Loctite on flywheel bolts

[dxhall]

I separated the motor and transmission from the donor bike yesterday and found that the prior owner replaced the flywheel bolts, but didn’t use threadlocker on the threads.  I’ve always used loctite on flywheel and clutch bolts.  Am I an outlier on this?  I thought threadlocker was standard practice.

[guzzisteve]

I use blue on the 6 but nothing on the 8. Haven't had one come apart yet at 30ftlbs on crank & 23ftlbs on ring.

[Wayne Orwig]

I always use a bit of blue loctite. I may worry too much. Just think it is a good idea.

[BMCMOTO]

Many years ago, and at the encouragement of others, I conducted a very unscientific study of the mechanism of loctite usage.
I found a bolt size that fit snugly in a bit of copper tubing, measured the outside diameter of the tubing using a micrometer, coated a bolt in blue loctite, inserted the bolt in the tubing and waited for the loctite to cure. After curing the tubing had expanded by a few thousandths of an inch. I repeated the unscientific experiment using different grades of loctite, the more aggressive red loctite expanded slightly more than the blue ect.,etc.. I have seen one and only one Guzzi crankshaft fail at the flywheel bolt hole and then only at a single hole splitting to the outside of the crank journal. After all the guessing and opining was done the group of us could not draw a conclusion if the use of loctite had contributed to the failure. Most suspected an overabundance of any fluid could have hydraulically fractured the crankshaft etc., etc.. Soooo if using loctite in locations like this where a fracture can cause catastrophic failure of an expensive part I use little but I do use it. I do know that many Guzzi flywheel bolts I have removed show evidence of loctite being used at the factory. YMMV

BRIAN

[usedtobefast]

From my latest reading, threadlocker on flywheel bolts (and new bolts each time), not on clutch bolts.  So that's what I did. 

[Chuck in Indiana]

Back in the day, I went to Loctite school when they came through GM. basically, they told what kind and *how much* to use. It's not much, literally a drop about 1/4" diameter at the bottom of the fastener. I use it on flywheel and clutch instead of shnoor washers. They are hardened, and hardened washers occasionally break. A broken lock washer isn't a lock washer.. JHMO.

[LesP]

Loctite galore including the flywheel and ring gear plus new Schnorr locking washers on anything steel, wave washers on alloy.

Applied like I am paying for it. (MGC)

[SmithSwede]

Many years ago, and at the encouragement of others, I conducted a very unscientific study of the mechanism of loctite usage.
I found a bolt size that fit snugly in a bit of copper tubing, measured the outside diameter of the tubing using a micrometer, coated a bolt in blue loctite, inserted the bolt in the tubing and waited for the loctite to cure. After curing the tubing had expanded by a few thousandths of an inch. I repeated the unscientific experiment using different grades of loctite, the more aggressive red loctite expanded slightly more than the blue ect.,etc.. I have seen one and only one Guzzi crankshaft fail at the flywheel bolt hole and then only at a single hole splitting to the outside of the crank journal. After all the guessing and opining was done the group of us could not draw a conclusion if the use of loctite had contributed to the failure. Most suspected an overabundance of any fluid could have hydraulically fractured the crankshaft etc., etc.. Soooo if using loctite in locations like this where a fracture can cause catastrophic failure of an expensive part I use little but I do use it. I do know that many Guzzi flywheel bolts I have removed show evidence of loctite being used at the factory. YMMV

BRIAN

That is a very interesting post.   I've been pondering this.

Brain, when you did your admittedly unscientific experiment, did you do a control test by screwing in a bolt into the copper tubing but without any kind of Loctite?   Maybe the cooper just slowly expands in response to the forces imposed by the presence of the bolt, and the Loctite has nothing to do with this.

My other thought--wouldn't corrosion itself create this sort of internal stress?  I would think that as any metal oxidizes, it gets physically larger, which is one reason why an old corroded bolt can be so difficult to remove.  If that's right, then I guess the issue would be whether Loctite expands and puts more internal stress on the component compared to what the eventual and inevitable corrosion does. 

[BMCMOTO]

SS,
The bolt was not threaded into the tube, simply a snug slip fit as I remember, surely not full thread engagement, possibly hand threaded. I honestly can't remember the details, they became unimportant after drawing the conclusion that at least to a certain degree the Loctite worked to anchor the bolt by expanding and only cured anaerobically (lack of air) so could have contributed to the fracturing of the crank hole but that was unlikely unless way to much was used and had caused an hydraulic compression fracture. I just took from that to use Loctite in small amounts, in fact I find the stick style easier to use although extremely expensive. I am sure Loctite has way more scientific information out there in this information. When we conducted our experiments there was no information age.

Brian

[kirby1923]

FWIW

I use the shnoor washers on my steel flywheel instead of Loctite.

The bolts (flywheel) are torque to yield so I'm happy with just the washers.

 If you do use Loctite Instead of the shnoors then you need to make real sure you really clean the both the bolt and the holes with something like acetone and use a small drop(or two) of loctite  on the bolt so it won't effect the           torque to yield specification.(most use too much).

Use what ever method that makes you feel safe but...

 DO IT RIGHT

:-)

[Chuck in Indiana]

^^^^ Do it right is right.

[Mike Tashjian]

So if a bolt normally uses locktite the torque requirement stated is probably correct.  If the same bolt does not usually require locktite it's torque requirement would be affected.  I see some reference to reduce torque values 20% when using locktite instead of a lock washer.  I would assume that is in line with a dry vs. lubed bolt torque.  I like to use locktite sparingly as many have stated and I have not experienced any problems.

[Chuck in Indiana]

So if a bolt normally uses locktite the torque requirement stated is probably correct.  If the same bolt does not usually require locktite it's torque requirement would be affected.  I see some reference to reduce torque values 20% when using locktite instead of a lock washer.  I would assume that is in line with a dry vs. lubed bolt torque.  I like to use locktite sparingly as many have stated and I have not experienced any problems.

As far as I know, if used *sparingly* it doesn't affect torque values.