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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Location: Iowa Park, TX

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



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