 25mm bolts should fit with 3mm spare. So this seller has them for £7.95 for 10 with free first class delivery. I've ordered 10 - any reason that people know of why these won't work? Would the same 44 ft lb + quarter turn apply to longer bolts?

[CJH]

Would the same 44 ft lb + quarter turn apply to longer bolts?

I found an online torque calculator - it gave the same recommended torque for both 10mm and 15mm of 'mating thread length'. So I'm happy that these longer bolts will need the same torque. Interestingly it recommended that the mating length should be at least 1.5 x the bolt diameter, so with these M12 bolts it's recommending at least 18mm of mating thread length. That makes the original 20mm bolts (with 10mm of mating thread length) look a bit short.

[itchyfeet]

Bentley says 110Nm and thats what I do.
Haynes says 60Nm + quarter turn

who do you trust?

No idea on bolts but I'd not risk it, how do you know the pedigree of an ebay bolt, I'd trust BW to buy from a reputable source, not like your saving lots £7.80 from brickwerks+ post


Will you be checking end float while you are in there?

[CJH]

Bentley seems to give both specifications, and I'm not sure why. Both arrows point to the same flywheel bolt, and there's nothing to say whether there's a date change between them.



A few pages later, on a page marked 'Water-cooled from 1986' they quote 44 ft lb + a quarter turn. And VW Heritage say the same on their flywheel bolt page. So I don't know who to trust actually. Maybe 44 ft lb (60Nm) + a quarter turn ends up close to 110 Nm anyway.

Interesting question about reputable sources - not sure I'd know how to trust one bolt supplier over another. The Brickwerks bolts are marked FKE - evidently a Taiwanese manufacturer. The ebay seller I've linked to is based in Halesowen.

I wasn't planning to check the end float - don't expect to have time to do it properly - I was going to save that for when the engine's out and I'm giving it a re-seal and a good going over prior to maybe selling it.

[silverbullet]

I have only once tried the torque plus angle method and nearly hurt myself.
I now torque to 90 lb.ft and use screwlock (after a thorough degrease)
I also re-use the bolts because they are 12.9 grade.
Going to 25mm seems to be a good move for hi-po engines. I will ring my fixings suppliers on Monday

[silverbullet]

In which case I wont be re-using them from now on!
I wouldnt sweat about the origin of the bolts, the last channel ferry I took was made by Daewoo

[bigherb]

From their last manual, VW recon 60Nm + 1/4 turn.

[itchyfeet]

my Bentley manual is 1989 and only shows 110Nm, never been a problem for me.
Plenty of low grade steel about, plenty of fake products about, saving is a couple of quid

[silverbullet]

As a business we have always bought our fixings a from the same local supplier.
http://www.quality-suppliers.com/" onclick="window.open(this.href);return false;
I wouldnt go to ebay for anything safety critical or where reliability could be compromised.

[CJH]

Spot the difference.



My cheapo ebay supplier apparently gets his bolts from the same manufacturer (unless there's a bolt forgery racket going on).



I double checked and there's definitely still about 3mm to spare with these longer bolts in the crank. I wonder why the original bolts are only 20mm.

[itchyfeet]

I double checked and there's definitely still about 3mm to spare with these longer bolts in the crank. I wonder why the original bolts are only 20mm.

Production tolerances and it's hard to tap full thread to the bottom of the hole, if it locks up on the thread first you are in trouble

[itchyfeet]

Looks fake to me, one has a chamfer head to thread the other a radius, also knurling is poorly defined

[CJH]

Production tolerances.

[CovKid]

Seems fine to me Chris - if you wanted a degree of confidence. After all, none of these smaller parts places make bolts - they buy them in. Even VW does. You can pay WAY over the odds for nuts and bolts in some places (B&Q for starters and theirs are hardly quality bolts). I stopped doing that a long time ago, but I do go to people who specialise in them.

Get all mine from one of the biggest wholesale fastener places in the UK (Kebrells). I trust them and they seem to supply just about everyone else down the supply chain. Never caught them out on any weird bolts sizes or thread pitches but you do have to buy quite a few if you go in on foot Every new bolt I've ever fitted in the last 10 years comes from them. Fit and forget.

http://www.kebrell.co.uk/socket-screws.htm" onclick="window.open(this.href);return false; - any use?

[itchyfeet]

Yeh only jokin on the fake post, looks ok to me too as long as the threads are deep enough