I’ve got a 1935 Ruby with the Low Comp. head, re-bored to +0.040” in 2002 at 79000 miles.
She’s always run with a little blue smoke but the spark plugs were dryish and brownish and she ran fairly smoothly.

Now the problem

The exhaust valves were found to be badly burnt at Christmas so they were replaced and all the valves were then lapped in (hardened exhaust valve seats previously fitted during the re-bore) Plus at the same time I fitted new spark plugs, points, condenser, dizzy plate and cap and the current mileage is 81000mls.

Since then I’ve had terrible problems with the engine backfiring through the carb, and the exhaust. She’s now oiling up to the extent that it’s dripping out of the exhaust pipe and the plugs are soaking. She will not run smoothly and generally it’s a mess.

A compression check shows that all four cylinders are at 80psi

So what is wrong? Where should I start to put things right? What have I cocked up?

Surely the engine doesn’t need re-ringing after 2000miles and if so why all of a sudden after improving the compression with new exh.valves?

Is there anyone out there who can provide some sensible advice or a path to eliminate the possible causes? Help please I'm desperate.

when you say "oiling up" Do you mean the plugs oil up? what are they D16 or jap. ?What have you set the valve clearences ? What grade of oil? Mac

Dave,
There are several questions amongst the points you have made but the one that is formost in my mind is the timing. There are two aspects to the timing, the ignition timing and the valve timing.

For the engine to backfire out of the carb it means that the explosion in the engine is happening while the inlet valve is open. This may be caused by several factors.

1. The valve timing is wrong in relation to the piston position in that the valve is open too long or too late.

2. The valve(s) is not seating properly

3. The ignition is happening too soon because the distributor is not time correctly, ( too advanced )

4. You are getting pre-ignition due to glowing carbon in the engine setting off the fuel charge too early. This could also be caused by excessively weak mixture due to an air leak at one of the manifolds.

5. It could be ( and most likely will be ) something else I haven't thought of !!!!

With a backfire out of the exhaust most of the above points could also be the cause.

Often engines are accused of 'oiling up' when what it actually is on the plug is a mixture of unburnt fuel and carbon. Once a plug becomes 'wet' it does not fire properly, if at all, causing this build up of wet carbon which does look very much like oil.

I would start by checking all my timing and valve seating which is easiest to do by removing the head and watching the action of all the valves, pistons and contact breaker while slowly turning over the engine with that very helpful starting handle.

Good Luck, knowing Sod's Law it will be the last thing you think of!!!!

I once built an engine for my modern....

I ran it for 500 miles and then decided on an oil change. I removed the old filter and "spun" on the new one, I then went for a cup of tea, I then had a yap with my mate, I then put the fresh oil in.........

The "oil pump" I had magically created ran.. just about. It sounded like someone stirring paint and pumped considerable quantities of oil out everywere.

The next day I drained out about 4 litres of oil, cleaned the plugs and all was well.

Almost certainly not your problem but just a thought?
Methinks Malcolm and Mac are pointing you in the right direction.

p.s I see from reading last weeks posts that after years of trying I have finallly achieved idiot status. I shall wear the badge with pride..

Sun tanned Steve

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Steve,

Absolutely no charge. Medals to be presented at some future occasion.

Mike

Dave,

My commisserations.

This is a nlong shot, but as Malcolm says, Sods Law will probably apply.

You said that you have replaced the Distributor Cap and other bits in the Distributor. Have you tried reverting to the old parts?

I have heard all sorts of stories about poor insulation properties of some "aftermarket" parts which are made abroad. If you have managed to "cop" such a spare, then that just might be the source of your misfiring.

In your sort of desperation, it may well be a simple matter to try.

Also, have you done the standard "advance mechanism" check on the Distributor. With the distributor at rest (obviously) grab the rotor in your fingers and twist the rotor in the direction of normal roation. You should feel the firmish resistance of the advance springs and the rotor will move until it is stopped by the action plate. Then let the rotor go and it should return positively to the rest position.

