Ever wonder what's inside the PCV valve?
1 - 20 of 36 Posts
Joined
·
869 Posts
Perhaps, but the system itself seems to be problematic IMO due to all the very minute orifices and passages, as well as being somewhat of a "Rube Goldberg" design...
Joined
·
9,328 Posts
How do you come to that conclusion?
Joined
·
2,046 Posts
Lol so we see why proper maintenance is important. Not all Recommendations by Honda warrant the the hurry up must do attitude IMO but brake, coolant I follow closely
Joined
·
9,328 Posts
Fair hypothesis, but this is a part from a twelve-plus year old motorcycle. dadztoy might have mileage that was on the motorcycle it was removed from, but we have zero information on service history from this specific find.
Due to the 'Rube Goldberg' design - 100% on purpose, I'm certain - the likelihood of correcting a malfunctioning PCV by flushing a 1/2 gallon of brake fluid thru the whole system (per SB#23) sure seems to be a bit sketchy - to me.
Now, if one was to consider passing a liter of fluid thru that PCV valve directly (bypassing SMC), could *that* solve some of our brake response woes?
Joined
·
869 Posts
BTW - I was up on the Cherohala this afternoon checking Fall colors... I usually ride the downhill part (heading toward Tellico) fairly aggressively using liberal amounts of rear brake searching for judder... Today, at 70 degrees, none was present... kwthom and myself have been working this problem for a while so the disassembly of the PCV was the "next step" in our/my research...
Now I know how it comes apart so I'll probably pull mine during the down winter months here as I'm doing routine maintenance on the bike... I built a pressure bleeder earlier in the month and ran several liters of fluid thru the system... That seemed to help, but the judder was not entirely eliminated and both kwthom and I have come to the conclusion it is a heat related problem along with possibly air in the lines and dirty, goopy. fluid...
The PCV lives behind the left radiator and that gets me to thinking about the heat related issues - that's one of the reasons I want to see it's location on the bike... Perhaps some heat shielding might help - just another thought...
WATCH THIS SPACE!!
Les
Now I know how it comes apart so I'll probably pull mine during the down winter months here as I'm doing routine maintenance on the bike... I built a pressure bleeder earlier in the month and ran several liters of fluid thru the system... That seemed to help, but the judder was not entirely eliminated and both kwthom and I have come to the conclusion it is a heat related problem along with possibly air in the lines and dirty, goopy. fluid...
The PCV lives behind the left radiator and that gets me to thinking about the heat related issues - that's one of the reasons I want to see it's location on the bike... Perhaps some heat shielding might help - just another thought...
WATCH THIS SPACE!!
Les
Joined
·
17,815 Posts
Joined
·
8,305 Posts
Thanks for clarifying this, for us non-mechanical types.
I have the brake shudder issue on my 2006 and I was blaming it on a slightly bent front rotor but I think that it's worse when the bike is hot. I'll have to pay more attention. The only resolution I've seen, other than good rotors, is a good bleed of the brake fluid.
Joined
·
2,691 Posts
Joined
·
2,691 Posts
Heat and location, interesting thesis, but I would interject that the heat would be affecting the springs and seals inside. I’ll keep watching. :nerd::nerd:
Joined
·
869 Posts
Yeah, lots of ideas and thesis' - maybe one day we'll find the actual cause...
Greg - near as I can see, those little fingers help hold the spring in place - difficult to see though... As far as I can see, the bores look fine, but difficult to see in the smaller bore...
Joined
·
9,328 Posts
:doorag:
The proof simply becomes recognizing that in (nearly...) all cases I have read about, either the ambient temperature was 'elevated', or the motorcycle was run in an environment with extreme heavy braking (mountain roads, competitive range riding, etc.)
The design does not lend itself to rebuild - no kit available.
There is no proof of a single point of 'failure' in the design. As always, it's a multitude of items that induce the rear judder.
This video (I've shared before...) shows a Honda CBS brake system from a fairly simplistic point of view. We simply have the secondary master cylinder in our path for the purposes of understanding what the PCV does specific to this design implementation.
The proof simply becomes recognizing that in (nearly...) all cases I have read about, either the ambient temperature was 'elevated', or the motorcycle was run in an environment with extreme heavy braking (mountain roads, competitive range riding, etc.)
The design does not lend itself to rebuild - no kit available.
There is no proof of a single point of 'failure' in the design. As always, it's a multitude of items that induce the rear judder.
This video (I've shared before...) shows a Honda CBS brake system from a fairly simplistic point of view. We simply have the secondary master cylinder in our path for the purposes of understanding what the PCV does specific to this design implementation.
Joined
·
498 Posts
Looking at that video and applying it to our bikes, here is a theory.
When you apply just the rear brake, you have a higher pressure on the input side of the delay valve, than the output side.
Once you have reached enough pressure to open the delay valve, the input pressure is reduced because it is now feeding the output side(s) of the delay valve.
I'm sure there is some built in hysteresis, but if there is enough air in the output side, the pressure will drop more than planned. If it is hot, that air is now expanded (taking up more volume) and would cause an even larger drop of pressure causing the delay valve to get into a chatter mode.
I'm not an engineer, but I play one at home
.
When you apply just the rear brake, you have a higher pressure on the input side of the delay valve, than the output side.
Once you have reached enough pressure to open the delay valve, the input pressure is reduced because it is now feeding the output side(s) of the delay valve.
I'm sure there is some built in hysteresis, but if there is enough air in the output side, the pressure will drop more than planned. If it is hot, that air is now expanded (taking up more volume) and would cause an even larger drop of pressure causing the delay valve to get into a chatter mode.
I'm not an engineer, but I play one at home
.
Joined
·
869 Posts
Sounds good to me - I don't have a clue as to how it works and at least that makes sense...Looking at that video and applying it to our bikes, here is a theory.
When you apply just the rear brake, you have a higher pressure on the input side of the delay valve, than the output side.
Once you have reached enough pressure to open the delay valve, the input pressure is reduced because it is now feeding the output side(s) of the delay valve.
I'm sure there is some built in hysteresis, but if there is enough air in the output side, the pressure will drop more than planned. If it is hot, that air is now expanded (taking up more volume) and would cause an even larger drop of pressure causing the delay valve to get into a chatter mode.
I'm not an engineer, but I play one at home
Quite honestly I don't see how there can be any air in my system and after running nearly 2 liters of brake fluid thru the system with a home made Pressure bleeder...
I'm rather hoping that when I open mine I find a gooey mess - at least that would explain the shudder, but it would not explain why there is a gooey mess in there, as I am fanatical about maintenance...
I will say this though - I have noticed on my last 2 Goldwings (1500 and 1800) that the Honda brand of brake fluid gets gummy and gooey much faster than any other type... Just my observation and my opinion, and we know what that is worth!!
Joined
·
17,815 Posts
Getting back to basics. Let's not forget that air in a brake line will give an inconsistent peddle and/or mushy peddle. Heat causing brake fluid to boil will give a fading brake peddle.
1 - 20 of 36 Posts
Join the discussion
Join now to ask and comment!