More great responses, The engine has been running well for a few years now before the crank called it quits so I believe we have a good starting point. Bob cars of this era had brass plugs for priming so are easily identifiable from later items. I agree that a '37 or Ricardo head would do the business very easily (The ricardo being vintage would be my choice), but we would be happier going a bit slower, and seeing the original head when we open the bonnet. With this in mind Malcolm do you have details on how to do the skim on an angle? as we don't know how much has already been skimmed I guess thicknesses each side would be most helpful? Have had some great responses on and off the forum, so think we have got the confidence to give some bits a try. With regards timing the cam in what degrees are we looking for, and does anyone have a source for offset keys?
Thanks again
Tim

Location: New Forest

Timothy,

Ian's and R's advice is sound. I would suggest you consult the oracle on this subject - Jack French's 'In sheeps clothing'. This is in the green book, the Companion, and was originally published in a A7CA magazine (I think, or was it 750MC Bulletin?). It expands more on this topic and includes R's sound advice about gearing.

I suspect every one of us has a slightly different view on what works and what's worth the effort in doing, so you'll get a compendium from the Forum! My latest fad on this is getting the cam timing right, those gears and keyways aren't as consistant as I'd assumed! (Assume = make an ASS of U and ME).

It's fun trying to get the best out of your A7; as our American cousins (irritatingly) say - enjoy!

Dave

Timothy

Your question has prompted me to look at the skimmed low CR head again. Not being on the spares shelf, it turns out it is on the engine in the Pytchley saloon, which is basically a standard engine with flattened cam followers, cleaned up ports and a lightened flywheel. It has twin 1 1/8" SU's and a bunch of bananas exhaust. It goes like a bomb and would leave the Ulster in its wake!
As the head is on an engine I cannot photograph the underside but fortunately I have found the calculation I did of the combustion chamber, which is about 37cc. I reckoned the CR is about 6.3:1.
The head is dated March 1934. The thickness (taken from the underside to the flats for the securing nuts) is 33mm on the offside and 37mm on the nearside (ie where the valves are).
My pal Andy Hastings machined the head on his lathe very slowly with it clamped to a face plate. The skimming was done in several stages and as the tool worked towards the centre it was arranged so that this was over the combustion chamber so that a 'pip' did not form.
It is fascinating to see how the shape of the combustion chamber alters as metal is taken off. We continued until we were beginning to encroach on the flat area of the head above the cylinder bore.
He did two of these heads for me. I don't remember parting with one so I might have the other somewhere!
Fortunately low comp heads are still plentiful and most of us have a pile on our shelves. You need to start with one that is not too badly corroded internally so there is a good thickness of metal where it is going to be machined.
Hope this is of assistance.

Tim,
I believe heads were 1.5" thick when new so you can tell if anything has already been taken off, either a few thou as a clean up or more to boost compression. If you're wanting to retain the brass priming plugs - you could glue dummy ones on the later 18mm heads.

I haven't seen any of our esteemed suppliers doing A7 offset keys. I'm not sure how the geometry would work out for the cam key on the tapered shaft. I'd go for the one on the crank. I used to make my own for Mini's and AH's on a surface grinder out of a bigger thicker woodruff key. I haven't got a Mini key to compare dimensions with but this Mini specialist do a range http://www.ebay.co.uk/itm/Mini-Offset-Key-Cam-Camshaft-Timing-Austin-Morris-BMC-Rover-Woodruff-Kent-Piper-/152094888322?_trksid=p2141725.m3641.l6368

Send them a standard A7 key and they probably will make one to your required offset? However it may be an easier first option to try different gear combinations if, like the rest of us, you've got a box full of spare gears. They're all slightly different in the accuracy of where the keyway was cut relative to the gears.

This site gives a good write up of how to time in a cam - bearing in mind the different engine design. You need a big 360 degrees protractor and a dial test indicator (DTI or 'clock').
http://www.burtonpower.com/tuning-guides/tuning-guide-pages/camshaft-fitting-timing.html

Dave

Tim

I have found my second skimmed low comp head and as it is not on an engine I have taken a couple of photos which I will arrange to have posted.
This head is machined at a similar angle to the first with one side measuring 34mm and the other 38mm. As you can see the combustion chamber over the cylinder bore is still as original except that it is only 1mm deep at the side away from the valves. The other skimmed head went an extra 1mm or so and this removed all the original part of the combustion chamber to the offside of the plug hole.
I think we called it a day with this head as we were worried about the thickness of the metal in places.
The machining marks are visible, the head was set up in the lathe so that the centre was at the stud hole between cylinders 2 and 3.
If I ever use this head again I will clean up the surface to remove the machining marks.

