Hints and Tips - Austin Seven Tuning

From: Mike Lunch
Sent: 24 February 2003
To: British-Cars-Pre-war
Subject: A7 Tappets - mild tuning advice please

Those with a long memory may recall that I am restoring a 1930 Austin Seven Chummy. Things are getting (at long last) to the exciting stage - putting it back together again. Listers have previously provided some excellent advice, and I hope will be able to again.....

I have no aspirations to use my Chummy competitively, however I can't help feeling that a few extra horses are always a good idea if they do not compromise the life of the engine.

So...the block has been re-bored, new pistons, rings, re-metalled bearings etc etc. I managed to get a '37 head (for that extra 2 bhp!) and some double valve springs (just in case I hit those exiting peak revs!)

I recall that in the excellent books by 750mc - Austin 7 companion, and also the A7 specials book, mention is made of grinding a flat on the cam follower (bottom of the tappet). I understand this is to change slightly the timing and dwell of the valve openings and closings.

Is this a sensible modification? I have no plan to do anything else (standard CR on the '37 head, standard updraught carb, standard exhaust system etc).

If a good idea, what are the details of the mod - how much of the radiused cam follower must be ground off? What is the correct treatment after grinding - case hardening? Harden and temper etc etc.

Is this crazy and should I just forget the idea?

Kind regards,
Mike Lunch


From: Bishop Peter
Sent: 24 February 2003
To: 'Mike Lunch'; British-Cars-Pre-war
Subject: RE: A7 Tappets - mild tuning advice please

Mike I think the theory is that flattening the followers improves the breathing by increasing the time the valve is fully open, but it also increases the overlap. The overall result is a trade off; more power at higher revs but less torque at the bottom end. Vince Leek will do you a set on an exchange basis at a very reasonable price, but beware -you need to shorten the tappet guides as well so that the adjusters don't bottom out with the new shorter tappets.

If its only a touring engine I am not sure the double valve springs will do much for you. I run standard single springs ( with standard followers) in my trials engine and get all the revs I need. Any listers know what revs valve bounce sets in with standard springs? The double springs will obviously put more load ( and wear) on the cam, bearings and tappets.

The biggest improvement you could make is probably to put an SU Carb and manifold on it, as that is what is likely to be restricting the performance most.

Pete


From: Mike Lunch
Sent: 24 February 2003
To: Bishop Peter
Subject: RE: A7 Tappets - mild tuning advice please

Hi Pete,

Nice to hear from you again. Are you using a '37 head too? All that buggering around with tappet gyuides sounds a PITA - especially since they are in the engine and ready to go now...

I enclose a couple of shots showing the progress before "Bluebell" went into the paint shop - I recall seeing your equivalent shots a LONG time ago now!

Have you bothered to do the upgrade to 12 volts?

Cheers, Mike


From: Bishop Peter
Sent: 24 February 2003
To: 'Mike Lunch'
Subject: RE: A7 Tappets - mild tuning advice please

Mike its looking great, what was your bonnet fit like? I spent hours bxxxxxg about trying to get mine right.

Yes I have got a 37 head, but with an SU carb and decent exhaust. (see enclosed picture)

Yes the tappet guides have to be pressed out of the block to shorten them, or you have to modify the tappet locking nuts so they will fit inside them

I have converted to 12v and found a very simple, cheap and reliable way of doing it. Let me know if you want details.

If you send your pictures to Guy Weatherall Guy.Weatherall@vintageknowledge.co.uk. he will post them on the vintage knowledge web site for everyone to see your progress!

Pete


From: Charles Ping
Sent: 24 February 2003
To: Bishop Peter
CC: British-Cars-Pre-war; 'Mike Lunch'
Subject: RE: A7 Tappets - mild tuning advice please

Mike

When I nailed together my Ulster it first ran with a standard cam, flattened followers (2 inch radius) and a standard box. Went pretty damn well and was more drivable than with the race cam that it's got at the moment.

Double springs - probably not needed.

Charles


From: Brian Adam
Sent: 25 February 2003
To: mike lunch
Subject: A7 tappets

Mike; I see you are getting all the proper advice, 2," etc. I wonder what Tim will say? I have been through all the tuning mods. but found that a lot of overlap really kills the low down torque, then a standard car will go better than you up a hill, unless you thrash it. Then you will want a 4-speed box!

