Exhaust Bubble Popping Sound

[Jeff Bennetts]

Got two smaller issues to address yet: weeping at brake seals (all rebuilt with new kits, disappointing)

There are too many variables to guess what the problem is without having the calipers in front of you (apart), bad bore, caliper pistons that are pitted, the groove in the caliper where the square seal is, isn't clean, it's always a crap shoot when someone else does the work.

[NobleHops]

Got two smaller issues to address yet: weeping at brake seals (all rebuilt with new kits, disappointing)

There are too many variables to guess what the problem is without having the calipers in front of you (apart), bad bore, caliper pistons that are pitted, the groove in the caliper where the square seal is, isn't clean, it's always a crap shoot when someone else does the work.

Jeff is of course correct, I gave a 'thin' answer at best. I did end up replacing my CBX caliper pistons for that very reason - in one case there was a big pit right where the piston transited the seal. Also, after I 'cleaned' the caliper bore I went in with a brass brush on a Dremel tool to clean out the groove in the bore and WHOOSH, a small dust cloud of dried brake fluid was lurking in the corners of the groove.

N.

[Fojyie]

All good observations. I had to replace all pistons due to pitting. I used some emery cloth to gently wipe the bores out and really looked them over closely, but apparently something has gotten by me. By the way, I had no trouble priming them. I used a pull down vacuum and carefully held the hose over the bleeder while opening and closing. I never let the vacuum fall below 5 in Hg to ensure constant pulling downward. I used Teflon tape and a little Vasoline at the bleeder to help seal it tight. That part went well. It was about two or three weeks later the weeping has shown up on all three plus the rear master cylinder which was in the worst conditiion. I'll just pull them one by one and carefully clean and look for nicks and pits affecting the seal. They were in terrible condition with dried fluid when I broke into them. This is another good example of poor storage, so often the case. Will get back with findings if I can sort it out clearly.

[Larry Zimmer]

Sorry to take so long to reply to this thread. One thing to note when 'cleaning' caliper bores, DO NOT run the abrasive material along the bore in an axial direction. You might think that a 1500 grit won't 'scratch'. It will. Move whatever you are using around the centerline of the bore surface. After you've gotten things cleaned and smoothed, just gradually release your pressure while still going around the bore. When you get to 'zero' pressure, you can pull the paper. Same thing applies to any hydraulic cylinder or piston/rod. If you are using a honing type thing, keep it oscillating axially as you work it up and out of the bore. Brake fluid makes the best lubricant while doing this on brake parts. Be certain to clean things better than hospital clean. Use either boiling water or alcohol. Obviously, if you use water, be certain things dry before assembling. (Air blow out followed by 250F in the oven overnight works good for calipers and m/c.)

P.S. The exhaust burrble noise occurs when run without pipes due to the high velocity exhaust gas meeting the very sudden change of flow section. It can be likened to a form of fluid flow cavitation. Of itself, it won't hurt anything. Running an engine in that manner, probably loose 15%, maybe more, power. As a side effect, I like Rick's comment relative to quick cooling.

[Fojyie]

Thank you Larry for those helpful hints. I won't expand on the brakes here (save for that topic heading), but you guys were right about the bubble sound. I no longer hear it with the exhaust on and after several heating and cooling cycles. I didn't run it that long w/o exhaust and haven't since. It was simply a weird sound coming from an engine. At one time I thought it was a diaphram popping, but it wasn't. Now the brakes are another issue for this winter. Still weeping after second take apart and carefully cleaning. More later at Brakes.