John Deere A Making Noise/KNOCK A LONG POST SORRY

Ok have recetly overhauled my 46 A after starting it had developed a noise/ knock here is what I have done so far bought later model A gas aluminum pistons, milled head .125, bought later model A/60 rods with insert bearings, had mains and rods turned. had to put some shims under nuts on head studs because of milling, rocker arms had just enough adjustment. not a heavy knock but a noise not sure u could even hear it with a straight pipe. noise is more at idle seems to go away at high speed, can hear when loading engine
I have tore it back down and rechecked everything I can think of. re plastigauged rods, mains checked endplay, flywheel is tight, clutch driver is tight ,running 92 octane adjusted timing what little there is, rods not hitting top of crankcase. wristpins tight. I can short out left cyl and it goes away when I adjusted carb it changed noise too listened with stethoscope and hard to pinpoint where it is coming from u can hear noise pretty much anywhere on the tractor mains are quiet noise isn't a double clunk like a rod or wristpin, had another mechanic listen he didn't know either I have run 5 gals of fuel through it and it hasn't changed, I have more ring gap (top and bottom) in ring land now than when i started. I know the cylinder isn't worn as much at top than at bottom because old pistons didn't come up at far but not it was smooth no ridge, Could the ring knock in ringland gap looks the same on both cylinders. it made like 115 cranking psi so I don't think it spark knock but im going to get some 100 octane to try. ANY IDEAS???????
 
I think you just answered your question . Head has been milled before or the guy that milled it went to sleep .The head studs suddenly got too long .You have way too much compression .Also it could be the ring ridge , wear is on top . Had an old 1952 G do that , 100 Octane didn't do any good . Finally beat the rod bearings flat , blow'ed head gasket . It had the old flat head with high altitude pistons .
 
(quoted from post at 16:26:17 03/19/18) I think you just answered your question . Head has been milled before or the guy that milled it went to sleep .The head studs suddenly got too long .You have way too much compression .Also it could be the ring ridge , wear is on top . Had an old 1952 G do that , 100 Octane didn't do any good . Finally beat the rod bearings flat , blow'ed head gasket . It had the old flat head with high altitude pistons .

the head is the all fuel head and we measured it before we milled it and it showed original thickness before milling still has a lot of combustion chamber like 3/4 to an inch far from a flat head. it could be spark knock but I don't know my buddy has one that he has to open blow downs to start it and it sounds a lot meaner than mine . im gonna try 100 and see thanks I am open to try anything
 
what all did yours have done to it- did you ever do a compression test on it what was it running. I was hoping for a little more power but wanted to still use also thanks
 

Details are not clear about the cylinder condition..

IF there was (is) any ring wear at the top and a New piston/ ring is installed, ya just cannot do that..

Those cylinders should have been Power-Honed to erase the existing wear area..otherwise, the new rings are not going to last a week of running..

The cylinders will be at Factory spec size, above the top ring-land..BUT worn most at the top ring location (worn area) and will be less and less as you measure deeper down into the bore..
 

Had re rung it in December 16 pulled cylinder had it honed at my machine shop. pulled the tractor probably 10 times tore it down this Dec 2017 bought pistons and just now getting it back together there wasn't a ridge a little carbon buildup but it cleaned Up but yes I'm sure there was some taper
 
I agree w earlier posts in that detonation is likely the issue. Fixed a '49 w same issue (different head/block) by installing an aftermarket water pump and using a water surfectant. Was a puller w a .130 mill job. The thermosiphon system only cools once block/head temps get hot enough to encourage flow, which creates hot spots in cylinder head. Hot spots create detonation under hi compression. The '39-'47 head (and, later ones, too) get warm around the valve ports. Although seeming somewhat counterproductive, knock the static ignition timing back a little (5 deg) as will warm the head more evenly. Exhaust temp will be a little higher but combustion cyl temps will be more even. Run higher octane fuel, see if helps. Heat itself isn't the issue, uneven heat is. Might richen the mixture, just a bit, fuel cools. Run a cooler plug. Good luck & keep posted
 
Response assumes noise occurs largely under load. If all the time, tolerances. If crank wasn't turned at rod journals before installing precision insert rods, could be there. Tendency is to leave clearance loose, allowing non-bind condition but loose under power stroke. Plastigage is good for an idea, but micrometer and bore gauge will tell much more, especially diagnosing out of round. Babbitt wears differently than inserts, as does crank. As earlier response indicated, could also be excessive bore runout. Good luck and wanted to clarify...
 
(reply to post at 19:10:23 03/20/18) thanks for info going to get some 100 octane and try. I have messed with timing it has mag so not much adjustment doesn't change it, I did adjust carb and it did change noise somewhat. it only makes noise at idle wide open no load no noise. Crank was turned and bearings ordered. But it starts making noise as soon as u start it. But I will say noise goes away when I hit the kill button on the mag, and when I pull short left plug wire out. I am wondering about piston slap though my machine shop said bore should work from cast iron pistons to the aluminum ones. I have heard different on that issues also the aluminum are cam ground so a bit of egg shape which should round out when at operating temp. I haven't been able to warm it up past 165 ish. I under stand about hot spots I had I didn't mention i gasket matched ports and smoothed up combustion chamber pretty good.
 
Ok I put some 100 octane in it and went to a
colder spark plug i run it until 170 degrees
didn't help it any so I tore it down looks
like piston slap does anyone know what the
piston to cylinder wall clearance is suppose
to be for the aluminum pistons my book says
5 to 8 thousands for the cast iron ones.
Thanks for all the help everyone
 

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