Flywheel to Crankshaft Bolts. What Grade?

[Tom H]

Well the title says it all. I need the bolts and don't know what grade is required or what can be used instead.

Thank you,
Tom

[Huzo]

Well the title says it all. I need the bolts and don't know what grade is required or what can be used instead.

Thank you,
Tom

Is this week particularly bad for flies ?

[GeorgiaGuzzi]

Well the title says it all. I need the bolts and don't know what grade is required or what can be used instead.

Thank you,
Tom

I just took mine off, they’re 8.8 grade. MG cycles sells 10.9 grade. I’ll prolly just reuse the 8.8 that were on there already.

[moto-uno]

  They're fairly highly torqued and loaded , so if you're not in a rush , get new ones . Having said that
I've reused them twice and they were fine ( no failures ) , but I've used my bikes as guinea pigs for what I'd
call questionable mechanical practices  . (No one else has had to pay the consequences)
   It's my Scottish side that's driven me to do these things to my own bikes , but jeez , those bolts are cheap enough aren't they ?
Peter

[Tom H]

I have 8.8 in the right size. I had a feeling they were supposed to be10.9. I'll have to get some.

Thank you!!
Tom

[LesP]

The flywheel bolts are grade 10.9 @ 30 ft/lbs. (42 N/m)
The ring gear bolts are grade 8.8 @ 22 ft/lbs.  (30 N/m)

I used new 8 mm Schnorr washers also with blue Loctite.





http://www.thisoldtractor.com/moto_guzzi_tonti_torque_specifications.html

These are easy to remember.
I was taking pictures as I built my engine and forgot to take one torquing the grade 8.8 ring gear bolts so after dinner on a Sunday staged a picture but set the torque wrench to the flywheel setting of 42 N/m by mistake.
Someone asked the same question on FB and Charlie M posted the correct torque (ring gear) and I added that picture then noticed the to high value setting on the torque wrench 

I was sure I had torqued to the correct number (42 N/m is to high for 8.8 grade) but that picture haunted me for a week or more. (The engine and gearbox was back in the frame)
In the end I pulled the gear box back out of the bike to find they were torqued to the correct value so replaced them with more new bolts again torqued to the right value.
There was a lesson learned in that episode. 

[bmc5733946]

Call me anything you want, I never reuse crank and flywheel bolts. I just hate having problems that require a disassembly that involved for the price of a bolt.

Brian

[Don G]

10.9 is the correct grade, if sourcing these @ a bolt store do not get plated bolts, plain Jane black bolts only, plated bolts can fail due to hydrogen embrittlement from the plating process. DonG

[Wayne Orwig]

Call me anything you want, I never reuse crank and flywheel bolts. I just hate having problems that require a disassembly that involved for the price of a bolt.

Same here.

MGcycle sells a pack with new schnorr washers. Done.

[Antietam Classic Cycle]

10.9 is the correct grade, if sourcing these @ a bolt store do not get plated bolts, plain Jane black bolts only, plated bolts can fail due to hydrogen embrittlement from the plating process. DonG

I asked my bolt supplier about this and they don't agree.

[Chuck in Indiana]

There is plated and there is "plated." Chrome, that is..texas tea.. Oh, sorry, got carried away.
You get hydrogen embrittlement from the chrome plating process. It can be relieved with heat..but then you lose the temper of the bolt.
Don't use *chrome* plated bolts in high stress or vibration related applications. Zinc cad? They be fine.

[Don G]

Scope this out then and use your own judgement:
The subject of the plating of fasteners is one that causes some debate. Many companies refuse to contemplate the use of plated fasteners, while some manufacturers will supply them only at a customer's insistence and with a waiver that absolves them of any responsibility for losses resulting from a breakage.

Other companies are much happier to supply plated fasteners, however, having taken every precaution to minimise the chances of embrittlement before, during and after the actual electroplating process. Although we see fewer zinc-plated fasteners being used in high-strength materials, cadmium plating is still a popular process - 'NAS' airframe bolts are an example of a cadmium plated fastener - and silver plating is often used to prevent seizure of materials prone to galling or in situations where conditions are too harsh for lubricants to continue to work over long periods.

The reason for the strong opinions held by some is due to a phenomenon called hydrogen embrittlement, which leads to a drastic reduction in fatigue life and static strength. While there are a number of precautions that may be taken to lower the risk of damage from hydrogen embrittlement, ISO 4042, an international standard relating to electroplating of fasteners, states, "Complete elimination of hydrogen embrittlement cannot be assured."

During the electroplating process, and commonly also in any earlier cleaning and descaling processes, hydrogen is evolved at the surface of the components and, particularly in the case of steels, is absorbed by the surface of the metal. Higher strength steels are particularly sensitive to hydrogen embrittlement.

In order to reduce the risks, mechanical cleaning and descaling processes are recommended, and acid cleaning is said to present a greater risk of damage than alkali processes. In an acid, iron reacts to form a salt, with the result that hydrogen (H+) ions thus liberated combine with electrons to form hydrogen gas.

Any electrochemical cleaning processes used should be carefully selected by the plater; cathodic process liberate hydrogen, whereas anodic processes do not.

fasteners-socket-head-cap

Following the plating process itself, it is widely agreed that a baking process, carried out soon after plating, can be an effective way to reverse much of the damage that occurs during plating. This is done at relatively low temperature (around 200 C) and there are guidelines for how long it process should be carried out for (1) according to the strength of the steel, with higher-strength alloys requiring longer treatments. For steels with a tensile strength of 1700-1800 MPa (247-261 ksi), the minimum recommended time for a post-plating bake is 22 hours.

We should not be under the impression though that only steel fasteners suffer from this problem, although they are probably the most likely candidates for plating processes as far as fasteners are concerned. Titanium, nickel and aluminium materials have been reported by Dini (2) as suffering from this phenomenon. However, some of the more exotic fastener materials are known not to suffer from hydrogen embrittlement.

It should also be noted that it is not only electroplating processes that cause steel fasteners to suffer in this way. Electroless plating processes, such as electroless nickel, also produce hydrogen embrittlement, as can phosphate coatings in a more limited way.

1. Raymond, L., (editor), "Hydrogen Embrittlement: Prevention and Control", ASTM STP 962, 1988

2. Dini, J.W., "Electrodeposition", published by William Andrew, 1993, ISBN 0-8155-1320-8

Fig. 1 - In solving a corrosion problem in plating fasteners, we should be careful not to damage them during the plating process

Written by Wayne Ward

[Antietam Classic Cycle]

There is plated and there is "plated." Chrome, that is..texas tea.. Oh, sorry, got carried away.
You get hydrogen embrittlement from the chrome plating process. It can be relieved with heat..but then you lose the temper of the bolt.
Don't use *chrome* plated bolts in high stress or vibration related applications. Zinc cad? They be fine.

 

[bmc5733946]

When I split the engine and trans on the two 750 Brevas I did clutches on in 2015 I found that the original flywheel to crank and pressure plate bolts were all black oxide so that's what I replaced them with. I don't think that cad plating is going to cause a problem although I sometimes wonder about the zinc plating because of the electrolysis component, I know that cadmium plating is also done the same way. It was explained to me many years ago that the zinc process used more current and hence made more changes to the molecular structure of the surface of the bolt. I don't know if any of that is true. I have trusted it since I heard it and my trust has not been failed. Of course the black oxide will rust when exposed to weather but inside the clutch housing there is little if any moisture. Just my thinking.

Brian