Topic: Grinding stem on valves question 78 750 F3

[754]

 I put in a rebuilt F3 motor in my 750.
 Not sure what was replaced or not, but it was very clean with assembly lube under valve cover and no carbon inbthe ports.
 So 2500 miles mostly hiway, and I have adjusted valves  several times.
It seems noisy, was very  quiet at first.

 So I have a theory.  I was told by an engine shop you can take  a lick off the stem, not a lot, hard portion is thin.
But I don't know if valves were ground or replaced

 So I have to wonder, if I am maybe having a lot if stem  wear. I pulled one adjuster and nut out  stem appeared to be pocked. End of adjuster had lines on it, radially.. like a sort of star look.
 Anyone seen a lot of stem wear on reused valves  or re ground valves..?

 I just hope I did not bugger yet another cam .  Every time I adjust  each valve looks wet. Don't think it's low on oil supply.

[kmb69]

Frank, If you see boogers on the valve stems, they're toast.
You might be able to grind them flat and use some stem caps.
I would be suspect of the adjuster screws as well.
Mike might be able to point you to some stem caps.

[scottly]

Valve grinding machines have a fixture on one end for facing off the ends of the stems, but that would require disassembly of the head, which I doubt you want to do.
I've seen those radial lines on the ends of the adjuster screws; they get formed as the end of the adjuster sweeps across the stem, forming a "flat". When you re-adjust the valves, it puts the worn edge into contact with the stem, and the narrow contact area wears quickly, and so on until the adjuster gets to a less worn area.
If the worn areas on the end of the valve stems are deep enough, you won't get a good clearance check with feeler gauges, as the gauge will bridge the pocket in the stem. If lash caps can be fitted, that will solve that issue. You could also set valve clearance with a dial indicator.   

[754]

Scott ain't much there to grind m you get one go I think  if it's very much depth it's into  softer metal..
 It runs fine,  aside from poor mileage and a bit of valve noise m it's fine for now.

[scottly]

Scott ain't much there to grind

That's where the lash caps come in. As far as mileage, the last time my bike only got 40ish MPG was bucking a 45 MPH headwind for 100 miles. Not sure where you should look, but if the plugs aren't sooted up I would suspect retarded ignition timing?

[PeWe]

My K6 head had F2 inlet valves. They mushroomed really quick. Adjuster screw carved a dimple in the tops. Last set were a little bit grinded for good surface, lash caps from Mike. I thought that the lower valve got dimple easier due to the different angle of adj screw that is rather flat.

I had to grind the sides to get out the valves thru the guides. Valve on photo had not been used for long.
Are these Honda valves of a softer material?

[scottly]

Per, the greatest wear is well off center of the valve stem, (and that is some considerable wear!) which indicates improper valve/adjuster geometry. IIRC, the F2 valves have shorter stems, which, when installed in an earlier head, would require the adjuster screws to be threaded further down into the rockers, shifting the contact point away from the center of the stems.

[seanbarney41]

My f3 had pitted valve stem tips which would chew through a fair amount of tappet adjusters.  I just dealt with it as best I could.  I got about 10,000 miles out of it before the valve guides were consuming excessive oil at about 28,000 miles.

[PeWe]

Per, the greatest wear is well off center of the valve stem, (and that is some considerable wear!) which indicates improper valve/adjuster geometry. IIRC, the F2 valves have shorter stems, which, when installed in an earlier head, would require the adjuster screws to be threaded further down into the rockers, shifting the contact point away from the center of the stems.

Yes, that what I noticed. Lash caps prolonged the stems a little.

[kmb69]

Per, the greatest wear is well off center of the valve stem, (and that is some considerable wear!) which indicates improper valve/adjuster geometry. IIRC, the F2 valves have shorter stems, which, when installed in an earlier head, would require the adjuster screws to be threaded further down into the rockers, shifting the contact point away from the center of the stems.

That is correct. They shortened the stems on the F2 & F3 because they sank the valves deeper in the combustion chamber.

