Low compression starting

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gzec
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Low compression starting

Postby gzec » Wed Jul 10, 2019 8:10 am

I have a yanmar 3tna72uj2 in a deere 430.
shows 300, 190(middle) 320 compression readings
It takes about 2 minutes of intermittent cranking to get it started.
After it starts it runs great. Has approx 1000 hrs .
Any suggestions besides a rebuild to make starting easier.
I do use cetane.
Thanks for any help.
Glenn

Aaron
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Re: Low compression starting

Postby Aaron » Wed Jul 10, 2019 1:26 pm

Those are very low numbers. I am really surprised it will start at all. Have you checked your valve settings? There is a (slim) chance that they may not be set right. Otherwise... there is not much you can do but plan on a re-ring & possibly bore the cylinders & new pistons if there is significant wear/damage.

You could check for a (severely) blown head gasket. That could make low compression too.
https://www.hoyetractor.com/BlownHeadGasket.htm

Resist the urge to use starting fluid.

Any idea what happened to cause the low compression in that few of hours? Ran without an air filter? Starting fluid use?

winston
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Re: Low compression starting

Postby winston » Wed Jul 10, 2019 5:06 pm

Not likely but could be leaking valves, not caused by to tight setting.

gzec
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Re: Low compression starting

Postby gzec » Fri Jul 12, 2019 1:53 pm

I assume it was a bad air filter in a dusty environment. When I bought it, it started hard, but ran great. I figured I could fix the hard starting, not knowing diesels. I've learned a lot since this, my first diesel purchase.
Thanks
Glenn

gzec
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Re: Low compression starting

Postby gzec » Sun Jul 14, 2019 7:05 am

I suppose taking off the head is the next step to inspect? I suppose I will need a new head gasket. Anything else I need to be aware of besides torque values?

winston
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Re: Low compression starting

Postby winston » Sun Jul 14, 2019 2:53 pm

Take head off, yes. I do not know torque value but I do know some Yanmar engines require new head bolts. I do not know about your engine. Maybe Aaron knows, if not you may need to purchase a manual.

jimjumper
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Re: Low compression starting

Postby jimjumper » Fri Jul 19, 2019 7:45 pm

My 240D is also a bear to start due to low compression. Since I use it mostly in the summer for mowing, I installed a screw-in block heater and plug it in when I plan on using it. I use a handheld laser thermometer and when the block gets to about 80-85 it fires right up. I can generally tell how long it will need to crank before it starts from the temp of the block. I know, its not ideal, but I'll be able to use it right now when I've got weeds growing everywhere. I re-build it this winter when its raining and cold.

winston
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Re: Low compression starting

Postby winston » Sat Jul 20, 2019 5:23 am


gzec
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Re: Low compression starting

Postby gzec » Tue Jul 30, 2019 10:53 am

I verified the compression readings with another gauge. I measured through the glow plug hole. A mechanic friend of mine asked if that was the correct place to measure and not the injector hole. Does it matter?

winston
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Re: Low compression starting

Postby winston » Tue Jul 30, 2019 1:08 pm

gzec wrote:I verified the compression readings with another gauge. I measured through the glow plug hole. A mechanic friend of mine asked if that was the correct place to measure and not the injector hole. Does it matter?


No, not if is a normal glow plug and reaching the cylinder compression.

Aaron
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Re: Low compression starting

Postby Aaron » Wed Jul 31, 2019 7:55 pm

Do you have glow plugs in each cylinder or just one in the intake? If you have one in each cylinder then that will be just fine.

gzec
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Re: Low compression starting

Postby gzec » Thu Sep 05, 2019 5:07 pm

Changed the head gasket. Everything looks good except cylinder walls are smooth. Oil in glow plug hole increases the compression by 100%.
Next step is new liners, pistons, rings? I presume I can do this job. Anything besides sleeve puller i will need?
Does hoye sell the parts?

winston
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Re: Low compression starting

Postby winston » Thu Sep 05, 2019 5:49 pm

Probably need to click on the "Yanmar tractor parts" above and then on the "contact us" box.

Torque wrench which you must already have.

gzec
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Re: Low compression starting

Postby gzec » Wed Oct 02, 2019 7:38 am

Installed new rings and pistons. Cylinders were acceptable. It now starts nicely. Blow by is almost non existent. Ring gaps were huge. Rings were worn to the naked eye. Machine only has 850 hours for a 1987 model. It must have had poor air filter management in a dusty environment.

Aaron
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Re: Low compression starting

Postby Aaron » Sat Oct 05, 2019 7:04 pm

Good to hear. Glad you got it running again. It is really amazing how fast dirt will erode piston rings.


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