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Austin A40 Sports Valve Adjustment
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victoriacoffees



Joined: 12 Nov 2015
Posts: 2

PostPosted: Fri Feb 19, 2016 1:03 am    Post subject: Austin A40 Sports Valve Adjustment Reply with quote

Hello from Victoria, TX, USA. I've been enjoying driving our 1952 A40 Sports around town and she runs great, except for a slight miss at idle. Timing looks good, although I have not checked it with a timing light. Carbs are tuned and have been rebuilt. Only thing not checked has been the valves. Before I get started on this task, I'd like some advise how to adjust them as I don't see any timing marks to follow. My Austin manual says 1-3-4-2 firing order but nothing more.

Thanks!
John V
1952 A40 Sports
1959 Austin Healey 100/6
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peter scott



Joined: 18 Dec 2007
Posts: 5948
Location: Edinburgh

PostPosted: Fri Feb 19, 2016 9:44 am    Post subject: Reply with quote

Hi John,

Welcome to the forum.

To adjust valve clearances you want to arrange for the cam follower to be on the back side of the cam. This is very simple, especially on cars fitted with starting handles. All you need to do is turn the handle until the valve to be adjusted is fully open then turn the handle one complete turn and you are now on the back side of the cam.

All the valves use the same clearance which is 15 thou measured cold.

It has just struck me that perhaps you were not asking how to adjust valve clearances but to check valve timing. Valve timing doesn't need to be checked routinely. Assuming the engine was assembled correctly then the only thing that will change the valve timing is a worn/stretched timing chain and it's not difficult to detect that because the chain will be clattering if worn.

It's not terribly easy to check valve timing on the A40 because it's not symetrical. Inlet opens 5 degrees before TDC and closes 45 degrees after BDC. Exhaust opens 40 degrees before BDC and closes 10 degrees after TDC.

Finding TDC you can try to assess it by gauging piston height in a plug hole but it would be easier to assess it accurately by observing the crankshaft, but that requires taking the sump off.

In trying to detect the cause of your slight misfire I would suggest that you check your compressions. A low compression on one cylinder might indicate a burnt valve or broken rings that might cause your problem.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 litre saloon
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Keith D



Joined: 16 Oct 2008
Posts: 910
Location: Upper Swan, Western Australia

PostPosted: Fri Feb 19, 2016 2:06 pm    Post subject: Reply with quote

Hi John,

Welcome to the forum.

To check valve timing on the A40 you must remove the timing chest on the front of the motor and using a straight edge between the centres of the camshaft and crankshaft made sure that the timing marks on the both sprockets are on this line when #1 and #4 pistons are at TDC.

If you remove the small cover at the top of the bell housing inside the car you will see a vertical line on the flywheel that indicates pistons #1 and #4 are at TDC.

Valve clearances are, as Peter has said, 0.015" set when cold.
To set the tappet clearance you number the valves 1 to 8. Remember the magic number 9. When #8 is fully open, then set #1. (8 + 1 = 9) When #7 is fully open, then set #2 (7 +2 = 9) When #6 is fully open, then set #3 (6 + 3 = 9) and so on until they are all finished.

Keith
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victoriacoffees



Joined: 12 Nov 2015
Posts: 2

PostPosted: Sat Feb 20, 2016 6:28 pm    Post subject: Valve Clearance adjustment Reply with quote

Keith & Peter,
Thank you both for your responses. Not have a timing mark to assist with finding TDC when adjusting the valves made it a bit concerning and I didn't want to proceed without a clear plan.

Once completed, I'll move on to compression checks and report back.

-John[/img]
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