[ROSKO]

I know a bunch of people run these and I'd like to hear the reasons why.

Why ask? Well, I would think that pressure buildup in the bottom-end is one of the causes for clutch pushrod seal failures. C'mon, it can't ALL be the little ridges worn into the pushrod itself.

Pressure has to be a factor, I blew this seal on my streetbike and the seal was only 1 year old. No ridge in the pushrod AND I do quite a bit of engine braking PLUS I am guilty of the occasional mis-shift.

..or it could've been human error at assembly. I didn't do it myself so who knows.

Anyway, back to lower breathers.... opinions?



BORN TO LURK, FORCED TO WORK.
www.NYCvinMoto.com
www.VinMoto.org

 

[jbranson]

There has to be something unusual going on in the 350 engines. First of all they are 180 twins...meaning while one piston is going up the other is going down...so it's not like you have huge crankcase pressure pulses. It would take a couple of PSI to blow out a seal...and even a small vent in the crankcase would prevent the build up of a couple of psi. It would take huge amounts of blow by on the rings to do it....you'd see lots of smoke out the tail pipe.

Upper or lower vent wouldn't really matter since the pressure can equalize through the huge cam chain tunnel many times the size of any vent installed. If enough crankcase pressure was built up and maintained to blow out the seal the engine would be weeping oil from every gasket constantly while it was running.

Something else is at work. 175 twins are 360 twins...both pistons going up and down at the same time...big pressure pulses...they never blow out the clutch rod seals.

I'm just assuming people are properly venting the engines...no the stock vent won't do for racing....you probably could see some pressure build up. But it's hard to believe properly race vented engines are building up that kind of pressure.

The main reason for venting race engines has been for the most part preventing pressure build up in the crankcase which robs the engine of power, second would be oil loss and blowing seals. There really is no other reason.

If seals are being blown out of 350 with stock vents...well then I can understand why. I'm just assuming any bike on the race track has proper venting, and not the tiny the head cover vent.
JohnnyB

 

[monkey]

i have a secondary vent located at the dipstick. this in combo with the stock breather seams to work for me. others run breathers from the starter motor block off etc etc..


matt


latered

 

[jbranson]

Same setup I have on my bike and I've never had a problem...but then it's not a 350.
JohnnyB

 

[lastman]

Hello All,
Hm, this is from an idiot tending towards moron, but maybe the extra power in the 350 compared to the 175 is causing the cases to flex more during high speed gear changes, bending the clutch rod slightly so when the clutch is released, it pushes the seal out, when power goes to the rear wheel.
Only a thought.

 

[ROSKO]

I don't think flex is an issue, not with the spindle the pushrod runs through.


Johnny, Monkey, My 350 only has the stock breather and was wondering if that was enough. Of the FCB's @ the track day most I saw just had the original set-up. I've been looking at the f160 stuff since they require a clutch pushrod seal retainer also. One reason they cite for failure is the pressure buildup when using only the stock breather. Sure it's a 360 but the reasoning is the same.

Waiting to see the retainer they use.

might as well do it right the first time, I gots to be doing all this sht anyway.....

BORN TO LURK, FORCED TO WORK.
www.NYCvinMoto.com
www.VinMoto.org

 

[jbranson]

Rosko,
When I heard about the seal problem on the 350's I was stumped because I just assumed that the engines would be vented adequately for racing....which is definately more than stock. Didn't see any way a 350 could build up enough pressure with the typical 1 square inch or so of venting typical on a race bike.

However....seeing as people are using the stock vent...doesn't surprise me at all that pressure is building up. In my opinion the stock venting on almost all vintage bikes is totally inadequate for racing. Stock 350's were just never designed to spend 30 minutes running around at full throttle. It typically won't break them...but it will show up weaknesses in any engine...like venting.

Lastman....the 350 is pretty much a different engine...looks the same as the 175 on the outside except larger...but it's got bigger stronger cases etc. It's not like it's a punched out 175... so I'd think the cases are plenty strong enough. But I do guess there is probably something odd about the 350 clutch rod setup that agrivates the problem. Maybe a tight fit around the rod and a loose fit in the case, maybe the rod moves a lot in the seal, something....that when added to the venting issue makes them blow out.

