Topic: Tappet Clearances

[M 750K6]

I think also known as 'valve lash'?

750K6. When I re-did my top end I reset the tappets while on the engine stand. Once complete and all running, I had some tapping from the valves. All in spec. However, 2 appeared fine, a nice sliding feel when I put the guages in, but I was able to lift the tappets a fraction with my fingers and tap them onto the feeler guage. I adjusted this out, tested the feeler guage a couple more times, removing the guage and sliding it back in, to be happy it was still a nice sliding fit. Some grip, but not tight on the guage. The bike now runs without any rhythmic tapping. And runs nicely.

However, this has been gnawing on my conscience! Is this normal and was I right to adjust out this additional movement?

What happens as they wear. Do they tighten or loosen?

Thanks, Martin

[69cb750]

However, this has been gnawing on my conscience! Is this normal and was I right to adjust out this additional movement?

There should be some friction with the feeler gauge, not super tight, not very loose.

What happens as they wear. Do they tighten or loosen?

The valves and seats wear reducing clearance over time, thousands of miles.

[bryanj]

Did you check if the top of the valve stem was flat? They can "dish" in which make using a feeler impossible

[M 750K6]

Bryan,
I didn't check. So that's a risk.

I did check the other end, to make sure the guides were good, and checked the seal after a gentle lapping. (+ New stem seals etc.) But, didn't think to check the tops.

Since readjusting, I've done about 1200 miles. I do have goòd plug colour on the two cylinders the tappet clearances were previously too big. It runs well, pulling evenly and willingly throughout the revs. So, I was puzzled over why the two tappets initially appeared correct, but I was able to lift them further with my finger tips and adjust again, whereupon they were good on the feeler guages again. I was wondering where that play might come from and why these two tappet weren't automatically in the most open position.

I did scrupulously clean the cam tower and carefully torqued everything down to spec. I did have assembly lube on the cam lobes at the point I set the tappets on the bench. I thought that might possibly explain why they were out of adjustment, but not why I was able to manually lift them when I subsequently readjusted those two, after about an initial 80 miles. It wasn't much movement. very little. But enough to be able to feel a light tap against the feeler guage, whilst the feeler guage had felt a nice smooth sliding grip when I first inserted it.

[bryanj]

I will probably upset the purists here but when i was a full time tech on Hondas it was quite common to not use gauges and do the clearance simply by "feel"
When you are sevicing several bikes a day you get to know that you can just about feel the gap on 2 thou and if it makes a slight "tick" its more like 4 thou.
The other thing is the adjuster bolt turns 1 turn for 1mm so 1/8 turn for 5 thou, you can get adjusting tools where there is a knurled knob with calibrations on a shaft to turn adjuster that goes through a hollow socket with handle for the locknut.

Now I DO NOT RECOMMEND ANYBODY TRYING MY METHOD without having a lot of workshop experience OR on a tuned, high reving, motor

[MauiK3]

I go for slight drag feel.
When my K3 750 is right, when I'm riding I open the visor and look down, the sound is scooped up and it sounds like a waterfall, nice even sound. I love it.

[Deltarider]

I go for slight drag feel.
[...]

Yep, like if you slide it along a magnet.

[M 750K6]

That's what I look for. I was just surprised I got that, but was then still able to move those 2 tappets and then adjust those 2 further.

I guess nothing to worry about?

[HondaMan]

The guy who taught me to 'feel' in the tappet drag (it was on my old SuperHawk) was adamant about it: his exact quote was:
"It should feel like a new bride while pulling it and snugging the screw."

...hard to forget that one...
...I wasn't married yet then, either...

[MauiK3]

Pretty accurate (if bawdy:-) description

[rotortiller]

Unless she was ridden hard and put away wet before the ring job.

[Don R]

It will change a tiny bit as you tighten the nut, I think they usually tighten as the valve sinks into the seat but it is possible the rocker assembly can loosen with wear also.

[PeWe]

Honda clearances are very tight.
In  0.05mm
Ex 0.08

I use 0.10mm on both sides to avoid mistake making a valve not closing enough.

Tuned engine with a hotter cam gets more lash.

[Bodi]

It takes experience, basically. Tightening the locknut pulls the adjuster up a tiny bit and can drag it and turn it tighter as well. I adjust for a pretty strong drag, hold the adjuster back so the nut doesn't turn it (with a little driver with a square hole tip that fits the adjuster that I got somewhere 40 or more years ago) and tighten the nut securely. Recheck and it's a snug but lessened drag on the feeler.

[bryanj]

Bodi, dont forget some adjusters have a square tip others a screwdriver slot

[newday777]

Bodi, dont forget some adjusters have a square tip others a screwdriver slot

restoration?
I don't remember hearing of there being a square tip adjuster screw. What uses the square tip?

[bryanj]

I think the 400 has a square

[RAFster122s]

Cx500, gl500, gl650, cx650 use square adjuster head on valve's rocker arm.

[Don R]

 I think motion pro makes adjusting tools for the square tips, and several sizes. I think I used an old set of forceps.

[Deltarider]

Honda clearances are very tight.
In  0.05mm
Ex 0.08

I use 0.10mm on both sides to avoid mistake making a valve not closing enough.

[...]

Good policy, especially for the exhaust valves.

[M 750K6]

Honda clearances are very tight.
In  0.05mm
Ex 0.08

I use 0.10mm on both sides to avoid mistake making a valve not closing enough.

Tuned engine with a hotter cam gets more lash.

Do you not get tapping at 0.10mm?

[PeWe]

Honda clearances are very tight.
In  0.05mm
Ex 0.08

I use 0.10mm on both sides to avoid mistake making a valve not closing enough.

Tuned engine with a hotter cam gets more lash.

Do you not get tapping at 0.10mm?

No, 0.10mm is tight enough.

My K6 has had 0.10/0.15mm since 1984

0.30/0.30mm with DP315 cam during a season or 2.
Less lash, less power on that cam.

[MauiK3]

I can be fiddly getting them right

[HondaMan]

Honda clearances are very tight.
In  0.05mm
Ex 0.08

I use 0.10mm on both sides to avoid mistake making a valve not closing enough.

Tuned engine with a hotter cam gets more lash.

Do you not get tapping at 0.10mm?

No, 0.10mm is tight enough.

My K6 has had 0.10/0.15mm since 1984

0.30/0.30mm with DP315 cam during a season or 2.
Less lash, less power on that cam.

You bring up a good point, Per: I've more than once "fixed" an ailing 750 with an aftermarket cam by changing the valve clearances larger. Honda really liked the close tolerances for quiet, but in all of my own bikes I have always increased it for hiway riding, in particular, with good results. If I'm heading out on a long trip (haven't lately, but did many before) I set the intakes at 0.003" and the exhausts at 0.004", adding 0.001" to Honda's spec for both, with the stock (K2) cam. I did this for racing, too (sometimes even 0.004" on the intakes and the exhausts), and it seemed to help when the engines were held at high RPM for long periods of time. They ran cooler and made more power for longer time at the high engine speeds. From behind my Vetter fairing (all of these 52 years later) I can say the engine isn't as quiet when cold, but when heated up it quiets back down and 'settles in' to the long stretches of 4k-6k RPM much happier and smoother. When I've had the clearances at the 0.002" and 0.003" and took a long trip with it (more than 150 miles at freeway speeds) it gets less gas mileage, has a slight 'flat spot' at about 4200-4500 RPM, and is a little harder to start after it cools down (like for lunch). It also tends then to not idle very well for a while when pulling off of the freeway for fuel stops, etc.

[Dime]

This is great info. Thank you