VTEC Valve Adjustment

Discussion in 'General VFR Discussions' started by Mr. Philadelphia, Jan 17, 2022.

  1. Mr. Philadelphia

    Mr. Philadelphia New Member

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    First post here, though I've been a longtime reader on the forum.

    For those interested, I thought I'd post the first valve clearance check on an '06 with 67K miles. I haven't bothered to check them on my '96 with only 26K miles. Both bikes are ridden fairly hard, generally getting 5-6K miles on an ST rear tire and 7-9K miles on an ST front, doesn't seem to matter whether it's a Pilot Road, Roadsmart or whatever ST tire Bridgestone is offering. Bike was running perfectly and probably could have gone at least another 50K miles without intervention.

    Cylinder---Intake---IntakeV---Exhaust---ExhaustV
    -----1-------0.178-----0.100------0.270-------0.350
    -----3-------0.150-----0.100------0.230-------0.350
    -----2-------0.180-----0.100------0.280-------0.320
    -----4-------0.178------0.110------0.270-------0.350

    Specifications
    Intake: .20+/-.03
    Intake VTEC: .20+/-.08
    Exhaust: .35+/-.03
    Exhaust VTEC: .35+/-.08

    Trying to make sense of the trends here, the exhaust side standard valves showed more seat wear as expected and were all out of spec. The exhaust VTEC valves were all within spec.

    On the intake side, just the opposite was true, all the VTEC valves were out of spec while all but one of the standard intake valves were within spec. The question is why? The only trend I can see is that all the inboard valves were out of spec., maybe because they run hotter. Exhaust VTEC valves are outboard (farthest away from the centerline of the engine) while intake VTEC valves are inboard (nearest the centerline).

    I've ordered new VTEC buckets for the intake valves and will swap in one of the original intake VTEC buckets to open up the clearance a bit on the #2 exhaust VTEC valve.

    Swapping a few of the standard shims around and a shim kit will bring all the standard buckets closer to the upper range of the spec.

    EDIT:
    My initial measurements of VTEC exhaust valves were incorrect. Please see post #9 below. Turns out that VTEC valve seats are wearing at a higher rate than standard exhaust valves, same as the VTEC vs . non-VTEC intake valves.
     

    Attached Files:

    Last edited: Feb 1, 2022
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  2. Mr. Philadelphia

    Mr. Philadelphia New Member

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    Just to update my original post. I've included the final adjustment numbers. Although only 9 of the 16 valves were out of spec (red font), I adjusted 13 of them (green font). I had initially planned on going another size down on the intake VTEC lifters in order maximize time between adjustments but decided instead to stay on the lower range of the specs. to maximize valve lift & duration on these higher rpm valves. I'll probably open things up again at 100K miles anyway to see how things are trending.

    Specifications
    Intake: .20+/-.03
    Intake VTEC: .20+/-.08
    Exhaust: .35+/-.03
    Exhaust VTEC: .35+/-.08

    Cylinder---Intake----Intake V---Exhaust---Exhaust V
    -----1------- 0.178-----0.100-------0.270------0.350
    -----3--------0.150----0.100-------0.230-----0.350
    -----2--------0.180----0.100-------0.280-----0.320
    -----4--------0.178-----0.110-------0.270-----0.350

    Adjustment at 67K miles:
    Standard 7.48mm Shim Range: 1.600 - 1.925
    VTEC Ex. Buckets: 4x 2.93
    VTEC In. Buckets: 1x 2.93, 3x 2.86 (new)
    Old VTEC Buckets not used: 1x 2.93, 2x 3.00

    Cylinder---Intake---Intake V---Exhaust ---Exhaust V
    -------1 -----0.201----0.190-------0.354--------0.350
    -------3-----0.207----0.184-------0.356--------0.350
    -------2-----0.209----0.194-------0.355--------0.386
    -------4-----0.208----0.195-------0.349--------0.350
     
    Last edited: Jan 24, 2022
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  3. NorcalBoy

    NorcalBoy Member

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    Excellent. It is always interesting to see the results of these measurements, vs. mileage. It could provide a better take on what is possible, with respect to extending checks and adjustments.
     
  4. Mr. Philadelphia

    Mr. Philadelphia New Member

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    I have a friend with 111K miles on his '04. The clearances have never been adjusted, and you'd never know it by the butt dyno. What I wonder is at what clearances do you start burning exhaust valves. It was my only fear in waiting so long to check the valves.
     
  5. NorcalBoy

    NorcalBoy Member

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    That's hard to say, as a noticeable drop in engine performance is usually the first symptom, as the valve isn't closing completely. The only way to see what was really happening would be to pull the head and perform a visual inspection. Too loose and you start smashing the valve seat and the valve face itself.
     
  6. Mr. Philadelphia

    Mr. Philadelphia New Member

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  7. Mr. Philadelphia

    Mr. Philadelphia New Member

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    I'm not tuning a race engine or anything so that kind of testing isn't in the cards. In my experience, once you have perceptible performance loss, some physical damage had already been done, not always catastrophic but damage nonetheless. I'm always curious about the limits of any spec. Maybe I should volunteer to have a peek under the valve cover of my friend's '04 for curiosity's sake.
     
    Last edited: Jan 23, 2022
  8. NorcalBoy

    NorcalBoy Member

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    I agree 100%. It's all said and done by the time the engine performance drops off.
     
