The V8 Owners Forum -

Hi engine turns over and runs fine when cold. when it is hot and stop the engine and you try to start it the engine just about turns over. disconnect the coil and it turns over quite fast. reconnect the coil and hard to turn over. timing checked ok but retarding it a fraction and it bursts into life but then it doesen't run . as good and uses more fuel. anyone with any answers much appreciated.thanks.

Sounds like its too advanced for easy hot starts for one!

Does this engine have a carb and dissy or is it efi?

Hi it has carbs and dizzy tried new dizzy and retimed it runs good but same problem when hot . retard just a fraction and it will turn over ok but doesen't pull as good and uses more fuel.

What's the engine spec, and what are you setting the static timing to?

ivysboy wrote:Hi it has carbs and dizzy tried new dizzy and retimed it runs good but same problem when hot . retard just a fraction and it will turn over ok but doesen't pull as good and uses more fuel.

Have you got the vacuum advance connected to the correct port on the carb ???

the timing was done to the book specs useing a snapon timing light the timing advanced when engine revs increased so vacumn unit ok .have had two distributers and no difference. vac pipe connected correctl engine P6 9.25 -1 3.5ltr. been told it could be that the timing chain may be so slack ? could that do that.

I had a mega slack chain on my 1st RV8.

I could time it to run smooth while pulling, but the idle was naff.
Or set it to smooth idle but it lost power under load.

The chain was so slack that I could move the crank 10 degree's each way before the slack took up and the cam started to move.

It didnt stop it turning over though, whichever way it was set.??

Even if the chain is very slack. Once you start turning the engine the right hand side of the chain goes tight and the ign timing operates pretty much as it should while the engine is running, even though the other side of the chain might be flapping about.

Set the timing so it starts and idles ok. Then fit the strobe to see what the timing is doing. Pull the vac pipe off the engine to see if it retards at idle. This will give some indication of the vac modules performance.
Timing increasing with rpm doesnt really tell what the vac module on the dissy is doing.

Keep the vac line off the dissy and blank it off so it doesnt pull air into the manifold.
Set the timing to where you think it should be at idle. I reckon 8-10 degrees BTDC OR until you get a smooth idle.

Now run the rpms up gently so you can log the ign advance. Jot down what the timing does at 1500, 2000, 2500 and 3000 rpm. Then take it to 4000 to see if anything else happens. We just need to know that the mech advance is doing its job smoothly and not sticking.

You should see the timing settle back to the initial setting when you bring the revs back down.

It would also help if you have a vac gauge so you could log vac readings while doing the ign timing checks.

Appologies if you have already done these checks. But we need to know some stuff to help with diagnosis.


Perry

thanks will give that a try. many thanks.

While your messing about with the ignition you could try setting it up the 36 degree advance all in. Really you want the 'all in' at around 2700-3000 RPM.

(You may have to rev it to 4000 RPM check when the all advance is in, if its past 3000 rpm you should consider fitting a weaker bob weight spring in the dizzy)

Hopefully the idle timing will be somewhere around 12 degrees and it should not increase when you re-connect the vac system.

If you can manage to run the above settings you will find that your engine makes more BHP and has a better MPG then the standard setup.

At the end of day the timing figures at any RPM above idle at what are important, the idle figure just determines that 'starting point' for your timing curve.

Now the only problem with the above is that when you connect your vac system back up it may kick in too hard which means that the total advance at any RPM on part throttle is too high, if it is you will feel the engine kick back just as you apply the throttle. It may well be OK if you are using SU carbs, allI know is that the Eddy 500 carb definable does not work well with the Lucas vac system.

I presume that the SU vac system is 'ported' i.e. there is no vacuum at the take off point on the carb at tickover, if there is vacuum at the port at all times that forget all the gumph I've said because it will add more timing as soon as it's connected even when the throttle is shut.

ivysboy wrote:engine turns over and runs fine when cold. when it is hot and stop the engine and you try to start it the engine just about turns over. disconnect the coil and it turns over quite fast. reconnect the coil and hard to turn over. timing checked ok but retarding it a fraction and it bursts into life but then it doesn't run as good and uses more fuel.

Clearly, changing the timing as you have found is always going to make a difference, removing the coil has a weird effect too, but all the symptoms you describe make me think there is another fault happening at the same time, so you may never resolve your situation by timing adjustments alone.

The possibility is that the other fault is either fuel, ignition or mechanical.

However, to get the best possible timing have a butchers at this with particular reference to the last secton:

IGNITION TIMING

Optimum ignition timing for any given engine with any chosen fuel, is to achieve the most advance it can tolerate under heavy load without audible pre-ignition (pinking).

An easy way is to carry out empirical test/adjustment under full load.

However, before one can achieve that happy situation one needs to get the basic timing at idle approximately correct.

