Agco 6690 engine trouble

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   I am helping a friend work on his 6690 agco. 4 cyl air cooled engine. He was running the other day when he noticed that there was oil pouring out from behind the starter.  We investigated today and noticed that there is a crankcase vent on the back of the motor and it is coming from that.  So it seems there is excessive blow-by in the engine.  It seems odd that it would start so abruptly.  He said it never overheated or anything like that.  Is there something else to the crankcase venting system we are missing?  Im thinking maybe a blown head gasket.  There is some oil around the top of the cylinder on #3.  Im not sure how these engines are if that could be the issue.  We really need to get this fixed so hay can be finished mowing and baled. 
Thanks 
Pat

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patf10 Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 17 Aug 2020 Location: Pennsylvania Points: 6	Post Options Post Reply Quote patf10 Report Post Thanks(0) Quote Reply Topic: Agco 6690 engine trouble Posted: 17 Aug 2020 at 10:11pm
	I am helping a friend work on his 6690 agco. 4 cyl air cooled engine. He was running the other day when he noticed that there was oil pouring out from behind the starter. We investigated today and noticed that there is a crankcase vent on the back of the motor and it is coming from that. So it seems there is excessive blow-by in the engine. It seems odd that it would start so abruptly. He said it never overheated or anything like that. Is there something else to the crankcase venting system we are missing? Im thinking maybe a blown head gasket. There is some oil around the top of the cylinder on #3. Im not sure how these engines are if that could be the issue. We really need to get this fixed so hay can be finished mowing and baled. Thanks Pat

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tbran Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 14 Sep 2009 Location: Paris Tn Points: 3545	Post Options Post Reply Quote tbran Report Post Thanks(0) Quote Reply Posted: 17 Aug 2020 at 11:22pm
	The engine has an oil separator … https://na.apb.agcocorp.com/p/agcoallis/79013783/l/46?tocGuid=95f4d4d9-75e8-e0a2-75a1-a4a6e1b9770f there should be a seal on the block / vent tube. "these engines" are like all diesels in that pistons sieze for the same reason - heat - lack of lube - or dirt. The 'head gasket' has nothing to do with oil - if it is 'blown' you will hear a loud popping noise. Oil on the top could only come from tappet cover or push rod seal leakage. IS the radiator clean ? it does have one - if you can't feel a hot blast of air coming from it - it is plugged - it is an air/oil cooled engine.
	When told "it's not the money,it's the principle", remember, it's always the money..

patf10 Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 17 Aug 2020 Location: Pennsylvania Points: 6	Post Options Post Reply Quote patf10 Report Post Thanks(0) Quote Reply Posted: 18 Aug 2020 at 9:47am
	Well the thought is that maybe the head gasket is blown into an oil galley that would allow compression to enter into the crank case. The engine isnt very dirty. the oil cooler that runs along the engine and inside the ductwork is fairly clean as well. Just trying to figure out if there is an issue with the crankcase ventilation system. We took the "breather/separator" off and didnt see any issue with that i dont think. However we dont have anything to compare it to. tbran, that link you sent didnt seem to work

Amos Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 11 Sep 2009 Location: Ontario Points: 1318	Post Options Post Reply Quote Amos Report Post Thanks(0) Quote Reply Posted: 18 Aug 2020 at 4:10pm
	I think the only oil supply to the head is up the center of the push rod...but I may be mistaken, I have not taken apart a 6690, but a couple 5660 which I am thinking is the same engine, just smaller displacement. Oil return should be down the push rod tube. Head gasket should be just a fire ring.

tbran Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 14 Sep 2009 Location: Paris Tn Points: 3545	Post Options Post Reply Quote tbran Report Post Thanks(0) Quote Reply Posted: 18 Aug 2020 at 9:13pm
	Sorry , a blown head gasket would be only a 'fie ring'. Blow by is going to be a bad piston.
	When told "it's not the money,it's the principle", remember, it's always the money..

Rusty Allis Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Access Joined: 16 Jul 2020 Location: Rhode Island Points: 170	Post Options Post Reply Quote Rusty Allis Report Post Thanks(0) Quote Reply Posted: 18 Aug 2020 at 9:52pm
	I actually had to look this engine up. kind of goofy, like a inline motorcycle engine. I would suspect a stuck ring. seeing it's air cooled I would have to wonder if the fan sucked in a bunch of garbage and it's packed around the fins. I have zero experience with these engines, but seeing the size of the machine and the fact it's air cooled....It seems to me to be a WTF were they thinking kind of design post photos if you can. curiosity is killing me

patf10 Members Profile Send Private Message Find Members Posts Add to Buddy List Bronze Level Joined: 17 Aug 2020 Location: Pennsylvania Points: 6	Post Options Post Reply Quote patf10 Report Post Thanks(0) Quote Reply Posted: 19 Aug 2020 at 5:12am
	Well I was wondering about the fire ring thing. So maybe it’s not a gasket like I was hoping. I’m going to make an adapter and we are going to compression test it. I guess we’ll see what that gets us. If I have decent compression. Anyone familiar with the crankcase vent / oil separator system?