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air filter K&N air box

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#1 Fletch

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Posted 04 March 2015 - 10:54 AM

A newb question, (couldnt find any previous posts covering this, so if there are i apologies for any repeat)
but anyway..
I was browsing through F2 motorcycles for various spare parts, i came across their air filters page.
http://www.f2motorcy...neprengine.html
i see that they are offering up new K&N air filters for 750 ural.

I have a Dnepr k750 with this air box:
Posted Image

does anyone know if K&N do an air filter that will fix this box? or have replaced theirs with K&N option?
there are so many different filter choices, and im not sure what to go for, from the schematics, the original russian one looks like its just a wad of cotton type material and i'm looking to update with a modern equivalent.

thanks
1965 Dnepr K750

#2 dneprlover

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Posted 04 March 2015 - 11:09 AM

No idea whether it will fit but why spend good money on an item that will need regular replacement at extortionate cost.

The airfilter housing on your bike was originally packed down the centre with lightly oiled coarse steel wool. This is easily cleaned or replaced. I usually pack mine with stainless steel pan scrubbers from the pound shop. ( thrift store to our USA bretheren)  that is then needed is a squirt of aerosol oil or WD40.

This method works, is cheap, and you don't have to deal with the most expensive supplier that exists. It's up to you.

#3 Fletch

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Posted 04 March 2015 - 01:19 PM

interesting solution that is worth considering.

how does it fair with dust though?
1965 Dnepr K750

#4 dneprlover

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Posted 04 March 2015 - 02:14 PM

Very well. The wire wool creates a labyrinth and the oil makes dust stick to it. The Soviets used that system for nearly 50years without problems. Easy to clean , cheap to replace if needed and soldier proof. Steel wool filters performed in all weathers unlike paper ones that choke the engine when they get wet. They only moved over to paper systems because it was 'expected' in the west, and the Russians wanted to sell bikes here to earn foreign currency . Similar to why they started making leading link forks. Millions of outfits including all the military ones ran on tele's but the west thought combinations had to run on L/L, so they started supplying them to help sales.

#5 Bilge Keel Dave

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Posted 04 March 2015 - 02:49 PM

A K&N filter is not a paper filter, it is an oiled filter. It also can be washed, reoiled and reused, but if filters out smaller particles than a steel gauze oil bath filter.

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#6 racepres

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Posted 04 March 2015 - 05:02 PM

I like Oil Bath...But, Have Never replaced a K&N filter...Cleaning for me is Knock it against a Tree, and get any big pieces off and stick it back in...But, The oldest one is only new in 1988...May Fail yet. And...It is in a Street bike, that has not seen extremely harsh Conditions..no worse thanGravelRoads
A  word of caution...On most Bikes [generally Harleys for me]the K&N provides better breathing, and May necessitate a Jet Change [richer] watch yer plugs...You do Not want to Member up into the Holy Piston Club.

#7 Fletch

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Posted 05 March 2015 - 05:47 AM

View Postracepres, on 04 March 2015 - 05:02 PM, said:

.... Have Never replaced a K&N filter.....

this is what i hear about k&N filters which is why the interest. They may be expensive to initially buy, but worth it if you never need to replace, and occasionally 'wash'. Cant quite work out how one would fit into my particular filter box though.

I guess its a bit of anxiety about crap getting into my (nice new/clean) carbs that initiated this thought. Also perhaps an attempt to try to avoid some unnecessary maintenance/cleaning for something that can be solved with a better/modern equivalent part?

Sure the 'original' filtration method (or as dneprlover described) would do a sufficient job, as said, it has worked very well for a variety of conditions in the past  etc..

For now i'll stick with the original but..

i know the saying, " if it ain't broke don't fix it", but if there is an improvement available what do you do?

food for thought.
1965 Dnepr K750

#8 guzzidude

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Posted 05 March 2015 - 07:37 AM

You can always buy some filter foam sheet from bike bandit and cut to fit. Washable as well and you have some left over for another.
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#9 Count Zero

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Posted 05 March 2015 - 09:30 AM

Might this from Oldtimer Garage fit?

http://www.oldtimerg...ir_cleaner.html

As I understand it, the old type filter is a bit more complex than just dragging air across a steel wool (or rubberised horsehair) element.  The upper, larger diameter portion is an oil bath, should have a quantity of oil in the bottom of the pan.  Air is drawn in under the Bakelite lid, and then passes over the oil and up to the main intake (stuffed with fibres).  As the air passes over the oil, particles stick to the oil and are filtered out.  The steel wool is a secondary filtration medium.

They were common usage on a lot of vehicles until the '60s or so, when the replaceable paper filter type came in which is easier to clean / replace, and traps finer particles than the oil bath.

The oil bath is still used on some offroad and military vehicles as it can filter a large amount of dirt without reducing the amount of air it passes to the engine.  On a lot of them, an offset intake pipe causes swirl in the oil bath part of the filter, centrifuging the dirt out.  I can't see this feature on 'our' filters, unless the flow from the timed breather can influence the flow enough.

