Oil leaking from push rods

[Tony Fearn]

A Very impressive bit of fettling Chris!
If George Garside was still posting on here, I'm sure he would have commented.
Tony.

[k. rogers]

Hi Chris, I know it has been a while since this post, but has there been an improvement with the oil leaks since doing the breather flap?

[ChrisE]

Hi,

yes I think it has cured it.

Chris

[k. rogers]

I've taken your lead and used a piece of tape measure as a spring on mine and I believe there is a further improvement on oil loss!

[Brucegirvan]

Thank you for this thread. As Eddie 1930 7hp has been coating it’s underside with oil for some time, I was heartened that here was a possible solution. Apologies for the poor images, but as you can see the oil breather is somewhat different to those posted, it is not a separable unit but is part of the engine housing casting. The 5 holes connect straight through to the oil fill pipe and hence will see crankcase pressure. The circumference on which the 5 holes are drilled means that the holes align with the outer ring in the cover plate. A few measurements show that when assembled there is clearance between the inner faces of the cap and the cast plate with the 5 holes. Which means that there is space for a valve! Should this be a disc of leather with a light wire spring located in the outer ring of the cover plate and the leather valve material? Or does it operate without a flapper valve?

Any help welcome. Engine oil pressure shows a healthy 30-40psi when running.

58EE31B3-56F7-46A4-8F5C-CA85721A5EBE.jpeg

Inside of the breather cover

2E72EF9A-C164-4F70-844E-6AB2CE99FECC.jpeg

Oil filler cap removed and breather cover on the left. The breather cap faces the bulkhead of the car and is not separable.

929EA75B-D317-4634-BBCF-09C99EC99BEA.jpeg

Breather cover off showing 5 drilled holes that go through to the oil filler pipe. The drain hole is just visible at the very bottom.

Regards
Bruce Girvan

[Tony Fearn]

Hi Bruce,
There should be a thin, spring steel 5-vane breather valve covering the holes, with a smaller stiffener plate over it.
The latter keeps the former against the casting with the holes in it until crankcase pressure opens it.
The scanned scribble below should give an idea.
JCS advertised them in the Jowetteer sometime this year I seem to remember.

Image (102).jpg

Tony.

[Brucegirvan]

Thank you Tony - I have just located a description in the Technical Information for Pre-War and Veteran Jowett book that is on Jowett Talk, which I stumbled across reviewing another oil leak link this morning. It is very useful to have the sketch too. I will contact the JCC Spares on Monday. It will be interesting to know if this does reduce the leakage. I have checked that the drain hole is clear. I also noted in the book that there is a drain hole I should check in the timing cover and rear crank case. Not sure I have seen these yet. I will report back on degrees of success. I do look forward to meeting you some day, Tony. Best regards and thank you again.

[Brucegirvan]

For those intrigued as to how Tony’s sketch looks in the metal. I’ll update the result in due course.

983F3176-E39C-4114-9FA1-DFBCC9E11853.jpeg

C72642A2-60C0-44A2-81DC-7E8FDA609DD7.jpeg

153FF079-0A37-4301-A72F-8536ABBE4DB9.jpeg

25B928AA-DE37-4852-9C2B-198DBAD19300.jpeg

8C504D7E-58C5-48BF-91DA-F4C4CC1258EE.jpeg

[ChrisE]

The breather valve is far, far more important than the benign thing it looks to be!

see viewtopic.php?f=4&t=5461&p=42732#p42731 about negative air pressure in the crank.

Well done for making it so good!

Chris

[Tony Fearn]

Bruce, I have sent you a PM
Tony.

[Brucegirvan]

Thank you, Tony.

My initial try out with the breather valve indicates partial success. Now I need to tidy up around the sump and service a few joints etc....after a good clean that is.

[ChrisE]

Hi Bruce,

where did you get your new star-shaped-springs from or where did you get the material to make them from?

thanks
Chris

[Tony Fearn]

I've just found a reference to pre-war 7hp crankcase pressure hidden in my miscellaneous file.
It may be of use to add it to this thread it for posterity.

The thing to remember about a flat twin is that both pistons travel to BDC together, and then to TDC together. In doing so, they displace from the crankcase the same amount of air as the total swept volume (piston area x stroke) of both cylinders; that is to say if the engine displacement is [for the sake of argument] 800 cc, then that amount plus piston ring blow-by must come out through the breather and then a fresh 800 cc must return back into the crankcase for each revolution of the crankshaft. That is a lot of air and would require a large breather pipe, otherwise the work involved in constantly pumping that air in and out through a small breather pipe would be a definite parasitic to engine power.

What makes sense to me is that the Jowett breather is intended to let all the air plus blow-by out of the crankcase as the pistons travel to BDC but then prevent air from getting back in as the pistons move to TDC, thereby creating a depression in the crankcase. Then during the next 180° of crank rotation, the only air that needs to exit through the breather is the relatively small amount of gas blow-by past the piston rings, hence only a relatively small diameter breather pipe is perfectly adequate. Then the cycle starts again.

Therefore, it is necessary that the breather flap, whether it is made from leather, neoprene, or other compliant material, will form a positive seal over the breather hole under the vacuum conditions that temporarily exist in the crankcase. It also makes sense that there would be a light spring over the flap to encourage it to seal. When working properly, the advantage of this arrangement is that for 180° out of the 360° of crank rotation, there is a vacuum in the crankcase which is a strong deterrent to oil from leaking out of the engine through the crankshaft seals or out of the tappet bores. When not working properly, i.e. the flap is not sealing, then there exists a positive pressure in the crankcase which give the oil a strong incentive to leak out of every clearance available to it.

Tony Fearn.
P.S. The text ended in 'Philip'

[PJGD]

Hi Tony; That is me: Philip Dingle, and that posting was made 30 January in this same thread!

I am happy to see that there is a very active pre-war section and activity on this forum. Back in the early 70's, I had an early 30's Weasel (if I remember correctly), two tone black and green.

One of the things that I have a strong opinion on is that some of the engineering of the early engines had much to teach the later engines, and particularly the Javelin. I am thinking of the early engines with the gear drive to the camshaft, later changed to chain, probably as a cost reduction feature. Also, the 10 HP engine with the common crank pin for cylinders 2 & 3, it requires a 4 bearing crankshaft for a modern engine rather than the 2 bearing of the 10.

Philip