M1R Lower Clamp Bolt

2

2Types

Junior member
Location
Wales
Can anyone please identify the spec for bolt that should be used for the lower clamp on the 41.7mm Marzocchi M1R forks on a 1000SFC.
It is item 3 on the diagram below.

The bolt that came out is clearly wrong but cannot find anyone who stocks it and keep getting asked for the spec, length diameter of shank and thread etc.

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8 x 40 Allen head? 1.25 thread?
Always measure a screw from under the head and invest in a thread gauge, one of the cheapest and most useful tools in the workshop.
Paul
 
Paul Marx said:
8 x 40 Allen head? 1.25 thread?
Always measure a screw from under the head and invest in a thread gauge, one of the cheapest and most useful tools in the workshop.
Paul
Click to expand...
Paul The bolt that came out is an M10. From the damage on the threads I assume that it has been tapped from out from M8 in the past, but now fouls the fork tube. Do you know the length of the unthreaded part I assume about 20mm from the diagram.
 
2Types said:
Paul The bolt that came out is an M10. From the damage on the threads I assume that it has been tapped from out from M8 in the past, but now fouls the fork tube. Do you know the length of the unthreaded part I assume about 20mm from the diagram.
Click to expand...
Ok, it's the fork tube that has buggered up the thread on that I presume. Thread would be 1.5 on a 10mm.
Are the screws like that on both sides? I suppose so, otherwise you'd have measured up the other side.
I presume that screw would have been M8 then and longer than 40 because there's not much on there to bite on the far side of the fork tube.

Paul
 
On both the Sfc 1000 fitted with the M1R forks we have in the workshop they are both fitted with M 10 x 1.5 grade 8.8 high tensile Allen head bolts , they are a special bolt relieved of thread in the middle of the bolt to clear the fork tube.
This is as supplied from the factory.
I will make a drawing or take a photo with dimensions on it for you later today.
You may even get lucky and l can find some in the old bolt box.
Obviously four are required.
Cheers Chris.
Italbrit Classic Motorcycles.
 
The Allen Head bolt is M 10 x 40.
Diameter of the recessed area is 7.9 mm.
The recessed area starts 14mm from the end of the bolt and covers an area of 11.5mm.
Any Machine shop will be able to turn the recessed area for you on a standard M 10 x 40 high tensile grade 8.8 Allen
Head bolt for you.
 
Cccg said:
The Allen Head bolt is M 10 x 40.
Diameter of the recessed area is 7.9 mm.
The recessed area starts 14mm from the end of the bolt and covers an area of 11.5mm.
Any Machine shop will be able to turn the recessed area for you on a standard M 10 x 40 high tensile grade 8.8 Allen
Head bolt for you.
Click to expand...
Thanks this is really helpful. I was thinking of making something like this which seemed a bit of a work around the problem not a factory solution.

I guess they were using an existing casting and then found a problem fitting the 41.7mm fork tubes and hence a factory specification work around.
 
2Types said:
Thanks this is really helpful. I was thinking of making something like this which seemed a bit of a work around the problem not a factory solution.

I guess they were using an existing casting and then found a problem fitting the 41.7mm fork tubes and hence a factory specification work around.
Click to expand...
Correct ! the inner part of thread closest to to the cap head has no bearing on the clamping of the fork yolks.
It's just how the factory did it.
 
Reckon they're the same casting as for the 38s. As for thread at both ends, you could use a thread with shank if you don't like it. Still need to grind the curve into the middle section though.
 
Chris
Cccg said:
On both the Sfc 1000 fitted with the M1R forks we have in the workshop they are both fitted with M 10 x 1.5 grade 8.8 high tensile Allen head bolts , they are a special bolt relieved of thread in the middle of the bolt to clear the fork tube.
This is as supplied from the factory.
I will make a drawing or take a photo with dimensions on it for you later today.
You may even get lucky and l can find some in the old bolt box.
Obviously four are required.
Cheers Chris.
Italbrit Classic Motorcycles.
Click to expand...
Hi Chris, you are absolutly right. I thought upper and lower bolt are the same. Yust measured the upper yesterday. But the lower is as in your photos, M10 x40 with no thread in the middle secion. At the lower tripple clamp the bolt is closer to the fork tube as at the upper. So the bolt needs its special shape.
 
None of the above has a shank. Personally i would want a shank the size of the hole on the part of the bolt next to the head so its supported
My original suggestion of a Caliper bolt M10 x 50 to give you a good length shank, cut down to 40mm looks like the way to go TBH. this would give you an 18mm plain shank
 
piranha-bro2 said:
Reckon they're the same casting as for the 38s. As for thread at both ends, you could use a thread with shank if you don't like it. Still need to grind the curve into the middle section though.
Click to expand...
Reckon that would be the best explanation Quentin, Marzocchi wasn't exactly a huge company back then and prototypes often made it to production without the necessary alterations, this is probably a very early example. Just need to remember the bolts are waisted when removing stanchions. Later M1Rs definitely do not have waisted bolts.

If the bolt is waisted to 7.9mm, it won't be weakened at all, core diameter of M10 is 8mm anyway. So, what's the fuss? Max. torque for M10 in alloy is around 40-45Nm. These bolts are often done up far too tight, you don't need 4 ft. pipe over the ratchet handle... I've often needed one to get them undone though!:rolleyes:

piet
 
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