Malcolm's cylinder head





Steve

Location: North Yorkshire

That is great, thank thank you Malcolm for checking your heads. I like the look of that, definitely appears worthwhile verses a regular skim.
We have all the bits for timing the cam, the Companion says that the inlet opens at TDC and closes at 40 degrees after BDC (220 ATDC) so assuming reasonable symmetry I make that fully open at appx 110 degrees ATDC. does this sound like the right figure to aim for when timing the cam?
Thanks again everyone, it may be a while but we will report back with what we do and the result.

Location: New Forest

For an unmodified cam, fully open is best determined by splitting the difference between identical lifts on each flank, turning in the normal direction. The position where the valves are equally open is often more easily established.

The series of posts Austin seven Crankshaft and Camshaft gear timings, late 2014, may be of interest.

I gather aftermarket gears were often different, intentionally or otherwise. In view of the gearing and the expected speeds for the earliest cars, the Seven timing seems somewhat on the retard side. If anyone has objectively explored alternatives on ordinary cars at medium speeds, could be of interets.

Location: Auckland, NZ

That looks like a reasonable head for a blown engine!

The other skimmed head which had an extra 1mm machined off has a very different combustion chamber shape, not dissimilar to photos I have seen of early GE Brooklands heads.
I used the more radical head on my old 'works prototype replica', three of which were made by Andy Hastings. It was used on the engine that had previously been supercharged, with pressure fed Reliant crank and Honda pistons. It did used to go very well! On a VSCC Measham Rally a chap in a supercharged MG tried to out drag me from a Control, he lost!
I still have the engine which one day will go in the sprint car I need to finish.

Tim,
Yes your sums are right; 110 degrees ATDC for inlet fully open with a standard cam.

Bob's advice is sound - don't try to gauge where fully open is, there's very little change over a number of degrees movement; measure it at say -0.030" on the way up and the same -0.030" on the way past fully open - then half the angle between. It's the same for checking the timing marks for TDC by measuring the piston rise. If you take a full set of figures I'd be interested in what a 'real' cam clocks in at - I don't know where those figures in the book came from?

Dave

I recall reading somewhere Stanly Edge claimed it had always been his intention that the head was flat rather than recessed above the piston but the old man was against such a high CR. Stanley also said in the same article that he left enough meat in the casting patterns to allow this should a rethink happen later. Interesting to me also is that the 12/4 had a HC Ricardo type head with reasonably decent plug position almost 10 years before the Seven even came close. (Sports models excluded)

Location: Auckland NZ

Timothy,
when I wanted a bit more power with our RN saloon I used a Paul Bonewell trials camshaft, standard tappets, standard weight flywheel and a standard head with 1/16" taken off the combustion chamber side tapering to almost nothing from the valve side. The top face was then machined over the spot faces where the studs are. Doing it this way you don't have to open up the stud holes. Photograph below shows the setup on the lathe although this one is a Ruby head that I skimmed without the offset. I also thinned down the butterfly on the FZ carburettor and opened up the inlet manifold and also the inlet holes in the exhaust.
With this set up the car has bags of torque, holds on much longer and will cruise comfortably at 55/60mph.
Hope this is of interest, regards, Robert.

Location: Deepest darkest Kent

I have wedge machined a fair few heads, not all side valve ones, wedge machining has the potential to produce a higher compression Vs. metal removed on any head where the combustion chamber has a markedly larger area on one side.

Here's some early A7 heads I prepared earlier -as Val Singleton might have said



On the right is an as-yet unmodified early head. The middle one has the area above the valves milled out .050" deep. The leftmost head has the milled area blended into the combustion chamber, and the sides of the combustion chamber opened out to match a '37 head gasket. Don't have a picture of these finished, but basically there is .060 of "wedge" with .125" machined off in total. Never had a problem with the studs fouling the holes, but the holes are spotfaced on the top of the head so that they are parallel to the "new" head face.

Powerwise, as part of an A7 build I would definitely be looking at the cam timing. Not sure how good the factory was with this, but after 80 something years, loads of motors have mis-matched -i.e. not a factory pair- gears, The "line up the marks at TDC" method was used as a start- this should result in maximum inlet lift at 110 degrees After TDC; but checking with a degree wheel and dial guage revealed one was 6 degrees advanced and the other was 5 degrees retarded -this particular timing would probably be excellent for a racer, not so much on an average weight road car. Making an offset key fixed this, in the absence of machine tools, this is quite do-able with a file starting off with a larger key -here's a use for those battered half shaft keys you can't quite bring yourself to throw away.

The fitting the offset key to the cam has greater degree impact than if it is fitted to the crank -cam degrees count twice at the crank because it runs at half speed. of course, the cam and crank keyways are the same size so you can swap the offset key over between the two if you want.

Location: N W Kent

Thank you for the further responses. Dad has started work, and we will let you all know when it's together what we've done and what the results are like.

