MF 275 CAV issue?

[jjgurley]

First, I want to apologize for not following up my prior posts, as "notify" does not seem to work. Second, sorry for the length of this recap.

I have a MF275 that belongs to a local non-profit ranch, which I volunteered to try to fix. It ran 10 years ago, but sat since.

I found that the diesel tank was full of crud, as was the lift pump and fuel filter. The tank was cleaned and the lift pump and filter were replaced.

I then re-built the CAV (3241F541) pump. I found that the inlet strainer, the poppet below it, and the entire top of the pump were all full of the same crud. The metering valve was also stuck, as was the governor mechanism.

Interestingly, the spring settings in the top chamber were NOT as documented for that part number. I left them where they were as opposed to where they should be per PN. Someone must have messed with it long ago.

The shuttles in the high pressure section were also stuck. After a thorough cleaning, the CAV reassembled according to documentation, and the pump "squirted" sequentially as hoped.

Re-installing it on the tractor, I still got no trace of starting - no coughs, no smoke or mist from exhaust, and not even any reaction to ether. After acquiring a compression test kit and fabricating a custom adapter, I found all cylinders had 210psi of compression. I know that is lousy, but I'm told it should at least run with those numbers, and maybe improve with a little exercise of the rings. I then tested all the injectors, and they all popped at about 2100psi, again not great, but probably okay. Reassembling, I still get no sign of life, so that leaves me with thinking the CAV is failing to provide the needed pressure. If I put my finger over a high pressure line while cranking, I can feel a tickle, but it doesn't force past my finger, which I'd guess should happen.

I'm not sure what could result in the CAV failing, unless there is some air trapped somewhere that is creating a cushion. I have cranked for many minutes with the injectors disconnected and all lines are squirting as expected. I primed the CAV as shown many places.

I haven't figured out how to hook up a gauge on the output, due to the myriad of various thread sizes, although I'll probably do that eventually.

My questions are 1) is there anything else that can defeat the CAV, and 2) there are many CAVs for sale (e.g. ebay) that claim MF275 compatible, but none share the last digit. Is the spring position more of a tuning issue than go/nogo issue?

 

[Dieseltech]

Pump should have been gone through and calibration checked. If you only have 210 PSI compression that's way too low to start, they barely start with 300, and 350-400 is ideal. If you have lots of white exhaust smoke, fuel is getting into the chamber but compression heat is too low to burn fuel correctly..

 

[jjgurley]

As stated, no smoke of any sort from the exhaust. Other than timing, and the spring tension, there's really no adjustments in the CAV. The timing only has a few degrees of adjustment if you don't mess with the gears on the front of the engine. I simply marked the position and put it back to the same place.

 

[jjgurley]

Okay, now I finally have some light smoke on cranking it. I guess it took awhile for the air to get out of the injectors. Still won't start, and ether won't fire, either. I guess it's just the lousy compression...it's frustrating 'cause if I could get it to run, the rings might re-seat a bit raising the compression.

 

[ptfarmer]

Pull the injectors, squirt some motor oil onto the cylinder walls, put the injectors back in, and I'll bet starts right up, and runs until the oil in the cylinders go away. The oil seals up the piston rings thus raising compression. You could also pull the injectors, squirt some automatic transmission fluid on the cylinders walls, and let it sit for a few days. The atf (since it's a thin, high detergent oil) could help loosen up the any crud in between piston rings on the pistons giving you compression back. It's worth a shot!

 

[jjgurley]

I had to do the squirt of oil to get the 200psi reading. I can try again, but I'm pessimistic.

 

[Dieseltech]

I doubt any oil got to the rings where it's needed, probably just stayed inside the piston bowl the injector sprays into. Squirting oil into the injector hole will get it right into the bowl..

 

[jjgurley]

I'm a little confused. On the 4-248, the injector is a deep hole that doesn't give you a lot of ways to aim the oil. I stuck the flexible oil can spout down the hole and gave each cylinder two doses, which I'd guess is about a CC per dose. How do I do better than that to get it to the rings? I've never seen the piston design, so I don't know how deep the bowl is...

 

[ptfarmer]

All you can do is to see if you get the piston when it's all the way down in the bore. If the compression was like 100 psi without oil (or a wet compression test as it's known) I'd say the piston rings have seized to the pistons. You could pull the head, drop the oil pan, and pull the rods/pistons then look at the piston rings. More than likely it will need new sleeves, pistons, and rings which can be done with the engine in the tractor.

 

[ptfarmer]

(quoted from post at 00:40:40 03/21/20) All you can do is to see if you get the piston when it's all the way down in the bore.

Dang no edit!! When the piston is all the way down in the bore look to see if you can see the cylinder wall through the injector hole (if you can see the cylinder wall you be able to get oil on it). Maybe re-work the end of your oil squirt gun so it makes more of mist rather than a stream.

Liners, pistons, and rings. https://www.yesterdaystractors.com/...and-Piston-Kit-Perkins-248-Diesel_PK4248.html

Gaskets. https://www.yesterdaystractors.com/...op-Perkins-236-and-248-Diesel_3638661M91.html
https://www.yesterdaystractors.com/Massey-Ferguson-275_Oil-Pan-Gasket-Perkins_3638519M1.html

 

[jjgurley]

I stumbled on the existence of the block heater (cord is sort of hidden), so with that, a warm day, and a touch of ether, it started. Seems to run fine although I want to check the oil, transmission, and coolant before letting it warm up. Thanks for the advice!