Acidic drops under bike

[ddreger]

About two weeks ago in cold weather I noticed some drops under my RT1150. Baking soda revealed that it was acidic. So, I replaced my original battery with a new closed gel battery. There was some minor corrosion of the battery plate but nothing bad

 

Yesterday I noticed the drops again. I was wonding if moisture in the cat or exhaust can become acidic? Since I replaced the battery and removed the drip hose (since it is no longer needed) it cannot be the battery.

 

Thanks for your help

Doug

[T__]

About two weeks ago in cold weather I noticed some drops under my RT1150. Baking soda revealed that it was acidic. So, I replaced my original battery with a new closed gel battery. There was some minor corrosion of the battery plate but nothing bad

 

Yesterday I noticed the drops again. I was wonding if moisture in the cat or exhaust can become acidic? Since I replaced the battery and removed the drip hose (since it is no longer needed) it cannot be the battery.

 

Thanks for your help

Doug

Doug, vehicle exhaust moisture can be very acidic.. It can condense & drip out of exhaust system seams or joints.. That is why it is ALWAYS advisable to ride a motorcycle once started to evaporate the moisture in the engine & exhaust system..

 

Twisty

[ddreger]

I thought the exhaust fluid would be acidic. I always ride my bike once started and then usually for at least one hour. Before I noticed the drips the weather changed (much wetter) and therefore I hadn't been riding so I wonder if it is due to condensation. I suppose that it also means that I may have some corrosion on the exhaust system though I don't see any.

[RFW]

I suppose that it also means that I may have some corrosion on the exhaust system though I don't see any.

Why? The exhaust is stainless steel.

 

By the way, you really should not have opted for a gel battery. Gel batteries have no business on a bike. They are sensitive to overcharging, and tend to have relatively short lives. Lord knows why BMW have used them on some models!

 

Next time, consider an AGM type. They are much more robust for motorcycle use, and still are sealed and maintenance-free. Panasonic makes an excellent range of AGMs, available at a good price, delivered to your door next day, from DigiKey.

[ShovelStrokeEd]

Why? The exhaust is stainless steel.

 

Just cause it is stainless doesn't mean it won't corrode. Particularly in the environment it is subject to in the region of the catalytic converter. Most stainless gets its corrosion resistance from passivity in a similar way that aluminum does. A light surface corrosion forms an impermeable layer protecting the base metal underneath. A highly acidic environment coupled with heat can break down that layer. It will reform, but, at the cost of some more of the base metal. The process is slower than with the plain old steel or even chromed steel of yore, but it still happens.

[RFW]

Why? The exhaust is stainless steel.

 

Just cause it is stainless doesn't mean it won't corrode.

Yes, of course, but the low-300 series austenitic stainless (e.g. 302 or 304) used in BMW mufflers is pretty darned resistant to corrosion and their mufflers tend to last the life of the bike. Cats are generally made from 400 series ferritic stainless which is less corrosion resistant than austenitic stainless, but serious corrosion of a cat does not typically happen.

[ShovelStrokeEd]

Agreed, provided it can come to operating temperature and evaporate and expel the corrosive liquid. Short running periods=bad juju to get technical about it.

 

HNO3 (nitric acid) will badly pit 300 series stainless steels, depending on concentration, of course. There is still the passivity working for you but that can vary greatly with the concentration of the acid. Mild seems to promote passivity, higher concentrations can form the pitting.

 

Doubtful, in the application here, that the concentration reaches a very high level. Witness the longevity of most SS exhaust systems. I have noted, on the systems I have removed, a good deal of pitting within the pipes immediately preceding the mufflers but, even on pipes with some 10 years of service, no failures.

[T__]

Most of the pre-cat exhaust components are made from 409 stainless steel .. It works quite nice for the intended job & is CHEAPER than the 304 or 321 SS used in the polished areas.. 409 SS doesn't polish up very good & when heated it tends to turn a tan/brown color (seem familiar?)

 

409 can develop light surface rust with time & heat cycles but has some advantages for exhaust system usage that are repeatedly heat cycled as it doesn't crack easily in highly stressed areas or near welded brackets & is not prone to cracking next to welds or bends..

 

The exposed & highly visible parts of the exhaust system (like muffler) are usually made from either 304 or 321 Stainless Steel.. The 304/321 series of stainless is significantly more expensive than the cheaper 409 stainless.. It’s claim to fame is: it will polish out to a great shine & will usually retain its appearance even when subjected to high heat or many heat cycles.. I would guess most are actually made from the 304 as it does work great for the application & is considerably cheaper than the 321 SS.. BTW, the 304/321 SS does rust when exposed to moisture or corrosive elements but the rust layer is so thin you can’t see it with the human eye..

 

Twisty

[AndyS]

By the way, you really should not have opted for a gel battery. Gel batteries have no business on a bike. They are sensitive to overcharging, and tend to have relatively short lives. Lord knows why BMW have used them on some models!

I think the your comments about Gel batteries are not quite right.

They are used on many military aircraft applications. One of the reasons is that the Gel dampens out the destructive vibrations that can cause conventional plates to loosten and short out. Secondly the Gel is safer in an inverted (or laid on it's side!) application. Thirdly it doesn't out gas in the way conventional batteries do.

I do accept the charging has to be much more closely controlled, and also to some degree the discharge. Some battery manufacturers haven't got design spot on yet, but don't dismiss the Gel battery out of hand. I have had one fitted to a 650 V twin for many years, and works wonderfully.

Cheers

Andy

[Boffin]

I have to agree that the BMW Gel battery is not a good choice and indeed I would never spec a gel battery for a motorcycle application as they are very easily damaged by even mild over-charging. The GEL electrolyte does not allow dispersion of gassing products from the charge cycle, lifing sections of electrolyte from the plates. This leads to a reduction in capacity and increase in internal resistance which tends to make over-charging easier.

 

Now, AGM batteries (often confused with and wrongly labled as GEL) are a very different story. All the benefits of conventional lead-acid with all the plus-points of the GEL battery. The glass mat controls acid and stops leaks - I have seen an AGM battery work perfectly after being completely penetrated by a high-velocity rifle bullet.

 

The use of GEL in aerospace cannot be compared to automotive use - modern aerospace charging circuits are vastly more sophisticated than the simple voltage monitoring used on a bike. On a bike like a BMW with a high-output generator (55Amp) a 18-20 Amp-hour battery is a very small load and overcharge is easy to envisage. A typical Japanese bike with an alternator output closer to 20 amps is much less likey to be able to do so.

 

Andy

[Ken H.]

Gel dampens out the destructive vibrations that can cause conventional plates to loosten and short out. Secondly the Gel is safer in an inverted (or laid on it's side!) application. Thirdly it doesn't out gas in the way conventional batteries do.

As do AGM batteries. Plus AGM doesn't have the electrolyte shrinkage separation from the plates problem that gels do.