John Deere 425

[DevonD]

Hi everyone,

First time user of this site and hoping to get some help on a 425 I just purchased. I bought this mower from a John Deere dealership that I had to make a 14 hr round trip to get. They had it listed for $1800 and it was a 2000, so that is why I drove so far to get it. I figured part of the reason it was so cheap was that they said they never serviced it. I don't know if this is common practice, but I'm starting to think not. I was promised it ran, drove and mowed good, which it did. I had noticed an oil leak out of the front main seal which was no big deal beings it could easily be replaced by removing the battery, prying out the old one and putting in the new one. I got it home and replaced the front main seal and also replaced the o-ring on the bottom of the dip stick beings I noticed someone had caulked it and it was leaking, also did all the other maintenance on it, which included changing oil, oil filter, air filter, trans fluid, trans filter and fuel filter. I didn't change the plugs because they looked brand new. Upon further inspection after driving and mowing with it for 10 min at home, I noticed the top radiator hose was loose and leaking, so I tightened that up. I am thinking the mower is still using coolant cause it keeps dropping little by little every time I use it and when I drained the oil when changing it, it looked like it had a green tint to it and it seemed like there was water in it. So my question is... what is my first step to figure out where the coolant is leaking? There are no leaks externally. Also I noticed that the temp gauge will rise up to 3/4 on the gauge and then drop back down to 1/4. It does this continuously. Is this normal? Sorry for the long story... and thanks for the comments!

 

[mechanic mark]

"K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts" 7 down engine shop manual, new head gaskets, heads need to be reworked at machine shop or by yourself, new thermostat, check hoses & belts for replacement, flush radiator and pressure test, check water pump for replacement as well as belts & radiator cap, change oil & filter last.

Yes to first two questions, no to stopping fuel, follow directions in manual starting at 4.6. Let us know how it goes, thanks.

 

[DevonD]

thanks mechanic mark. So would a compression check of the cylinders be ok to do first? Would that tell me if the head gaskets or heads were bad? I have a compression tester? Should I stop the fuel pump from injecting gas into the cylinders when doing this and how would I go about doing that? I read that the cylinders should have a minimum of 180lbs of pressure in the manual. How long should it hold this pressure?

 

[NorthBama]

An air leak down test will tell if a gasket is leaking.

 

[DevonD]

OK...had a chance to do the compression test on the mower today. The thermostat side had 175psi and would hold it for 8-10 min and the other side had in-between 180-185psi and would also hold pressure for 8-10 min. I never tried any longer, I figured this was long enough wait. The plug on the thermostat side was black and had carbon on it and this was the cylinder at 175psi. The other side the plug looked like a new plug. I ran the mower for another hour in the past two days and couldn't get the coolant level to drop anymore. It has been on the low fill line since then. So... maybe it took the first couple times of running it for the block/heads to fill back up with coolant after I tightened the hose up that was leaking. Now back to the manual I guess to see what I do next unless someone has some advice on what to do next?

Also I was wondering if these motors have a ticking noise to them? Cant tell if its both sides or one. I use to have a 345 with the 18HP liquid cooled Kawasaki OHV and I thought it purred and never made a ticking noise.

 

[bertsmobile1]

stick it on your trailer and take it to your local car mechanic / radiator repair shop[.
Get them to do a pressure test on the radiator.
If it is leaking externally you will see the little stream of water and if it is leaking internally you will see a pressure drop.
I am guessing there is no overflow tank so it might be the drop in the water level is caused by thermal expansion.
The temperature variations could be due to blockages, thermostat or water pump

 

[DevonD]

Yes there is an overflow tank for the coolant. That is how I noticed that the coolant was dropping, but has stopped dropping since I fixed a hose. It just took longer than expected to fill the system back up with coolant after I repaired the leak on the hose. I don't think it needs a coolant psi check anymore beings its not using anymore coolant. I do agree that is prob needs a thermostat beings the temperature gauge fluctuates so much. The thing I am wondering about now is why one cylinder, the plug looks brand new and the other cylinder the plug is all black and full of carbon? I did look at the manual again and I guess the minimum cylinder pressure is 170psi and cant be more than 14psi difference from one cylinder to the next. So the engine does fall into normal operating specs. Would this mean bad valves or the valves need adjusted on the one cylinder? Don't understand why on one side everything is good and the other side looks like crap?

 

[bertsmobile1]

Both of those plugs are bad.
The clean one is lean, not clean and the other is rich.
So you have problems .
I will go with a cracked head at worst or a blown gasket at best.
Pull the rocker covers and watch the operation of the valves.
While you are in there check the valve lash.
Both sets of valves should look & move identically.
When the valves are fully closed rotate the pushrods and look for eccentric movement indicating a bent pushrod and most likely a sticky valve..
Not uncommon for a carburetor to be adjusted to counteract a problem further down the line.
We have all done it

 

[DevonD]

Ill try and get at that within the next couple of days and let you know what I come up with. Thanks for the input!

 

[DevonD]

Ok I finished up mowing what I had to before tearing into the mower. The only thing I have done so far is took the plug back out on cylinder 2 I believe (thermostat side) and I noticed the prong on the spark plug is bent in towards the center piece of the plug and there is only .005 gap on the plug and it looks like an indent on the piston where it was hitting the plug. Not sure how this happens? I will keep updating once I check the other side and get the valve covers off and check out the rods on both sides. You can see how the prong is bent on the plug. There is also a flat spot on the plug from the piston hitting it.

UPDATE: Cylinder 1 (non thermostat side) pulled plug, looks like very slight contact with piston, slightly bent .019 gap. Valves lashes were way off on a couple.

Cylinder 2 with smashed dirty plug had Exhaust .016 Intake .025
Cylinder 1 with lean plug Exhaust .025 Intake .008

According to the manual they should all be set at .025. Would this cause the pistons hitting the plug(s)? Will check the rods next I guess by pulling them out. Do I pull the heads and see if the valves are bent or should I just adjust the valve lash and call it good?

I looked up the NGK BPR4ES factory spark plug gap and they are suppose to be at .030.