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MG Midget and Sprite Technical - Total advance adjustment ?

First of all, this is a Nissan A-series engine..

Ive modified my engine quite a bit, bored out by 1mm, longer stroke by 5mm, new cam with longer duration and higher lift, higher compression 9.8:1, Weber 38DGAS.

First time i have done anything of this complexity so quite proud of myself.

All runs ok with quite a big gain in torque and power, ( I will take it to the rolling road to be measured once i have it sorted.)

I have an issue with pinging at around 3000 RPM at partial throttle. If i'm cruising along at 60mph ish in 5th gear and i press a little harder on the pedal i get pinging, if i just floor it i get the pinging for a second before the power cuts in and no more pinging.

Is it that maybe the mech advance is coming in to early ?
Or maybe the total advance is too much now ?


Any advice ?

I'm running 95 RON fuel and just made myself a cool air intake as its been 42 degrees C here last few days.
Static timing is set at 5 degs and i think the total timing is around 32 degs. but i need some one to help me measure that, maybe tomorrow...

Andy Phillips (frankenfrog)

Basic advice is to advance as much as possible up to the point where pinging just occurs when driving hard up a hill.
M Ogden

Have you set the carb to cope with the extra capacity?

Predetonation is avoided by getting the mixture AND timing in balance, and a higher octane fuel also helps. Having higher compression than standard will also increase the chance of it occurring. And don't believe it's only happening when you can hear it, it will be occurring at other running states too. It will be putting major stresses on your newly built engine, and needs to be addressed quickly. Running lean when under load will also contribute to the problem.

Try a higher octane fuel, and if that helps, try richening the mixture a little, then retard the ignition a little, and you should be able to go back to the 95. But as your compression is quite high, you may have to stay on the 98 and also retard the timing and richen the mixture as well.
dominic clancy

Are you running vac advance, if so the momentary pinking may be the vac advance too much, try disconnecting the vac advance if fitted and see if it helps.

Peter
Peter Burgess Tuning

Just guessing id think the dawg springs are to light or the dogs can be to light as well

for ideas look up mallory dissy ... 27 series duel point adjustment...

they have a number of tricks and tips that are probably universial for adjusting the curves
prop

Ahh-
I've had a 1275 midget with a pinging problem
Checked the mechanical advance - all good then moved onto checking the vac. and found the dizzy had been fitted with the wrong vac servo giving it heaps too much advance on light throttle.
And
Some of them little Webers are far more active as far as vac supply compared to SUs - They come on stronger/ earlier and hold on longer causing pinging like this on light throttle
As Peter says check if it pings with the hose off----

Also--my favourite subject------setting max advance

Setting max advance by the M Ogden method, while being ok (just) for lazy road use is asking for trouble if you are going to drive it hard. As Dominique suggests, audible pinging is the final warning, there can be damage done without hearing it at all
Your rolling road man should be onto that but the correct requirement is the least amount of advance while maintaining max power, not the most advance you can give it

Them little Nissan engines usually cope well with timing out a bit so you have got yourself a problem there somewhere- guess you know that already
Were you running the Weber before, If not what did it come off ,new-secondhand

Interesting project

willy
William Revit

95 RON is the highest octane i can get without going to E20 or even E85 .
Weber carb is new and came pre jetted.
I have an AF meter and it shows 11:1 when accelerating and between 13 and 15:1 when driving normally.

I had engine at 11:1 CR when i first built it and with the ignition advance set at the normal 7 degs BTDC it was a horrible pinging monster. Then i set the timing at 0 deg static and it was drivable but still had this pinging at around 3000 rpm.

I decided 11:1 CR was too much for this fuel ( i had used a chart from America which said it would be ok, but didnt realise about the MON and RON differences)and this weekend put at thicker HG on to bring it down to the 9.8:1.

With the thicker HG i reset the timing to 5 degs BTDC and now i get the same issue at around 3000 rpm.

My instinct is that the springs on the bob weights need to be stronger to delay the mech advance, or Peters Vaccum suggestion makes sense.

i'll try disconnecting the vaccum and also play around with the static timing to see if i can get any improvements.

in at the deep end, best way to learn !!
Andy Phillips (frankenfrog)

Although not strictly applicable I have 1293 with a modified cam, head, 10/1 CR and running on a single HS6. On the rolling road the guys found standard distributor (with no vacuum setup) gave insufficient advance (7 - 23) so if the top end was taken to 28 - 30 degrees, the mid range was advancing too early. So the disributor was gutted and the internals ohanged to slow it down at around 3000RPM yet still allow full advance at the top end. It could be that your CR is higher than you think Assuming it's running on like the plague I 'd get it booked in sooner rather than later.
Fergus

Fergus, i think very applicable, when i had it at 11:1 CR it dieselled really badly.
I changed to two levels cooler running spark plugs which seemed to help at first, but also found keeping engine cooler helped.