If the rotor instead simply "flops" about or will not move as described above then you may have problems in the advance mechanism.

A "floppy arragement" means that it is virually impossible to properly set up static timing and the timimg can be virtually anyware within probably at least ten degrees or so.

a "frozen" mechanism is not quite so likely to give you misfiring problems just no advance.

At least probably worth a look



Best of luck

Barry R.

Remember preparing a Box Saloon for a French touring holiday about 30 years ago, I rebuilt the engine including a rebore and changed all the electrics.At first the car was wonderful from cold but after a mile or so started to run rough and oiled plugs. Took the engine out and returned the block to be checked ,all OK so back together in time to set off for France .Seemed Ok on the way down to Dover so thought problem cured ,but on starting up on the ferry was rough again and would barely pull the car off the ferry.Crawled through Calais ,then had a brain wave ,I had fitted a brand new coil ,so called in at a Renault garage and bought a 6V Renault 5 coil fitted it and no further problems!!!! Renault coil stayed on the car for the rest of my ownership . Moral of the story just because its new doesnt mean it functions correctly.

My 34 box had been running badly since a piston and block change for over a year. It would kick back on handle unless well retarded at starting, would spit back thro the carb and backfire thro exhaust and foul its plugs. I checked timing, valve clearances, plugs/ points gap.manifold/carb gaskets. It finally died on the brake tester at mot station, and had to be pushed out of the garage!! (still passed its mot--no visible smoke I suppose) . What finally cured it was opening up the points from the handbook setting(12thou??) by a few thou.It ran perfectly after that. Possibly something to do with dwell angle but im unsure how it could have such a profound effect.
Regards
Andy

Hi Mac, The plugs are new D16, the valve clearances are 6 & 8 thou inlet & Exhaust and the oil is SAE30.When I remove the plugs they are black oily and wet.

Hi Barry, the dizzy cap was very badly worn, but I'll refit the original dizzy plate and check out the advance mech. thanks for the advice

Two points from the above, no three, third point first. That is, blaming the ignition is a long shot, but just might be worth trying!

First Point - Just becasue a distributor cap looks "worn" inside doesn't necessarlily mean it is no good. The fact that there is a bit of "etching" of the brass posts (at the ends of the HT lead connectors inside the cover) does not have to mean the end. The slight gap there, unless it is really excessive can actually benefit the delivered spark - some may remember the "spark enhancers" which were marketed in the 1960's - they really only were a fancy way of introducing a "gap"

Second Point - On the matter of Contact Gap, there are a couple of hidden facts there. Original Lucas DK4A specs were for 0.012" gap on the standard distributor cam of the day. ( more correctly 0.014" initial adjustment on new points, then 0.012" in service, on the basis that there would be initial heel wear) Then just after the war there was a cam introduced which had sharp opening and slow closing. (Also from memory 0.012" gap) Then later again (circa 1952) they introduced the "High Lift" Distributor cam and specified 0.014" to 0.016" gap. Over the years, these cams which are generally interchangeable no doubt can and at times have been mixed up. Also, I have seen some of the original cams which have been horribly worn.

The whole point of the above diatribe is to get to the point that unless you have a proper relationship between the "real time" the coil is provided with current to build up magnetic flux in the coil, and the interruption of the current to allow that built up flux to decay, then you won't get an optimum spark. There is also the added effects of the varying current characteristics of various (sometimes nefarious and uncertain) brands and types of coils.

I always try and replace the old type of cam with the later type. (I would never use the interim type.) You then adjust points to the wider gap. I have found that the one out of Series 2 Morris Minors fit ok (and also for what its worth the Auto Advance Springs from this model also work satisfactorily in an A7 DK4A, but you must be sure that they come off the old "lead" type weights and not the later roller types)

Barry R

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Barry

From what you are saying, (which I hasten to add I agree with from an electronic principles point of view)then the "dwell Angle" is what we should be setting, not points gap, which of course is subject to operator error. The question now is what would be the correct dwell setting for said dizzy/coil, and is this taking things a bit too far maybe given the vagueness of everything else?