BASIC TIMING

# follow the manufacturers instructions to connect up the wires of your basic/cheap stroboscopic timing lamp

# clean the timing marks on the front (harmonic balancer) pulley

# remove the vacuum advance feed at the distributor

# clamp off the open tube

# loosen the clamping bolt to the distributor

# start the engine

# set the idle speed to 600 rpm

# switch on the timing lamp

# observing the timing marks on the pulley as illuminated by the lamp

# rotate the distributor body as needed to set the timing to approx 4 degrees before top dead centre

# tighten the distributor clamp, reconnect the vacuum advance tube and reset the recommended idle speed

# 4 degrees BTDC will be close enough to run most carb or Efi V8's for today's available fuels and an engine in fair/good condition

# only when the rest of the engine and its fuelling system is accurately set up you don't need to move on to the next phase.

EMPIRICAL TIMING

# loosen the distributor so that you can just turn it by hand

# make a small scratched mark on the distributor body and engine block

# in a safe manner, drive the car under heavy load in high gear, say uphill or with brakes applied

# apply more throttle and the engine should respond without pinking

# Find a safe place to pull over, open the bonnet and turn the distributor through a small amount (say 0.5 to 1 degree) only, anticlockwise, to add a small amount of timing advance

# repeat the test and re-adjust as many times as it takes until pinking can be heard

# stop the car and turn the distributor clockwise by the same amount as the last adjustment and retest to check that the pinking has disappeared again.

# this setting is now the best possible maximum timing advance for your car, in its current condition and with the chosen fuel.

# back at the garage, mark the new timing position and secure the distributor clamp

# for good measure set up the timing lamp and accurately measure the timing with vacuum disconnected at 600 rpm

# record the new timing setting for future use, when required

# any permanent future change of fuelling mixture and/or fuel octane rating may necessitate a new empirical timing setting

NOTE:

# in most circumstances where the ignition timing is thought to be reasonably OK, one can jump straight into the empirical timing process to avoid faffing with the basic set-up.

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Hope this helps, but for articles containing loads more ignition stuff - check out these new web pages!

http://www.vintagemodelairplane.com/pag ... ion04.html

http://www.vintagemodelairplane.com/pag ... ion05.html

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Moving on. To get some idea of what else may be wrong it would be help full to know what carbs you are running, what dizzy is fitted and what is the condition/colour of the spark plugs after a run - one from each bank.

From what I read so far this may not be a standard set-up for the original engine so a good deal of informed fettling may be required.

Advancing the timing until the engine pinks then backing it off in my opinion is no way to find the best total advance setting for an engine, some engines may never create enough cylinder pressure to cause detonation no matter how advanced to ignition ends up being set at. Other engines such as full blown race motors will be damaged the instant that the motor runs into detonation according the A. G Bell. If the peak cylinder pressure happens too early in the power stroke BHP will fall even if the engine does not detonate. If its too late BHP will also fall.

So in my humble this leaves you with two choices:-

1. Stick the car on a decent rolling road a spend a couple of hours and a couple of hundred quid setting it up.

2. Go for figures that other people have found to work well. Now in the case of RV8 lumps they have been around for years and loads of people have dyno'd these engines and published the results on the web. 36 degrees will be spot on or very close to what is required for a NA 3.5 lump. (You maybe able to use the 'real' road and a stop watch to get the ignition up but you will probably end up losing you licence by the time you have driven flat out up and down the same bit of road 30 times).

Really all you are trying to do is get the maximum combustion chamber pressure at 15-20 degrees ATDC regardless of the engine, research by companies like Ricardo have come up with the 15-20 ADTC figure for the max pressure.

This graph shows the cylinder pressure during the various phases of the complete cycle

http://performancetrends.com/Definition ... re-Lrg.gif

sidecar wrote:So in my humble this leaves you with two choices:-

1. Stick the car on a decent rolling road a spend a couple of hours and a couple of hundred quid setting it up.

2. Go for figures that other people have found to work well. Now in the case of RV8 lumps they have been around for years and loads of people have dyno'd these engines and published the results on the web. 36 degrees will be spot on or very close to what is required for a NA 3.5 lump.

That's as maybe, but the former will be an unnecessary expense at this early stage and the latter may not account for engines that are in less than peak mechanical condition.

So I think the OP really does have three choices, the above possibly inappropriate two, PLUS the empirical method previously suggested.

