23-11-2018, 12:00 PM
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.
![[Image: 30740399990_df88cc4621_c.jpg]](https://farm6.staticflickr.com/5696/30740399990_df88cc4621_c.jpg)
![[Image: 31072727147_7370a9a667_c.jpg]](https://farm5.staticflickr.com/4815/31072727147_7370a9a667_c.jpg)
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.
![[Image: 45962142302_6eaff6c48b_c.jpg]](https://farm5.staticflickr.com/4918/45962142302_6eaff6c48b_c.jpg)
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.
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.