Surging/Bogging

[Cogswell]

12 hours ago, Kalikiano said:

Amusingly, I'm sure a 'mild rider' that I haven't even encountered the EVIL VTEC spirit, yet...unless this issue is somehow connected to the extra complications of that system.

 

 

Since VTEC is oft-discussed and seemingly gets a bad rap, maybe it would be interesting to see where VTEC lives and see some of the components.  Most owners never see it or know where it is.  The top two photos, below show where it lays at the base of the "V" underneath the throttle body (circled in red and in the second photo only the electrical portion of it).  VTEC is an actually simple system (much simpler than variable valve timing on newer engines).  It is a solenoid controlled oil valve, that when actuated, allows pressurized oil to flow through a spider web of passages in the upper portion of the block in to the 4 pairs of VTEC valve buckets. The solenoid / valve in the photos is a plunger style - the solenoid moving a spring loaded small rod back and forth to open the passageway from pressurized oil in to the valve buckets.  There isn't much to go wrong with it.  I don't ever recall an owner reporting a VTEC solenoid / valve failing .  "The combination is referred to as "the spool valve". 

 

While conventional valve buckets have a shim that sits between the bucket and the valve stem, inside each of the 8 VTEC valve buckets is a hydraulic latch (last photo, right).  The latch has a spring loaded slide that when force closed, closes off the central opening.   When pressure is absent the valve stem can transit through the hole in the  latch and even though the bucket is rising and falling with the cam's rotation, the valve is not actuated and remains closed.  Hence VTEC valves have two springs - an inner spring to close the valve just like the non-VTEC ones, and a lighter, outer spring that keeps the VTEC bucket in contact with the cam at all time regardless of valve movement.  That action is what raises the latch off the valve stem on each cycle and allows the latch slide to move (direction arrow in the photo) to "close the hole over" and allow the latch to contact the valve stem.   When oil pressure hits the latch, it closes almost instantly after the cam lobe leaves the bucket thus contacting the top of the valve stem on the next cycle, operating the valve.  Hence the abrupt "hit" the rider feels as airflow through the engine nearly doubles (? maybe it's not that much - but is significant) almost instantly.  At VTEC engagement RPM, the valves are opening and closing around 50+ times per second.  In the photo, I placed arrows at the 2 holes in the bucket that allow pressurized oil in to close the latch (you have to look closely).

Note that inside the bucket is scribed "279".  That is the thickness of its shim.  The shim is not separate from the bucket - it's part of it.   That, is one of the Achilles heel of VTEC - if VTEC valves are out of spec you don't replace a shim, you replace the entire bucket.  They run in the range of $40 each +/-  and there are 8.  You get the idea . . . 

 

So mechanically VTEC is pretty simple.  Complexity comes in both service and control of the nearly instant change in airflow.  If 6th gens did not have VTEC but still chain driven cams, I doubt there would have ever been much if any talk about the complexity of 6th gen motors.   What makes VTEC adjustments a PITA besides dealing with chains vs just setting gears back in place are the latches.  You can't check valve adjustment on one that has an open latch and does not contact the valve.  To do that the latch must be closed - and that's what the 1st "take the cams out and put them back" sequence is about.  Each VTEC bucket must be removed and a small pin placed in the slide of each latch to hold it closed (that's what's going on in the photo) - once the pin is in, the latch is replaced in the bucket and then back on the valve, latched closed).  Repeat X7 and then reassemble chains / cams to check clearance.  From there it's the same as any other shim / bucket check.  Remove the cams a 2nd time to replace needed shims/buckets. Reinstall with latches in place to check final clearance.    Finally, the latching pins must be removed so they'll operate normally so out the cams come once again to remove them and then final assembly.  So in and out with the cams at least 3 times.  Anyone that complains about the cost of a VTEC valve adjustment should give this a go and see if they would like to make a living at it.  I for one, would not . . .

 

The other part of the puzzle is how the change in airflow is dealt with.  At VTEC engagement RPM's, the cams are rotating as mentioned at about 50+ times per second.  That's a lot to ask of ECU's that were developed about 20 years ago.  I don't think Honda had all this well refined at the time.  I remember the 1st time I felt that "hit".  It didn't bother me, but I came to understand what owners had talked about.  In 2006 Honda raised the VTEC engagement RPM by 400 and probably did some other engine management tweaks to try to smooth it out but it wasn't until nearly 12 years after its initial development that Honda really got it right with the 2014 model introduction. 

 

I don't think VTEC's should be avoided or have anything to be concerned about. Any issues with it are control, not mechanical.  Early on mine had the stumbling and sometimes erratic running at around 4,000 rpm in on/off throttle situation.  Personally I think that had more to do with trying to comply with tightening regulations than with anything VTEC related.  Some maintain that VTEC was an attempt at complying - that's above my pay grade.  At any rate, I cleaned / flowed my injectors and with at the time a PCIII it all smoothed out.  Now, however I'm using RB for that.  I never have had the 5,000 to 6,000 rpm changes going along at a steady speed some experience.  Owner's experiences seem to vary to a mild to significant degree in some of those regards.  VTEC is not bad and IMO very reliable, but as I've said before I don't think it adds anything and the complexity and cost of service are detractors given no material change in power or torque delivery. 

