flywheel bolts

[lazlokovacs]

changing out a flywheel, ordered new bolts from Guzzi and some 10.9 hardened bolts turned up...

BUT

they have an allen head.

I'm worried that they'll foul the pressure plate, as the heads are obviously bigger than the standard hex heads.

Anyone been there done that and can let me know?

Bike is a Cali 1100

[Stevex]

Ask the suppliers?

[dxhall]

I don’t recall ever seeing Allen-head bolts used to hold a flywheel.  The danger would be that the internal hex would strip when the (locktited) bolts were removed. I don’t think I’d use them.

[pete mcgee]

Ive fitted 12.9 allen headed bolts to mine, they fit, nothing fouls.
The level of butchery required to strip out a 10.9 or 12.9 is unthinkable to anyone with any level of mechanical ability or mechanical sympathy.  At worst drill off the head and remove with vise grips.
Cheers

[lucky phil]

I don’t recall ever seeing Allen-head bolts used to hold a flywheel.  The danger would be that the internal hex would strip when the (locktited) bolts were removed. I don’t think I’d use them.

My Guzzi RAM clutch assembly on the Daytona engine uses allen head bolts and as someone pointed out if you're going to butcher the drive on one of them at the required torque then you'd probably butcher a hex head as well.

Ciao

[lucky phil]

The harder grades are also more brittle.  Matteo can tell you what happened when the heads broke off my 12.9 flywheel bolts.  I'll just say that they then sheared flush with the crankshaft and were a girl-dog to drill out in situ.

BTW -- IIRC, my 1200 sport flywheel was held on with socket head bolts out of the crate.  Someone else can confirm.

If you sheared 12.9 flywheel bolts in operation then I'd suggest they were never tightened up to the correct torque in the first place.

Ciao

[lazlokovacs]

I think the old hex bolts have been superseded in guzzi's inventory and now they send you the 1200 sport/griso/breva etc bolts when you order the old ones.

I'm not gonna strip them and they'll definitely hold the flywheel on, but I think I'll only end up with a 3-4mm clearance for the pressure plate to move, is that enough?

[lazlokovacs]

Pete Mcgee - Ive fitted 12.9 allen headed bolts to mine, they fit, nothing fouls.

Thanks for that info, which bike did you fit them to?

[Chuck in Indiana]

You amuse me.  I'd suggest you get more information before passing judgement.

Now where *is* that popcorn emoji? Oh, here it is..

[Scout63]

I just order new hardened bolts from MG Cycle every time. I do reuse the schnorr washers. Always new ring gear bolts while I’m in there also.

[lucky phil]

Now where *is* that popcorn emoji? Oh, here it is..

Ok Chuck seeing you got the popcorn out I'll expand on my rationale. A 12.9 grade fastener has higher tensile and shear strength than an 8.8 or 10.9 so if the correct torque is applied to the fastener which for a 12.9 is obviously higher to create the required stretch to maintain the clamping load and prevent the bolts loosening you have a greater capacity to transmit in this case engine torque. Unless the greater fastener torque required for the higher grade bolts has a detrimental affect on the material of either or both of the 2 clamped components such as compression with the additional clamp load or thread deformation then the higher grade bolt will offer a benefit. Whether or not that is required or desirable is another matter.
In the case of flywheel fasteners a large proportion of the transmitted engine torque is carried by the flywheel and crank interface, the fasteners don't transmit the majority of the engine torque. The only times I've seen fasteners that have been well above the capacity to provide the required clamping load fail is when they are under torqued. Then the fastener stretch and clamping force isn't adequate and the bolts are asked to transmit all the engine torque or shear and shock loads as the clamped faces aren't doing their share of the work anymore eventually this combined with the "working" of the fasteners causes shear failure.
So if for instance the std flywheel bolt is a 8.8 or 10.9 and a 12.9 is substituted and the bolts torqued to the lower factory spec for the original grade fastener then you could run into an issue with an under torqued fastener and failure even though it's a higher spec than the OEM.
Sometimes going over grade on the fastener is detrimental if for instance the fastener is quite short. Going from an 8.8 to a 12.9 might mean that there is inadequate  length in the higher grade fastener to achieve the required stretch for reliable maintenance of clamping load for the higher grade bolt.
The turbine case flange bolts on a lot of commercial jet engines have this issue and the way around it is the designers actually provide a long spacer or what appears to be a bush between the fastener head and the clamped flanges to accommodate a longer fastener to get the adequate fastener length to support the stretch needed to maintain reliable clamping force. 


Ciao       

[Wayne Orwig]

Does the lock washer get crushed properly under the allen head?

[pete mcgee]

Pete Mcgee - Ive fitted 12.9 allen headed bolts to mine, they fit, nothing fouls.

Thanks for that info, which bike did you fit them to?

1984 mk3 Lemans

[lazlokovacs]

thanks mate

[geodoc]

A few years ago one of the flywheel attach bolts failed on my 1000SP engined Loop. Stopped at a stop sign, pulled in the clutch and when released it wouldn't engage. Pulled and released a few times and it worked, but would jam up every once in a while. Got it home and pulled apart to find that one attach bolt's head had broken off leaving almost the entire threaded portion in place. They were new parts from MG Cycle w/ schnorr washers torqued with an old dial-type Snap-On 360 in. lb. torque wrench (admittedly not recently calibrated. I took the wrench to a calibration place and they found that it didn't even need to be re-calibrated so torque was correct per the manual. I replaced all the bolts at correct torque and no problem since. They BTW, had been in service for about 10,000 mi.

