Low compression Fx28d

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JRT
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Posts: 3
Joined: Sun Jun 21, 2020 8:20 pm

Low compression Fx28d

Postby JRT » Mon Jun 22, 2020 10:16 am

Hi Everyone,

I have had my Fx28d for 11 years and it has pretty much done its job with basic maintenance on my end.
Heard the coolant bubbling a few weeks back and confirmed the head gasket was leaking. The head had corrosion, took it to the automotive machine shop and they removed about 30 thousands of material.

Also noticed that #2 cylinder has damage up top and will need to be machined oversize, and the other three need honing at a minimum. I am hoping to put it back together as is and run it until winter before a rebuild.

Put the new gasket(Hoye) in, got it running but heard a loud clanking sound I did not remember-if I spill the fuel to cyl 3 the noise goes away. Pulled the head, no valve damage. I found three valve lash adjusting screws that were worn at the pushrod connection, fixed those on a lathe. Measured the compressed gasket from Hoye (.052) against the gasket that had come with the tractor(.062). So .040" total difference from the old head. Tested compression last night #1 380psi, 2 280, 3 440 and 4 was 340. Pretty bad, but it was running and doing its work before I opened it up.

I did the math, about 3 inches in both bore and stroke, so 7 inches of area times 3 inches of stroke. 21 inches of volume compressed at 20:1 is just over an inch of final volume. The .040 reduction in head volume times the 7 square inches is .280 which is about a quarter of the previous total which I believe leaves me at about a 30:1 ratio.

I am planning to add the 40 thousandths in shim material and see if that helps. The compression should drop by about a third from the numbers above, bad to worse. Oh well. If it runs without the clanking noise I will be happy.

Any thought are appreciated,I guess I am hoping someone might have something to add that I have missed.

Thanks

I tried to post this last night with a youtube link of about 25 seconds which has the noise and also shows that the noise comes from cylinder 3 as it goes away when I cut the fuel to cyl 3. Is there some way to provide a link so that people can hear the noise that I am talking about? Tried to add it as an attachment but the mp4 format was invalid. Probably a mistake of some sort on my end.

Aaron
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Posts: 3256
Joined: Thu Jul 26, 2007 12:39 pm
Location: Iowa Park, TX

Re: Low compression Fx28d

Postby Aaron » Mon Jun 22, 2020 2:05 pm

If you move the #3 injector to another cylinder does the noise move with the injector or stay with the cylinder? An injector that is squirting instead of misting can cause that knock since the fuel is not atomized enough to ignite and the liquid fuel collects on top of the piston.

JRT
Volunteer Poster
Posts: 3
Joined: Sun Jun 21, 2020 8:20 pm

Re: Low compression Fx28d

Postby JRT » Mon Jun 22, 2020 3:56 pm

Will do.
3 of the 4 injectors were good with one a bit less atomized or more of a stream. I thought it was #2 but I may have mixed them up.

Thanks

JRT
Volunteer Poster
Posts: 3
Joined: Sun Jun 21, 2020 8:20 pm

Re: Low compression Fx28d

Postby JRT » Fri Jun 26, 2020 6:45 pm

Pulled the #3 injector and was surprised to see that it had gotten hot. Pintle was stuck in the nozzle, so the stream instead of mist idea makes sense.

Replaced with a new nozzle, put it back into #3 and ran it. It sounded good for about 5 seconds and then the clacking was back. Surprising.

I then removed and tested injector #3(I had only run it for a few seconds after the noise returned- no sign of overheating with this new nozzle) and injector #4, the spray pattern looks good on both of them, no leaking and the opening pressure matches the other injectors.. I went ahead and switched #3 and #4 and it sounds better, but it seems to run rich(black smoke) when I depress the throttle with no load until the air ratio catches up with the fuel. I dont remember this being the case before.

I have been trying to puzzle out how liquid fuel on top of the piston can cause that knock, you seem to be right, but I am having trouble visualizing how that translates into the noise. Is it because there is still fuel burning as the exhaust stroke begins and you are putting pressure on the bottom end or the piston? some sort of piston slap?

I am planning on plumbing up the coolant and letting it run for half an hour or so that it gets upn to operating temp at idle and see if the noise returns. I have been running it for 45 seconds or so, maybe a minute tops and havent exceeded 155 degrees f on the head according to my infrared thermometer.

Also noticed that one of the front axles are starting to leak, I have the knuckle seals and stub axle seals in my cart. I am guessing that you would recommend replacing both while you are in there?

The water pump I received from you has 4 ports, 2 were plugged leaving 2 open. The original just had one open for the t-stat. I believe the ports are tapered pipe so I put in a 16x1.5 bolt(non tapered thread) with an o-ring for the extra port-temporarily. Both the bolt I put in and the temp sensor are incredibly loose in the threaded bore and only tighten when the o-ring gets compressed. I will need to order a tapered plug for the extra port. Is there a better way to do this?

Any thoughts are appreciated


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