 

I would set your mind at ease.  Yes a 5th gen is a delicious treat - but, both ABS and factory luggage were never available with 5th gens, so the 6th and 8th gens have a number advantages over a 5G.  My advice is to have one of each! 

 

[ShipFixer]

24 minutes ago, Grum said:

Appreciate your comments Shipfixer regards potential design flaws with Honda closed loop for the early 6gen.

 

I guess what I'm really getting at is that there is heavy evidence (and this particular thread is a classic example) that a very common (but not always) cause for a bike to start surging and bogging is fuel delivery and this is what should be assessed first before jumping to a PC or RB potentially masking a fundamental root cause of the problem. YMMV.

Cheers.

This is actually the first time I've seen someone post a picture of a fuel filter and narrow it down as the root cause of their problem 😄

 

Words like surging and bogging and whatnot can cover a lot of things that are difficult to diagnose just from reading the words.  And fuel is a potential problem across any engine.  But power falling off slightly between 4K and 7K RPM, when at steady state on the highway, on a stock 6th gen, with the rider trapped in a do-loop...well, that's just how they are.  There were a bunch of people here who bailed off their VFR's to go back to Blackbirds and such, partially because of the ECU.  

[Grum]

2 hours ago, ShipFixer said:

This is actually the first time I've seen someone post a picture of a fuel filter and narrow it down as the root cause of their problem

 

The picture is only showing the suction filter on the pump input side, the main filter is on the pump output. Given the state of it I guess its a good indication the main filter wouldn't be too healthy.

 

Had a bit more of a read regards surging and bogging. Some more interesting things that 6gen owners claim to have greatly reduced or cured their issues apart from fuel filters.

- Air intake velocity stacks incorrectly positioned.

- Dying battery.

- ECM connections poor or high resistance.

- Spark plugs.

- Poor Starter Valve synch.

 

Guess Kalikiano at least has a few things he can check.

[ShipFixer]

Yup, we've all chased all of those over the years.  Some of them like the velocity stacks never really made good technical sense but we tried anyway.  You can also add trying the starter valve sync pattern from a 5th gen instead of all-even, and a few others that are closely related.  

 

But on the fueling bit, think about any clogged media...it results in consistently lower flow, not something like the dial back at steady cruise.  You would also have a lot of other symptoms that would show up other times.
 

It could be that Australian models don't have the same ECU logic.  The US ones are definitely got screwed over.

[Grum]

2 hours ago, ShipFixer said:

Words like surging and bogging and whatnot can cover a lot of things that are difficult to diagnose just from reading the words.  And fuel is a potential problem across any engine.  But power falling off slightly between 4K and 7K RPM, when at steady state on the highway, on a stock 6th gen, with the rider trapped in a do-loop...well, that's just how they are.  There were a bunch of people here who bailed off their VFR's to go back to Blackbirds and such, partially because of the ECU.  

Have to agree with you, having this issue would drive you nuts.

What does my head in is that many owner's don't have the problem.

I've travelled thousands of kilometers up and down boring highways coasting around the 5000rpm zone and just fine tweeking the throttle locker for constant speed - never any surging issues.

Given such very consistent build quality and tolerances I would have thought this issue would be far more consistent, to the point of every bike having the problem, but that clearly is not the case.

 

24 minutes ago, ShipFixer said:

 

It could be that Australian models don't have the same ECU logic.  The US ones are definitely got screwed over.

Maybe the U version 6gen for Australia and New Zealand allowed for richer fuelling maps.......completely guessing here!

I'm even wondering wether our fuel differences between countries could even have an effect!....more straw grasping!!

[ShipFixer]

Hard to say...I think it's more like how most "consumer grade" headphones that cost a decent amount are really terrible in specific ways that make them palatable to non-audiophiles, and they're doing the best they can for the business line's expected return on investment.  The vast majority of owners probably also don't notice the flat spot in the middle of their fuel injection maps for example, but that's there for the same emissions reasons as the closed loop mode.  A small handful of owners gathered here and VFRW, etc. get into this but I doubt even most people who plug in Power Commanders really dig in that far.  They never mod suspension (which comes undersprung for the average American), etc., or, you know...even think about changing their car's shocks ever 30K miles or so.  And in 2020 the odds of someone coming from a carbureted bike with a linear power delivery is pretty slim to none. 

 

It is also possible along with this that it's somewhere in the tolerances in between bikes.  Motorcycles are turning twice or more the RPM, with a much smaller cylinder volume, with much smaller amounts of fuel coming out of the injectors, with far less sensors than road vehicles.  And...motorcycles do not have near the revenue base or regulatory drive that cars do.   It requires higher precision than bigger engines that you can't just scale down effectively, so you really need more funding and work to get it to the same place but...not going to happen.

 

Look at how far variable valve technology in cars has gone since 90's Honda VTEC Preludes.  Pretty much everything has at least variable intake timing, to the extent where most of my friends don't even know that's a thing, or what a cam phaser is.  I have a friend who is a retired turbine engineer with the same engine as my truck, and I had to show him in an app (designed by some smart Australians who cracked Nissan's proprietary signals) that the cams advance between zero and forty degrees continuously.  We get...something less sophisticated than the Prelude.  It's a really good idea  but Honda just doesn't have the business case to invest a whole lot more in development of these engines or bikes.  Making the fuel delivery perfect for the rider as well as emissions is probably not high on that list past "good enough."