Ref the carburettor, this is something I will want to try, a 1 1/8" SU, or 1", but they are hard to find, let me know if you locate some! Because of the petrol tank in the scuttle you will need a petrol pump, SU 6 volt, to get the flow.

The double springs do load other components; a combination of these and higher lift cams I believe caused broken teeth on my timing gears.

brian f adam


From: Mike Lunch
Sent: 25 February 2003
To: Brian adam; British-Cars-Pre-war
Subject: RE: A7 mild tuning

Lots of excellent advice arriving from all over the world - thanks all...

Spoke with Tim Mayall last night, he suggests:

1. The size of carb is likely to be limiter on breathing, therefore forget the tappet stuff, and double valve springs too

2. The 37 head is apparently capable of being skimmed by 1/10" (wow!) and this will produce a good result across the rev range even with restricted breathing.

3. As long as the 37 head is bored out to take 18mm plugs, it is still accepted by VSCC.

Also lots of other good advice about:

crack testing con rods,

put correct small end bolts,

check no 2 & 3 piston clearance is at least 20 thou below top of block

I think this all fits well with your comments about flexibility - also I dont want to fit the 4 speed box if I can avoid, I have a lovely gate change top (again slightly earlier vintage) it looks great, and is a laugh to drive...

I don't want to change the appearance - so fuel pumps, external oil filters, twin webbers, flowed manifolds, turbo chargers, spoilers, nitro, sodium valves and all other works of the devil are banned...

any more comments welcome...

Mike


From: Mike Lunch
Sent: 25 February 2003
To: Bishop Peter
Subject: RE: A7 Tappets - mild tuning advice please

Hi Pete,

Thanks for your comments, I reckon you are right on the tappet & springs - not worth the fag..

What do you reckon to Tim Mayall's "skim the head by 100 thou" idea!!!

Cheers, mike


From: Peter Bishop
Sent: 25 February 2003
To: 'Mike Lunch'
CC: British-Cars-Pre-war
Subject: RE: A7 Tappets - mild tuning advice please

Well I have heard that the real trick is to skim the head at an angle. This leaves the clearance at the valve side to allow breathing, but still gives you the advantage of a higher compression ratio.

Pete


From: Mike Lunch
Sent: 25 February 2003
To: British-Cars-Pre-war
Subject: FW: A7 Tappets - mild tuning advice please

I thought that was a trick for use on the pre-'37 heads which didn't have enough space in the "throat" for breathing, however the '37 head fixed all that - or did it?

Mike


From: David Cochrane
Sent: 25 February 2003
To: british-cars-pre-war
Subject: RE: A7 Tappets - mild tuning advice please

Pete,
> Well I have heard that the real trick is to skim the head at an angle.
> This leaves the clearance at the valve side to allow breathing, but still
> gives you the advantage of a higher compression ratio.

I thought this really applied to the pre-1937 head?

David


From: Bishop Peter
Sent: 25 February 2003
To: 'David Cochrane'; british-cars-pre-war
Subject: RE: A7 Tappets - mild tuning advice please

Well will it not help on the late head too? If you skim the head flat the valves end up very close if not hitting the head ( when using a high lift cam).

Pete


From: Barry Lovelock
Sent: 25 February 2003
To: Mike Lunch
CC: Brian Adam; British-Cars-Pre-war
Subject: Re: A7 mild tuning

Tim Myall did the work on my A7 special (now sold). It used one of his "Fast Road" cams - extreme imho, like all the cams he does! Like a piece of bent wire. It also used Tim's big valves (Hillman Imp I think) and Austin Maxi springs. The springs were very long and almost coil-bound when compressed. The valve chest was modified by machining out the top part of the tappet guides until the bottom was flat. It went like a Dingbat!! See this link, for the uninitiated: http://freespace.virgin.net/john.lovelock4/prfile15.mpg

I had 80 thou taken off the '37 head. This gave a (measured compression) of 7.6:1. This was lowered to about 7.2:1 after I opened out the chambers to clear the big-valve block (1.2" inlets btw). Unfortunately, like many of these old pieces of metal, the head was thin in at least one spot and broke through; I successfully repaired this as the hole was near one of the waterways. It enabled me to insert, at an angle, a 12mm stud I happened to have, through to the waterway hole which was opened up to 1/2" or so. By sleeving it back down again with an interference-fit cylindrical piece of steel, the stud was locked in place and was then re-profiled in the combustion chamber. It didn't leak!

