YM186D Compressiontest

[ajaukema]

For what it is worth, this is the compression specs for the YM220/222. A little larger than yours but I feel it would be real close to your 186. Specified pressure 568 to 639 psi. Lower limit 426 psi.

That is true for this engine. 426 PSI is the lower limit in the manual.
There's 3 considerations:
-Manual does not tell you if this is in cold or hot condition.
-The tools for pressure measurement enlarges the volume of the combustion chamber a bit, not shure how much this affects it
-I have no idea how much rpm the cranckshaft is running on the starter motor, if it is too low you wont get the max pressure.

Anyone had a value between 568 and 639 PSI on a compression test...?

 

[ajaukema]

Great point.

I do wonder how severe the valve seat pitting that @ajaukema mentioned is. With new rings and the correct ID sleeves with limited scoring, that leaves pretty much the valves and springs for low compression. In my experience, Yanmar normally has pretty stiff springs compared to other makes.

All the best,

Peter

Compared to my Deutz engine I find the Yanmar valve springs easier to press, but that doesn't tell you anything.

During leaktest there's 10% which is hearable at the carter vent. Before the valve lapping I could hear air leak out on the intake and exhaust ports.

Leak test is of course at lower PSI like 80/90 so it doesnt tell you how it leaks at higher PSI.

Maybe the valve spring pressure is too low, not shure how to check on this. Any ideas?

 

[ponytug]

Not being a routine engine rebuilder, I don't have a valve spring force tool, but if it were me, I would probably just fab something up to compress the spring with a scale at one end of a lever. Or maybe be not, there is this (I've never used this);

Valve Spring Tester Pressure Checker Gauge Tool, Measurement from 20-600psi | eBay

Accurate Valve Spring Measurement: Easily and affordably measure valve spring rates with this valve spring rate tester tool., Versatile Usage: Use it with a hydraulic press, shop vise, or drill press for convenience., Precise Readings: Liquid-filled gauge prevents needle vibration and provides...

www.ebay.com

Plus a v-block in a vise and a micrometer would probably get you there.
Or find a local shop that could test them.

These are high compression engines, so yes, you do want the chamber volume to be as close as possible to the real thing. I know some folks who use a modified injector as the adapter for the compression gauge. That way the chamber volume is exact.

Do you by chance have any photos of the valve seats and valves after lapping them?

From what you wrote above for the low throttle, generally low power use, that type of usage is going to be prone to carbonizing the combustion chambers, valves, injectors, and muffler. Once the engine is running well, if it were me, I would look around for something that the tractor occasionally could do at wide open throttle under full load for a couple of hours. It doesn't need to be every week, just every so often.

All the best,

Peter

 

[ajaukema]

Not being a routine engine rebuilder, I don't have a valve spring force tool, but if it were me, I would probably just fab something up to compress the spring with a scale at one end of a lever. Or maybe be not, there is this (I've never used this);

Valve Spring Tester Pressure Checker Gauge Tool, Measurement from 20-600psi | eBay

Accurate Valve Spring Measurement: Easily and affordably measure valve spring rates with this valve spring rate tester tool., Versatile Usage: Use it with a hydraulic press, shop vise, or drill press for convenience., Precise Readings: Liquid-filled gauge prevents needle vibration and provides...

www.ebay.com

Plus a v-block in a vise and a micrometer would probably get you there.
Or find a local shop that could test them.

These are high compression engines, so yes, you do want the chamber volume to be as close as possible to the real thing. I know some folks who use a modified injector as the adapter for the compression gauge. That way the chamber volume is exact.

Do you by chance have any photos of the valve seats and valves after lapping them?

From what you wrote above for the low throttle, generally low power use, that type of usage is going to be prone to carbonizing the combustion chambers, valves, injectors, and muffler. Once the engine is running well, if it were me, I would look around for something that the tractor occasionally could do at wide open throttle under full load for a couple of hours. It doesn't need to be every week, just every so often.

All the best,

Peter

I keep the valve spring tester in mind, thank you.

The pressure gauge has an adapter screwed to a pipe (at the green section), I think together it is like 15cm before the valve (at the red section).

I don't have photos of the valves/seats.

 

[ponytug]

How narrow is the inside bore of the adapter barrel? (I'm thinking of the dead volume.)

All the best, Peter

 

[ajaukema]

How narrow is the inside bore of the adapter barrel? (I'm thinking of the dead volume.)

All the best, Peter

Pipe is 6mm inside diameter over length of 150mm
Adapter is 9 mm inside diameter over length 10mm

 

[ajaukema]

Did some tests tonight.

First checked the injection timing, it is spot on 21 degree before TDC.

I did a new leaktests tonight in cold condition.
Got the valvecover removed.
All 3 cylinder have a leak of 10%-15% at TDC, the leak is blowby and hearable from the carter at the wide ports where the pushrods are positioned. Hard to tell if there is a bit leak at the intake/exhaust ports, it is not noticable by hand and ear.

Did compressiontests in cold condition
All 3 cylinder have max readings between 310 and 320
The first 3-4 cranks get it to 280 and the next 3-5 cranks bring it to 310-320

Maybe should do compression test at operating temp tomorrow just for reference.

 

[ponytug]

Pipe is 6mm inside diameter over length of 150mm
Adapter is 9 mm inside diameter over length 10mm

Check my math and logic on this, but here goes;

Cylinder head volume at minimum volume (i.e. max compression, 23x) on the 186D 3 cylinder 0.9L engine is normally 13cc (300cc/23).

Your adapter/pipe volume is (4.24+0.636) 4.88cc

So,... a measured psi of 310 needs to be scaled up by (13+4.88)/13=1.375 or 427psi plus (+, as this does not account for the increase in cylinder volume of an adapter vs an injector).

Thoughts?

All the best,

Peter

 

[ajaukema]

427 PSI would not be that bad! Problem is you can find al lot of measurements on the internet of bad values, you never see information about measurements when repaired

Today I also took the starter apart, cleaned it (it was a mess) and gave it new grease.

So the leak and compression test combined with the leak mostly on the cylinder wall brought me back to the injectors as most possible cause for the smoke.

Took em out and tested them again. Guess what, 2 of 3 failed for the leak test and the
spray pattern obvious. Decided to give the injectors another cleaning cycle in the ultrasonic.
Reassembled them and did another test. 2 where ok now on the leaktest just like the earlier leaktest after the first cleaning cycle. 1 was a bit leaking. Patterns and opening pressure ok on all 3. I think the engine only run for 30 mins between these cleaning cycles, this means they go bad very quick when in use.

Put the injectors and the starter back in the tractor and for some magic it just starts reasonable. It still smokes, but it is less and more grey, so I think a new set of injectors wouldn't be bad.

I decided we first let the tractor work a little bit and then we'll see how it will develop.

Thank you for your help and support!

 

[ponytug]

Congratulations on getting it running! I would see if you can find a job or two to get it hot under load for a while. You didn't mention where you are, but if you have access to SeaFoam cleaner, I would put a bottle or two in the fuel tank for a dose of cleaning. I would also consider that perhaps another new fuel filter, filled with SeaFoam, and then run for a minute, and allowed to sit overnight might help. I have a concern that perhaps there is some debris is in the injection lines.

I think that I agree with you that it is worth considering some new injectors, as at some point poor injector performance is in the replace rather than clean category.

All the best,

Peter