Slacking valve

[Ken13559]

I was gapping my 2GM20F valves and notice gap for cylinder #1 exhaust (nearest to gearbox side) changes whenever I jiggle the pushrod. There's slight play in the pushrod. Also its rocker arm can slide along the rocker arm shaft slightly like 0.5mm. Are these normal? Cylinder #1 Intake valve gap is good and pushrod doesn't play when I jiggle it and rocker arm has a spring to load it so it won't slide.
Turning the crankshaft 180* for #2 cylinder, the exhaust pushrod moves only very slightly when jiggle.
Engine runs normally as best as I could tell although I suspect its not developing full power as expected. Just a suspect.
So do I have a problem with my valve and pushrod? Could problem be bad/wore Valve Screw?

 

[Ken13559]

Well nobody has any idea I suppose since I've got no reply. Ok, I've looked at an engine top head overhaul work on youtube and it seems the jiggling pushrod is normal. So what I'll probably do is slide the rocker arm by removing the C clip and check and change the tappet adjusting screw, lock nut and maybe the pushrod if it has uneven wear at contact end with adjusting screw.
Any comments, suggestions or .....? Thanks in advance.

 

[woodster]

ken it's sort of hard to answer that question without being there ...is the rocker arm dead center with the push rod.... have you removed the push rod and checked it to see if it is straight and true ...also make very sure you have the stroke on that valve with the push rod on the down side of the stroke you may have to rotate the engine by hand with fuel shut off at the injector pump a couple of times to be sure ...you can check for straightness by laying the push rod on a flat surface and rolling it...if it rolls smooth it is good...hope this helps

 

[Bill Roosa]

first things first: the # 1 cylinder is probably not on the tranny side of things. That would be a singular departure from standard cylinder numbering. the "front" of the engine is where you would find the #1 cylinder
This may be most of the problem as when you are adjusting the valves you want the cylinder being adjusted to be at TDC of the compression/power stroke. If one push rod is really loose and his partner is not then you probably don't have the piston at TDC of the compression/power stroke.
You can tell by watching the valves as you turn the engine, intake opens, 180 crank degrees, BDC, compression begins, 180 degrees (no valve movement) of compression stroke, TDC (you want this one), 180 more degrees with no valve movement (power stroke), exhaust begins to open and .........
So rotate the engine in the normal direction till the intake valve begins to open. Go one complete crank revolution and align the TDC marks on the crank and that cylinder is ready for valve tappet adjustment.

 

[Ken13559]

Bill, I've checked the service manual, #1 cylinder is tranny side. When at TDC, both intake and exhaust tappet were "loose" so can be gap. I'll take the pushrod out to check for trueness like how you describe.
Thanks for the advise on how to check. Appreciated

 

[Benny17441]

In some engines built in baffles in the inside of the valve cover is what limits lateral movement of the rocker arms. If you are not experiencing a problem with the engine or excessive valve lash chatter I would leave it alone. I would say what you are looking at is not uncommon and usually inconsequential to the useful life of the engine.

 

[kloudie1]

I agree that pushrod should have a little looseness to it ; same clearance as the lash setting when ya hold the rocker tight on the valve.. Doesn't sound like a problem but do check the pushrod for trueness .. The only other thing to check (besides thee adjuster screw bearing surfaces) is that little "button" on top of the valve right above the keepers. That button is what the rocker arm bears on when it pushes the valve open.. the button (valve top retainer) is part # 104211-11370 or referenced as #11 in the part diagrams.

 

[woodster]

if i had to guess i would say the same amount as the feeler gauge thickness when adjusted properly only on the relaxed rocker arm

 

[Ken13559]

I did gap the tappet to rocker arm clearance to 0.2mm. But when jiggle the rocker arm, the gap increases even with the nut already tighten. What i did not do is turn the pushrod with fingers after tightening to see if that will change the valve gap clearance. Is it possible there's uneven wear between the screw captive portion and the pushrod end? Also the adjusting screw thread wasn't smooth to turn. There might be some bad threads as well.

 

[woodster]

if your threads are bad you may have to replace that rocker arm if it will not clean up with a tap

 

[Ken13559]

if your threads are bad you may have to replace that rocker arm if it will not clean up with a tap

Thanks Woodster. Didn't occur to me that the rocker thread could be bad. Noted.

 

[Dan_Y]

The mechanic who adjusted the valves on my 2gm20f said they are difficult to get perfect because they "move" after one is set and the crankshaft moved to get the next cylinder's valves closed for adjustment. I can't recall the exact mechanism for the change... rats. I'll post his response if I see him again this season. He said that he goes through the check and adjust process a few times to get it right, ie set them, then start over and check again...2 or 3 times. He seem to imply this was normal and didn't
try to sell me new rocker arms, etc. My engine is a 1991.

 

[Ken13559]

The mechanic who adjusted the valves on my 2gm20f said they are difficult to get perfect because they "move" after one is set and the crankshaft moved to get the next cylinder's valves closed for adjustment. I can't recall the exact mechanism for the change... rats. I'll post his response if I see him again this season. He said that he goes through the check and adjust process a few times to get it right, ie set them, then start over and check again...2 or 3 times. He seem to imply this was normal and didn't
try to sell me new rocker arms, etc. My engine is a 1991.

i ordered a new rocket arm and pushrod, eta 3-4 months! Will remove the rocker to check threads, screw, nut and pushrod hopefully next weekend to size up problem.
Ok perhaps i should redo the gap couple of time since your mechanic mentioned. Thanks for info
Oh surprising outcome, just yesterday i took boat out after giving it a very good warmup like after couple minutes at idle, then race engine to 3900rpm max for a fraction just to "stretch the arm", then left in reverse gear at dock for about 15mins @1500rpm. When motoring i cannot achieve 3500rpm max! Im still wondering do i have problem with the said valve??

 

[woodster]

i don't think your valve is your problem i would be looking at the prop for correct size and pitch i am assuming your engine ran smooth as it can ...i am also having a hard time with 3 months for the part especially scene you are in the far east ...go on line and look up hoyt or Hoyle tractor parts in Texas and look under the engine model 1450 or some thing like that and see if you can get the rocker arm from them Kloudie may be able to confirm the tractor engine model...... but before you changing props make damn sure your rocker arm is in good repair or you could do more damage than you want to bargen for

 

[Ken13559]

Woodster, doubt ive prop problem. My problem is with the cylinder #1 exhaust valve gap changes each time i jiggle after gapping. Its rather weird behavour for a valve gap.

 

[woodster]

how could you run that engine up to 3900 rpm with a bad exhaust rocker arm and push rod....if it wont stay set it would effect the rpms and limit the rpms....i am missing something here

 

[Ken13559]

Hahahaaa Woodster, thats a good one! Yes indeed if the rocker is problem, engine shouldn't be able to spin 3900rpm. Still I'm baffled by what I saw. I'll check it again this weekend.

 

[woodster]

pull the adjusting bolt all the way out and check the threads in the rocker and the bolt ..also check the the lock nut as well i am trying to find a pic of the rocker set up so i can see if there is a spring missing in the rocker shaft that is letting the rocker arm slide back and fourth

 

[woodster]

i can't get the pic from my file on this engine to post .....but there is a thrust washer on each side of the rocker arms to keep it spaced properly and from what i see in the manual there is only one spring on the rocker shaft in the middle of the rocker arm to keep the two middle ones separated...make sure you have all the thrust washers on the shaft there should be one on each side of the rocker

 

[Ken13559]

Woodster, the nut can be removed easily but not the screw as it has a bell shaped bottom to locate the pushrod. Ill check for thrust washers.