Rubber Intake Boot Cracking Solved?

[Guest tmartin]

I think that I may have found the cause for rubber intake runners cracking on V11S models--at least on my bike. I have new intake boots and in the process of replacing them found that the two mounting brackets (especially the lower one) puts pressure on the rubber boots because the mounting holes in the bracket are not located properly. This misalignment can be seen when installing the new boots.

 

To remove the old boots I took out the four screws (two upper/two lower) on the right throttle body and pulled it out of its boot. The left TB was removed from its boot with the brackets attached. After installing the new intake boots on the heads I pushed the left TB on its boot with no problem. I pushed the right TB on the right boot and found that when I tried to line up the lower bracket’s screw holes with the holes in the right TB that the bracket had to be pulled toward the right side of the bike with mild force. The effect of this misalignment causes pressure to be placed on both rubber intake boots forcing each to the inside. I more closely inspected the old cracked boots and found that the cracks were on the outboard side of each boot (where you can see them). My theory is that engine vibration and constant pressure towards the center of the bike caused both boots to crack on the outside where the rubber was stressed. Because the lower bracket screw-mounting holes are countersunk they cannot be elongated to fix this misalignment. To partially solve the problem I biased both rubber intake boots towards the centerline of the engine (pushed them to the inside when I tightened the hose clamps). This relieved about 60% of the pressure on the boots with the bracket installed. The upper bracket’s holes line up more closely with the TB and it appears to be less of a problem.

 

I feel that this is not a “quality of rubber” issue but instead an alignment problem. My original intake boots had 16,000 miles on them and the crack was about 1/8” deep but did not go through to the inside. You may want to look at your intake boots and see where the crack is located.

[callison]

My right side one on my Sport 1100i had a spiral tear an inch and a half long on the inboard side. The throttle body hardware on this bike and the V11 is indentical. I had more than 56,000 miles on this bike before I discovered the tear. The tear occurred on the only boot I had ever tightened and I had made it really tight! I don't know if that contributes directly or not, but I would suspect that it aids in the disruption of the boot.