johnakay
Member
- Messages
- 1,772
I've bought some crash bars for my bike.
guys on the bike forum recon that to fit these correctly for strength etc.
need to fit longer bolts ..in other words thread's pass the the nut's head by a few mm.see pictures
I would of thought this ok but apparently not.
this stronger and better for strength...
so you clever bods out there what do you think.
this what he wrote..seem to have a valid point.
Repeating my (condensed) comments made on the ADV Rider board...
The basic product is sound and well constructed. They attach to the four main engine mounting bolts and clamp mid-way of a very substantial frame member, however, they re-use the stock engine mounting bolts. In the case of the sidebag mounts, they provided longer bolts to make up for the thickness of their brackets. In this case, they did not. An economic decision probably, as these are rather expensive grade 10.9 bolts, but I think it is a big issue here. The four engine bolts pass through flanges on the frame and thread into tapped bosses cast into the aluminum engine. Givi apparently assumes that the fastening points are strong enough with 5.3 mm less thread engagement, even though they will now potentially be called on to absorb an impact force for which they were not designed. With aftermarket crash protection, there is always a possibility that an ill-designed engine-saver can be turned into an engine-destroyer. This was often the case with BMW airhead cylinder protectors. They transfer the force to the frame, thereby often bending it. Without them, only a new valve cover is often all that is needed because the cylinders are hell for stout. So I ran my airheads with only sliders on the valve covers and I now question EVERY "crash bar" design before it goes on my bike.
In this case, I think the engine guard and the mounting points are fine, but I disagree strongly with re-using the stock engine bolts. So, I plan to install longer bolts to achieve NO LESS than the original amount of thread engagement as it represents the best that we can do. All four of the threaded attachment points are open to the inside, so a bolt longer than necessary will do no harm so long as there is sufficient length of thread to get to where the threaded portion starts. I will install somewhat longer than necessary bolts so that I have some reserve in case I add a later accessory, such as a skidplate, that wants to mount to the same place.
Here are the numbers for the engine bolts on the US spec 700x with manual transmission (not DCT). All are grade 10.9 M12-1.25 hex washer head bolts.
UPPER LEFT: 35mm long bolt with 7mm from face of frame flange to start of thread
UPPER RIGHT: 45mm long bolt with 17mm from face of frame flange to start of thread
LOWER LEFT: 80mm long bolt with 46mm from face of frame flange to start of thread
LOWER RIGHT: 55mm long bolt with 30mm from face of frame flange to start of thread
The stock bolts are not exactly flush with the exit of the bosses, so the numbers above don't clarify that the thickness of the threaded bosses are between 25 and 27mm thick. I don't want to reduce it by 20% and add potential impact forces. I publish them here so that you don't have to do the research. In order to keep the engine in position, you have to remove, measure, and reinstall them one at a time. Since they are open on the inside I plan to get bolts 10mm longer so long as the distance to start of thread is adequate. I could not find these bolts in washer head, but +10mm will allow enough length to add a washer under the head. The upper right bolt can be re-used on the upper left. I purchased three new bolts in 55mm, 70mm (65 was not available), and 90mm length with grade 10.9 washers from:
guys on the bike forum recon that to fit these correctly for strength etc.
need to fit longer bolts ..in other words thread's pass the the nut's head by a few mm.see pictures
I would of thought this ok but apparently not.
this stronger and better for strength...
so you clever bods out there what do you think.
this what he wrote..seem to have a valid point.
Repeating my (condensed) comments made on the ADV Rider board...
The basic product is sound and well constructed. They attach to the four main engine mounting bolts and clamp mid-way of a very substantial frame member, however, they re-use the stock engine mounting bolts. In the case of the sidebag mounts, they provided longer bolts to make up for the thickness of their brackets. In this case, they did not. An economic decision probably, as these are rather expensive grade 10.9 bolts, but I think it is a big issue here. The four engine bolts pass through flanges on the frame and thread into tapped bosses cast into the aluminum engine. Givi apparently assumes that the fastening points are strong enough with 5.3 mm less thread engagement, even though they will now potentially be called on to absorb an impact force for which they were not designed. With aftermarket crash protection, there is always a possibility that an ill-designed engine-saver can be turned into an engine-destroyer. This was often the case with BMW airhead cylinder protectors. They transfer the force to the frame, thereby often bending it. Without them, only a new valve cover is often all that is needed because the cylinders are hell for stout. So I ran my airheads with only sliders on the valve covers and I now question EVERY "crash bar" design before it goes on my bike.
In this case, I think the engine guard and the mounting points are fine, but I disagree strongly with re-using the stock engine bolts. So, I plan to install longer bolts to achieve NO LESS than the original amount of thread engagement as it represents the best that we can do. All four of the threaded attachment points are open to the inside, so a bolt longer than necessary will do no harm so long as there is sufficient length of thread to get to where the threaded portion starts. I will install somewhat longer than necessary bolts so that I have some reserve in case I add a later accessory, such as a skidplate, that wants to mount to the same place.
Here are the numbers for the engine bolts on the US spec 700x with manual transmission (not DCT). All are grade 10.9 M12-1.25 hex washer head bolts.
UPPER LEFT: 35mm long bolt with 7mm from face of frame flange to start of thread
UPPER RIGHT: 45mm long bolt with 17mm from face of frame flange to start of thread
LOWER LEFT: 80mm long bolt with 46mm from face of frame flange to start of thread
LOWER RIGHT: 55mm long bolt with 30mm from face of frame flange to start of thread
The stock bolts are not exactly flush with the exit of the bosses, so the numbers above don't clarify that the thickness of the threaded bosses are between 25 and 27mm thick. I don't want to reduce it by 20% and add potential impact forces. I publish them here so that you don't have to do the research. In order to keep the engine in position, you have to remove, measure, and reinstall them one at a time. Since they are open on the inside I plan to get bolts 10mm longer so long as the distance to start of thread is adequate. I could not find these bolts in washer head, but +10mm will allow enough length to add a washer under the head. The upper right bolt can be re-used on the upper left. I purchased three new bolts in 55mm, 70mm (65 was not available), and 90mm length with grade 10.9 washers from:
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