Compression test results

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Blue76
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Compression test results

Postby Blue76 » Sat Apr 25, 2020 11:31 am

Got the adapter today from Hoye to test my compression. Hope I was sent the correct one. It is much smaller in diameter than the injector hole but I centered it up and bolted it in.

Tractor is a YM2500

Results were.
#1 = 450psi
#2 = 350psi
#3 = 450psi

So... are 1 and 3 bad enough that I should replace pistons and rings?

Guessing I should go ahead and tear down and inspect before I order parts.

Plan is to pull head and oil pan, unbolt from crank and pull out from the top. Hone cylinder walls and replace.

Questions are... how do I check connecting rod bearings and it there a simple way to check crankshaft bearings while in there?

This tractor will not see heavy use but I do want it to last a while.

Thoughts and opinions welcome

Greg

Let me add... I went ahead and pulled the head. I guess I expected to see scoring marks or something that showed obvious damage but nothing. The cylinder walls look the same in all three... very smooth. You can tell by looking number 2 was wet where the other two were dry looking. Remembering that the symptoms were smoke from #2 and blowby from the crank case. Could it just be a stuck ring? The pistons wiggle a little in the cylinders. All three the same if that means anything.

If you read this far you must be quarantined and bored. :D

Thanks again... going to drop oil pan next.

Blue76
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Re: Compression test results

Postby Blue76 » Sat Apr 25, 2020 1:58 pm

Replying to my own post...

Pulled the pistons... can’t see any damage or anything... however. Look at the pic I am attempting to post. This is how the rings lined up... you can see the piston is clean under the first ring except where the gaps are... looks like maybe the rings are not lined up properly...

The only spot on the piston that I don’t think is right is a little impression right under where the injector is. Maybe you can see it in the pic. Can’t see any damage to the lower injector nozzle.

No mechanic here. Just an observation.

Pulled the other two and they look pretty much the same. I honed the cylinder walls... looks like new.

Guess I need to decide if I want to just re-ring or replace pistons as well...

Greg
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winston
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Re: Compression test results

Postby winston » Sat Apr 25, 2020 5:49 pm

I can tell you a 3T75HA is to have 568 to 639 psi at 300 rpm. I can only guess yours should be close to that. I would ring all three cylinders, I think you could use the installation pattern in this picture. There are lot's of clearances you can check if a mind too. If you do you may want to consider getting a manual. Plastigauge is my preferred way to check rod bearing clearance. If they are ok I wouldn't worry about the mains.
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Blue76
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Re: Compression test results

Postby Blue76 » Sat Apr 25, 2020 6:39 pm

Thanks Winston... i will plan on ringing all three... any real merit to replacing the pistons? No scratches or other marks on them that I can see.

Greg

winston
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Re: Compression test results

Postby winston » Sun Apr 26, 2020 5:18 am

Sounds like your pistons are good to go. All kind of clearances you could check but likely they would be good. I would check ring end gap just for peace of mind. I would check it in at least 3 different depths of the liner, maybe just with one ring per cylinder.

Blue76
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Re: Compression test results

Postby Blue76 » Sun Apr 26, 2020 7:10 am

Hadn’t thought about that... any idea what the end gap spec should be? Do these liners have a taper?

I don’t have torque specs to reassemble either... hate to buy a $70 book to find torque specs for connecting rods and head bolts.

Guess I should just to make sure i am not missing anything.

Greg

winston
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Re: Compression test results

Postby winston » Sun Apr 26, 2020 7:36 am

I can tell you the 240 engine (2TR20A) all rings are to have .0118-.0197" with a wear limit of .0591". Liners do not taper.

44-88-118 and 133 + or - 3.6 ft lbs. for head bolts. Connecting rod caps 33-36 ft lbs. Rocker arm support bolts 58-72 ft lbs.

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Re: Compression test results

Postby Blue76 » Thu Apr 30, 2020 7:43 pm

Latest update...

Got parts in today. Managed to get pistons back in, head back on but... I goofed on the rocker studs... set wrench to 58lbs and snapped one off. I thought it felt too tight. Oh well...

Winston told me to check ring gaps... the old rings had a consistent gap of .058. The new rings had a gap of .015. So there was quite a bit of wear on them.

Need to find correct torque specs for those rocker studs.

Greg

winston
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Re: Compression test results

Postby winston » Fri May 01, 2020 4:56 am

36 ft lbs. My apologies for wrong information.

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Re: Compression test results

Postby Aaron » Fri May 01, 2020 2:01 pm

Wow.. Im not really sure how I completely missed a thread that has been going on for this long. I didn't even notice it. Looks like you are on a roll now though.

Blue76
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Re: Compression test results

Postby Blue76 » Fri May 01, 2020 4:21 pm

winston wrote:36 ft lbs. My apologies for wrong information.


All good. Aaron said I should get a service manual but me being a cheap skate I didn’t. Now it will cost me more.

That’s life... I really appreciate the help.

Greg

Blue76
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Re: Compression test results

Postby Blue76 » Sat May 02, 2020 3:45 pm

I got it back together today thanks to Hoye for the Saturday delivery of parts.

Started right up but still smoking. Is that common for a ring job? Has a little blowby smoke.

Seems to run ok but still has the smoke. Going to pull exhaust manifold and see if it is all or one smoking.


Addendum.... I just let it idle for a while and it started to clear up a little. It would start knocking and smoking heavy periodically but that has smoothed out. The blow by it all but gone.

Of course I ran it out of fuel... fixed that and put it back in the garage and called it a day.


Greg

winston
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Re: Compression test results

Postby winston » Sun May 03, 2020 5:30 am

Maybe you just need to put it to work.

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Re: Compression test results

Postby Aaron » Sun May 03, 2020 4:06 pm

It will take a little while for new rings to seal correctly. A break-in oil will help the process but I don't know if it is 100% necessary.

Blue76
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Re: Compression test results

Postby Blue76 » Mon May 04, 2020 4:58 pm

Ran it for a few hours. Bush hog, tiller and push some gravel around with a box blade. Ran pretty good. The blow by disappeared or it is so little I can’t see it. Still a little smoke and a little more when you rev up the throttle but goes back to just a small amount.

Hopefully it will get better... thinking I might try one of those break in additives. I must have not cleaned up the old oil pan gasket good enough as it is leaking. So I will live with the leak until I change the oil after several hours of break in.

How long should I give it before I change it?

All...on another topic... th elite leaders boot on the gear shifter has some oil leaking out under it. Does that boot just slip over the flange or go inside the flange?

Greg


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