All you guys with FCB bikes....vent those engines...it's worth probably 1/2 a hp too...sometimes more. Pumping loses can suck up more power than you might think.
JohnnyB

 

[texmawby]

i run the stock vent, abuse the hell out of my bike, and have never blew out any seal. i am curious about johnny's statement about more venting = more hp gain and would like to look into this. i'd love to do a little thing to my bike to make it even faster than clancypants.

suggestions in places like what latered-man said or anywhere else?

texy

 

[lastman]

Hello Again,

Checking a 350SL upper case against a 175 case, the inner width of the gearbox is 4 inches versus 3.5, the cast wall thickness is the same, but on the clutch side of the 350 case there are two large areas with no material, each about a square inch, above where the gearshaft bearing sits containing the clutch rod and either side of the changing barrel. Not much material to resist those bending stresses and the extra half inch width would increase the bending to the other side where the seal sits. I feel a nerd alert coming on here so I will finish.
Interesting issue though. Oh what the heck, to continue, as John Branson correctly points out, the 350 is a 180 engine and so no pressure should build in the crankcase unlike the 175 which is 360 and so as both pistons go down, crankcase pressure increases. On the 350, blow by past the rings could increase pressure in the crankcase - this may be the culprit as well.
Nerd attack over!!!

 

[parks61]

on any bike/engine, blow-by will create/increase crancase presure. on 2 strokes, it creates seizures. blow-by always sucks. it is never acceptable. the piston skirt usually tells the story...have a look.
parks

 

[jbranson]

Like I said from the very beginning....I got a feeling something is up with the seals other than simple crankcase pressure...some design flaw somewhere.

Anyway,

Tex, research the effects of positive crankcase pressure...it's a no-no. Any time you can "rarify" the air inside the crankcase you decrease pumping loses. Remember...every time those pistons go down...and that's up to 200 times per second, they have to push air to do it. Those are your "pumping loses" and they represent a substantial portion of the hp lost in an engine (friction and pumping loses). So...the better a crankcase is vented, the less dense the air is...the less oil vapor flying around, the less hp is used to move air around instead of going to the wheel. On a race automobile it can be as great as 20+ hp lost to pumping air. On a full bore 1000cc race bike it can be 6-7hp. It varies with the type of engine...a 180 degree twin is not a real bad case....as one piston goes up and pull air...the other piston goes down and pushes air....however...air is still moved from one side of the engine to the other...A LOT...and that requires power to accomplish. The less dense the air, the easier it is to move. Might seem a small thing...but like I said..at 12,000 rpm you engine is doing it 200 times a second....imagine if you had to build a machine to accomplish the same task...how big an engine would you have to attach to it to get the job done?
There is a reason racers have for many years gone to the trouble of coming up with some fairly exotic crankcase evacuation techniques. Ever see the check valves and tube that goes from the headers to the valve covers on a V8 race engine? They use the negative pressure waves in the exhaust to pull vapor from the crankcase. There are also reed valve setups that serve as a high speed check valve...letting the air on the piston down stroke exit the crankcase and then not letting air re-enter on the up stroke. Lots of different techniques have been used. Supposedly it also helps the rings seal, helps to prevent ring flutter and a host of other things.
Next time you see a really hot, race winning vintage bike....you'll see the large venting system. It's not just for looks.
JohnnyB

 

[Bret]

Rosko said:
"I've been looking at the f160 stuff since they require a clutch pushrod seal retainer also. One reason they cite for failure is the pressure buildup when using only the stock breather. Sure it's a 360 but the reasoning is the same. Waiting to see the retainer they use."

Rosko,
Here's the newly mandated F-160 clutch rod seal retainer installed on my CB175 vert. It's made from teflon and is designed much like a sewing thread bobbin. Once installed the bobbin has a bit of end float, about 6mm, on the clutch rod. The end float is necessary to allow movement of the clutch actuation mechanism. With the clucth properly adjusted the 6mm of travel is enough movement to operate the clutch correctly. With only 6mm of free space and a clutch rod seal that is 8mm tall, the drawing board says that 2mm of the seal will remain engaged into the case if it tries to spit out. If the seal does spit, the drawing board also says that when the clutch mechanism is operated, the bobbin "should" push the seal squarely back into the case. These have just been made mandatory and today was the third F-160 race at Seattle. So far there have been no reports of loose seals, loss of oil, or clutch issues.
Prior to the retainer guys were drilling a 1/2 inch hole vertically through the floor area of the case below the clutch rod seal and just ahead of the triangular webbing gusset. The hope was that, should the seal spit, the resulting oil would be encouraged to drain through the hole and into the bellypan instead of following along the crankcase towards the back tire. Hopefully the new retainer bobbin will eliminate the need for the drain hole.

Cheers, Bret @ Glass from the Past

 

[ROSKO]

Bret,
Muchos gracias! Exactly what I was hoping to see. I e-mailed the maker of the 'bobbins' a couple days ago hoping to get a picture. Thanks for posting that.

I also like the back-up plan 'drain' idea.

The combo of breather/ bobbin should wipe out any chance of a seal blow-out.



