gt550 crank drive gear nut torque, conflicting info..

[smokey]

the GT550A that we are restoring this winter just got a crank seal job.
when we we sent out the crank to Bill Bune, the main drive gear nut on the crank shaft was left on.
the crank came back with the nut removed. not a big deal. But I'm finding conflicting info on the torque for this nut.

Some places say 36 ft-lb , others say 101 ft-lb ...

thats a huge difference. my conundrum now is the engine is assembled and the nut is set to 36 ft-lb.
so some sort of jig will need to be made to hold the primary drive gear while the nut is tightened...

can any one confirm the proper torque.

thanks all!!

[Alan H]

101ft/lb is VERY tight. I wouldn't expect a nut that size to go anywhere near that. Remember that it will equate to a weight of 101lbs on the end of a spanner 1 foot long (or 50lbs on a spanner 2 feet long).
I've looked through the manuals I have and can't find any details, but isn't there a tab washer under it? If so, it can't undo anyway.
Regarding a locking tool, just use a clutch tool LIKE THESE

[GTandcbr]

Had the same problem myself last year. 101 ft in a Suzuki bulletin (they are notorious for typo's) seems too much so set mine to 36 ft. I put bike in 1st gear got a mate to hold on brakes. Another option is in gear and clutch holding tool if you have access to one

[smokey]

All I can figure is there was a torque spec change from a tab type (fold over) lock nut on early models to the Belleville spring washer this bike has.
the 36 ft-lb fully compressed the Belleville washer, but it felt like it wanted to be tighter, but I have learned the hard way to just trust the torque wrench!

Essentially the service bulletin "specifications #1" dated May 1, 1975 says 101 ft-lb.
I have a service manual, and nowhere can I find this spec, but a similar nut (clutch shaft) is also 36 ft-lb
Torque charts on this site say 36 ft-lb , most all other bikes are also 36 ft-lb.
there are lots of vibrations on the crank, the gear is just held by a key way and the fit is barley interference. I'd hate for it to come loose and pound the living snot out of the key-way!

[Alan H]

If a spring type washer is used, it's good engineering practice to change it and the nut every time the nut is removed.
The spring washer actually cuts into the nut as it 'tries' to unscrew, so there will be witness marks showing that, and the edge of the old spring washer will not be as keen as a new one.

[smokey]

using the tables on the fastenal site...
for a 18mm 2.5 pitch grade 4.8 bolt the the lubricated torque is 65 ft-lb
for a 18mm 2.5 pitch grade 8.8 bolt the the lubricated torque is 167 ft-lb

the actual threads look to be 18 mm "fine" , likely a special nut reduced height for this application.

so I think for this nut, 101 ft-lb is within the safe range.

[diablo]

Yes, sounds right 101 lbs being within safe range, in our line of business (structural) we cannot torque a lock washer because it will just open up at a 100 lbs of torque, that may be why Suzuki is only using 30% of the torque value, also, is the crank drive gear spinning counter clockwise on a right hand thread & would that help keep it tight. Would like to know the right answer to this one, cheers

[yeadon_m]

It actually is 101 lbft on the later GT550 models. They did a Suzuki service mod (it'll be in the oldjapanesebikes.com website). The earlier lower torque settings used a tab washer under the nut and sometimes the nut still came loose. So they replace the tab washer with a dished spring washer and raised the torque.
I have B model and 101 came up easily with a large torque spanner. I put wadding between the primary pinion and clutch basket.
Clutch hub nut torque was unchanged.
Cheers,
Mike
ps: here it is! check out bulletin GT8 http://oldjapanesebikes.com/mraxl_GT_Re ... ins/page-2" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[Alan H]

Never had a problem with that so far, but 100ft/lbs is about as tight as a pelican's arse.
And that's watertight.

[diablo]

Seems like it would be a good place for some loc-tite

[Suzukidave]

http://www.suzukidave.com/index.php?cmd ... Yjg1ZmNmMg" onclick="window.open(this.href);return false;

[smokey]

the primary gear nut was tightened to 101 ft-lb. there was no breakage, screeching or other metal breaking drama.
After that, got the bike back together and ran it around the block for the first time since we had it. nice running bike.