I can only surmise that it was a defective bolt. There has been a lot of issues with crap fasteners for quite a while (especially aircraft spec). For actually meeting spec, it's sadly a bit of a crap shoot nowadays unless you go to extra expensive trouble. (shrug)




.

[lucky phil]

A few years ago one of the flywheel attach bolts failed on my 1000SP engined Loop. Stopped at a stop sign, pulled in the clutch and when released it wouldn't engage. Pulled and released a few times and it worked, but would jam up every once in a while. Got it home and pulled apart to find that one attach bolt's head had broken off leaving almost the entire threaded portion in place. They were new parts from MG Cycle w/ schnorr washers torqued with an old dial-type Snap-On 360 in. lb. torque wrench (admittedly not recently calibrated. I took the wrench to a calibration place and they found that it didn't even need to be re-calibrated so torque was correct per the manual. I replaced all the bolts at correct torque and no problem since. They BTW, had been in service for about 10,000 mi.

I can only surmise that it was a defective bolt. There has been a lot of issues with crap fasteners for quite a while (especially aircraft spec). For actually meeting spec, it's sadly a bit of a crap shoot nowadays unless you go to extra expensive trouble. (shrug)

Were they plated bolts? Did you lube the bolts when you installed them?
On really critical bolts or bolts you might be suspect of you can pull them up to torque on the bench with simple fixture and measure the stretch then back them off again and see if they have taken a "set" or come back to their original length. It's not a bullet proof test but gives you some idea if they really are poor quality. Plated bolts are a no, no in high stress applications and Moly lubes can lead to as much as 20% over torqueing when not specified. 

Ciao

[geodoc]

Were they plated bolts? Did you lube the bolts when you installed them?
On really critical bolts or bolts you might be suspect of you can pull them up to torque on the bench with simple fixture and measure the stretch then back them off again and see if they have taken a "set" or come back to their original length. It's not a bullet proof test but gives you some idea if they really are poor quality. Plated bolts are a no, no in high stress applications and Moly lubes can lead to as much as 20% over torqueing when not specified. 

Ciao

They were black oxide finished as one would expect for a 10.9. Since there is no call-out in the service manual for lubrication they were installed dry.


.

[Chuck in Indiana]

I can only surmise that it was a defective bolt. There has been a lot of issues with crap fasteners for quite a while (especially aircraft spec).

Agreed on all the above.

[n3303j]

Clamping force is the result of thread pitch and torque applied! It has nothing to do with what the bolt is made of**.

If the bolts are the same pitch  and diameter (same surface finish and lubrication) they will apply equal clamping force at an equal torque value whether they are 8.8, 10.9 or 12.9 as long as they are not torqued beyond limit.

Therefore using a higher grade bolt in an application does not require applying a torque beyond that specified for the stock (lower grade) bolt. They both apply the same clamping force at the specified torque.

Really shouldn't be exceeding Young's Modulus of Elasticity on any Guzzi flywheel bolt**. They should return to initial length at removal. They don't need "stretch" to provide clamping force. They are glorified wedges.

Only reason for bolt replacement is the potential for fatigue.

[lucky phil]

Clamping force is the result of thread pitch and torque applied! It has nothing to do with what the bolt is made of**.

If the bolts are the same pitch  and diameter (same surface finish and lubrication) they will apply equal clamping force at an equal torque value whether they are 8.8, 10.9 or 12.9 as long as they are not torqued beyond limit.

Therefore using a higher grade bolt in an application does not require applying a torque beyond that specified for the stock (lower grade) bolt. They both apply the same clamping force at the specified torque.

Really shouldn't be exceeding Young's Modulus of Elasticity on any Guzzi flywheel bolt**. They should return to initial length at removal. They don't need "stretch" to provide clamping force. They are glorified wedges.

Only reason for bolt replacement is the potential for fatigue.

Stretch is needed to maintain the bolt tension and therefore clamping force and the higher grade the fastener material the greater the force required to obtain the required stretch to maintain the bolt tension. A grade 12.9 bolt torqued to 8.8 torque may not have the required stretch to maintain it's tension. If that happens then the clamping force drops off and it's then the slippery slope to failure. 

Ciao   

[normzone]

Ooh, I'll have some of Chuck's popcorn ... A thread discussion.

You guys know more than I do about the topic, but I began my mechanical inspection tour of duty checking threads.

These days most people I work with are computer geeks.

[n3303j]

Stretch is needed to maintain the bolt tension and therefore clamping force and the higher grade the fastener material the greater the force required to obtain the required stretch to maintain the bolt tension. A grade 12.9 bolt torqued to 8.8 torque may not have the required stretch to maintain it's tension. If that happens then the clamping force drops off and it's then the slippery slope to failure. 

Ciao   

You are entitled to your opinion even though, in this instance, you are wrong.

[lazlokovacs]

Just in case anyone wants to know.

I actually fitted the flywheel and clutch up twice, once with the allen head bolts and once with the traditional hex head bolts... (new washers both times)

With the allens I had 3 -4mm of free play between the pressure plate and the bolts
with the hex 7-8mm

Glad I went back in there to be honest

[DAMMAG]

I installed 12.9 socket heads in my Le Mans 20 years ago and the flywheel has stayed firmly attached to the crank.

Damian

[lazlokovacs]

I don't doubt that DAMMAG,

I was worried about the pressure plate potentially fouling on the heads of the bolts...

[Scout63]

Why buy new from MG Cycle for $10

https://www.mgcycle.com/index.php?main_page=product_info&products_id=1640

when you can buy used for $35

https://www.ebay.com/itm/361108968360