This (2 bearing) engine, with Australian pistons, Austin rods with file marks etc(!) and a 1 1/4" SU with a No.6 needle and blue spring, was mercilessly thrashed whilst in my tenure to 6,500 rpm. It appeared to be lacking in torque a bit at low speeds, but this was mainly dependent on engine temperature - the modern rad core overcooled it and I think icing might have occurred in the manifold too. A change to first was needed always on slow junctions, otherwise it stuttered like a good racing engine. It backfired a lot too, once blowing the Brooklands Can apart!

The other problem was exactly why the Ulster blocks had 10 studs eventually - it tried, unsuccessfully I might add, to blow itself apart all the time at the block to crankcase joint. When ticking over, which it still did reliably, oil could be seen to be squeezing it's way out of the joint faces.

One other thing - DON'T use the silly paper gasket for the top water branch on the head. It is impossible to "torque" the Ruby head down properly with this design and I blew two head gaskets until I ended up with a copper head gasket (compression lowered to 7:1 then) and a copper one for the water branch too. An ordinary H/C gasket works just fine though without the water one.

Barry Lovelock.
http://www.theaustinseven.com


From: Barry Lovelock
Sent: 25 February 2003
To: Mike Lunch
CC: British-Cars-Pre-war
Subject: Re: FW: A7 Tappets - mild tuning advice please

Tim says take 150 thou off the early head........

Slanted heads are pretty radical as the studs present a 'minor' problem too. Believe this mod is done in Oz quite a bit.

Suggest we remove the "mild tuning" from this title in future posts!

Barry.


From: David Cochrane
Sent: 25 February 2003
To: british-cars-pre-war
Subject: RE: A7 Tappets - mild tuning advice please

> Well will it not help on the late head too? If you skim the head flat the
> valves end up very close if not hitting the head ( when using a high lift
> cam).

Yes probably, but it won't make nearly such a difference as it will on the earlier head. Also, milling at an angle is more difficult to do, and it's rather a nasty arrangement from a mechanical point of view when attaching it to the block!

David


From: Derek White
Sent: 26 February 2003
To: British-Cars-Pre-war
Subject: RE: A7 Tappets - mild tuning advice please

Hi Mike,

I'm building a few A7 engines at the moment and have the 750MC companion and Bill Williams' Specials book. After lots of reading and thinking and doing most of the suggestions, here's what I would do for a zippier chummy without loss of low down torque and too much effort/cost:

Must do:

*crack test crank.

*clean and re-clean the oil galleries

*make sure the oil jets are pointing at the troughs in the crank (squirt oil or paraffin through them) and better still bend them inwards towards the centre of crankcase by about 20 degrees.

*Put a thin, even coat of silicone of both sides of the crankcase-block gasket, assemble loosely, tighten after the silicone has cured.

*use rubber engine mounts and only two engine bolts (front left, back right) to stop the crankcase twisting in corners.

Also helps: *up to 2 lbs off the rim of the flywheel to reduce torsional loading (mark position and size of balance holes and replace them after lightening.)

* Shot peen rear web of crank, check rods for grooves/cracks. I found a crack in one after polishing the shanks.

To go faster:

1) Skim .040" off the head (better fuel today allows this.)

2) On the valve side of the top of the bore grind a slope from near the valves down to just above the TDC position in the bore of the top piston ring. This slope can follow the width of the combustion chamber in the head. You can also widen the combustion chamber to give even more flow. This is shown well p256-257 of the companion. You may need to adjust your head gasket if you widen the combustion chamber.

3) Bore the vertical part of the pre '33 inlet manifold to 15/16". Better still get the later manifold or still better, fit a sidedraught SU.

4) remove the corners in the walls of the inlet ports and match the ports to the inlet manifold.

5) the standard springs are good for 4000rpm (if they are in good condition), if you need more than this go with stronger springs. If you want to go over 4000rpm I suggest you skim 020" off the top of No2 and No3 pistons and also scrape the No2 and No3 big end bearings so that they are slightly tapered from the centre to the outside. This will allow for the crank whip at higher rpms which would otherwise try to bend the middle rods.

6) I would take 050" off the cam base circle and many racing people say that rehardening the lobes is not necessary. This is less dramatic (and gentler on the valve train) than the follower modification.