[Old Scrambler]

I measured the F2-3 chamber roof to be 1mm taller than the K models and correspondingly the valve-stems are 1mm shorter. I have 4 F2 motors and all have dimpled stems. The valve angle is the same when all parts are new.

Frank, if you get some lash-caps, be sure to use fresh adjusters to avoid rocker contact.

[simon#42]

i have 5mm stem valves in mine with lash caps , they have been in for about 35 thousand miles and are still ok , they have some wear but are still fine . the beauty of them is you can easily change them when they are worn out

[PeWe]

I measured the F2-3 chamber roof to be 1mm taller than the K models and correspondingly the valve-stems are 1mm shorter. I have 4 F2 motors and all have dimpled stems. The valve angle is the same when all parts are new.

Frank, if you get some lash-caps, be sure to use fresh adjusters to avoid rocker contact.

Finally got it confirmed what I first saw in the middle of the 80's! F2 stems really soft.
I thought the local shop had made a mistakes with the valve stems. Understood later that stems must be softer.

If using lash caps, stem must be shortened with same lenght as cap is thick for the correct geometry if correct from the beginning.

[seanbarney41]

I was always under the impression that these problems were the result of Honda not getting the geometry right in the first place.

[BPellerine]

at one time I was going to put an f3 top end on a k motor to get the bigger valves and better breathing,untill I read about all the issues with them,cancelled that idea.bill

[kmb69]

I was always under the impression that these problems were the result of Honda not getting the geometry right in the first place.

You are 100% correct.

[seanbarney41]

I was always under the impression that these problems were the result of Honda not getting the geometry right in the first place.

You are 100% correct.

and that new valves and guides from a supplier that is aware of the correction necessary, such as APE, solves the problem once and for all

[kmb69]

I was always under the impression that these problems were the result of Honda not getting the geometry right in the first place.

You are 100% correct.

and that new valves and guides from a supplier that is aware of the correction necessary, such as APE, solves the problem once and for all

Doesn't solve the geometry problem but they use materials that solve the wear problems associated with the bad rocker geometry.
Honda fudged on the rocker geometry to keep the engine as short as possible. Pretty much got away with it until the F2-F3.

[bwaller]

I've measured valve angles, and as Dennis mentioned, that didn't change in any of the 750 heads including the later F's.

I'm not sure why duplicating earlier stem height with better valves/guides wouldn't return reliability??

I still don't care for bigger chambers & the needed huge domes to match.

[MRieck]

 A lot of good points here. Personally I like lash caps as you can easily replace them. All the 5mm conversion kits use them and Brent runs them on his race bike. I have 6.5mm caps on hand if anybody needs them. The stems need to be ground -.040. The tip also need to be flat and perpendicular to the stem.....you can't get in there with a Dremel and expect them to work.

[754]

 If my valve stems were ground and are now soft, then I expect it to continue to wear.  And I may not be able to run lash caps, unless I tear head down.
 Then I would need a length measurement to know how far to grind them.
I suspect if they ground them,  they took around 15 to 20 thou off.
 if I were to try to install caps without removing valve I would mask it off and stone them to knock off any burrs..

[simon#42]

if you did decide to install caps without removing the valve it would be a mistake .

[MRieck]

if you did decide to install caps without removing the valve it would be a mistake .

Yes....I have personally seen that AND the lash cap quality was blamed (which was total BS). The cap will tiddly wink around and all sorts of bad stuff starts to happen.

[gschuld]

if you did decide to install caps without removing the valve it would be a mistake .

Yes....I have personally seen that AND the lash cap quality was blamed (which was total BS). The cap will tiddly wink around and all sorts of bad stuff starts to happen.

Mike,

Is “tiddly wink around” a technical term?🤔.  😁

George

[MRieck]

if you did decide to install caps without removing the valve it would be a mistake .

Yes....I have personally seen that AND the lash cap quality was blamed (which was total BS). The cap will tiddly wink around and all sorts of bad stuff starts to happen.

Mike,

Is “tiddly wink around” a technical term?🤔.  😁

George

Pics to follow....you'll see.