Bonneville America Forums Forums Technical Forums General Tech Why do we use air filters?

Well?

Just been to the Stafford Classic Show and a lot of the bikes of the time were running without filters and just used...velocity stacks? (I'm not sure of their name-funnels attached directly to the carbs)
What are the pro's and con's of this set-up? I realise it's to maximise airflow but what would be the worse that could happen if, for example, I did it to my bike? And, if it would mess up my bike, why not the older bikes? More tolerant carbs?

As an aside, saw a 62 Beezer Gold Star...and fell deeply and madly in luv. Nothing superfluous, just the essentials to do the job in hand. It was immaculate, too; it made my bike (07) look old and knackered! Anyone got a spare 13k quid to lend me?!! Anyone?!

I can't remember the name of the racer but it seems just as he was leading the Isle of Man TT to the finish he sucked a nice piece of gravel into his engine and kablooey he was done. That pretty much sums it up, although I do admit velocity stacks sure are pretty (and they can be fitted with filters of a sort).

sand, dust, pollen, etc will destroy the smooth walls of the cylinder and you will lose compression and have to rebore/rebuild the top end.

There is only a small % of hp lost due to filters. They're a good idea!

You said it was at a show.
That's what the stacks are for, show.
Maybe some racers where dirt isn't a major worry.
Tiny pieces of dirt sucked into your bike engine will scrub down the innards very quickly. The air filter slows this process.

First post, so HI.

Must admit I had thought bellmouths would be good. I was used to seeing them as a kid and in the British climate (i.e. where I am) I'd be surprised if there would be much reduction in engine longevity. Might give it a go in the near future.

Hi Blue.
Lotsa sand here in the American Southwest .

How do your paper filters look after a few thousand miles? That'll give you a pretty good indication of whether or not you have much to worry about.

Back in the day I rembember they caught a guy trying to spit cherry pits into the velocity stacks on an altered dragster.
After that most guys started using those tennis balls between rounds. Also I've heard that some old timers used gauze to keep the pea gravel and bugs out. Filters are so much more efficient now. I wouldn't think of firing an engine without some type of filter.

We used to run flathead Fords with no air filters or, at the most, small wire mesh ones. Also, those engines had no provision for an oil filter. We also used to have to overhaul them every year or two, and spent about an hour scraping the mud out of the oil pan and valve area with putty knives.
The recommended time between valve jobs on the Lincoln V12 was something around 16K miles. They also used wire mesh filters because there was no room for a proper oilbath one like the Chryslers and Packards used.
I had wire mesh filters on my '49 Triumph and had to do a ring job on it after 2 years.

Thanks, guys. So, what you're saying is, use filters.

Racers used them but threy rebuild their engines on a regular basis.

mike

Hi, guys. So, I now know that I should use an air filter or 2. Cheers.

On to my next, related, post...

I've got some big plans for my scoot, including the intake mod., as follows. Firstly, tho, you should know a few other bits I'm gonna do.

Single seat conversion.
Remove rear mudguard (fender)
Install hugger (for legal purposes)
Remove airbox.
Relocate battery.

Intake mod.

As we all know, cold air contains more oxygen than warm air for a given volume so directly behind the engine probably isn't the best place for an air filter. My plan is to relocate the filter/s behind the seat. I figure I could use a single, large filter and suspend it transversely between the frame behind the seat in a custom bracket/cover thingy and then run a hose from there, under the seat to attach to the intake manifolds.
Alternatively, if I didn't want to go the custom cover route, something like

K&N 'Apollo':
http://www.knfilters.com/universal/apollo.htm

Green 'Twister':
http://www.greenfilters.co.uk/Green_Filt...2ab926aaf0f3310

mounted in the same place might do.

All comments/queries/relevant information welcomed.

Neill

Had a snowmobile that had a "ram tube" as we called them in the early days, a screw worked it's way loose from somewhere and got sucked into the carb. After taking the cylinder down found the screw wedged into the piston and the cylinder wall with a pretty gouge that made the head a nice paper weight. Never looked at an un-protected carb the same since.

use filters

>Just been to the Stafford Classic Show and a lot of the bikes of the time were running without filters

Early Bonnies came out that way.
I think the filters started appearing on the US versions around '63, with UK getting them some time later.

- Foggy recollection of info from Gaylin's restoration guide.

see anguspt's wise advice above,,,,,,, some 50's and early 60's cars and pick-ups had "roll of toilet paper" oil filters, i can remember how odd i thought at time, used to give my brother-in-law the dickens when he'd put one in,, still laugh about this 50 years later.