The real JD 4520: Compression Issues

[used red MN]

What turned out to be the problem after 3 pages of having everyone believe it was low compression?

Compression testers were leaking I guess.

And the possible fact that the manual may have listed a compression spec that was higher than could have been achieved. However the leaking compression tester adapter really means the OP has no idea what the actual compression readings are. It would be interesting if he acquired the proper tester that would seal and retest it. It is a bit of work to take the injectors out again.

 

[Hay maker2]

And the possible fact that the manual may have listed a compression spec that was higher than could have been achieved. However the leaking compression tester adapter really means the OP has no idea what the actual compression readings are. It would be interesting if he acquired the proper tester that would seal and retest it. It is a bit of work to take the injectors out again.

The chance of me getting a third compression tester and pulling an injector to see what the actual cranking pressure is, is slim to none at this point.
I would like to know for sure, and I bet it is as stated in the manual.
I should have captured a video of the blow by when i sprayed it with soapy water, it was not just bubbles around the tester it was shooting out.

 

[Powered By IH]

The chance of me getting a third compression tester and pulling an injector to see what the actual cranking pressure is, is slim to none at this point.
I would like to know for sure, and I bet it is as stated in the manual.
I should have captured a video of the blow by when i sprayed it with soapy water, it was not just bubbles around the tester it was shooting out.

What brands of compression testers did you use?

 

[Fritz Maurer]

Let me rephrase. Why does it start now and not after the overhaul? Was it still not starting after the new injectors were installed?

 

[Hay maker2]

I bought a cheap one from Amazon, because of the low readings I did not trust.
I borrowed the second tester kit from my JD Dealer. Almost positive that this was made by OTC.
Both testers leaked and both testers were consistently within 5-10PSI of each other.

 

[used red MN]

I bought a cheap one from Amazon, because of the low readings I did not trust.
I borrowed the second tester kit from my JD Dealer. Almost positive that this was made by OTC.
Both testers leaked and both testers were consistently within 5-10PSI of each other.

Could you give us a photo of the adapter for the pencil injectors on the one you have? To me it seems like pencil injectors were so common(or at least at one point) that you would think that they would have been able to design one that wouldn’t leak for that application. I am extremely surprised the OTC one leaked.

 

[brendonh]

Thanks Used Red, for the kind words. Got lucky most likely... I'm pleased that his issues have been resolved.

I suppose we'll never really know the cause on this one. Might just have to be satisfied that it works now...?

 

[J.Wondergem]

Now we'll wait and see if it starts at 90 degrees this Summer.

 

[Hay maker2]

Let me rephrase. Why does it start now and not after the overhaul? Was it still not starting after the new injectors were installed?

It starts now because it has the proper compression. The remanufactured head that I purchased had issues with the valves not seating properly as well as the guides. After the valves, seats, and guides were replaced I checked the compression prior to starting and as stated the compression was 300PSI and should of been 400PSI. After i found out that the tester was not making a good seal against the head and leaking I installed the injectors one at a time to verify that they were not leaking. Once confirmed I was able to start the engine as anticipated as the compression is where it belongs.
As for the injection pump, if the tractor does not start next summer due to heat then the injection pump will be rebuilt as simple as that.

 

[4010 puller]

1969 John Deere 4520 with the correct 4520 engine (rear mount injection pump, JDB). I have owned this tractor for 3 years and have been slowly fixing it up. I have a starting issue and the compression is low. I have to use either, plug it in on a 65-degree day, or crank the snot out of it on a 90-degree day to get to start. Per the manual the compression should be between 385 – 410PSI @ 215 – 245RPM

I initially pulled all the injectors and tested compression and on average, each piston was about 300PSI. I did an in-frame overhaul and when I got the head off, the sleeves looked excellent, no wear marks or anything to my surprise. I pulled one sleeve just because. These were manufactured by Clevit and I did some research and was able to verify that they are correct for the application. While researching I located a set of NOS Cleveite piston kits a couple of hours from me, so I bought them for little to nothing and installed all of them for peace of mind. At the same time, I sent the head to my machinist, and he said it was cracked. It took some time, but I found a refurbished head and reassembled everything with a JD Head gasket. To my surprise I have the same issue, low compression (300PSI). I even put on my dyno, and it holds 125HP

I blamed the Clevite piston kits and sucked it up and bought the Reliance High Compression kits (I have had excellent success with these High Compression kits). I installed these and sent my refurbished head to my machinist and he said that the seats and valves were misaligned. He repaired this and I reassembled everything and still have low compression, 300PSI.

Currently I have the basic engine back together, but the coolant pump and hydraulic pump are not connected for testing. Oil in the pan and no water in the engine. Compression is still at 300PSI.

I have done the following:

Valves are set per the manual 0.018” intake and 0.020” exhaust. I have checked these several timed and even gapped these to 0.020” and 0.022” with no luck.

Before placing the head on I brought piston #1 to TDC using a dial indicator, this is within 0.001” of true TDC. The TDC mark on the fly wheel is about 3/16” off, but per my service bulletins it can be off as much as ¼’ with no effects.

I even timed everything based on TDC on the flywheel to the casted line in the inspection window with no change in performance.

Timing marks on cam gears are aligned along with TDC on the piston and flywheel.

Injection pump is timed.

Cranking RPM is averaging 225RPM (coolant & Hydraulic pump not hooked up) with photo tachometer

I have used 2 different compression testers, and both are within 5-10PSI

Suggestions?
Thanks

There is probably quite a difference in the piston bowls of the clevite pistons and reliance high compression pistons isn’t there? I’m surprised that didn’t raise the compression.

I’m not sure on that exact 404 but I know on the 30 series Deere offered two different thicknesses of head gaskets.

The reliance pistons you installed were indeed hi compression and not regular pistons ?