John Deere 420 cranks, won't start

[dustball8504]

Compression is 100# and 90# on the cylinders. I'm unsure on the control module. I'll have to look at that for sure.

Just a question here, someone told me to hold a ratchet on the front of the motor and turn the driveshaft by hand, I can't turn it, would that indicate my flywheel key is ok? I'm trying to rule out as much as possible before pulling the motor.

 

[JerryK]

If you somehow lost the key [ doubt it ], and the flywheel bolt was still fairly tight, the flywheel still could be hard to turn on the tapered crankshaft. If you go to the trouble to pull the motor [ not that hard ], AND pull the flywheel, I'd replace that sender just for the **** of it.. I still bet a barley pop on it being bad.... I don't remember a plastic magnet on the cast flywheel, but I don't remember a lot of things these days...

 

[Kish318420]

The magnetic collar is on the crankshaft it is keyed too, It sits behind the ignition module, The flywheel has magnets that create flux for the stator as it spins.

I doubt that it will turn if the PTO and belt are still in place.

 

[bruceatlam]

Those compression numbers are too low. They're either wrong or they are the problem. Should be more like 165 psi.

 

[Kish318420]

They are close to being worn out minimum is around 80 PSI with no more than 10 PSI difference between cylinders. So it might need to pull the heads and measure the bores down the cylinders. Also note to see if the pistons are std or .010, .020, ,030 size. I would check with boomers_influence@yahoo.com for the normal and max compression values because I've never have read where they are published at. But he might know since he is man with the knowledge.

 

[dustball8504]

I shot him an e-mail to see what he says on the values. I will report back.

 

[Richard001]

I found a Onan shop manual for this engine.

The 90 and 100 lbs is well within the service range.

See attached PDF

View attachment onan_p224_service_manual.pdf

It's pertly big file so may take a minute or two to load.

Richard

 

[Richard001]

Also here is the companion Onan parts list PDF.

View attachment Onan_P216G_P218G_P220G_Parts_Catalog_19981000.pdf

 

[citytransplant]

I've got a neighbor with same issue, JD 420 that turns over but doesn't fire. I've have read through 3 similar threads where the OP never bothers to post a resolution. GRRRRR.
How about it dustball? How'd things turn out for you? Any resolution?

 

[Kish318420]

It is probably the ignition module and plastic rotor that has the magnets that trigger the ignition module which in turn applies that to the coil. There is a test in the manual to check that out.