Author Topic: Valve Adjustment...when? (Read 1219 times)

jazzphil · « **on:** February 07, 2023, 12:54:10 PM »

New to the world of Jazz and very confused about when/if valves need adjustment. The Honda service book says not at all (for the Jazz engine), the owners handbook says 62,500 miles in one place and 25,000 miles in another, while people on this and other forums say they haven't bothered for over 100,000 miles and all is well.

It's easy to tell if the gaps are too large (top end rattle) but if the gaps are too tight, how does one know? Coming from the world of hydraulic valve lifters it would at least be good to know when one is supposed to carry out adjustment...

Any thoughts?

Jocko · « **Reply #1 on:** February 07, 2023, 02:56:09 PM »

Different engine, but my Mk 1 manual said to check every 25,000 miles. When I scrapped the car (for rust) at 150,000 miles, they had never been checked.
The link for the GE8 varies between regions from 25.000 to 62,500, so not a lot of help.

http://www.hondafitjazz.com/manual3/index.html

madasafish · « **Reply #2 on:** February 08, 2023, 07:43:12 AM »

Mine never touched in 52k miles.
Noiseless.
I expect OK at 100k

Westy36 · « **Reply #3 on:** February 08, 2023, 09:53:10 PM »

Mine came with Honda stamps upto 80k ish. Hoping it's been done. If it hasn't, for 118k engine, my motor sounds sweet as a nut and unless it starts making a rattle or running weirdly, I don't ever expect to check the clearances.

I also run a Honda CBF1000 motorbike. Honda want the valves checking very regularly. Folk have done 100k plus before checking, and they are still within tolerance. I think Honda are a bit over/uber-cautious with their valve checking. If it were the VW group or BMW, bet your bottom dollar they would never want it checking!

As long as problems happen outside of warranty they don't give a fig!!!

fatal · « **Reply #4 on:** February 27, 2023, 11:42:33 PM »

I read somewhere that if the valve gaps are too big (loose) it's likely the engine will sound a bit rattly. If the gaps reduce you may notice a reluctance to start, especially when hot.

jazzphil · « **Reply #5 on:** February 28, 2023, 09:22:36 AM »

Thanks for the comments guys. Seems I don't need to be in a rush to check the valves! The reason most cars don't call for valve clearance checks is of course because modern cars generally have hydraulic valve lifters that never need adjusting. Honda engines are unusual these days in having adjustable valves.

embee · « **Reply #6 on:** March 01, 2023, 11:17:00 AM »

Just for interest, many engines of recent times have used roller finger followers with hydraulic pedestals. There are three principal reasons for this arrangement. First the consistent valve event control is very useful for emission control with the ever tighter regulations, second it is a convenient way to introduce a roller follower (the cam lobe operates a roller rather than sliding on a solid surface) which substantially reduces frictional losses especially at lower speeds, and hence fuel efficiency, and third it is essentially maintenance free and reliable.

One other comment regarding clearances/noise. Cam profiles have a "ramp" at each end (opening and closing) which is usually of what is known as a "constant velocity" design, the velocity being defined as lift per degree of rotation, cam profile data is related back to angle round the cam so actual engine speed has to be considered to get true velocity in absolute terms.
Depending on the design (rocker/finger/direct bucket/pushrod etc) the ramp height will allow for a working clearance to avoid it going tight and keeping the valve partially open and allowing for thermal expansion. This also means that providing the clearance is taken up while still on the ramp, the actual impact ("jerk") which causes the noise remains essentially the same regardless of what the clearance is set at. The ramp rates are empirically set as a compromise between length of ramp and thus uncertainty of when it actually starts to open, the impacts and hence noise and wear especially when the valve is seating.
Hydraulic elements used in valve lash adjustment actually operate with a certain amount of compliance, some slight compression occurs as they are loaded up when the valve starts to lift, so a ramp is still required to accommodate this. There is also a small amount of "leakdown" during the lift so the closing ramp is invariably slightly higher than the opening side.
https://www.tildentechnologies.com/Cams/CamDesign.html
Over the years I've done quite a bit of valve train development on a variety of engine types during my career. The instrumentation side of this is quite challenging sometimes but very satisfying when it works.