valve float, shimming springs? (1 Viewer)

[stumpy]

hey guys-

i notice i get some valve float when i am under full load going uphill. with the standard 8/14 valve adjustment, it is still present when the pedal is to the metal. it is an '86 motor in front of a toy 5 speed in my '40.

anyone have any tricks for reducing float? different valve adjustments? is it possible to 'shim' the springs to get a tighter seal? the motor has 41K miles on the rebuild, and i am sure it is still nice and tight. i built a 3FE head with chev valves and springs partly to eliminate float, but i dont really want to go through the expense on the 2F head when it otherwise runs fantastic...

any tips?

TIA

 

[2badfjs]

new springs.

 

[soggy60]

I'm learning: What are the symptoms of 'valve float' ?
(I understand 'what it is', but not 'how it feels')

Thanks

 

[stumpy]

i put new springs in it when i rebuilt it 40K ago. can they break down that fast?


the only way i know to peg valve float is to get a vacuum gauge. you can see the needle flutter when the valves are floating. i would guess the symptom of such is a general loss of power, something that would be pretty hard to peg on valve float in an underpowered land cruiser.

 

[Mace]

And what RPM are you experiencing valve float???

40 K is silly to expect the valve springs to die. I hit mine a 5K without floating with over 150K on a motor..

 

[stumpy]

well, it seems to crop up mostly above 2500. probably most noticably above 3000. always under hard load, and worse when cold. it still runs strong, but if i can eliminate float, might as well...

 

[Mace]

Just trying to figure out why you think it is valve float. load shoudl not have anything to do with valve float from what I remember.

You sure it is not pre detonation? or poor mixture?

 

[stumpy]

well, i guess it could be a thousand things. but, the reason i believe it is valve float is that it happens under heavy load, it shows up on the vacuum gauge as a ~2 in-hg float, and it quits when i back off the gas. everything i have seen says those are typical valve float symptoms. i run premium gas because my compression is higher and at 7000 feet above sea level, 12 degrees BTDC is my timing mark. i do tend to run lean though, as my mixture gauge suggests. would that affect valve performance? getting preignition under heavy load? any other ideas?

 

[Mace]

I used to tell when the valves were floating on my old VW by the CLOUD of unburnt gas that would exit the tailpipe and the motor would suddenly lose all power and I mean all power.

Course that was at 6400 rpm. Good limiter IMHO


Your vac gauge should read almost if not Zero when you are on the gas. No fluttering available when there is no vac..

Heavy load at altitude, sounds like pre ignition to me. 12 deg is probably a bit high on timing.

What does the motor sound like when the issue happens..

 

[grant5127]

Misfire will be noticed in a valve float situation... caused by valve springs or push rod flex in solid cam follower applications.....

 

[FJ40Jim]

well, it seems to crop up mostly above 2500. probably most noticably above 3000. always under hard load, and worse when cold. it still runs strong, but if i can eliminate float, might as well...

Valves don't float under load. Valve spring load is throttle position insensitive.

If valves are floating at 2500RPM, there is something very wrong.

It's not valve float. not w/ a cam that has .385 lift!

 

[Mark W]

Jim beat me to it.

You are not dealing wiuth valve float. Load has nothing to do with valve float. RPM only. You don't get valve float at 2500-300 rpm. With 441+ of valve lift I turn 4500 every single day and have never had valve float at that rpm. Multiple motors. Stock springs.


Mark...

 

[Pighead]

Put in a tank of the highest octane fuel that you can afford, see if you still have the problem. Worked for me.

 

[stumpy]

ok, i will buy the non-float opinions, that low an RPM to have valve issues doesnt seem right. but why the vacuum gauge flutter?

would preignition cause such a gauge response? an inch of flutter? i already run 91 octane because of the compression, i would guess the gas can be the issue.

it runs smooth and strong all the way up to 4000 RPM if i want it to. power is solid through the RPMs. vacuum at idle at 4500 feet is 18.5-19 inches, 7000 feet is 17 inches. my interest in this issue really lies in understanding how to tune my engine better and keep it running its best. the float idea is what i concluded after discussing the gauge readings with a machine shop and 'mudders.

can a lean condition cause such a flutter under load? the gauge flutter goes away as i change throttle position too... more gas pegs the gauge at 0 inches, less gas makes the flutter go away. i have a mixture gauge that consistently reads "past" lean while at highway speeds. i am completely de-smogged and ~9:1 compression, using a saudi-spec asian carb that is also smog free on an '86 2F block. need to jet up? carburetor was new-in-box ~20K miles ago and i havent touched it.


thanks for the discussion

 

[FJ40Jim]

Does it read lean or rich under cruise?

Does it read rich at WOT?

 

[stumpy]

generally speaking, it is lean under cruise. it runs lean most of the time above ~2000 RPM.

WOT, i can see it go toward rich with accel pump squirt, but as i hold, it slowly ticks back to lean.

need larger jets?

 

[alkaline747trio]

This is definately pre-ign. and not float. Try cleaning the carb a little bit just to make sure there isnt any gunk holding your fuel back, you could also (maybe, I'm no LC carb expert) richen up your overall mixture a little to get you from running past your lean mark.

 

[stumpy]

carb is CLEAN. not sure what places i might find gunk. you can see that nice yellow zinc coating through the barrels. the only mixture screw i know to adjust wont help with cruising speeds - idle screw on the engine side of the carb.

 

[alkaline747trio]

If it's like an MGB's carb, there should be a high, mid, and low speed needle for adjustment...but that is the only carb I know how to **** with.

 

[Tinker]

You could have an intake leak causing the lean condition. Try spraying carb cleaner around the intake manifold mating surfaces & see if the idle picks up. If so, your manifold is leaking.

Don't know about a desmog, but the HAC was designed to lean out the carb for high altitudes & it works at 6,200' where I get my stocker smog-tested.