Has anybody dug into the torque values that Guzzi have put in the manual , part number 14920120, V7 Sport, 750S, 850T and 850 T3 ?
I normally only use the torque wrench for critical things, like cylinder heads, flywheel bolts, stuff like that.
The reason I ask is when I changed my clutch a few years back I reused the flywheel bolts and the 8 M8 8.8 bolts holding the ring gear onto the flywheel forming up the clutch pack. I saw that the flywheel bolts were M8 10.9 and figured if they’d used different grades of high tensile bolts, it was probably for a good reason and brought out the torque wrench. 42Nm seemed awfully high, but hey, that’s what the book said. While it was out I used it on those 8.8 ring gear bolts, too. 30 Nm, Guzzi’s standard torque for M8 bolts. Seemed tighter than I’d normally do up my ‘2 grunts’, calibrated elbow. On one of them, I’m convinced I started to feel it yield and stopped pulling.
Now I’m back in there again, several years on and I looked again at the chart in the manual. I compiled a chart of recommended maximum torque values from Norbar, a reputable supplier of fasteners and a high end manufacturer of special stainless bolts to get a consensus of three different sources. Maximum recommended torque for M8 10.9 is 36Nm dry, 32 lubed. Considerably less than the 42 Guzzi are saying.
Similarly for the M8 8.8; Max recommended is 26 dry, 23 lubed. Way less than Guzzi’s 30Nm.
Now, those 10.9s have Schnorr washers under them, which is going to increase the friction under the bolt head and thus the torque value required to get the desired axial load. Also, I’m sure Guzzi don’t grease the bolts before assembly, so perhaps the dry values are the better comparison. But this is a big difference.
Guzzi seem to be overtorquing these bolts and so I’m replacing these flywheel and ring gear bolts as being ‘single use’.
Perhaps 42Nm is about right; take the 36 dry and add 20% for the Schnorr washer. Perhaps 30 is about right; take 26 dry and add 20% for a normal split spring washer.
All sounds a bit marginal to me, though.
I’ll cut to the chase; I’m about to torque up my flywheel bolts. What have others found and what have they done ?
My own workshop manual G5, LM2, 1000Sp and T3 gives - Bolt, flywheel to crankshaft 4.2kgm that equates to 41.2Nm. Standard M8 2.5-3kgm that equates to 24.5-29.4Mm.
I have always used these settings
I was hoping you might chime in, Chris. I’ve got that manual, too. They do appear to have hedged that ‘standard’ M8 setting a bit by giving it a lower range, but that upper value is still up there. They no longer have settings for the ring gear. And yes, I’m approximating my kgm to Nm conversion. These industry recommended max values would require the ‘standard’ to use a 10.9 and the flywheel bolts to be 12.9 to just come in safely at 41.2Nm. I tried to get 12.9s, by the way, just to be safe but they’d have been special order from our local bolt shop so I figured I’d just buy the parts from Gutsibits, which are 10.9.
I seemed to get away with using the book values last time ( apart from that one on the ring gear ), but relying on manufacturing tolerances for the bolt to not snap didn’t seem the right approach.
So, you’ve used those values in the past and it’s all worked out, eh. Did you grease the bolts ( I normally do to get a smooth torque-up ) or assemble dry ?
This is only the second time I’ve been down this far on my Guzzi so I’m trying not to do anything stupid.
I was thinking of backing off and using 32Nm greased on those flywheel bolts.
Yes, I try to grease everything I take apart!
Like Chris I use settings as in SP1000/ G5 manual.
Bolts lightly oiled not greased.
I have reused flywheel to crankshaft bolts multiple times.
Ps I have a decent torque wrench and its calibration has been checked by a lab.
When I rebuilt my flywheel/clutch I lubed the bolts and used the standard “2 grunts” torque setting on my arm. Only thing I was careful with was to use high-tensile bolts because “ordinary” ones shear like cheese on start-up.
Hello speedy, I’ve not heard that about bolts shearing on start-up. What do you know ? And when you say high tensile, do you mean 10.9 or 12.9 ?
Based upon Speedy’s report about bolts shearing on start-up and a branch member who related a mate’s flywheel bolts popping when the ring gear was hit by the starter motor which didn’t engage properly, I’ve fitted 12.9 bolts in the flywheel, with Schnorr washers and torqued them to 40 Nm lubed.
I’ve also refitted my ring gear using A2-80 with spring washers torqued to 28 Nm lubed.
This is close to the industry recommended maximum for these fasteners and within a whisker of Guzzi’s specified torques.
The nice new 10.9s bought as spares from the Guzzi shop will go into The Stores.
Thanks for all input received.