The Crankcase Breather Valve on old Suffolk Mower Engines

[Ross365]

The old Suffolk engine has a breather valve that sits in the "valve chest". It allows air to leave the crankcase on the downstroke of the piston.

Perhaps more importantly, these engines are lubricated by "oil mist", and the only oil mist that can get to the valve stems must go through the breather valve, but you'd have to believe that not much can go that way.

I've seen lots of pictures of old Briggs and Stratton engines and Tecumseh which are comparable in design (the so-called "L" engines where the valve seats are upper most). From what I've seen the B&S has a hole in the bottom on the valve chest to allow breathing and lubrication (just like the Suffolk), but I've not yet seen picture of one that has a valve fitted in that hole, nor the Tecumseh.

Can anyone confirm that the B&S and Tecumseh doesn't have the valve, and the possibility that taking the valve out of the Suffolk might improve lubrication of the valve stems? I realise that someone at Suffolk thought the valve was a good idea, but he may not have thought that these engines would be working 40-50 years later, and worn stems and guides got to be a problem?

I just re-fitted the valves in the Punch and compressed the valves in a vice and held them compressed using cable ties. Never done that before, but it works well in the absence of a small compressor tool.

 

[merryman]

Modern car engines have seals on the valve stems to stop oil getting down them and into the inlet/exhaust ports. How are these stems lubricated? They are not, so Suffolk were ahead in the trend to un-lubricated valves. The breather valve creates a vacuum in the crankcase at every up stroke, so you are less likely to get oil leaks. No valve, and the piston would produce pressure in the case every down stroke, leading to oil leaks. That is why Royal Enfield singles were known as Royal Oilfields. B & S have a one way reed valve in the cover plate for the valve chest. Fairly sure later Suffolks had one there too.

 

[Robotstar5]

Here you go, start of the video shows them removing the spring loaded check valve

 

[Robotstar5]

Villiers used a different approach, the check valve was mounted in the side of the valve chest, just a simple ball bearing drawn onto a seat by vacuum and pushed against a retaining pin under pressure.

 

[Ross365]

Many thanks for those responses and I now realise I was not seeing the issue clearly. I am nearly finished re-assembling my Punch engine and carefully cleaned and checked the breather valve (it should, and does, rattle!) and installed it with the push-spring above it. The latter plays no role in the working of the valve but just helps keep it in place. I've heard the comment that people sometimes find that spring missing when they open up the valve chest, but it really ought to be there. The engine was not in too bad a shape, except that the head had a lot of soot inside and the exhaust valve clearance was way down at ~2 thou. As it wasn't burning oil, and the piston and bore were in fine shape, I'd have to believe that it's been running quite rich for sometime.