As for misrepresenting what was advised:

You maybe able to use the 'real' road and a stop watch to get the ignition up but you will probably end up losing you licence by the time you have driven flat out up and down the same bit of road 30 times

Not sure where the ficticious stop watch, or scary driving "flat out" comes in, or the jokey threat of lost license when the original advice was a sober

in a safe manner, drive the car under heavy load in high gear, say uphill or with brakes applied

The job really can be done safely and with about 5 stops at the most, and at the end of it, the timing will be as close as it needs to be for normal urban driving. All in my opinion, of course!

ramon alban wrote:

sidecar wrote:So in my humble this leaves you with two choices:-

1. Stick the car on a decent rolling road a spend a couple of hours and a couple of hundred quid setting it up.

2. Go for figures that other people have found to work well. Now in the case of RV8 lumps they have been around for years and loads of people have dyno'd these engines and published the results on the web. 36 degrees will be spot on or very close to what is required for a NA 3.5 lump.

That's as maybe, but the former will be an unnecessary expense at this early stage and the latter may not account for engines that are in less than peak mechanical condition.

So I think the OP really does have three choices, the above possibly inappropriate two, PLUS the empirical method previously suggested.

As for misrepresenting what was advised:

You maybe able to use the 'real' road and a stop watch to get the ignition up but you will probably end up losing you licence by the time you have driven flat out up and down the same bit of road 30 times

Not sure where the ficticious stop watch, or scary driving "flat out" comes in, or the jokey threat of lost license when the original advice was a sober

in a safe manner, drive the car under heavy load in high gear, say uphill or with brakes applied

The job really can be done safely and with about 5 stops at the most, and at the end of it, the timing will be as close as it needs to be for normal urban driving. All in my opinion, of course!

I was not misrepresenting what you advised with my statement about testing on a real road, in fact a was offering it up as a way of testing the car in order to optimize the timing whilst also mentioning that it is not a totally socially acceptable thing to do. A drag strip could be called a straight bit of road with a stop watch, I dare say you could get the ignition setup quite well using a drag strip if you had enough runs down it.

The rolling road method of setting up the timing is to start with the ignition retarded from where you expect the best setting to be by something like 4 to 6 degrees. After each run on the rollers the timing is advanced 2 degrees and another run is carried out. The process is repeated as long as the peak power continues to go up on each run. As soon as the power level drops then the timing is retarded back to the previous setting and another power run is taken in order to prove that this setting is best for peak power. If at all possible at no point is the engine forced into detonation. If during the tests the engine does detonate before the drop off in power setting is detected then obviously the timing will have to be retarded from this setting. What this is indicating is that the engine probably has a CR that is too high for the octane rating of the fuel being used. This setting is basically retarded from the ideal setting but unless the engine is run on a higher octane fuel or the CR is lowered it will have to be used.

Your statement of the optimum timing being as much as the engine will take before detonating is something that is often bandied about on the web and in some books, it is basically wrong, just because an engine is not detonating does not mean the it will make more power or run better with more advance. Like I said some engines will never run into detonation so just how are you supposed to use this method to optimize the timing? Do you keep advancing it until the dizzy is a full 180 degrees from the point that you started the test?

Even if an engine can be forced into detonating then running it a degree or two retarded from this setting could still mean that the peak cylinder pressure is happening well before 15-20 degrees ATDC, this is no good and means that power is being wasted due to the pistons trying to compress and already expanding gas. If the engine is setup like this but not detonating all this means is that at no point the pressure is getting high enough to start the process of detonation.

Your statement about it being 'weird' that the engine will turn over quicker when the leads from the coil are removed is odd because there is nothing weird about this at all. The OP has found that the issue is due to a faulty/weak starter motor, it is obviously under more load when the plugs are firing BTDC (as they should do) because the expanding gas is making it harder for the starter motor to turn the engine over. It could be that the timing is setup with too much intial advance but without knowing the figures it is impossible to say. Sometimes a compromise between the timing that the engine wants at tickover and what the starter motor can handle has to be made but ideally the timing should be setup to suit the requirement of the engine. There are ways and means to testing this.

All just my humble of course.

Could be two things going on. And the only 'one' thing I can think to ask is, is it a solid state starter motor? as I understand that they have less power when they are hot?

We were concearned enough to put a solid state on temperarily while the lucas one was fixed, but it stayed on in the end. But I guess it depends on hot your engine gets?

I know I'm having a wild guess there, but it would turn over well when cold?

It sounds like a nightmare of a fault

teamidris wrote:Could be two things going on. And the only 'one' thing I can think to ask is, is it a solid state starter motor? as I understand that they have less power when they are hot?

We were concearned enough to put a solid state on temperarily while the lucas one was fixed, but it stayed on in the end. But I guess it depends on hot your engine gets?

I know I'm having a wild guess there, but it would turn over well when cold?

It sounds like a nightmare of a fault

Do you mean a permanent magnet motor with reduction gearbox? Often called hi-torque?

If so, my findings are the exact reverse. My Lucas motor used to slow down dramatically when the engine got very hot. The hi-torque replacement, not.