Suggestions please...

Post by **bmcecosse** » Mon Jul 16, 2012 10:21 am

Yesterday - long day in the Trav, ran well but a bit smelly. Returning home with full load on board, hard flog (but not foot to floor) on the M8 at 60 mph (3.7 final drive) with serious head wind and long long uphill drag - and it started to run roughly with some worrying 'back fires' through the carb. Once over the top it ran steadily enough on the down slope, and then all the way home over more normal roads. Obviously I was then 'taking it easy' to make sure we got home. On opening the bonnet - found no loss of water or particular signs of overheating - but the oil filler cap was off - hanging on the plastic retainer. I may have left it off (anything is possible these days..) or it may have 'blown off' ! No oil spatter on the engine though - which makes me think it can't have been off all day long - although the slightly oily smell throughout the day suggests it may have been.
So - I have some ideas - but all thoughts and suggestions are welcome !

Post by **chrisryder** » Mon Jul 16, 2012 10:32 am

I can't imagine what would have caused it to blow off. You don't get that much pressure in the rocker cover do you? Even if the breather pipe was blocked?

Odd backfire going up the hill... dare i mentioned the coil? Or, of course, a loose connection to it? All plug caps on firmly? Could the condenser be showing signs of ageing?

Post by **bmcecosse** » Mon Jul 16, 2012 10:56 am

It's 'never' the coil

Connections all good. Condenser is a good old un - almost as old myself I imagine........

Engine has full power etc after it came off the hill.

Post by **chrisryder** » Mon Jul 16, 2012 11:36 am

Well a backfire, to me, would either be failure to ignite in the engine, so pumping charge into the exhaust, or a valve failing to close allowing combustion straight out the exhaust...

So if you can rule out the head, it must have been an ignition stutter or some sort. Rotor arm? Is it clean inside the dizzy cap? Plug leads tight on dizzy cap?

linearaudio · Post by **linearaudio** » Mon Jul 16, 2012 11:54 am

It's the coil-no doubt about it!!! Breaking down at peak power, peak load.
But as you only use your trav as a sunny sunday driver

, don't worry about it, and you have a spare in the boot anyway!
Of course, if you wanted to avoid these annoying reliability problems, then converting to electronic ignition is the obvious answer- more power to fire difficult mixtures/pressures, and, dare I say, fault free!
Just remember- it was you who titled the topic "suggestions please"

Post by **kennatt** » Mon Jul 16, 2012 12:18 pm

isn't back firing through the CARB.usually caused by over advanced ignition,fires just before the inlet valve is fully closed hence the backfire through the inlet side of the system,With the cap off could the vacuum system be altered, causing the auto advance to go too far when under heavy loading.Won't be the coil "never is" and the wolseley brakes will be fully adjusted so not them

Post by **moggiethouable** » Mon Jul 16, 2012 12:19 pm

This is a test isnt it? It cant be the coil, that would be bigger than the discovery of the Higgs Boson,Successful Nuclear Fission, or a Yorkshireman getting the first round in

Post by **chrisryder** » Mon Jul 16, 2012 12:37 pm

kennatt wrote:isn't back firing through the CARB.usually caused by over advanced ignition,fires just before the inlet valve is fully closed hence the backfire through the inlet side of the system,With the cap off could the vacuum system be altered, causing the auto advance to go too far when under heavy loading.Won't be the coil "never is" and the wolseley brakes will be fully adjusted so not them

The ignition would have to be very over advanced for that. The charge goes through a full compression stroke (valves shut) before the spark gets involved. Indeed you can get this issue if you've just put the dizzy in way out, but it wouldn't happen in road use.

Post by **moggiethouable** » Mon Jul 16, 2012 12:47 pm

Its gone viral

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Post by **brucek** » Mon Jul 16, 2012 1:20 pm

Very funny - well done guys and girls

Hope the 'problem' is fixed soon Roy!

Post by **JOWETTJAVELIN** » Mon Jul 16, 2012 1:59 pm

That clip is hilarious!

Post by **IslipMinor** » Mon Jul 16, 2012 2:02 pm

Roy,

Valve nipping and 'on load' misfire? Combination of higher than normal engine temperature, maybe mixture/needle a tad weak and ignition slightly over advanced at high engine speeds (out of the audible 'pinking' zone') giving rise to local internal overheating? I wonder which cylinder it was? Or more than one?

