Noticed something odd on my bike's airbox, which has never fit quite right on the carbs. The panel of the airbox that holds the air inlet boots for the carbs is caved in ~0.5" (12mm). It makes the inlet boots point slightly inward... the reason, I suppose, that the thing's never fit quite right.
Has anyone seen this before? And how to fix? My current plan is to strip the box of rubber and filter, and use a heat gun to soften the box and pull it back out straight.
Second issue. Looking at the carb boots, they don't fit tight to the head. I've bought new o-rings and compared them to what's there. They are different sizes (current ones appear too large.) Assume that carb boot should fit flush to head with no gap... right? What's the torque spec for these things? Otherwise will use generic fastener-to-aluminum spec.
Airbox caved in: all seem to be. Not an issue.
Intake boots to go flush to the engine head. If not, they're warped. There is metal in the boots at the engine side so it should be flat. o-ring does fit but like all o-rings in a groove, they may be slightly big or small and need to be smooshed in there.
Torque for intake boots: I've always done "hand snug and an extra 1/4 turn". There is an o-ring so bad-ass tight is too tight. If in doubt, I have seen some with liquid gasket on there. Maybe because they didn't have a new o-ring. They tend to get hard and flat. Remove carb boots and always put on new o-rings.
Torque spec on the boot to the head? I don't think they have that spec listed... but, I took a look in my Haynes manual (89 to 08 GS500) and under "Crankcase bolts," it lists torque settings for 8 mm and 6 mm bolts, which if you know the thread size of the bolts holding the boots on, these should be perfect to use (since torque settings are usually porportional to thread size when it comes to metal applications of the bolts). For 8mm bolts, 20 to 24 Nm, and for 6mm bolts, 9 to 13 Nm.
Now, I don't recall how the bolts held on the boots, but if they start crushing the rubber (rubber starts expanding too much), obviously disregard these torque settings. But I imagine they're somewhat rigid where the bolts pass through.
Compared to the other bolts, the boots have a rubber o-ring. The other parts have paper gaskets. Gaskets require torque. You don't need that mnuch torque when you have rubber o-rings. Like the oil filter cover, the rubber o-ring does a lot for sealing and high torque is not required.
The boots have a steel plate in them. That's what holds the o-ring and mates with the head. It should be perfectly flat. If not, replace the boots because they will never seal.
Squishing the rubber is not an issue since the steel plate is what holds it to the head and holds the o-ring.
Think of this: tighten as you would the oil filter cover. Snug, sort of tight but not kick-ass tight because there is an o-ring in there.
And use high temp. thread lock or a washer & lock washer on them so they don't work lose, even though a lock washer is not specified.
Because of the steel plate, you can tighten pretty hard but not necessary. I guess case bolt torque spec would be a good one from my experience, if you want to use a torque wrench. 9-13nm.
OK, that's what I thought re: torque on carb boots. More like a valve cover gasket. Boots are flat... already checked that. So pull out old gaskets and gasket gook (some sort of sealant was used) and re-assemble.
So the airbox warping is common? I thought it was due to mis-installation... sound more like due to heat from engine inherent in design then. Should be an easy fix in either case.
I had same problem with airbox warp over time. Forget, but I used something to push the plastic back out.