Location: New Forest

I have a 1929 fabric saloon in more or less standard trim.
It performs very well and has only minor modifications.
They are as follows:
1) Vertical section of the inlet manifold reamed to the same diameter as the 22FZ carburetor. Important not to go bigger than that.
2) The carb butterfly and spindle have been thinned down as much as I could manage - not a lot!
3) The inlet to exhaust manifold joint is well aligned. Hven't done manifold to block yet.
4) The cylinder head is 1933 and I believe it has been skimmed about 0.050" but not by me.
5) The clutch pressure plate had three new holes bored to make the withdrawal pillars a good fit and give some hope of it being balanced. Still not great but a big improvement. It's worth looking at these plates as they seem to come in a variety of diameters and balance is better if it's a good fit. Some have a very large clearance.
6) The flywheel has been lightened and engine balanced.
7) When I rebuilt the gearbox I fitted an 'Andes' high second gear. This means I can reach 40mph in 2nd. The dog for top is chamfered on these gears making top selection much easier and quicker. This does leave a gap between 1st & 2nd gears but for me is only a small disadvantage.
8) It has a 1-1/8" Phoenix crank.

Visually the engine appears almost standard. Close inspection shows the later head and bronze instead of Mazak carb.

It covers the ground very well. I have just returned from The Scottish Austin Seven Club's AGM in Blair Atholl. I came down the A68 from Edinburgh to Melrose easily able to maintain 50mph on the level. 40 up most hills and 30 in 2nd up the steeper hills. I can on occasions reach 60mph downhill.

Thank you Jim, sounds like we should be able to get some good performance gains with simple work. I had read some thing you had written previously about the andes ratio second, but can't recall seeing whether you still have a 4.9 back axle. Sounds like a great option for the future.

Location: New Forest

Still 4.9 axle. Fitting a lower ratio is possible but not that easy.
I think a lower axle ratio and a close ratio gearbox would work well. By raising both 1st & 2nd gears the gap between them that the Andes gear has would go. However without the lower axle 1st would probably be too high for steep hills/hill starts.
The lower axle ratio would probably give a higher top speed.
The Andes suits me here because there aren't many hills steep enough to need 1st gear.
When on runs with other cars I find I am slower on steep hills where I can't use 2nd gear, but faster on less steep hills where I can climb at 30 mph in 2nd easily but a standard geared car can't.

I had the Andes ratio 3 speed box on my 1931 RL saloon with standard 4.9 rear axle ratio. I found the gap between 1st and 2nd too great for the power of the engine and the weight of the car, especially two up. The clincher to revert to a standard box was on one of my Pennine Runs when I spent almost a whole day in 1st gear grinding up the steep hills of northern Derbyshire and West Yorkshire. The factory knew what they were doing! Jim's car is lighter than a steel saloon so the Andes box is better suited. If ever I put a 5.25 ratio in the saloon I may well have another go with the Andes box.

Thank you both, definitely food for thought, it sounds like both boxes can work well depending on how steep the hills you regularly climb are, and how heavy the car is. For the moment at least getting the engine back together is priority number one, and I'm sure once it's back together it will be a while before dad wants to have the car off the road again (Though with building the gears into another box a swap could be effected reasonably swiftly).

Location: New Forest

I now have special thinner head gaskets which are the right shape for low compression (and Ricardo) heads, but are the same thickness as the ones for the high compression head. See BC29r here. This should give a slight increase in power (every little helps, as they say).

David

A couple of points - Re Jim's boring the vertical part of the inlet manifold, I thought it was of not much use if the horizontal pipes are still restricted, so more recently I cut away the rear of the top bit and ground out to the same ID as the upright. After doing the same to the cut-away piece, I then welded it all together again - mods unseen. Re Bob's comment in October re the small diameter shaft not standing up to too much compression etc - when I raced an Ulster special for an Adelaide friend, his engine was just that, with an Ulster head. He was a brilliant engineer and I don't know what else he modified, but we never broke the light crank. I think I've boasted here before that in one race I beat all the blown Sevens, so please don't think it was slow. I think it silly to make such comments as Bob's, when they don't have the experience. The factory mods done when still using light shafts are legion. UK people would have seen this car first hand when in the hands of Bob Duguid it won a race at Castle Combe during the famous Aussie Raid and I doubt it was altered after I drove it. Cheers, Bill

Location: Euroa, Australia

Location: Teignmouth

The blown cars Bill mentioned were at Castle Coombe Stuart, also remember that with more open regulations the Aussies were well ahead of the Brits when extracting that last bit of speed during the 80's and early 90's.

Location: NZ

Just one point Ian, although I may be corrected. From memory, Max Foster in a blown Oz Seven and Bob D in the unblown car were the only two Raid cars to compete at Castle Combe and I know Max had trouble all day with his. Maybe Tony Johns (s/c) was also there and likewise had trouble. (Haven't had time to check, not at home). Cheers, Bill

Location: Euroa, Australia