Gas in transmission in 250R ATC

[rmcollector]

Ok, wasn't aware of this. Im thinking the only other way for gas to get into the transmission would be from a failed center gasket?

[ps2fixer]

I'm sure sure what the part looks like, but it's possible it could have a groove worn in the metal for the bearing seal. I'd think it would have to be pretty bad to have it leak though. Based on what ironchop said, it might just be normal unless assembled.

[yaegerb]

Any thoughts on this?

Yeah.....all new bearings and seals. It’s leaking behind the collar because your o ring is worn out. It Hides right behind the collar. Putting it in backwards is not necessary and don’t even know why you are doing that. Also, Check your crankshaft runout and make sure there’s no up/down play in your big end bearing.

[bkm]

Did the pressure test and found the left crank seal is leaking, it holds pressure for some time, but drops after awhile. Also, I took the right case off and pumped some air into the boot to find that the right side has bubbles coming out of the bottom of the collar, when I put the collar in the other way...it doesn't leak at all. The collar is smooth on the inside. Crankshaft splines are in nice shape.Attachment 261498Attachment 261499 Any thoughts on this?

Were you testing the right side (water pump side) seal with the crank gear torqued down? That side has to be pressure tested with the crank gear torqued down. There is no o-ring behind that collar and is held tight to the end of the crank by the gear to form an air tight seal. When the transmission is full of oil, the viscosity of the oil in the splines and under the collar prevents air leaks. The older air cooled bikes used an o-ring there, but not the liquid cooled bikes. It looks like the face of that collar has been very hot in the past indicating it was stationary while the crank was spinning at some point in its life. If that's the case, the surface that goes against the crank may have high or low spots causing the leak. I still think you have a center gasket issue though. I'd lap both side of that collar to make sure its perfectly flat.

[rmcollector]

Yeah.....all new bearings and seals. It’s leaking behind the collar because your o ring is worn out. It Hides right behind the collar. Putting it in backwards is not necessary and don’t even know why you are doing that. Also, Check your crankshaft runout and make sure there’s no up/down play in your big end bearing.

What part # is the o ring? I am not seeing it on the list. bkm, you say there is no o ring behind the collar? Im not seeing one.

[bkm]

What part # is the o ring? I am not seeing it on the list. bkm, you say there is no o ring behind the collar? Im not seeing one.

No, not that I've ever seen and the parts fiche does list one either. The seal is formed by the collar against the crankshaft.

[bkm]

Here's my unscientific take on the whole collar o-ring deal. Guys rebuild these engines and pressure test them. They leak there because they are not checking with the crank gear installed or if it is, everything is new and super clean and dry, unlike in a full lubed running condition. But what is not being done is a leak test after it is full of transmission fluid and all buttoned up, plus, no one can prove this collar leaks when the engine is running. My opinion is the o-ring trick is used to mask a condition that doesn't exist in a engine while in its running state. But, a pitted or worn out crank/collar will cause a leak. How bad???? I seriously doubt enough to make a real difference in jetting or sucking gas through it.

[rmcollector]

Were you testing the right side (water pump side) seal with the crank gear torqued down? That side has to be pressure tested with the crank gear torqued down. There is no o-ring behind that collar and is held tight to the end of the crank by the gear to form an air tight seal. When the transmission is full of oil, the viscosity of the oil in the splines and under the collar prevents air leaks. The older air cooled bikes used an o-ring there, but not the liquid cooled bikes. It looks like the face of that collar has been very hot in the past indicating it was stationary while the crank was spinning at some point in its life. If that's the case, the surface that goes against the crank may have high or low spots causing the leak. I still think you have a center gasket issue though. I'd lap both side of that collar to make sure its perfectly flat.

Yes, I have the crank gear torqued down when trying to perform pressure test, problem is, I can't get any air to hold because all the air is coming out of the rear transmission bearing. Air shouldn't be coming out of the transmission area, being it is sealed off with the center gasket, correct? Either way, I am splitting the cases, just want to have a good understanding of the engine.

[bkm]

Yes, I have the crank gear torqued down when trying to perform pressure test, problem is, I can't get any air to hold because all the air is coming out of the rear transmission bearing. Air shouldn't be coming out of the transmission area, being it is sealed off with the center gasket, correct? Either way, I am splitting the cases, just want to have a good understanding of the engine.

Yes, you're pissing in the wind until you fix the big leak.

[yaegerb]

What part # is the o ring? I am not seeing it on the list. bkm, you say there is no o ring behind the collar? Im not seeing one.

Honda Part Number: 91301-250-000

Its on all 81-84 of the ATC 250R partzilla microfiche in the piston/crank section. No idea why 85-86 doesn't have this part called out as the collars' machined lip remained unchanged for the 85-86. The other interesting tidbit I will add is the aftermarket gasket kits (when you order the full kit) comes with the 21.5MM o-ring made for this application. I use it on 250R motors I rebuild and have removed it from other motors I have rebuilt.

Do what feels right.

[rmcollector]

Honda Part Number: 91301-250-000

Its on all 81-84 of the ATC 250R partzilla microfiche in the piston/crank section. No idea why 85-86 doesn't have this part called out as the collars' machined lip remained unchanged for the 85-86. The other interesting tidbit I will add is the aftermarket gasket kits (when you order the full kit) comes with the 21.5MM o-ring made for this application. I use it on 250R motors I rebuild and have removed it from other motors I have rebuilt.

Do what feels right.

Good info. I split the cases today and found the gasket has a pinch/tear in it where it keeps the crank/transmission separated. Almost looks like it happened possibly when put back together and maybe the transmission gear may have caught it. Not sure, but definitely needs replaced along with seals and possibly bearings.

When you put the center gasket in and seal it up, do any of you use any sealant or just the gasket alone? Im sure everyone has a different opinion on this, but curious.

What gasket sealant are you using on your rebuilds? I found Hondabond to do pretty good, but never used on a center case. Hi-temp sealant for the center case?

[yaegerb]

Good info. I split the cases today and found the gasket has a pinch/tear in it where it keeps the crank/transmission separated. Almost looks like it happened possibly when put back together and maybe the transmission gear may have caught it. Not sure, but definitely needs replaced along with seals and possibly bearings.

When you put the center gasket in and seal it up, do any of you use any sealant or just the gasket alone? Im sure everyone has a different opinion on this, but curious.

What gasket sealant are you using on your rebuilds? I found Hondabond to do pretty good, but never used on a center case. Hi-temp sealant for the center case?

Hondabond/Yamabond both work well. I use 1211 3 bond. No gasket sealer is needed if you can confirm the cases are completely flat or if you lap them. If you are unsure or don’t want to spend the time to true the cases use a sealant.

[ps2fixer]

I've heard of people using red rtv as a gasket sealer but it needs to be applied thin. Too much and the excess can come off and block oil passages. I suspect there are other similar products too that isn't that ugly red that most people hate to see lol. I think the product line for that kind of application is called gasket dressing.

[bkm]

Here's an old thread regarding the O-Ring on a liquid cooled 250r.

Dont use red rtv or rtv of any kind on cases. It gets into bolt holes and blows out the threads and really causes issues. If you're going to use sealer, take yeagerb's advise.

Skip past the idiot Barnett talking stupid. You'll thank me later.


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[atc300r]

I use this copper spray on all my gaskets now.