Do you leave the heater valve open all the time, so the back of the head gets a good flow to avoid local overheating? Another well-known A-Series problem with higher stressed engines.

Finally, if you have removed the by-pass hose, and not made any other provision for a by-pass, No. 1 can overheat and cause exhaust valve nipping - usually no other sign, other than very occasionally the water temperature would rise by 15/20°C for a minute or two. Haven't had a problem for a number of years now since restoring the standard by-pass hose (as is well recorded here!).

Post by **daveyl** » Mon Jul 16, 2012 2:09 pm

Water spray on the
dissy?

Post by **crossword** » Mon Jul 16, 2012 4:12 pm

When I accidentally let the filler cap off I had a misfire but my cap is metal , not sure about yours , could even a plastic cap be conductive at 10 - 15 KV ? going uphill may have slightly moved the 'rest ' position of the cap . As you suggest the slight smell may have been fumes allowed out by the open cap .

Andrew

Post by **Jefftav** » Mon Jul 16, 2012 4:16 pm

Is it
Wear in the dizzy so that it allows the timing to alter and the long drag up the hill with the throttle open has induced the misfire?
OIl Cap - A senior moment leaving the cap loose so that it has been lifted off when driving?

Post by **RobThomas** » Mon Jul 16, 2012 5:02 pm

Re: Suggestions please...

Momentarily stuck inlet valve. Spark ignites intake manifold contents through W.O.T., blows air filter to bits, ignites oil fumes in crankcase via breather system, fires oil filler off like a bullet. OK, maybe the oil fumes explosion bit is beyond reason but the backfire might have sent shockwave via breather line.

Suggest check air filter for scorch marks and action of dissy advance capsule.

I sent this message about an hour ago but it didn't arrive. Sin bin again?

Post by **kennatt** » Mon Jul 16, 2012 5:16 pm

its the scottish equivalent of the G C E A level,except B M C A series.

def a test,that news clips is wicked fell off the chair,fantastic.

bet it was the coil and he will admit that he has changed it,for an old new stock of course.

Post by **MarkyB** » Mon Jul 16, 2012 6:48 pm

I'm thinking oil cap off might give a weaker mixture with the breather connected to the carb.
The ignition might be slightly advanced for the conditions with the extra load and all.
I'd be a bit worried about the oil supply to the rockers as there wasn't much evidence of oil splatter.

Post by **bmcecosse** » Mon Jul 16, 2012 10:03 pm

All excellent suggestions lads! Obviously - it's not the coil....... The strange thing is - each backfire was a 'double report' back through the carb - not exhaust - and then it would struggle on. I agree with all the suggestions (well.. not the coil ones obviously) and yes I like the Newspaper clip! Well done all. My own guess is along Richard's lines - a partially sticking inlet valve caused by running extra hot under the long unrelenting climb - I suspect if I could have seen under the bonnet - the 3 branch exhaust manifold would have been glowing red! Or perhaps it's simply that the exhaust valves have been glowing red, and pre-igniting the fuel - or perhaps they have expanded with the heat - and closed up the valve gaps. When I get a chance I intend to run a comp check, retard the ignition timing slightly and increase the exhaust valve gaps to 18 thou. Sorry Richard - on this engine the bypass is still open - and the car had already run without a problem for ~ 200 miles before it hit the hill. And yes - heater valve never closes - and the heater was working well! Could be that the oil cap may have been 'blown off' - because of the lack of oil thrown around - yet it ran for a further 20+ miles after the hill, to home. The rockers are well lubed - no problems there. The oil pressure had sagged to 60 psi - under less stressful conditions it runs at ~ 70 psi at decent revs. The slightly oily smell however should have alerted me to at least have a look under the bonnet earlier in the day.......... keep the suggestions coming!

Post by **Andy Rose** » Mon Jul 16, 2012 10:17 pm

Wow! 3.7 diff must be great for cruising,but must make the engine work very hard on the hill climbs..perhaps the fuel supply fell a bit short of demand causing a lean mixture. Perhaps a clogged filter or a restriction in the pump to Darby hose., with the oil cap, it sounds like I was the last person to top up your oil