BORN TO LURK, FORCED TO WORK.
www.NYCvinMoto.com
www.VinMoto.org

 

[bfd]

Has anyone ever seen first hand or heard from THE person who had a seal pop out on a CB350? As Craig mentioned there are 3 seals on that side so why that one. If you run a 16 or 17t sprocket there is a risk of a loose chain hitting the push rod but bad prep/accidents can make lots of things leak.
Joe Ruth helped me pull out the motor on Bruce Smiths 350 yesterday. While this bike isn't on top of the podium it has been raced with this motor at least 7 or 8 seasons, been to every one of the Hawk track schools and was usually the endurance racer due to the Valdez-size fuel tank. He bought it used from another racer. That seal is poking it's head out 1-2mm and has relied on the stock breather this whole time.

That item Bret posted is really nice. Maybe a batch could made and handed out at tech. I be a bucnh of folks will still not have heard or read about this yet and will be rolling up to Gil on the 18th unprepared.
bfd

 

[craig641]

bfd,

I've only heard of an XS650 that's had a problem with a clutch pushrod seal coming out. And they aren't required to have this seal retainer. To me this sounds like a helmet ban because someone heard there might be a problem at some track somewhere.

But anyhow, it's not a big deal so I made a strap to hold mine in place. I took a 1/8" x 3/4" by about three inches long. Bent it so it will hold the seal in place and bolted it to the one bolt hole that's on the inside of that cover. I think it's the neutral switch bolt.

The clutch pushrod seal is located between the two case halfs. I suppose it's possible that the two halfs don't hold the seal in place around the whole seal, there may be a slight gap at the joint.

And if you folks are interested in putting a lower vent in the motor you may want to think if you really want to remove the vent tubing from the dipstick location everytime you check the oil level or change the oil. That's why I put a vent in the starter motor block off plug. Either place will work but the starter plug location just seemed easier in the long run.

Craig

 

[jbranson]

Seems like that Yam 650 that oiled the track was a sidecar that had a chain mishap. Don't ever recall a 350 blowing the seal out. The 175's have the exact same setup, I've never seen one blow the seal out.

If I remember the progression properly it was....the Yam 650 had the chain problem the rod and pulled the seal out....someone mentioned the 350's had the same setup...to watch out with oversize sprockets...then it progressed to Yam's have to have the retainer...then 350's have to have it. I'm sure 175's will be next.

I still say there is like no chance of blowing out any properly installed seal on an engine that doesn't have a clogged breather. Well...maybe with a stock breather if you holed a piston. But....heck it's not a hard thing to take care of...so do whatever it takes to keep the techs happy.
JohnnyB

 

[ROSKO]

It's good to know where this rule came from. These are all good measures to take but an odd reasoning behind it.

Did the f160 class see many blowouts/ failures?


As I said before I've blown this seal on a street bike but I'm pretty sure it's due to extreme retarded mechanic factor.




BORN TO LURK, FORCED TO WORK.
www.NYCvinMoto.com
www.VinMoto.org

 

[Bret]

Guys,
I'm not sure if other Honda twins or manufacturers are the same, but on the CB160s and 175s at least, the clutch rod seal is force fed direct engine oil pressure and is the reason a few of our seals have popped. In the photos below the view is of the under side of the upper crankcase half. In the first photo the red circle shows the oil fed bushing on the end of the mainshaft. The clutch rod seal is in the popped position just to the right of the circle. In the second photo the red circle shows the oil feed hole and the arrow shows the feed line's junction with the main oil gallery that crosses the case from the oil pump. The second hole in the bushing saddle is for the indexing dowel pin. Being oil fed, you can imagine the mess when the clutch rod seal pops. Does anyone have a split CB350 case they could check to see if it has the same oil feed behind the clutch rod seal?

Cheers, Bret @ Glass from the Past

Edited by - bret on May 07 2007 11:40:33 AM

Edited by - bret on May 07 2007 11:41:09 AM

Edited by - bret on May 07 2007 12:12:45 PM

 

[ROSKO]

bret, good to know. I'm heading to the worskshop now, I'll take a look.

BORN TO LURK, FORCED TO WORK.
www.NYCvinMoto.com
www.VinMoto.org

 

[jbranson]

Bret...very very good point. How many of the 160 guys are using punched out oil pumps? I've been very careful in my 175 builds that when I increase oil volume I redirect it to the top end by enlarge the metering orifices at the base of the cylinders. Also some work at the cam bearing to enlarge the metering holes. Get enough volume out of the pump without doing this and it will direct the extra flow to the gear box to which it has a much easier and shorter route than the head.
JohnnyB

PS. Not to mention that 350's running heavy weight race oil and running at high rpm are going to be generating oil pressures on the upper end of the design parameters.