Crankcase breather modification

[Zwartie]

As some of you already know, I had the top end redone on my '92 FJ in preparation for the 16,000 km (10,000 mile) ride to Alaska this coming July. When I brought the valves and other accessories from RPM to Mike at Raceworks Canada, one of the parts that I showed him was the new crankcase breather filter. The old one really looked like crap so I figured I was doing the right thing in getting a new one. Mike was pretty adamant, insistent even that I do NOT install a breather filter. He has 30+ years experience in motorcycle engine building and drag racing so I value his opinion on this sort of stuff. He said that it is vitally important that the crankcase be able to breathe to atmosphere. If not, the pressure built up by those pistons moving up and down will have to go somewhere which will likely be through the newly reinstalled base gasket. Definitely don't need that to go again! He has a '73 or '74 Kawasaki Z1 in his shop (should have taken some photos) in mint condition. He punched it out to 1200cc and other than the aftermarket exhaust it looks bone stock. The engine puts out 168 hp which is just insane given how spindly the frame and forks are on those machines from the 70's. Anyway, what he has done on that bike (and others) is to run the crankcase breather hose into a water bottle (about 1/2 way down) and then cut a hole in the side of the bottle near the top. This allows any oil from the crank case to spew into the bottle if necessary and it will still be able to breath freely. He said that the problem with the filter is that if oil and crap gets onto the filter media, it will restrict its ability to breath and then you risk blowing a gasket. I know he runs his bikes hard at the track and this maybe overkill for the average rider but again, I value his thoughts on this. So, in keeping with his advice (or command), this is what I did this evening on my bike:

1. Old (actually new) crankcase breather filter installed


2. Old breather filter and hose removed


3. Modified breather bottle. It was a large goofy drink bottle we got at Cedar Point last summer. Note the hole in the side.


4. New crankcase hose installed and connected. It's a 1/2" ID hose that is rated for oil and gasoline exposure and has a 250F temp rating. Got it at DeeTag, an industrial supplier in town.


5. Hose end cut to go into the bottle. Though I would cut both sides at an angle so there is no chance that it will seal against the inside of the bottle inadvertently - you never know!


6. Hose and bottle shown outside the bike so you get an idea of the assembly.


7. Hose and bottle installed under the tank, just in front of the battery case.


8. Another view of the assembly.


9. One more view. This gives you a better idea of the angle that it is at so fluids (if any) will sit at the bottom of the bottle and not get sucked back into the hose.


I put about 30 km on the bike with the old hose and (new) filter before doing this. I thought I better do this modification sooner than later as I don't want to disappoint my engine rebuilder! Thoughts / comments are always appreciated. If anyone things this is overkill and they would just as well stick with the filter and if you want a new crankcase breather filter, let me know and I will send mine to you.

Zwartie

[SlowOldGuy]

I'd call bullshit, but I'm not sure where exactly your friend is coming form.

The bottom of the motor (pistons) displace as much air as the combustion side.  As such, they must breathe.  The filter you have is as effective as the bottle.  You would't want the crankcase sucking in dirty air as much you don't want the carbs sucking in dirty air. 

Keep the filter!.

DavidR.

[racerrad8]

Zwartie, slow your roll until you hear me out and hang onto the brand new crankcase breather "filter".

I am to here to offer you my 19+ years of exclusive experience with the Yamaha FJ power plant from mild to wild. I would be really unhappy, in fact pissed, with a customer that I build an engine for had an unfiltered means of crankcase ventilation.

So, lets take a minute or two to examine this philosophy your engine builder has offered you; The filter could get plugged up and cause crankcase pressure.

That is the reason you need a filter...

But lets look at what you have there with the bottle.

1) Remove the filter and modify a bottle with a hole in the top to catch any oil that might come out of the engine. What means of filtration is there to keep the dirt & debris from entering the engine through the big hole in the top of the bottle and up the hose?

2) It is difficult to tell how far down in the bottle you have the hose, but you notched the hole to prevent it from sealing to the bottom of the bottle. What happens when the bottle fills with oil and blocks the bottom of the hose and you now have no form of ventilation?

3) The filter gets plugged with "oil and crap"; what do you think is going to happen when the crap gets into your engine?

So, the FJ engine is a 180* engine in regard to cylinder stroke. So, the pistons moving up & down do not really build pressure. So, what this means is when two of the pistons are traveling down displacing air into the crankcase, the other two are traveling up allowing the displaced volume of air a place to go. So on an engine with good ring seal you will actually fell a vacuum at the crankcase breather fitting, especially at cruising speeds. The reason there would be a vacuum in the crankcase is because of the windowed clutch basket passing the ventilation window of the clutch cover, creating the vacuum.

If there is pressure in the crankcase it can only be made by the blow-by of the piston ring seal on the compression stroke.

Another flaw I see in your bottle configuration you have there is water. If you get in a rainstorm, or wash your bike or are parked or riding, the water can travel down the back of the tank and fall into your bottle. Once that water comes up to the level of the hose it could actually suck in water or block the ventilation.

And finally, lets look at the filters surface area compared to the 1/2" hose that connects it to the engine. The breather filter is 1.5" in diameter and 1" in tall. So, the circumference around the 1.5" is approximately 6" and with the 1" height that would be 6 square inches. Now the filter media is pleated adding the circumference length of the media so without cutting one apart should make it approximately 10 square inches in media length. So, the amount of the filter that has to become plugged to prevent ventilation is 95%.

