Topic: breather question for high compression/ high performance engine guys

[paulages]

...those of you without stock airboxes: how do you have your crankcase breathers arranged, and how much positive pressure do you see at high RPM? i know there are a million threads on smoky breathers and all, but none of them discuss high perf engines spinning fast for long. if i take the 718 out for a good flog (and stay at 7-10K RPM most of the time), i get quite a bit of smoke from my breather filter when i come to rest. the tube coming from the starter plug is clear, and i can see it blows a fair amount of oil at high RPM. head and barrel temps are around 260F or so when it's nice and hot. not sure about oil temp, but the rest of the case and oil cooler are significantly cooler (180-200F).

here's my breather arrangement:



the top black tube goes to the crankcase vent on the cam cover, and the clear one to the vent in my starter plug. the bottom tube drains back to the crankcase through a nipple installed in the filler.

compression is good, and though i don't have an odometer, i definitely have at least a few hundred miles on engine by now so break in should be long done (though my bearing clearances were quite tight). should i be concerned?

[KingCustomCycles.com]

You are talking about what we call in aviation "breather speed" the more blow-by the rings have, the higher the speed at the vents. Your recovery system looks good, and it sounds like your engine runs well.  The only thing I would suggest would be to run a series of compression tests with the engine cold, warm, and over time, like once a month.  If they are stable, or increasing all is well.  If they are going down or are low, you could have some cylinder/ring sealing issues.  I hope this helps.  That is how I would handle it on someone's $25000 Lycoming. 

[paulages]

You are talking about what we call in aviation "breather speed" the more blow-by the rings have, the higher the speed at the vents. Your recovery system looks good, and it sounds like your engine runs well.  The only thing I would suggest would be to run a series of compression tests with the engine cold, warm, and over time, like once a month.  If they are stable, or increasing all is well.  If they are going down or are low, you could have some cylinder/ring sealing issues.  I hope this helps.  That is how I would handle it on someone's $25000 Lycoming. 

i've been doing compression tests periodically, but it's a bit hard to do on a kick-only bike without help, when the compression tester doesn't have the correct adapter for the plug threads. the rubber tip adapters are a pain in the ass. i hope not to have to re-ring anytime soon, but if i'm losing power or causing excessive crankcase pressure i will in a heartbeat...ok, maybe the first post-frost heartbeat. 

[Terry in Australia]

Yeah, that's what I thought too Paul, what were your "piston to cylinder" clearances when you bored them out? Have you posted any pics of the 718 yet? Cheers, Terry.

[754]

paul, what is the thinking behind the 2nd & 3rd breathers?

I am thinking that the factory designed  the system fairly well, although sustained higher rpm can affect the way it works. The addition of the starter one may fight against how the original works, and the drain, unless it has a check valve, also allows pressure to change.


Also, why would you want that oil back in the cases?

[paulages]

Yeah, that's what I thought too Paul, what were your "piston to cylinder" clearances when you bored them out? Have you posted any pics of the 718 yet? Cheers, Terry.

i can't remember the clearances- i'll have to check with my machinist, but they were per specs. i have posted some pictures, but here's a couple for you terry...






these pictures were at fireup. since then i've removed the starter, added the plug with breather tube, the catch can, oil cooler, pressure gauge at the pump, 1.5" taller rear shocks (wow, that helped with the turning in) and a few other changes.

[paulages]

paul, what is the thinking behind the 2nd & 3rd breathers?

I am thinking that the factory designed  the system fairly well, although sustained higher rpm can affect the way it works. The addition of the starter one may fight against how the original works, and the drain, unless it has a check valve, also allows pressure to change.


Also, why would you want that oil back in the cases?

you might be right about the tube at the starter hole. it blows much more actual oil than the one at the cam cover. i only installed it because it was on the race bike i took the plug from and i was felt like i was having blow-by issues. i think i could probably do without the return at the bottom, as it will naturally return to the starter hole. remember, the 550/650 doesn't have two vents like the 750 (not one at the transmission). i can't really see how having too many vents could be a problem though. as for return of the oil? it would surely be more pain to empty a catch can all the damn time than change the oil a little more frequently, but maybe my thinking's backwards.

[Dunstall_74]

Can't quite tell, Is that the Sprocket Specialties alloy rear sprocket?  Bike turned out nice!  Is it faster than the 550 racer?

[paulages]

Can't quite tell, Is that the Sprocket Specialties alloy rear sprocket?  Bike turned out nice!  Is it faster than the 550 racer?

yes, thanks, and...well, i don't know. i haven't even come close to finding top speed yet- the geometry is steepened enough that i start to get a little front end wobble over 100mph. haven't quite pushed it toward a tank slapper yet. i need a steering damper. the racer does 140 with the fairing.

shoulda called me today- i rode all over skyline, germantown rd, etc. for hours. had a blast. rode with 5 girls i met up there yesterday. it was really fun riding with an SV--- modern bike with the same HP as the 718. i kept up well. 