  9. Mr. Philadelphia

    Mr. Philadelphia New Member

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    Correction on Original Clearances:

    Cylinder---Intake----Intake V---Exhaust---Exhaust V
    -----1------- 0.178-----0.100-------0.270------0.240
    -----3--------0.150----0.100-------0.230-----0.210
    -----2--------0.180----0.100-------0.280-----0.190
    -----4--------0.178-----0.110-------0.270-----0.200

    All my VTEC valves were out of spec.

    They have only one spring holding them against the seat, whereas each of the standard valves employs two springs. The VTEC valve design coupled with the thicker (.35) and, therefore, stronger feeler gauges used to take exhaust valve measurements resulted in false readings because inserting the feeler gauge actually forced the valve open. As I was taking final measurements of the VTEC valve clearances, I could hear the valves snap close up against the seat as I pulled out the feeler gauge.

    This did not happen when I measured the VTEC intake valves because a .20 feeler gauge lacks the strength to force them open. The feeler just flexes and will not go in.

    As you can see, I had to adjust all the VTEC valve clearances: 7x new buckets ( 3x 2.86 & 4x 2.79) and reused a 2.93 bucket for #2 intake. Given the relatively uniform wear across all 16 valves, I would say that I have a relatively healthy top end with normal wear & tear. Other measurements I've seen online, particularly of the VTEC valve clearances, where some of the valves are way out while others are spot on would indicate an error in measurement due to the reasons stated above.

    Side note:
    I think Honda engineers use weaker springs on the VTEC valves in order to mitigate against seat wear caused by VTEC deactivation. Every time the slide pin disengages , the VTEC valve face snaps shut against the seat, which explains why rates of seat wear on all my VTEC valves were higher across the board even though they're not active below 6,100 rpm. The oil pressure circuit prevents the slide pin from retracting while the valve is fully open, but there's a last little bit of free travel as the valve stem pushes past the slide pin.

    So the lesson is to either ride at a leisurely pace or keep it on the boil between 7K rpm and redline and avoid hanging out between 6.5K and 7K rpm. Something I'm sure we all already do.
     
    Last edited: Feb 7, 2022
  10. zombie

    zombie New Member

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    Did you notice any difference after adjusting the valves? Mine just turned 100 KM and have been thinking about doing them too.
     
  11. Mr. Philadelphia

    Mr. Philadelphia New Member

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    Still snow on the ground here so I probably won't run it until March. It was running just fine last season before I put it away, and I don't think I'll notice much of a performance difference post adjustment. In any case, I'll update the thread at that point.

    Many BMW guys are keen on piling up the miles, and to their credit, are willing to wrench on their own bikes or to pay a shop to do it in order to keep them rolling, but I don't think most folks rack up the kind of miles to cause top end failure due to tight valves on these VFRs.
     
    Last edited: Feb 3, 2022
  12. Mr. Philadelphia

    Mr. Philadelphia New Member

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    Well, the buckets I needed are still not in US supply chain. I thought about having my local machine shop grind the old ones down but decided to order them from Europe, whence they arrived 2 weeks after placing the order. I also balanced the throttle bodies but changed nothing else from before the valve adjustment: Same air filter & plugs.

    There's a little more valve train noise at idle, which only confirms that an ominously quiet engine is in need of adjustment. I've put over 700 miles on the bike since the adjustment and finally had a chance today to rip it through some familiar twisties: Perceptibly more power across the RPM range, more noticeable after VTEC activation and especially noticeable at peak torque above 8K RPM. The added performance is also noticeable during 6th gear roll-ons making it to the top of 6th gear earlier than before.

    It's hard to confirm anything for sure with the ol' butt dyno so I really wanted to test things out on a section of road I like to run wide open in order to confirm my impressions. It's a straight followed by a 15mph corner that I like to take at 8 tenths, normally with a terminal velocity of no more than 100 mph before the braking zone. I was taking it easy today because the roads remained wet from an early morning rain, braking earlier than normal, but I still topped out at 107 mph. Under better road conditions, I imagine I'd hit 110 mph for a 10% increase in terminal velocity after the valve adjustment . I'll attach a link to a short video of a run through this stretch of road pre-adjustment -- I have my speedometer set to km/hr so 160 km/hr=100 mph.

    https://vimeo.com/manage/videos/700099800
     
    Last edited: Apr 18, 2022
  13. Vulcanator

    Vulcanator New Member

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    Good job on doing the valve adjustment. It seems a conventional wisdom to put off doing valve inspections, but as your bike proved you had to change a few buckets and shims. I had a tight normal and VTEC valve on my 2014 VFR, and I'm glad I did the inspection at the scheduled mileage.
     
  14. Mr. Philadelphia

    Mr. Philadelphia New Member

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    I think for most folks later or never is fine . These engines don't seem to fail catastrophically, but I've got plans for this one, provided my body doesn't break down, I'm going to put 200K miles on this thing. In any case, I was surprised by the performance gain, which wouldn't have been noticeable had I not waited so long to pop off the valve covers.

    Side note: I have my '96 apart waiting for a rear shock from DMr and a few other odds & ends and decided to pull the valve covers off at 25K miles: The rear cylinders were spot on at the middle of the spec.; All 8 valves on cylinders #2 & #4 were within spec. but 6 were at the bottom of the range so I brought them back to the middle of the spec. The interesting thing, however, is that 7/8 valves originally had a 2.05 shim with the odd one having a 2.025. That's some serious manufacturing precision. No wonder builders of performance motorcycle engines in Europe order their valve train components from Japan.
     
    Last edited: Jul 22, 2022
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