Recently ( 2000 km ) ago I fitted a new head gasket, re grinded the valves and made the engine run like it was new. In the last 400 km it seems to have lost some power. The tick over is still perfect, no oil in the water ( ore water in the oil !) and starts everytime without a problem. Down hill still runs fantastic, and on the flat, but as soon as there is a hill, starts to get a bit harder to keep going.
People I have talked to seem to think its pistons, ore head, but wouldn't that affect the low rev running aswell ?
I anyone has any suggestions I would love to hear them.... before I start a big job again !!

Location: Denmark

Have you checked the valve clearances lately? I would suggest this might be the source of your problems if you have too tight a tappet clearance.

Another adjustment to check is the contact breaker points gap. There are many other possibilities but I suggest look for the simple things first.

Location: Derby

hi Laxton

That high tech diagnostic device the crank handle, used with the engine hot and cold, will usually reveal any valve or other compression defects. If tried regularly get to know the normal feel and any changes become apparent.

I found on my car, with early head and burning a lot of oil, top speed performance fell off rapidly but a decoke instantly restored. This is somewhat in line with the servicing intervals in the handbooks, but others do not seem to have noticed similar.

If ignition has slipped to retard this saps pulling, and car tends to accelerate in the gears in surges. five degree of extra crank advance is a big adjustment and only 2 1/2 deg on the distributor body.

If the points have closed and ign advanced usually evident from engine harshness. The minimum possibkle advance for full power or near is the ideal.

On old cars I was often surprised how many had throttles which did not fully open, altho this mainly affects top speed. Has a mat or something shifted?

Bob Culver

Location: Auckland, NZ

Long shot - Have you changed where you normally buy your fuel recently? I happened to fill up the Opal with Tesco fuel (which I normally avoid like the plague) whilst on the Yorkshire Experience and it was as if someone had pulled a plug lead off. Dreadful performance up hill, OK'ish on the flat. Ran that through, filled up from the local XYZ brand garage and normal service pulling up hills (big ones!) was resumed.

Location: North Herts

Thankyou all for the replies, have been busy yesterday trying to find the problem. Reset all the valves, they were all a bit to open ( Some up to 10 thou !! ). Have reset the points, after cleaning them, and checked the spark plugs. Tried to adjust the timing a bit, but none seem to help... Have also checked the fuel filter, which seemed to be fine.
I have actually filled up with some "Discount" fuel, so think that might have something to do with it.... Anyway have organized to borrow a gauge from a mate to measure the pressure in each cylinder.... But hope its the fuel !!

Location: Denmark

Just to clarify. The tappet adjustment is potentially more a problem if the clearance is too tight. What happens is that as the engine heats up, the valve stems - particularly the exhaust valves - extend. If the tappet clearance is too tight, the valve can be held open resulting in reduced compressions and leading eventually to burning and valve failure.

The points gap can close up due to the heel wearing down. This results in an extended "dwell" period - the time when the points remain closed. The spark is also weakened resulting in a reduction in power.

It would seem that your problems have developed since replacing the cylinder head gasket. I would not alter the ignition timing. Unless the distributor clamp is loose, the timing cannot "slip".
Likewise, there is a saying that 90% of carburettor faults are ignition based. In short, don't adjust the carburettor. If it was working well before, it can't really alter it's settings. What you might look at are the jets to see if they are blocked. This is often the cause of problems such as you describe.

When you took the plugs out, what colour were they? If you have a weak mixture, the electrodes should look white. If this is the case it may be that air is being drawn in past the inlet manifold. Be careful not to over tighten the nuts.

Location: Derby

I am intrigued by the reported effect of different petrols available in UK. Have others observed? Has the motoring press picked up on? Modern cars with their adaptive systems and high power may handle without the driver being aware. Any theories on cause of low power? Presumably the heat content of fuels is similar, unless a very large % of alcohol.

