Hitchcocks Forum

Greetings! I am from sweden and i own a 1951 model g. Which is a lovely bike, the best motorcycle of the 5 that i have owned myself (22years old)

One big problem unfortunately... It has an massive oil leak.

Problem:
When idling there is no oil leak, it can stand there for 10-15min without leaking.
After a short ride with speeds up to 100km/h it has leaked massive amounts of oil from:
-Filling up and leaking from under the dymo/magneto, behind the timing chest
-Leaking from cylinder base
-Leaking from side cover (where you adjust the valves)
-Leaking from the crankcase vent on the left side of the engine.
-Leaking from the pushrod seals, in between head and cylinder.

Trying to fix it myself:
-Replaced every gasket possible, all felt seals and everything.
-Trying different amounts of oil, from very low to normal
-Open oil cap, to relif pressure? (riding with it open)
-Inspected crankcase breather, it seems normal to me.
-Inspections of oil pump and scavage pump, big displacement is at the front, correct?
i also checked that it has a good seal.

I really don't know why it is leaking this much oil, it is unrideable.

-Seems to me that it is filling up timing chest with oil and creating a very high oil preassure causing oil to leak out of every way possible really.

I really hope that someone is more knowledgeable than me on this kind of thing.

If not, maybe a email adress to a "Royal enfield expert"

/Marten Larsson Sweden.

hi, MARTEN.i have a 1949 model j , I had the same problems as you, oil everywhere, I am no expert but after a bit of research I realised the bike was not breathin properly, first of all as you know there are two positions on the oil tank cap, the cap pushed down hard is only for when the bike is not bein used , when the bike is bein used ,the oil tank cap is used on the first position. I checked the breather was clean, then drilled a hole in the oil tank cap and inserted a clear 10 mill plastic pipe with a duck bill breather on it and faced the pipe towards the chain, a simple job , and no more leaks. my bike just needed a bit more help to breath better,

Thank you chanpoon for the reply!

Hmm, does your "breather" have "reed-like" valves in it? Okay interesting about your oil cap, i am running it in the first position, but it didnt seem to make a difference. Maybe it need a larger hole in it. I will try, the bike looks good in the garage but i want to ride it much more this summer!

hi,MARTEN, yes the ten mill hole i drilled in the oil tank cap definatly decreased the crank case pressure ,and stopped the leaks . a few of my freinds on there older bikes have had the same problem, and made there bikes crankcase breathing better, even my 2005 bullet had breathing problems, the hole drilled in the cap was a simple fix but it works for me, i bought a new oil tank cap from HITCHCOCKS, and drilled the old one . a cheap fix

You shouldnt have to drill a hole in the oil cap. Despite the appearance this is a dry sump motor and any crankcase pressure needs to be relieved from the crankcase. Looking at the parts manual for the Model G I see breather pipe and body listed. You want to check this out first and formost and don't go drilling holes in the cap which the manufacturers in their undobted wisdom deemed unneccessary.

Hi Marten,
I have played with the Model G for many years and may be able to help. Built one up for vintage racing (somebody had to come second to last) so managed to keep all the oil inside. If you post your email address I can contact you with some possible remedies. Remember to spell your email address so the SPAM BOTs don't grab it and send stuff you don't want. Regards.

It sounds like the engine breather has stopped working. You say that the engine leaks a lot of oil out from all over the place when the motorcycle is being ridden but is ok when at idle. This sounds like the breather is blocked or not working and the pressure inside the motor has no where to go but out of the places that the leaks are coming from. The reed like valves in the breather sound like a place to look for a problem. I think that they are under the triangle shaped fitting on the engine where the breather tube fits on. There are 3 screws that hold this on. If I was trying to track down the problem I would take out the reed valves put the breather fitting back on and try riding the motorcycle that way. There would be no pressure build up in the engine as it could just breath in and out as the piston goes up and down. This is just to try this and not meant to be a permanant fixture. I would leave the duck bill off the end of the pipe as well. Just have an open pipe all the way out with no reed valves and no duck bill to get in the way of a clear open tube. Do not drill a 10mm hole in your oil cap. You tried riding with this cap completely opened and still it leaked. There is pressure building up inside the motor some how.

I have had a look at Hitchcocks model G 350 1951 parts book online and the breather tube is just a metal pipe coming from the triangle
fitting on the side of the engine. There is no duck bill with this set up. I recon that the reed valve opens when the pressure builds up inside the motor as the piston comes down and then closes to provide a vacuum when the piston goes back up again acting like a non return valve and keeping a vacuum inside the engine. I do not know, and just a thought. If you take the reed valve out and making sure that the metal pipe is clear by blowing through it, bolt it back on the engine and take the bike for a run. If the leaks are smaller then that points to a problem with the breather. One interesting point the Hitchcocks online parts book does not show a reed valve of any kind
associated with the breather at all. Who knows it is an old motorcycle that has had many past owners working on it.

Hi Marten, some models have a small hole in the oil filler cap, while others don't, make sure you have the right type. There are no two positions, or a 'transport' position for the filler cap, the engine should work with the oil filler cap shut TIGHT, you don't ride around with the fuel tank cap loose, after all - the slack position is just a catch to stop the cap coming off if it should be loose for any reason. It is possible your engine might have excessive blow by past the piston and rings, but make sure the oil scavenge filter gauze is clear before stripping the top end! Regards, Paul.

Thank you for all the replies! My email address is "m a r t e n 1 9 9 5 @ h o t m a i l . c o m" but no spaces!
I just yesterday took the primary case off and removed the reedvalves in the breather as an test to see if that made it better. It didnt, i made sure the pipe is free, its basically a hole out from the crankshaft(i can see it in the holes). If this doesnt relif the pressure then te pressute have to be somewhere else... Can it be a case of bad piston rings, compression blowing out??? Does the crankshaft it self have any oil seals worth replacing?