Forum

[chonpuun]

hi, i have a 1948 ,model j. oil is pouring out off the oil tank filler cap,after a good run, which makes me think the crankcase breather might be blocked. , the manual states that the breather is situated behind the primary case, hitchcocks, tell me the same thing , after pulling the inner and outer primary covers off, i am looking at the crankcase, no breather, only bolts holding the crankcase together. , any ideas? .thanks rick

[Mark M]

I think they mean the primary chaincase, that is the case that contains the clutch and it's chain. Sorry if that's where you're looking already! The Parts Book implies that the breather is a pipe that feeds from the left side of the engine to near the gearbox sprocket. There may also be a breather through the drive side (left) crankshaft axle into the same primary case but I'm no expert!

REgards, Mark

[chonpuun]

thanks, MARK , i just rang hitchcocks , they looked at 1948 crankcases. and the breather is where i thought it should be behind the primary. but my model j crankcase has not got one , so they are saying on my 1948 model j, i have pre 48 cases. so i am a bit lost i thought all bikes had breathers from the crankcase. or does mine breath thru the oil filler cap?.rick

[papasmurf]

Could just be over filled with oil. (A lot of us have been caught out by that over a wide range of models.)

[chonpuun]

thanks for all replies, found it thanks to hitchcocks, and a few other people. the breather outlet on a 1948 model j is on the crankcase facing the primary.. but on my 48 , for some unknown reason it has pre 48 cases, that have a breather that is under the magneto,a vent that is about 25 mill, running down the crankcase join.facing towards the gearbox.rick

[WDCO42]

Hello Chonpuun,
In fact, there are 3 breathers ont the J (as on the G and the CO) : the main, connected to the crankcase is on the left side of it, for the J model it is at the back, on the G and CO it is at the front of the crankspidle. The second one is by the oil filler cap, and vents the front oil tank. But there is too a breather for the rear oil tank, that is effectively on the rear of the engine and I suspect it is the one you are speaking of. The trouble is that it only vents the rear oil tank, and isn't connected to the crankcase. So there is some mystery about that. The best, if you can, should be that you send a picture of your left crankcase. Hope it will help you Claude

[Hopeless Rider]

Hi,
The problem that you decribe is not uncommon to the Model Gs and Model Js. The oil tanks on these have the front half of the oil tank and the rear half of the oil tank that balance through a small gallery in the bottom of the crankcase. One path of the returning oil is from the pressure relief valve under the oil filler cap, into the front oil tank chamber, thru the small internal oil pathway in the bottom of the crankcase to the rear oil tank chamber. 2 situations can cause your problem 1) the rear oil tank breather is blocked (partially) stopping or restricting the flow from the front to the rear tank, or 2) the internal passage between the front and rear tank is partially blocked causing the oil to slowly build up in the front tank and flow over from the filler. Depending on how long since the engine has been stripped the restriction could be caused by sludge in the bottom of the oil tank, or if the engine has been apart recently the sealer that was used has caused a restriction by encroaching into the oilway. I have experienced both of the these situations. The latter can be caused by liberal use of silicon (not a good sealer for Royal Enfield crankcases as unlike the Indian models don’t have a gasket.) What you can try is to fix it is to remove the rear oil tank plug (with the gauze on it), poor some light weight oil into the front tank and push it thru to the rear tank with compressed air. Replace the rear oil drain plug and if you fill the oil tank you should see the level slowly drop as it balances out to the rear tank. As mentioned the rear oil tank breather is cast in as an ‘S’ into the crankcase mating halves under the magdyno. The only blockage I have seen here are bugs crawling up inside and causing a blockage (was actually ants).
Remember that this problem needs to be sorted properly because if you have oil building up in the front tank the rear tank may be getting too low to have enough oil to feed to the bigend. Hope this helps. Regards.

[chonpuun]

thanks for all the replies, there is a lot of information out there , and its good to share, yes you are right, the external breather i have found as you said , on the crankcase joins , opposite the magneto , its only about 25 mill long, had trouble finding it because all parts books for a 1948 model j , say its on the sides behind primary. all good . thanks rick