Maybe a best of both worlds effect could be had by keeping the oil bath half, and replacing the steel wool with a K&N conical filter somehow...

#10 fernf5

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Posted 17 March 2015 - 11:02 AM

Fletch-I have the same filter as you on both an M72 and a Chang 750. I use a Napa Gold 2032 paper filter. It's a 1/4 inch too tall but fits well enough otherwise. Lasts a long time and doesn't cost much. Been using them for 2 years now. No issues but I don't ride in the rain!
The one from Oldtimers looks like a good possibility, might try it myself.
Here's a link to where I learned of the paper filter.

http://changjiangunl...ed.com/tb71.htm

#11 lobofuego

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Posted 04 April 2015 - 07:52 AM

Went and fitted some K&N type conical filters to my 750...all went well initially...did get an occational misfire in the wet, but avoided rain for most of the time,...then there was this day I got caught out...It rained and hard...130 miles to go...the filters sucked up more water than air and I had to remove them to get home!...made it, and have fitted the original filter back on, for whilst it is ugly, it clears my feet easier, and does not fill with water...shame , but no other real solution , for the real world,

#12 Stromski

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Posted 20 April 2015 - 12:31 AM

View Postracepres, on 04 March 2015 - 05:02 PM, said:

I like Oil Bath...But, Have Never replaced a K&N filter...Cleaning for me is Knock it against a Tree, and get any big pieces off and stick it back in...But, The oldest one is only new in 1988...May Fail yet. And...It is in a Street bike, that has not seen extremely harsh Conditions..no worse thanGravelRoads
A  word of caution...On most Bikes [generally Harleys for me]the K&N provides better breathing, and May necessitate a Jet Change [richer] watch yer plugs...You do Not want to Member up into the Holy Piston Club.

I don't want to derail this topic, but as a recovering member of the Holy Piston Club, my ears perked up.

From your comment, an overly lean mixture could cause this problem.

When I ordered the replacement piston from Yuri, the first thing he said was "You put premium gas in it, didn't you?"  As a matter of fact, I did.  I couldn't get my non-ethanol "country gas", so I tried premium.

When I told my regular mechanic (for my regular bikes, he has never seen a Dnepr), he said that that was nonsense.  He runs premium in everything, including the ancient Triumphs he restores.  His quick response was "Too much spark advance.  I can't tell you how many race bike pistons I've blown because of that."

I can't be sure of the state of the carbs.  The air filter is original (shop vac paper type), but the PO included a box with partially uninstalled Kohler carb repair kits and partial original parts.  The jets in the box appeared unused, so I assume the original jets are on the bike.  One thing is clear, that he tried to do something to the carbs.

He called a few weeks ago, and I told him the whole repair saga.  He was unaware of the break in governors and did not know that the most he had ever given the bike was half-throttle.  He was probably trying to compensate for that.

Anyway, I do not want to rejoin the "Holy Piston" club.  For the last few weeks (I only see the bike on weekends), I have been trying to dial in the carbs.  At the beginning of this weekend, the bike started on the second kick, but once it got warmed up, it was idling at full throttle.  Yesterday, I stepped down the mixture and idle screws until each cylinder had a nice, slow idle.  This morning, I could not start it at all.  I gradually richened the mixture and raised the idle until it started.  After two 7 mile test rides (stop at the far point to see if it idled, then if it would restart).  It idled and started.  Faster than I would like, but within sanity zone.

So, I have been presented with three plausible causes for blowing a hole in my piston:  Lean mixture, premium gas, advanced timing.  Any suggestions as to how to step through this mine field as I set the bike up?

BTW, I installed a Russian electronic ignition and coil, before I realized that the piston was blown.

Thanks

#13 haj

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Posted 20 April 2015 - 04:50 AM

I'm using the filter from oldtimers on my K750.. Works fine..  I've not looked into the dirtyness of it since I fittet it 2 years ago but I don't ride in dirt much so I don't expect it'll need replacing / cleaning for some time.
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Living in cold Copenhagen/Denmark

#14 racepres

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Posted 20 April 2015 - 07:53 AM

Even premium gas these days Sucks...Bad. I run Regular with the least amount of Ethanol as possible...which for me is some in there...so I use a Fuel additive. All premium has an additive to prevent spark knock [lead and Octane] neither is used these days...Ethanol is an Inhibitor of Spark Knock also...tell you anything?...look at the Octane rating on E-85...But, No Do not run it.
I doubt Fuel was a Factor in your Piston damage..Timing??? well it would have to Ping and Rattle something bad before a Dnepr would hole a Piston with too much timing...More likely to erode theedges at the top ring.
Nope...Sorry I truly believe you had too lean a Mixture...Lean =heat and Rich = cooler.
Luckily the dnepr [mine anyway] tolerates a fairly rich mixture. Put those walboro needles in the carbs, set the float level, then install whatever aircleaner you plan to keep, then tune the Carbs...Timing set at The recommended "mark" or a bit retarded from there...




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