Now with the lower CR the dieselling has stopped at least..

People were telling me to adjust the ignition timeing to help stop the dieselling, but i cant see how the two would be connected given that dieselling occurs once the ignition is switched off....
Andy Phillips (frankenfrog)

Dieseling is caused by unburnt fuel being spontaneously ignited by a glowing plug electrode. So cooling the environment where it occurs by running a harder plug /retarding the inition /lowering tickover speed or richening the mixture will all help it to a degree. Often with 'short' advance curves you get a situation where the ignition is set so advanced the starter motor struggles to even turn the motor over.So typically on a Frogeye you cheat by whizzing it around on the starter and then switching on the ignition - and the inertia is often enough to get the thing going. But the real trick is get the advance and fuelling corrected on the RR so it starts easily, takes WOT in the low to mid range with no pinking, but still delivers 28 degrees total.
Fergus

Dieseling/running on is made worse with retarding the timing, the biggest culprit is overheated ex valves caused by the late burning charge having access to the open ex valve. The valve runs even hotter if you delay the ignition burn by retarding the timing.

Peter
Peter Burgess Tuning

My 2 pence, and the advice I give to all my customers is.....Get it to the rolling road and have them set it up. You might get it "close" but it'll never be as good as a rolling road set-up.
J White

good advice for the UK but Andy may have a bit of a problem as he (and the car) are in Thailand.
David Smith

I had bad pinking and dieselling (running on) on a 6 cyl T*****h after I rebuilt the top end. About 25 years ago now. It drove me demented for a week or so - nothing I did to the timing or mixture helped. Finally I twigged that the head had been skimmed and neither the machine shop nor I had thought to break the sharp edges around the chambers in the head. It was these sharp edges that were getting hot and preigniting the fuel/air charge.

(Truthfully I didn't twig - it was Dad who suggested it now I think about it).

One new head gasket later and humble pie for tea and problem solved.

Not saying that's your problem Andy, but it's a possibility not hard to miss on a newly built engine.
Greybeard

Good call young Greybeard, and a head scratching problem I have come across a handful of times. I think the Nissan head is aluminium so any sharp edges left do not glow and cause det. I hasten to add we always deburr ally heads as a matter of course as it feels completely wrong not to do so!

Peter
Peter Burgess Tuning

Sharp edges makes for a good looknjg crack

prop

Years ago when unleaded fuel was introduced here, the Ford Falcons had a pinging problem at highway speed and the fix was to pull the head and round over the end of the beak that pokes out between the valves to about the same profile as a pea and then smooth over the edge of the chamber around both valves from the beak to the headgasket --fixed em up
If I remember correctly the Nissan head has the same beak in it's chamber --yes/no
You would probably loose half a cc or so but that would work in your favour as well
In my opinion,I know high compression makes power but struggling with trying to get something running at it's peak you are better off with a bit less than optimum and that will allow you to set the timing up where it should be instead of compromising and also it allows for discrepancies in fuel quality

Also, larger engines don't seem to like as much cent. advance as little ones in the mid range - Your engine hasn't grown all that much I suppose but an example is if the ditributor out of a 3.5 Rover happens to find its way into a 5.0 converted engine as they do they get this real harsh sound on accelerationin the mid to upper rev range -not pinging, just harsh and by grinding a tiddle off the ends of the bob weights in the dizzy to slow the advance rate everything is good again
Better stop this as it is starting to produce too many options - back to the problem

Still interested though as to what happens with the vac line off
willy

William Revit

Heres a picture of the head when i took it off to put on the thicker HG.

If i can get out of taking care of 3 year old for half an hour i'll get out to test the vac-theory.

It is an Aluminium head.

I noticed when i removed the head that the rear cyl ex valve seemed to be hot, so i removed the plug that plugged the heater take off (not required in Thailand so plugged from the factory) and fitted a 6mm hose that connects to the bottom hose at the front.
Idea being to promote coolant flow at the back of the engine.

As part of my project i also had a custom 3 core radiator made, engine runs at about 78 degs, even with a 43 deg ambient as it was yesterday.

Head hasnt been skimmed.


Andy Phillips (frankenfrog)

OK, 2 gold stars for Peter Burgess ....

