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Ongoing unfixable oil migration issue

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Just rebuilt the motor on my 2006 250x. New crank, cam chain, piston, valves etc. For the first 2 years I had it I clocked up 170 hours and the whole time it would slowly put engine oil into the transmission. Never enough to cause an issue or need oil between changes (15 hours) but it was always  transferring.

Then after replacing all seals and gaskets and crank and inspecting everything it now pumps transmission oil into the engine at quite an alarming rate. 1/2 hour of riding and the transmission level drops by 1/2". I had used the updated right side crank seal supplied with the bottom end kit and it turns out I had it in backward. Then I took it back apart and put the old style seal that also came in the kit in (the right way) and it made no difference. Last weekend I pulled it apart and put new Honda seals (R Crank and balancer seals) and gaskets in it and it still isn't fixed.

What else could cause this? Cases are in great shape with no cracks. It was running when rebuilt. Just needed a freshen up. It makes no difference if I take the transmission breather hose off. Vents aren't plugged. I was under the impression that the crank and balancer seals were the only things that could cause this. Grand total of 8 hours on it with 3 different Right cranks seals and 2 different balancer seals

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CRF Doc is probably the one to ask on this and listen to as he has far more knowledge and experience, but a few things come to mind:

1. Is the engine side vent open?

2. Was the balancer shaft checked for wear and straightness or has it been replaced?

3. Did you replace the balancer shaft bearings?

4. A crack in the case that opens when it gets hot.

5. A defect in the case where the crank seal sits (i.e. not round).

Jim.

 

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Balancer shaft is in great shape and bearings were not replaced. They are quiet and no play or visible wear. Cases looked great when I had it apart. Seal fits tightly. Engine side vent- is that the one in the valve cover? That vent is hooked up like it's supposed to be. 

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16 hours ago, CarmanCRF said:

Just rebuilt the motor on my 2006 250x. New crank, cam chain, piston, valves etc. For the first 2 years I had it I clocked up 170 hours and the whole time it would slowly put engine oil into the transmission. Never enough to cause an issue or need oil between changes (15 hours) but it was always  transferring.

Then after replacing all seals and gaskets and crank and inspecting everything it now pumps transmission oil into the engine at quite an alarming rate. 1/2 hour of riding and the transmission level drops by 1/2". I had used the updated right side crank seal supplied with the bottom end kit and it turns out I had it in backward. Then I took it back apart and put the old style seal that also came in the kit in (the right way) and it made no difference. Last weekend I pulled it apart and put new Honda seals (R Crank and balancer seals) and gaskets in it and it still isn't fixed.

What else could cause this? Cases are in great shape with no cracks. It was running when rebuilt. Just needed a freshen up. It makes no difference if I take the transmission breather hose off. Vents aren't plugged. I was under the impression that the crank and balancer seals were the only things that could cause this. Grand total of 8 hours on it with 3 different Right cranks seals and 2 different balancer seals

It sounds like you have looked everything over closely and tried several seals just to cover those bases so its tough to add to that but a couple of other questions come to mind about it. You said all the vent hoses were checked and werent restricted, did you put air pressure through them individually?

The other thing I wanted to ask about was checking the fluid levels. So at this point does the engine oil level go up on the stick because of the trans fluid mixing with the engine oil? I dont check the trans fluid level because I dont have an accurate way to do it without draining it and then measuring it.

It sounds like you didnt change the crank main bearings when you put a new crank assembly in? Did the original crank put metal particles in the engine and oil?

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Breather hoses are clear. 

2 hours ago, TDW said:

It sounds like you have looked everything over closely and tried several seals just to cover those bases so its tough to add to that but a couple of other questions come to mind about it. You said all the vent hoses were checked and werent restricted, did you put air pressure through them individually?

The other thing I wanted to ask about was checking the fluid levels. So at this point does the engine oil level go up on the stick because of the trans fluid mixing with the engine oil? I dont check the trans fluid level because I dont have an accurate way to do it without draining it and then measuring it.

It sounds like you didnt change the crank main bearings when you put a new crank assembly in? Did the original crank put metal particles in the engine and oil?

Breather hoses are clear. Blew air through them. Makes no difference if I disconnect them and take it for a short spin around a field. I check oil by putting it in a stand and running it for 3 minutes and letting it sit for 3 minutes like the manual states.

Engine oil is constantly going up and transmission oil is constantly going down. I check transmission oil by pulling the inspection plug by the clutch cover and then comparing the level to the check bolt. The level can be seen quite clearly against the starter clutch on the end of the crank. 

New crank bearings. The old crank was fine and I didn't really have to replace it but it had a little more side to side rod play that I like to see. 

Here is what was replaced

all gaskets And oil seals

valves, springs, retainers etc

piston, rings, pin

Crank (2mm hotrods stroker), crank bearings,cam chain, cam chain slider, decompression spring, both mainshaft bearings and both countershaft bearings,

more that I'm sure I'm forgetting

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You have covered all the normal things so, it seems now its down to things that arent so obvious, such as the center case gasket or a lack of a proper gasket seal there. Is the center case gasket an OEM part?

