Topic: Oil blowout all over rear tire, swingarm etc. 750K3

[Duke McDukiedook]

OK, I have been putting up with minor oil leaks from the head, chain oiler, oil pressure sender unit that I replaced this last year and other nooks and crannies where oil likes to seep out of on these bikes.
Well it seems these last two rides, especially today's ride finally made the engine barf up some serious oil all over the rear. It looked like the crankcase breather put some oil out along with the overflow tube that was still dripping when I parked the bike just before I came in. When I went out this evening after work I noticed some decent puddles under the center stand and the rear brake drum adjuster bolt. The bike seems to run fine but the oil was pretty low after all this oil loss. I am surprised I didn't wipe out on any turns but was lucky I didn't have to lean the bike much otherwise wash out time.

Could this be a possibly be a leaky Tube A, Breather tube from the back of the crankcase leaking all this oil? Number 10 on the partsfische pic. What size tube is this in case I need to replace it because it does not appear to be for sale.

Any help is appreciated.

[MCRider]

This event usually occurs because that tube is possibly leaking or more likely is not hooked to the oil tank properly. It "breathe's" into the tank, not the atmosphere. How's yours?

It is not nearly as long as that picture appears. It goes from the trans to the lower spigot on the inside side of the oil tank, about 8 inches or so.

[Duke McDukiedook]

I dunno, I kinda pulled the oil tank back and tried to visually inspect the line to get a better look at it and got a quick look. It looked like it was attached but it could be cracked underneath. What size rubber line is this?
The fische gave no size description.

[MCRider]

I dunno, I kinda pulled the oil tank back and tried to visually inspect the line to get a better look at it and got a quick look. It looked like it was attached but it could be cracked underneath. What size rubber line is this?
The fische gave no size description.

Access is from the left side of the bike. Leave the oil tank hooked up. Remove the elect sidecover. Reach in. AS to size, dunno. sorry.

[scottly]

Could this be a possibly be a leaky Tube A, Breather tube from the back of the crankcase leaking all this oil?
Any help is appreciated.

Could it possibly be that when you awakened the trusty steed from it's winter sleep, you dutifully checked the oil level, and, finding it low, topped it up?

(I've done it. )

[Duke McDukiedook]

I topped it off from the last ride but I checked it after I was done riding.
I could have over filled it but I doubt it.
I have been riding it all winter except for the last snowstorms.

[scottly]

That hose on the back of the crankcase is an oil drain from the oil separator inside the oil tank; there normally isn't a large amount of oil that flows through it. The breathers are the 1/2"(?) spigots near the top of the oil tank, and the rear of the cam cover.

[Dream750]

Could this be a possibly be a leaky Tube A, Breather tube from the back of the crankcase leaking all this oil? Number 10 on the partsfische pic. What size tube is this in case I need to replace it because it does not appear to be for sale.

The size is 7.5 mm (inner diameter) If it’s hard to source locally, then genuine Honda fuel tube can be used as an interim fix.

http://www.davidsilverspares.co.uk/tubes/

[thrutheframe]

That hose on the back of the crankcase is an oil drain from the oil separator inside the oil tank; there normally isn't a large amount of oil that flows through it. The breathers are the 1/2"(?) spigots near the top of the oil tank, and the rear of the cam cover.

I'm glad I read this.  My K4 is currently dismantled awaiting $$ to buy all the parts to get it back together properly.  There was no hose connecting that to the oil tank.  I would have missed that or put a small air filter on it.

[HondaMan]

The K3 came in 2 sizes: the little one and the bigger one. The little one is about 7.5mm, the larger one is nearer 12mm. The spigot on the back of the engine is probably the easiest place to look, unless you remove the battery. Then it's easy to see. They tend to crack on the bottom of the upward bend, back of the engine. Then, if the tank drained some oil into the cases during an extended sit, this tube gets very 'wet' and if cracked, makes a mess!

Make sure the little hose clip is still there, on both ends. Even though they aren't very big, they sure make a big difference in leak-not.

[Duke McDukiedook]

Thanks, that sounds like what probably happened here, my bike sat since the last two storms we received in KC.
I'll check with my local Honda guys and then probably go to US spares if the dealers don't have it.

[Duke McDukiedook]

Eh, I ordered an oil pan gasket since it looks to be leaking from there too so I'll take a looky-loo at the pump and screen while i am doing that. Damn thing is leaking like I sweat in the summer time. 
I wonder if some of this leaking might have something to do with the fact that I changed to the full synthetic I was using on the VFRs this fall.