I am here to tell you to put that breather filter back onto your engine and you will not have any problem. You can clean the filter each time you change the oil, but you will find it will not be necessary.

I personally guarantee you will not have any crankcase pressure issues using the breather filter that I have sold well over 300 without a single complaint, concern or issue. After all you want to make sure your ventilation system is filtered. Yamaha filtered it via the air-box originally and RPM does it with the breather filter you have.

Plus, I have been using this same filter on all of my race car engines since 1994 with a single blocked filter resulting an a blow gasket or seal.

I would be happy to discuss this further if you would like.

Randy - RPM

[Flynt]

Thoughts / comments are always appreciated.

I'm not qualified to rebut on your builder's logic here, but you have essentially just created an oil catch can...  very common on turbo cars where the OEM PCV system will fail to get the oil out of the air before it gets sucked back into the engine.  These systems mostly have a bypass to allow the passage of external air in and out depending on intake vacuum level (that's the hole in the side of your bottle). 

If you think the bottle is a good idea and want to follow you're builders advice, just put a filter on that hole and you're covered...   

Frank

BTW - you could also just buy a catch can, mount it nicely, and have a little less "creative" looking setup... 

[Rhino]

just to add 2 cents

running engine heats up, air expands and needs somewhere to go. Catch can works fine for air exiting the motor.
switch her off while you have a coffee and it'll cool down and even more so overnight.
where's it getting that air from that's going back into the engine?
without a filter everytime you heat and cool the engine you'll introduce a few more grains of dust into the oil

[Zwartie]

Fellas,

Thanks for the feedback. I had a feeling it would draw some attention and perhaps some criticism from the group. That's one of the reasons I posted it in the first place. I had no problem with the filter as it looked like it would do a good job breathing - keeping the air flowing back and forth as those 4 pistons are moving up and down above the crank case. I am also thinking that as the pistons move, you've got two going up as two go down so the net difference in air displacement required is likely minimal. Again, I still understand that you don't want or need excess pressure to build up in the crankcase. I also know that what the bottle is, is really just a catch-can, designed to catch any thing that may spew out of the breather hose. The hose is up high enough in the bottle that it should not suck up oil and/or water that will get into the bottle. Correct me if I'm wrong, but on the FJ's with stock air boxes, doesn't the breather just run into the air box? Seems like this is a similar set up. I believe that Mike's main concern is that should the filter get clogged for any reason, that could spell trouble - potential base gasket leak.

I've sent Mike a link to this thread so he can add his thought in his own words should he choose. Will keep you posted.

Thanks again for the thoughts and compelling arguments in favour of the filter.

Zwartie

[racerrad8]

Correct me if I'm wrong, but on the FJ's with stock air boxes, doesn't the breather just run into the air box?

The breather hose is hooked to the air box after the air filter has cleaned the air preventing contaminates from entering the engine

Seems like this is a similar set up.

You have a set-up similar to a breather tank, but unfiltered. You are better off using a small breather tank with a filter on top, something like this; http://www.jazproducts.com/media/auto/breather_1_pint.jpg

I believe that Mike's main concern is that should the filter get clogged for any reason, that could spell trouble - potential base gasket leak.

I understand his concern, but I truly believe it is unwarranted. FJ's are all I do and if this was a problem I surely would not be selling the filter to anyone. The filter is there to prevent any form of contamination from getting into the engine and is required when you convert over to any aftermarket filter to protect the engine.

As I stated earlier, it is a filter and it should be maintained. I clean mine at the same time I service my air filters, but I have never seen or heard of a clogged breather filter. If your concern is that it could plug during the trip you are taking, I stand behind my guarantee that it will not plug on your trip.

Randy - RPM

[SlowOldGuy]

I am also thinking that as the pistons move, you've got two going up as two go down so the net difference in air displacement required is likely minimal. Again, I still understand that you don't want or need excess pressure to build up in the crankcase.

Try this little experiment to test for crankcase pressure:

Remove your clutch slave cylinder and start the engine. 

Let us know if you detect any crankcase pressure ...

DavidR.

[FJmonkey]

Try this little experiment to test for crankcase pressure:

Remove your clutch slave cylinder and start the engine. 

Let us know if you detect any crankcase pressure ...

DavidR.

Now your being very naughty David.... Trying to rid the world of cats one push-rod at a time... 

[Pat Conlon]

Ben, DON'T DO THAT...

David..BAD doggie.

[FJSpringy]

Been running the cc filter for nearly 10 years and never had a problem, I clean and oil it along with the pods every so often eg when I remember, while it's a bit dirty it is no where near clogged and I can't imagine it ever getting to that.

[racerrad8]

Try this little experiment to test for crankcase pressure:

Remove your clutch slave cylinder and start the engine. 

Let us know if you detect any crankcase pressure ...

DavidR.

Sorry, that is the wrong crankcase pressure...


The rod shoots out because the oil pressure around the rod down the inside of the transmission input shaft...

Randy - RPM

[SlowOldGuy]

Busted!

I was wondering if it was oil pressure that shot the rod out.  I didn't know it ran through the center of the trans input shaft.

I haven't done it, but I don't recall anyone telling of oil coming out with the rod....

DavidR.

[Pat Conlon]

Oh, hell yea...The word 'copious' comes to mind...

[SlowOldGuy]

Okay,
I didn't think there was that much positive crankcase pressure.  It's nice to learn something.

DavidR.