Ultra Black silicone in airbox breaks down

[motometal]

this is a follow up of sorts on an old thread where we discussed the MXbonz airbox kit installation on .02 and up CR250s, and speculated on the use of different sealants. I think it's a great kit, but can tell you that the Permatex ultra black silicone that they recommend eventually breaks down over time. Chances are, it's still doing it's job of sealing the airbox, but any excess material smeared beyond the mating surface has come broken down and flaking off. I read somewhere that there is a product called Hondabond 4 that works better, can't confirm though.

Speaking of CR250s, anyone else have trouble with the rear cylinder dowel sleeve? This is the second CR that I have disassembled with a corroded and seized in place dowel pin. It takes a lot of patience with a rubber mallet to remove the cylinder (DO NOT wedge a screwdriver in there!), and once the cylinder was removed, I was barely able to remove the dowel sleeve without making a real mess. The other (front) one looked like new.

I'm getting the "mo better" EG port job, i'm anxious to try it out this spring.

 

[darringer]

I use never sieze on the dowels before re-assembly. Never had any problems with that method.

 

[nephron]

My cheapo KX500 airbox broke in a couple spots following several standard violent altercations with objects or ground... ;) I also needed to 'replace' the vent windows, and just right off the bat, ignorantly or otherwise, used the Ultra Copper High Temp RTV. :yikes: I just have always liked it so much more than black silicone that I don't even have any black hanging around. Better adhesion, oil resistance and temperature fatigue--by far. So far, everything's holding up beautifully. Sure, it's ugly as piss, but it works.

 

[jaction125]

I'm with you on those dowels, nearly mangled my cylinder trying to get the back one out. Then forgot to never sieze it going back together. :ahhh:

 

[Rcannon]

I read somewhere that there is a product called Hondabond 4 that works better, can't confirm though.


I use the hondabond all of the time. It holds up much better than the black silicon. I believe the gas vapors eat the silicon.

Cylinder dowells shoudl be outlawed...for all bikes. Either that, or we shoudl all remove the cylinders when we first buy the bikes and coat them with waterproof grease.

If you use a pressurewasher, this problem gets twice as bad.

I recently pulled a cylinder from a 1979 kx 125. The previous owner had greased the dowells somewhere around 1981. They fell right out.

 

[Mike_socal]

Funny you mention the cylinder dowels. I just replaced all 4 studs and both dowels. They were getting nasty and making the cylinder real hard to remove. Just remember to grease the locating dowel before you put the cylinder on. It helps the next time you have to take off the cylinder.

 

[motometal]

Nepron--this is going to sound petty, buy I always liked the black silicone because it didn't advertise to the whole world that you used silicone. Maybe the copper stuff is chemically different and more chemical resistant. Actually the black suff didn't break down for awile. Either the filter oil or a small bit of spit back through the carb is what eventually got to it.

I know a guy that lost his temper with the cylinder/dowel problem and really buggered up the parts (he knew better but was very frustrated). It was never right again (leaked).

 

[flattie]

i use ultra black on my air bow and have had no problems, the key to it though is not to over do it. "just a dab i'll do" the only place the needs sealing is between the metal ring on the inside of the air box (the one your filter bolts too) and the rubber part of the boot the extends into the air box. that is the only place dirt can penetrate the boot. pull innner ring, clean both parts perfectly then apply a thin amount of any silicone to the inner part of your boot. when you get done you shoulnt be able to see any silicone. when i bought my cr used the previous owner had smeared the stuff all around every part of the sealing rings inside and out which had no effect on the actual problem.

 

[snb73]

This may sound a little odd, but try some "shoe-goo". It is a shoe repair glue, most likely an RTV, can be found in black. It is very durable and is said to be impervious to oil. We used to use it to glue about anything when I was in the military.

Good luck, Steve.

 

[motometal]

I suspect using race fuel doesn't help matters any. Some of the components such as the aromatics may not be found in pump fuel, at least not in such amounts.