yanmar 240 post engine rebuild compression

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Albert-in-Alberta
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yanmar 240 post engine rebuild compression

Postby Albert-in-Alberta » Mon Mar 15, 2021 2:19 pm

i jusr rebuilt my yanmar 240 engine with new sleeves, rings and valves, gides, springs etc..but reused the pistons. i did a compression check and it is 300 psi in each cylinder...half of what it should be. I don’t understand why this occurring. I installed the new rings in the correct order and orientation. I lapped the valves and set the gap according to the method Aaron described. could it be I need to use new pistons or is there a problem with my valves ....any suggestions would be greatly appreciated.

winston
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Re: yanmar 240 post engine rebuild compression

Postby winston » Mon Mar 15, 2021 5:15 pm

How much have you run it since overhaul? If you lapped the valves you should be able to see the seating surface on both the valve and seat. And if correct setting the valves should be eliminated as a possible problem area. Did your pistons have any evidence of gland wear or did you check gland to ring clearance as well as ring end gap?
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Albert-in-Alberta
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Re: yanmar 240 post engine rebuild compression

Postby Albert-in-Alberta » Mon Mar 15, 2021 7:26 pm

I only tried starting it today. ...so no hours on it at all. rings are new and end gap was within spec. Sorry what is gland wear? I did not check ring groove clearance with the new rings in the piston

Thanks for responding
Albert

winston
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Re: yanmar 240 post engine rebuild compression

Postby winston » Tue Mar 16, 2021 4:50 am

It is listed as ring to groove side clearance on the attached page. So it has not been started since overhaul? Your spin speed should be around 300rpm. Is your starter giving it a good spin? Assuming you have tried to start it?? Probably already have but if not you might want to start the spin with decompression engaged.

Albert-in-Alberta
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Re: yanmar 240 post engine rebuild compression

Postby Albert-in-Alberta » Tue Mar 16, 2021 9:00 am

Hi Winston....i just finished the rebuild yesterday and tried to start it for the first time. I did you use the decompression lever to ensure oil was circulating...I did not check the rpm when I did this but will do that this morning and report back....If it is not giving me that RPM then what is next.

Aaron
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Re: yanmar 240 post engine rebuild compression

Postby Aaron » Tue Mar 16, 2021 9:10 am

I think it just needs to break in. I would run it up to temperature , retorque the head gasket, re-check the valves, and then run an hour or so and repeat (until the head bolts don't move when torquing). It should get easier to start and better compression as the rings wear in. A break-in additive or break-in oil will help also. Just be sure you don't use starting fluid.

winston
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Re: yanmar 240 post engine rebuild compression

Postby winston » Tue Mar 16, 2021 12:53 pm

Albert-in-Alberta wrote:Hi Winston....i just finished the rebuild yesterday and tried to start it for the first time. I did you use the decompression lever to ensure oil was circulating...I did not check the rpm when I did this but will do that this morning and report back....If it is not giving me that RPM then what is next.


Good battery, good starter, you should get that rpm. Bleeding your fuel system is very important. https://www.hoyetractor.com/bleed.htm

Albert-in-Alberta
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Re: yanmar 240 post engine rebuild compression

Postby Albert-in-Alberta » Thu Mar 18, 2021 7:05 pm

Just wanted to provide an update. I did what Aaron suggested and got the tractor running, ran it for about 1 hour, then retorgued the head and checked and adjusted the valve clearance. tractor is now running perfectly and starts after about 4 cranks of the motor. Just a note on my yanmar 240 that might be helpful to others with the same model, the top dead center for each cylinder is marked on the crank pulley which makes checking the valve clearances real easy



Thanks to Hoye for the great service on the tech support discussion group.

Albert

Aaron
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Re: yanmar 240 post engine rebuild compression

Postby Aaron » Fri Mar 19, 2021 8:45 am

Very good! Im glad it all worked out and thank you very much for the follow-up.


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