[Dream750]

Probably a good idea to closely inspect the oil pan while you have it off, especially around the drain plug hole. As they have been known to crack and leak oil. Here are a couple of examples: 

[70CB750]

Eh, I ordered an oil pan gasket since it looks to be leaking from there too so I'll take a looky-loo at the pump and screen while i am doing that. Damn thing is leaking like I sweat in the summer time. 
I wonder if some of this leaking might have something to do with the fact that I changed to the full synthetic I was using on the VFRs this fall.

I heard that one before, the theory is that the synthetic oil washes out deposits in old rhino oil soaked gaskets and the engine starts leaking. But it takes more than few month to happen.

[HondaMan]

Eh, I ordered an oil pan gasket since it looks to be leaking from there too so I'll take a looky-loo at the pump and screen while i am doing that. Damn thing is leaking like I sweat in the summer time. 
I wonder if some of this leaking might have something to do with the fact that I changed to the full synthetic I was using on the VFRs this fall.

I heard that one before, the theory is that the synthetic oil washes out deposits in old rhino oil soaked gaskets and the engine starts leaking. But it takes more than few month to happen.

Yeah, that's why I have to take my engine out, now. After 2 seasons with the Mobil 1 15w50 synth, it leaks out of every gasket on the engine. Sure made it shift nice, though...

[Slug750]

Sounds like you might be sorted but reminds me of a close call I had a couple years ago on the Harley 883 Sportster I had at the time. Headed off one morning and felt rear slide out big time on a bend 2 kilometres from home. Luckliy managed to straighten up enough to stop. Back wheel and everything rear of the swing arm was dripping oil. Local Harley guy checked it and said it happened rarely but had also happened to him on his Heritage. He said a rubber bung that's meant to allow oil to flow one way through lines can sort of seize up with gunk if bike has been sitting for a while, and oil surges out when pressure rises. Not even sure whether 750/4's have similar rubber valve. Slug.

[70CB750]

My morning commute idea is to alternate it with dino oil, I am just afraid synthetic oil is addictive

[HondaMan]

My morning commute idea is to alternate it with dino oil, I am just afraid synthetic oil is addictive

I'm sure gonna miss the once-per season (or so) oil change when I go back to dino oil. I usually go 1000-1500 miles on that stuff, went 5000 on the Mobil 1 with no loss of power, no noises, still felt like a fresh oil change. Way cool stuff, if it would just behave better....like my dogs, I think it needs a leash?

[Kickstart]

Hmmm... I use Mobil 1.

I used 15w-50 for a couple years in my old 75' 750F... and don't remember any problems.  (that was a long time ago though... back when Mobil was really fully synthetic)

I'm using Mobil 1 V-twin in my current 75' 750F.  I've been using it for at least one year now and I don't notice any leaks.

[Kickstart]

Oh... Dukie.... was it the oil breather hose?

[Rigid]

Rotella. BTW, is it possible that a slight crankcase pressure is created with all the stock hoses attached and that aggravates the already thin synthetic?  I never have had gasket or seal leaks with dino oil and open vent lines on bobbers.

[MCRider]

Sounds like you might be sorted but reminds me of a close call I had a couple years ago on the Harley 883 Sportster I had at the time. Headed off one morning and felt rear slide out big time on a bend 2 kilometres from home. Luckliy managed to straighten up enough to stop. Back wheel and everything rear of the swing arm was dripping oil. Local Harley guy checked it and said it happened rarely but had also happened to him on his Heritage. He said a rubber bung that's meant to allow oil to flow one way through lines can sort of seize up with gunk if bike has been sitting for a while, and oil surges out when pressure rises. Not even sure whether 750/4's have similar rubber valve. Slug.

The CB750 one way valve reside in the oil pump. Probably not the problem here, but it can stick and drain the oil tank into the sump. Called "wet sumping".

[Duke McDukiedook]

Oh... Dukie.... was it the oil breather hose?

Still waiting on the oil gasket to come in from cyclepartsoutlet.com and I forgot to call the local shops because of some crap I had to take care of at work on Friday and had to pick up the missus at the airport. Flat out forgot to call the dealers on Saturday so I'll have to wait until Monday. Sounds like I may want to go back to my regular Castrol though and save the full synthetic for the VFRs. I just don't want to tear down the engine to change gaskets and seals when everything else is OK.

[Duke McDukiedook]

Ok, could not find a 7.5mm fuel hose at the local stealers so I decided to buy some smooth 7.5mm ID high pressure line from Bel-Metric.com
Should be getting that in the next couple of days.

https://www.belmetric.com/rh75hp-smooth-high-pressure-p-958.html?zenid=4ch4d2obms5fo4g3ad60kuvqs5&cPath=14_139

[Gregorymoto]

Back when I still ran a stock oil tank this would happen to me when I over filled the tank.