I have found very, very old petrol lacking, and requiring a lot of choke. Possibly the burning time becomes very modified, as well as much of the heat content gone if already oxidised, and more can be burned for the same air.

Can those with manual advance compensate for poor fuels?

As far as I know all our brands are commonly sourced and no great differences that I have detected in a low power older car.

Bob Culver

Location: Auckland, NZ

I would think Nick's initial statement "long shot" is correct. Whilst there have been instances of supermarket petrol being sub standard in the past it was been well publicised and I don't think it happens very often if at all now.

I would expect the problem to be with the car rather than the fuel. One thing to check on is the flow. Until I sealed my petrol tank, I was forever getting flakes of rust in the tank blocking the pipe at the outlet/tap. It is imperative these days that any tank sealer used be ethanol proof rather than just ethanol resistant. If a tank sealant has been used in the past (prior to ethanol petrol) it may be breaking up.

As the cylinder head has been off, it is important that the nuts are checked or nipped up after 500 miles or so but I plead with anyone tightening head nuts not to over tighten them. If it feels tight, it probably is.

Location: Derby

A bit of an update....

After re doing the valves I have been for a drive, and it has seemed to help. I have also measured the pressure in each cylinder, and they are all the same, very good (High!) .... Checked them cold and after tick over for 20 minutes.

The spark plugs are black and clean, nice and dry ! And tick over for 20 minutes is no problem, also starting is first time, every time.

Now just have to get the exhaust tight on the manifold again, seems to be blowing a bit, but hey thats the least of my worries !!

Thankyou alll for you help, and tips, seem to learning all the time with an austin !!

Location: Denmark

Just a thought, what condition is the silencer in, could it be partially blocked or poorly designed, you may be surprised by how much performance can be affected.

Location: NZ

Another thing to check is that when you fully depress the accelerator the throttle (butterfly valve) in the carb is actually fully open. Also ensure that the choke flap is not partially closed due to a weak or broken spring. I presume you don't have any serious oil or water leaks?. Overheating on hills will slow the engine down before it seizes - I once found that out just in time!

One thing that you might like to check is that all your brakes are fully off. A dragging brake will show up more on hills. A dry wheel bearing can have a similar effect. Jack up the car and check the wheels spin freely. Even low tyre pressures can make a difference.

It is easy to overlook even elementary things - we have all done it!

Location: Derby

Well the problem has been solved.... it turns out the distributer was VERY worn down, so much in fact the holes for the springs to the automatic adjustment of the timing were oval, which meant some times it has been getting stuck. Have replaced the distributer with another one, with round holes, and it works perfectly !

Location: Denmark

Thanks very much for letting all of us know, Laxton.
I hate threads which are left forever hanging in the air.

Ian Mc.

Location: Shropshire

Pleased to hear that you have fixed the problem, Laxton. I have never been to Denmark but always assumed that there are no hills!
Regarding petrol, the basic Tesco stuff is dreadful but the Tesco Momentum is very good, at least in my Austin.
If you want to try your Austin on some proper hills, we have some good ones here in North Yorkshire!

Hi Malcolm,
Denmark is actually very flat, compared to the uk, a perfect place for an Austin seven to spend its summers, gently cruising, with some medium hills..... I am sure North yorkshire has what we would call mountains !!

Location: Denmark

Good to hear you found the problem, Laxton. Sorry none of my suggestions included wear in the distributor.

Location: Derby

The discussion and ultimate solution shows that it is important to give full details of the car- age, type and model to assist in a meaningful discussion of possible problems- at no time was there any mention of an auto advance distributor !!

My entry in the forum has vanished- oh well time for a new avatar

Tony.

Location: Malvern, Melbourne, Australia.

hi Laxton

I second Ian McG’s comment. There are several threads for which many spent some effort responding but which just faded. Possibly the explanation was considered too embarrassingly obvious to reveal, but we have all been there.

Location: Auckland, NZ