...and in case you haven't heard these before: Never rev the engine in neutral, don't rev up when changing down. try to stay out of the 2300 rpm harmonic

Let me know what you change and what the results are. cheers, derek

Derek White
Colombo 7
Sri Lanka


From: Ian Kerr
Sent: 27 February 2003
To: Derek White; British-Cars-Pre-war
Subject: Re: A7 Tappets - mild tuning advice please

It is good to see some life back in the newsgroup, I found Derek`s piece of great interest.

Last Sunday I snapped the crank again in my 1936 Nippy , It is a cooking engine as I like to drive the car as it was driven like in the 1930`s . I do have a very rare 3 bearing pressure fed engine , probably a Speedy engine , undrilled oilways ,but I would worry about breaking it . Anyone know what it is worth ?

My broken 2 bearing engine had flattened tappets , larger valves , relieved at the top of the bores, relieved inlet ports on the block , lightened flywheel , nippy head and manifold.

These were simple modifications that just took a bit of time as opposed to money and made the car a nice fun car to drive . I did have a Jack French cam in at one time but it was horrid as a road car, I had to rev the balls out of the engine to make it go , I put a standard camshaft back in and it transformed the car , mind you , I had learnt with the high lift cam that you can rev these engines up until they sing , so one way to make a 7 go well is to give it more revs.

Has anyone got a spare Phonex or similar crank , or a quick up and running engine for sale as I would like to get back on the road as soon as possible ? I like in Birmingham . U.K .

Anyone for Hershey this year , not so much english A 7 stuff but a fair amout for the american bantams , and loads of cheap unrestored late teen and eary 20`s tourers , have a look at www.hershey2003.co.uk

Ian Kerr


From: Stuart
Sent: 01 March 2003
To: Ian Kerr
CC: Derek White; British-Cars-Pre-war
Subject: A7 Tappets - "Speedy" crankcase

> I do have a very rare 3 bearing pressure fed engine , probably a Speedy
>engine , undrilled oilways ,but I would worry about breaking it . Anyone
>know what it is worth ?

Ian, It is 30 years or so since I last saw one of these. Late Nippy, I would say. My old friend Pete Mumby put it, inappropriately, in his Speedy . I remember being horrified by the way the crankshaft was cross drilled to get oil from the centre main to the big ends. Not much metal between the oil and the outside world!

The Speedy went to live in the Midlands for a while. When I next saw it, it had a more suitable 2 brg. Speedy engine. I wonder if your crank case came out of it?

What's it worth? I presume it is indeed a Nippy case for an 8 stud cylinder block and not a 10 stud Grasshopper case! I think I'll evade the question and say that one could easily adapt a 3 brg. Ruby crankcase to the same spec., so it is the same relationship as that of an early unblown Ulster case to a standard 1930 crankcase. In other words, no practical advantage, but rare!

The main point that I think is worth considering is that this case does provide a solution to the "three bearing cranks always break" problem. In my opinion this is because premature wear in the centre main shells allow the 3 brg. crank to flex. I think this happens because the oil pressure to the centre main in the spit and hope engine is too low. This is not so with the pressure crankcase.

As I'm sure you know, it is possible to adapt a Reliant crank to this case, albeit with several other consequences. This makes a very strong engine, ideal for your purposes. I think this crankcase is of most value to you!

Hope this is of interest,

Regards, Stuart


From: Mike Lunch
Sent: 06 March 2003
To: British-Cars-Pre-war
Subject: A7 tuning update

Update to earlier discussions on A7 "mild" tuning.

Tim Myall's advice (which I am following) was:

1. If you stick with original bronze carb, this is the limiting factor on breathing - so no point in messing about with manifolds, cam followers, bigger valves etc.

2. With modern fuels no problem to raise CR substantially by skimming the head, which should deliver more power right across the rev range. He has taken 100 thou off and machined above the valve heads to ensure sufficient clearance over standard cam lift.

He looked at my JP Australian pistons and "had a fit" when they proved to be round. It seems that when leaded fuel disappeared, these pistons started to give trouble - "picking up" metal and partially or completely seizing. Anyway, Tony Leslie kindly agreed to swap them for the latest "oval" design which fixes the problem - thanks Tony.

Tim also mentioned the need to take some metal off top of pistons 2 & 3 to ensure they do not crash with the '37 head due to crank whip. He advises these pistons must be at least 20 thou below top of block for safety.

So, that is my plan - thanks for everyone's excellent advice.

Mike Lunch


Home | Hints & Tips | Suppliers | Engineering Data | Links | Events | For Sale | Gallery | Books | Videos | About Us