Steve.

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Steve,

Without initiating (I hope) a 'teaching to suck eggs session' may I try to help with this?

Dwell angle is the period during which the points are closed, and current is flowing in the coil. Looking down on the cam lobes in the distributor it is the angle between the point where the cam leaves the heel of the moving contact, and where it makes contact again. The period (or arc) when the moving contact is 'dwelling' in other words.

With a bigger contact gap the points will take longer to close, using up more of the cam rotation and thus produce a correspondingly smaller dwell angle - and vice versa. Adjusting the points gap is the only way to alter the dwell angle.

Obviously it is all a compromise between having a sufficient gap to get a clean spark, and giving the coil long enough dwell to recover. .012" will work in most circumstances. It is often easier to take the distributor out and set the points on the bench.

Whilst on this general topic, I hope that you have a good condenser. It is always possible to put one outside the distributor, between earth and the feed terminal (having disconnected or removed the existing condenser). I recently had a problem like this, and a new condenser found me instantly another three or four miles per hour in second gear.

Mike

Thanks Mike

I am familiar with the concept of "dwell" and have a meter to measure it, was just wondering on a figure for us to aim for? I guess the points could be accuratly set to 12 thou on bench and then the dwell measured on the car to give a figure. This figure could be used then when servicing or adjusting?

Steve.

Hello Steve,
You're probably right about that, provided you have an unworn and correct cam fitted. I tend to shy away from dwell meters. I well remember a "muchanics" day we had here years ago, about half a dozen people turned up with their "Auto Supermarket" dwell meters and we finished up with about half a dozen different readings, all off the one car with the same untouched "gap" adjustment. I have a distributor graphing machine and, when I get some time, and a decent DK4A Austin Seven Dizzie, I will have a little fiddle and measure what it says is the dwell on a properly set up Distributor. I have some Lucas Sevice bulletins on Distributors, but don't think they would have dwell details. My experience is though that a good feeler gauge is the best method, on clean square points, and err on the "too wide" rather than "too tight" side and you won't go too far wrong. My earlier comments on this matter were in response to another reply which adverted to the fact that opening up the points by a couple of thou had , on an occasion, radically improved running, but the respondent couldn't understand why.

There is another point, although I doubt that it is germaine to the matters in this thread, and that is that there is a right and wrong way to have the Low Tension side of the coil connected. Should be such that it drives the High Tension side so that the centre electrode of the spark plug is "negative" A bit too long winded to discuss here, but the sages say that it can make something in the order of a 20% difference to the quality of the delivered spark, and can therefore be of some significance in marginal operating conditions! (And isn't that all 6v systems?)

Regards

(and back to my "Blipping")

Barry R

Would be interested to know if Dave T solved his oiling up problems? I have similar, although nowhere near as bad. Some oil exuding from exhaust manifold/downpipe gasket, from around a couple of spark plugs and, even more curiously, from the centre cylinder head stud!!

Having said all that, the engine runs a treat but I am just a bit concerned about the head. (Brand new copper gasket about 300 mls ago)

Latest update on my original post. The new dizzy base plate was a copy from A7 service, I replaced it with the original and there was an improvement but on a 100ml run she broke down with a terrible misfire after 60ml. no matter what I tried she would not fire smoothly through the rev range but I managed to get home.(nearly got a speeding ticket in 40mph zone in Kirby Longdale) Anyway, compression check still had 80psi on all 4 cyls. So I bit the bullet and bought a new Bosch Dizzy from Willy McKenzie (01202 694351)fully modified and ready to drop in. This I did to-day and so far (fingers crossed) all sounds and feels very good smooth & no smoke! Tomorrow is the test with an 80ml run to Raby Castle. Then I will be able to say if all is cured or not! and that for the last 8yrs I've run like a bag of nails due to a worn tired 70yr old dizzy!! I'll let you know.