[Dunstall_74]

Damn! sounds like fun I was moving most of the day, just wishing I could be enjoying the weather we've been having.  Let me know when you put that steering damper on, I'd like to see how you set it up.  I've looked around a bit for ones that fit our bikes, still can't quite tell if mods are needed or not.  Give me a call next time you head out to ride.  I'll be ready to hit it sometime today.  The sun is supposed to shine through Wednesday. 

On the breather topic....What if any is the benefit of running a after market breather as opposed to the factory one?  I've noticed it is pretty popular with the chop crowd.  Think the first time I saw it was on Cycle Xchange  I wasn't sure if it was a year specific mod, beacause I would usually see it on like, '77-'79 Not necessarily SOHC.

[paulages]

On the breather topic....What if any is the benefit of running a after market breather as opposed to the factory one?  I've noticed it is pretty popular with the chop crowd.  Think the first time I saw it was on Cycle Xchange  I wasn't sure if it was a year specific mod, beacause I would usually see it on like, '77-'79 Not necessarily SOHC.

the factory breather routes through the airbox. get rid of that and you're breathing to open air. probably not the end of the world, but i'd rather have it filtered against contaminants.

[Terry in Australia]

Can't quite tell, Is that the Sprocket Specialties alloy rear sprocket?  Bike turned out nice!  Is it faster than the 550 racer?

it was really fun riding with an SV--- modern bike with the same HP as the 718. i kept up well. 

Hey Paul, is there a "718" thread I've missed? What are your HP figures? Cheers, Terry.

[paulages]

Can't quite tell, Is that the Sprocket Specialties alloy rear sprocket?  Bike turned out nice!  Is it faster than the 550 racer?

it was really fun riding with an SV--- modern bike with the same HP as the 718. i kept up well. 

Hey Paul, is there a "718" thread I've missed? What are your HP figures? Cheers, Terry.

there are several recent, actually. one for "tuning the 718," one for "718 on a dyno," and one for "550/650 hybrid how to." in any case, the initial dyno run produced 69.7 RPHP and 41 # of torque. the mains were very lean on that run, so i imagine i'll probably have squeezed another 5 HP or so out of jetting and timing. i can definitely live with 75HP from a cb550. 

[mark]

http://www.moroso.com/catalog/categorydisplay.asp?CatCode=13023

no b.s.  it works. maybe even another 5 hp worth.

Plug the starter hole. Put the funny pipe fitting and check valve in the header, just ahead of the muffler clamp. Run hi-temp capable hose from check valve to clear hose fitting on catch can. Violá. Breather filter on can will stay pretty red just like the pods.

 

[paulages]

bump to this old thread...


i got the bike out for a good run yesterday, and found that the breather filter is blowing oil all over the place.... and onto the rear tire. 

i need to try a larger catch can for sure, but does anyone have more thoughts on this? racing guys? what do you do? it's fine unless i keep it in the high revs for a while, and then it blows a lot.

[MRieck]

bump to this old thread...


i got the bike out for a good run yesterday, and found that the breather filter is blowing oil all over the place.... and onto the rear tire. 

i need to try a larger catch can for sure, but does anyone have more thoughts on this? racing guys? what do you do? it's fine unless i keep it in the high revs for a while, and then it blows a lot.

Baffling in the canisters would help. I think you could use more canister volume too. A low volume pressure gauge that holds highest value would be interesting too.

[paulages]

bump to this old thread...


i got the bike out for a good run yesterday, and found that the breather filter is blowing oil all over the place.... and onto the rear tire. 

i need to try a larger catch can for sure, but does anyone have more thoughts on this? racing guys? what do you do? it's fine unless i keep it in the high revs for a while, and then it blows a lot.

Baffling in the canisters would help. I think you could use more canister volume too. A low volume pressure gauge that holds highest value would be interesting too.

i did in fact use a higher volume canister today (vitamin water bottle with lid open to air) and had no oil blowoff at all. i plugged the line from the starter plug and vented only at the cam cover. it still smokes a little, but there was zero oil in the bottle. seems fine like that... no i just have to make a better permanent canister.

sure was nice to be able to ride hard today and know the tires were gonna stick... i gave some guy on a gixxer a run for his money up on skyline (hills west of downtown portland). he ended up pulling over to let me pass. 

[mlinder]

First off, Paul, screw you for scaring the guys on new bikes with your sohc on germantown, thats been my job for a couple years now. Second, screw you for not inviting me out. Not that I have a bike I could go on, but I'm sure you could supply.

There may be a bit more crankcase pressure, with your MUCH oversized displacement.
BMW used to put on a reedvalve on their crankcase on their engine cases, due to much higher RPM and such, on their boxers (back in the mid 70's) because the extra crankcase vacuum would move oil all over the place. Shouldn't be a big deal on the I4's, but you may be dealing with somethig similar.
Gimme a call.