Cylinder head

[Stuart Giles]

Have been reading this thread with interest; someone did mention wedge machining in a previous post.

 When I fitted the '37 head to my '31 Tourer, I found that it gave better power than an unmodified early head, but the plugs in this late head did seem to be prone to oiling in a motor that burnt a small amount of oil. Not having the time or the money for an engine rebuild back then,  I modified an early head as per the photos below. I found that this mod  gives good power without the plug oiling problem of the early head. Also has the advantage of looking "absolutely original old boy" on an early car 
to any rivet counting observers who might happen along.

The early head on the right is as per factory, the one in the middle has 0.060" valve relief machined in. The one on the left has been "opened out" to the fire ring of a '37 head gasket and has the valve reliefs blended in to the combustion chamber.






I then wedge machined the head -you can see the 0.060" shims under the head in the photo below. 0.120" off the head in total, which is 0.060" off on the valve side of the head. I re-did the spot facing of the stud holes on the top of the head after machining the face so that they were parallel to the "new" head face. I've always checked the heads by dropping them on a cylinder block after machining and haven't needed to do anything with the cylinder head stud holes as yet.

I have heard this A7 mod being decried by some, but wedging for improved power is commonly carried out as part of tuning work on the cylinder heads of all kinds  of motors. I have done this on cylinder heads for things as diverse as a V8 Ford Mustang and a Four cylinder Yamaha racing bike motor amongst others.





Something I found interesting when I checked a couple of A7 cylinder heads was that the difference between the high and low compression heads was basically the thickness of the gasket; i.e. when I the measured the combustion chamber volume was pretty much the same on the early and late heads I tested. Has anyone else checked and had this result? I only ask because I have come across one head where the "well" above the piston was unusually deep although the head was the standard 1 1/2" factory thickness -I'm not sure whether that was accident or design.

[JonE]

Stuart - that wasn't what was found here, but certainly with my bits done with less scientific methodry. http://www.austinsevenfriends.co.uk/foru...sion+ratio
And I didn't have a late head, just the range of the different LC heads (and a new Ricardo with max possible volume).

[Chris KC]

Very interesting write-up Stuart, thank you.

[Stuart Giles]

Stuart - that wasn't what was found here, but certainly with my bits done with less scientific methodry. http://www.austinsevenfriends.co.uk/foru...sion+ratio
And I didn't have a late head, just the range of the different LC heads (and a new Ricardo with max possible volume).

Thanks for that heads up -no pun intended- I hadn't seen that thread. Presumably I must have been measuring a '35 head along with a '37 head to come up with the same chamber volume; of course either of the heads could have been an oddity despite being at the factory thickness. I think it would be necessary to measure a number of heads of each type to come up with a definitive answer on what the CR actually was for any particular version.

[Malcolm Parker]

I think everyone agrees that the 37 head is a better design than the early low comp head and if fitted to an engine in good order will prove beneficial.   My comments on plug fouling were based on my own experience of fitting the 37 head to unknown worn engines, which generally are better using the early head.
I have a couple of the angled early heads and have found these to be very good, I had one on my old Supersports type special in which I had the pleasure of out-dragging a blown MG away from a control in a VSCC Measham night rally.   Nowadays I am a firm advocate of the Ricardo head as made by Dave Dye.  I recently put one on my 31 saloon in place of a bronze Ulster head and the difference in smooth running and power is noticeable.

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I think everyone agrees that the 37 head is a better design than the early low comp head and if fitted to an engine in good order will prove beneficial.   My comments on plug fouling were based on my own experience of fitting the 37 head to unknown worn engines, which generally are better using the early head.
I have a couple of the angled early heads and have found these to be very good, I had one on my old Supersports type special in which I had the pleasure of out-dragging a blown MG away from a control in a VSCC Measham night rally.   Nowadays I am a firm advocate of the Ricardo head as made by Dave Dye.  I recently put one on my 31 saloon in place of a bronze Ulster head and the difference in smooth running and power is noticeable.

[Alan]

It’s worth remembering that Harry Ricardo designed all four of the heads mentioned. As the ‘37 head was the last, it’s reasonable to assume he learned a bit along the way. Having said that, Malcolm, I use a Ricardo head on my SWB Saloon, too.

[JonE]

So if the '37 is latest, what are the practical differences in it and the Ricardo pattern head i.e. what were the likely differences in his presumed "brief" for Austin... and for his own perhaps freer vision... that cause them to be different?