Disconnected and plugged the vac hose. No Pinging at all, no matter what i did.

Engine down on power however, but now i can start advancing by turning the dizzy until i reach pinging again, then retard it back a degree from that point.

That will be close enough until i next get time and can fit the programmable crank ignition i have on the shelf.
Thats the point when i will get to the dyno, no point going to the dyno at the moment as the young guy who runs it dosent know anything about these old things, but will sort out a computer controlled job with no problem.

Thanks for advice guys,

Once i have been to the dyno and had the full tuning/testing done i'll post a full write up.

Peter, If i still lived in Stockport i would be straight round to see you, with donuts and coffee to last the day.
Andy Phillips (frankenfrog)

Hi Andy

With high CR engines we do not run vac advance. The engine is crisp even part throttle when the advance curve is correct.

Glad I could help Andy but you told me what your problem probably was with your accurate description. Another reason I like customers to stay with the car when I dyno them as they have the local knowledge of the car!

Peter
Peter Burgess Tuning

Andy/Peter
That cylinder head pic looks fairly lean in the two rear cylinders to me compared to the front pair
There must be something going on there as well--
Vac. leak maybe
I take it that the Weber is mounted cross wise on a common plenum type manifold

willy
William Revit

Hi Willie,
Carb is mounted on the standard manifold using an adadptor supplied by redline in a kit with the carb..

Its mounted at 90 degs to the axis of the engine.
Both barrels of the carb feed into a single plenum then into a two tubes which then split again to feed each port, see picture attached, not the exact one i have but similar.

Im not sure how you would adjust it.

I partly attributed, perhaps in my inexperiance, the different colours to the back of the head running hotter which is why i tried to get more coolant flow there.

When i had problems with dieseling it was like there was one cylinder that kept on firing like a slow running single cyl engine. I assumed it was the No.4 to the right in the cyl head picture




Andy Phillips (frankenfrog)

Thats an interesting looking intake

#3 looks like it had the beginnings of a hgf on the coolent side
prop

Andy
You are probably quite correct putting it down to heat from lack of coolant flow
It does look lean in the back half though-in comparison-

With the manifold you have, it eliminates the carby leaning on one end as it feeds into a common point and should have even mixtures on all four
A vac leak on the back half could still be a possibility
One thing, these engines, if I remember correctly had a fairly decent sized thermostat bypass hose which promoted a decent flow of coolant through the head at all times - Are you still running a bypass or has it been eliminated during your conversion-------
willy
William Revit

Hi Willy,

No, no bypass pipe on these engines, maybe the predecessor which was based on the BMC A-series ?

It has a thermostat which is fitted to the front of the head with a small hole for air i assume.

There is an option , depending on which head and inlet manifold you have, to have a water heated manifold.
The water came out of two small 3mm ish holes near the bottom and between cyl 3 &4, this then lead into the manifold directly with no hoses. Then a hose came from the manifold to the front hose.
My head actually had the holes for the manifold water, but i plugged them up as my manifold is a dry type.

My problem is keeping the manifold and carb cool enough without putting hot water through it. :-)


It may be worth while drilling a few 3mm holes into the thermostat flange just to help the flow though,



Andy Phillips (frankenfrog)

I always add a 1/8th inch hole into my state flanges...if for no other reason just good insursnce

id try one before id try 2 as a little goes along way

try a product called water wetter thst can also take a few degrees off the temp ... but only use what is recommended... or it becomes ineffective

also if your running 50/50 ... try 70 water / 30 coolant
prop

The bypass might be built into the engine somehow---
Drilling holes in the thermostat will flow a bit of coolant -but- it's not the same as a proper bypass
Drilling the thermostat allows coolant to escape out into the top hose and on through the radiator--resulting in cold water entering through the waterpump to replace what's lost out the thermostat
Too many holes will result in an engine that takes too long to get warm and runs below thermostat temp'
Whereas a proper thermostat bypass circulates coolant back into the waterpump causing it to go round and round in the engine only, until it gets warm enough to open the thermostat and then start passing through the radiator as well- this method gives a more even temp. in the engine
William Revit

Hi Willy,
Ive basically created the bypass by taking the unused heater port from the back of the head and plumbing it to a tee in the radiator bottom hose.

Improved the engine design again !
Andy Phillips (frankenfrog)

Yep
From the front of the head would give a more complete flow but yeah it has to help
My mate's Mini racer has a hose off the heater tap fitting at the back of the head like you have done and doing that solved his headgasket/heating problems--
William Revit

This thread was discussed between 15/04/2016 and 20/04/2016

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