Did you remove any of the three bolts that hold the starter gears? Number five in the parts diagram.

https://thumpertalk.com/shop/oem.php?partcategory=669018&manufacturer=1&category=5&year=2006&model=24683

Edited by TDW

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4 hours ago, TDW said:

You have covered all the normal things so, it seems now its down to things that arent so obvious, such as the center case gasket or a lack of a proper gasket seal there. Is the center case gasket an OEM part?

Did you remove any of the three bolts that hold the starter gears? Number five in the parts diagram.

https://thumpertalk.com/shop/oem.php?partcategory=669018&manufacturer=1&category=5&year=2006&model=24683

Yes I had the starter gears off. Cases were completely stripped down and cleaned. Center gasket and top end gaskets are the ones that came with the hot rods bottom end kit. They matched up well and looked good. The side cover gaskets I replaced with Honda parts when I replaced seals

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Just putting some not so obvious possibilities out there, IIRC those bolt holes go straight through but I dont remember right now if there was any type of sealer or loctite on the threads. Other than that I cant think of anything else to check right now. Hope its not a center case gasket issue!

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A crack in the case that opens when it gets hot.

A defect in the case where the crank seal sits (i.e. not round)

I just went through this same issue.
If you've did everything you say and it's still leaking, double check the 2 things Jim mentioned above.

It's possible you have a hairline crack in your crankcase (mine did).

In my engine, I assume it happened during the installation of the new crankshaft main bearings.

That aluminum is kind of fragile and it's not hard to induce a crack if you don't get the bearing cold and the crankcase hot enough during the bearing installation.

The crack can be hard to see, but when the engine gets hot, it opens up and allows the oil to migrate.



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There must be more pressure in the transmission cavity than in the crank cavity.  But the transmission side is vented.  Isn't there also a reed valve between the cavities?  I didn't see that mentioned here anywhere.  It would have been removed if the cases were stripped and cleaned. Could it have been missing, damaged, or improperly installed from the beginning?

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There must be more pressure in the transmission cavity than in the crank cavity.  But the transmission side is vented.  Isn't there also a reed valve between the cavities?  I didn't see that mentioned here anywhere.  It would have been removed if the cases were stripped and cleaned. Could it have been missing, damaged, or improperly installed from the beginning?

The vacuum from the engine will suck oil from the transmission side if there are any breaches.
There is an oil reed valve. The reed valve wouldn’t have any effect on oil migration. The reed valve is only in the engine side and it’s purpose is to allow oil to drain down into the crankcase while keeping the piston from sucking too much oil out on the compression/intake stroke.

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Here is another thread with the same topic, also some discussion about the reed valve and what it does.

 

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Here is another thread with the same topic, also some discussion about the reed valve and what it does.
 

Can’t get your link to work

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Like he mentioned in your link, the oil reed valve is totally encapsulated in the engine side of the engine.
It keeps too much oil from being sucked out of the sump when your piston moves up.
If it somehow were damaged or installed backwards, it would suck too much oil up out of your crankcase.
It’s possible it could push oil out of your cam chain breather when that reed in backwards, but if would have no effect on the transmission side because they’re separated

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15 minutes ago, spokeking said:


Like he mentioned in your link, the oil reed valve is totally encapsulated in the engine side of the engine.
It keeps too much oil from being sucked out of the sump when your piston moves up.
If it somehow were damaged or installed backwards, it would suck too much oil up out of your crankcase.
It’s possible it could push oil out of your cam chain breather when that reed in backwards, but if would have no effect on the transmission side because they’re separated

The reed valve can only be installed one way, the shape of it prevents it from being installed incorrectly.

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On 2017-09-29 at 10:28 AM, spokeking said:


I just went through this same issue.
If you've did everything you say and it's still leaking, double check the 2 things Jim mentioned above.

It's possible you have a hairline crack in your crankcase (mine did).

In my engine, I assume it happened during the installation of the new crankshaft main bearings.

That aluminum is kind of fragile and it's not hard to induce a crack if you don't get the bearing cold and the crankcase hot enough during the bearing installation.

The crack can be hard to see, but when the engine gets hot, it opens up and allows the oil to migrate.


 

Well I'm guessing I'll have to tear it apart and inspect it

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Well I'm guessing I'll have to tear it apart and inspect it

There is also an o-ring (Honda calls it a d-ring) behind the balance shaft drive gear (transmission side). If that o-ring is cut or damaged, it could cause the oil to migrate.It sits in the shoulder on the inner side of the counter balance drive gear and it seals the drive gear and the shaft

 

That’s the only other thing I know to checkIMG_3322.jpg.f29cf33803c0debfccfa0fe166f3d094.jpg

 

 

 

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3 hours ago, spokeking said:

There is also an o-ring (Honda calls it a d-ring) behind the balance shaft drive gear (transmission side). If that o-ring is cut or damaged, it could cause the oil to migrate.It sits in the shoulder on the inner side of the counter balance drive gear and it seals the drive gear and the shaft

 

That’s the only other thing I know to checkIMG_3322.jpg.f29cf33803c0debfccfa0fe166f3d094.jpg

 

 

 

No there is no sealing ring there at all. The D ring is on the countershaft behind the drive sprocket.

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