angle of valve guides

[JohnSchofield]

Need to replace the valve guides in a pair of Javelin/Jupiter cylinder heads, and am about to drill out the bulk of the metal, the big hammer and machined drift method having failed to shift the little blighters.
Does anyone know the angle between the guide axis and a line at right angles to the cylinder head face?

It looks like 10 degrees, but before I set up the milling machine head it would be nice to have independent confirmation.

Is it best to push them in or out?

Thanks in anticipation and happy Christmas to all.

John Schofield

[Keith Clements]

I am surprised you cannot shift them. Did you try some heat?
I do not know the angle but suggest you clamp the head to the mill bed and then set up the mill head with an HSS drill that passes through the guide. Then fit a larger drill to bore out. More accurate than knowing the angle, unless the guide is totally worn of course! But anyway the guides are brittle and will shatter if you have taken some of the meat out.

[JohnSchofield]

thanks Keith.

[johnairey]

Best if you have a drift with a pilot to prevent casting damage during the driving out.
The pilot needs to be an easy fit and the drift a few thou under the 9/16 O.D. of the guide.
The head needs to be well supported to drive out the guides.I have always driven the guides from the rocker face of the head without any problems.
Valve angles Inlet 30 degrees Exhaust 45 degrees.

[ian Howell]

Those angles are presumably the ground VALVE SEAT angles - not the angles of the guide axis to the head face?

[Keith Clements]

When racing, I did some research and experimentation on valve seats and gas flow around them. A good starting point are the Competition Tuning Notes Page 5 para e. Note the 60 deg turbulence (second) angle and 35 deg primary angle on the inlet port.
The angles quoted by John are in the tech notes and are for the valve faces.
Assuming 'standard' inlet valves would be pre ground to 30 deg, some regrinding of these valves to suit the modified inlet port cut to 35 deg was required prior to lapping into the dual angle valve seat.
To get the narrow seat of 1/16 inch, they may not have been so reground before fitting but lapped/ground in as they were, thus creating a triple angle seat with the valve only touching the seat on the face close to the stem end. My gut feeling is that this is not good (for performance) and the closing part of the valve should be as close to the valve head as possible.
Such a 'rounding' of the exit to the port may not be desirable as the sharp angle to produce the turbulence would be lost. This is similar to the rear end of cars that often have a sharp edge to induce turbulence to keep the rear end down.

No doubt examination of modern engines should yield the most desirable shape although it may not be the best for a Jowett combustion chamber. Any body fancy putting the Jowett inlet tract into a CAD system?

[JohnSchofield]

Well done, Ian. That was the angle I wanted, I think it's 10 degrees. Anyway, as Sarah Palin said, it's 'drill baby drill' time tomorrow.

I was hoping someone who had the drawings would have a quick look. But do we have the drawings? Someone in another car club I belong to rescued most of the factory drawings (blueprints), jigs and tools just before the company was about to throw them in the skip, and they are now available on that club's website or on loan as appropriate. Heroism!

Did anyone perform the same rescue operation in Bradford, and if so, who has them, and have we thought about getting them digitised?

thanks,

John

[ian Howell]

John: -

I suspect you are about to be descended upon from a great height! That is EXACTLY what a dedicated sub-group known as 'Archive' are doing!

They will no doubt tell you what drawings are available, although they may not yet have been digitised and added to the archive.

However, since all you need to know is an angle, I am sure someone with access to the relevant drawings will be only too pleased to help.

Watch this space!

[PJGD]

I have attempted to do CAD drawings of several Jowett components and many of them appear in my Gallery. Specifically, a drawing of the inlet valve seat angles appears here: here

[JohnSchofield]

Just what I wanted, many thanks and happy new year
John