A purely theoretical question. (for now)

[Tuga2112]

if the exhaust cam is 1 tooth out of alignment but the rest is correctly setup.

would the CAS require to be at the limit of adjustment to get close to the timing setup?

would the power loss be obvious ? or subtle ?

DIscuss.

i have an armchair theory, and i want to know what others think about it before commiting to a timing belt check.

note
this timing belt was installed by PMN... =S

and yes, this is purely theoretical, because the real scenario is with the NA engine where ther's no CAS, but i think the analogy makes sense

[Hector2021]

I would suggest that irrespective of the ability to adjust the ignition timing. If the exhaust cam is one tooth out then there will definitely be a running issue of some sort. Electrically the engine may be in sync, but mechanically the valve timing is a number of degrees out.

[dapinky]

Joao, the answer (theoretically) is probably, yes......

...however, checking if the cam is one tooth out is relatively straightforward - the sprocket will only fit on the camshaft in one position, and if the 2 cams are correctly timed, then the holes which you use to fit the bolt to prevent the cams from rotating will line up correctly - and you should be able to clearly see if it is a tooth out, just by "simply" removing the belt cover......

[Simon_P]

A tooth out in which direction?
Has the head been skimmed?

[Tuga2112]

Joao, the answer (theoretically) is probably, yes......

...however, checking if the cam is one tooth out is relatively straightforward - the sprocket will only fit on the camshaft in one position, and if the 2 cams are correctly timed, then the holes which you use to fit the bolt to prevent the cams from rotating will line up correctly - and you should be able to clearly see if it is a tooth out, just by "simply" removing the belt cover......

that annoying bolt under/behind the engine mount is installed. do you have any tips to get it out ? my issue with it is that i find it impossible to access.

A tooth out in which direction?

what i can tell is that with the distributor at the limit of its adjustment clockwise, i still dont get 16btdc when reading the timing with the ecu in diagnostic mode (under the assumption the NA enters diagnostics mode the same way as the SE)

Has the head been skimmed?

i would have to check the cars documentation. but it wasnt mentioned when i bought it.

[dapinky]

that annoying bolt under/behind the engine mount is installed. do you have any tips to get it out ? my issue with it is that i find it impossible to access.

this is why I put the word "simply" in the quotation marks!

There are more issues than just removing the bolt - as the plastic moulding of the cover doesn't allow it to "simply" slip off due to the spacer block, so it needs pulling away from the engine a bit.

That said, I made up a tool to remove the bolt without doing anything else, and it is a 1/4" drive 10mm socket, which I have ground down a bit to shorten it, then welded a metal plate/bar to the end. i t slips between the engine mounting and the cover, drops into the hole and you can undo the bolt half a turn at a time.....

..... if the PAS pipe (if fitted to your NA - it was an option from the factory) is in the way, I usually remove it at the pump end.....

..... but if you can undo the bolts there may be enough movement to be able to see what you need to see (or there may not!!!!)

[Tuga2112]

I have the means to make such 10mm ofset spanner, but if the cover doesnt come out with the engine mount installed, that ultimately means i need to hold the weight and access underneath in order to "just" free up the engine mount bolts to make some room for the cover to come out.

at this point i may as well remove the mount i guess. and this is why i want to follow the purely theoretical side of "what if" because if the brainstorming exercise leads to others things i can check easily, i woudl prefer that.
also, if i just dump into a post all the information i have gathered, it becomes a very boring read.

i have one clear symptom. and many diagnosis steps already done in a thoeretical way.. (eg. i have not taken the IAC valve out, but i have reason to believe its fine, same with fuel delivery etc)

the spark setting being this far out is the thing that im trying to address, which i hope is the core issue of my symptoms.

im sure starting a diagnostics thread from scratch saying "i have a surprisingly high idle speed" has its advantages, but I Have no interest in wasting anyone's time with suggestions like "the IAC valve may be faulty" or "have you changed your fuel filter" because regardless of those being an issue or not. i know for a fact my distributor wont reach factory advance at its maximum range of adjustment.

im trying to approach this in a inverse manner, as to see if what i fear is the issue would cause other symptoms that i am unaware of, and by investigating those, i may prevent myself from doing the "not quite timing belt change" for nothing.

truth is, im getting lazy. because if i just got down and my hands dirty yesterday, i think the engine mount would have been out by now.

[Simon_P]

im sure starting a diagnostics thread from scratch saying "i have a surprisingly high idle speed" has its advantages, but I Have no interest in wasting anyone's time with suggestions like "the IAC valve may be faulty" or "have you changed your fuel filter" because regardless of those being an issue or not.

oh ok then I won't suggest that as it's an N/A it has a distributor which works in a completely different way to a CAS and has a conventional coil ...no EST or wasted spark for you! (Am I wrong?)
If you did start a diagnostics thread saying you have a surprisingly high idle I might suggest that with a distributor retarding the timing will slow the tickover speed and make it more reliable whilst advance Will speed it up and make it less reliable.But as the thread is about a theoretical analogy with the exhaust cam being one tooth out I'll suggest it would have cock all effect on the scenario you describe as the analogy isn't valid and the advance you are trying to achieve would likely make it worse.

i know for a fact my distributor wont reach factory advance at its maximum range of adjustment.

what is the ignition timing for the N/A I can't see where it says 16 o BTDC

Might I suggest that you try retarding the ignition see if it improves things start with say 10o BTDC.. just a guess!

[Tuga2112]

no EST or wasted spark for you!

according to the manual there is EST.
how does that generate a spark when the rotor is mechanically driven and the leads seem only able to get close to the from the rotor as the cap is all plastic ? i have no idea.

If you did start a diagnostics thread saying you have a surprisingly high idle I might suggest that with a distributor retarding the timing will slow the tickover speed and make it more reliable whilst advance Will speed it up and make it less reliable.But as the thread is about a theoretical analogy with the exhaust cam being one tooth out I'll suggest it would have cock all effect on the scenario you describe as the analogy isn't valid and the advance you are trying to achieve would likely make it worse.

I dont really follow what your saying, given the case this is specifically on the NA and most people will shy away from a NA discussion, i am trying to describe what i believe to be a close analog in the SE in order to not discourage people from offering their thoughts.
the question is fairly similar in context to, "what happens if the exhaust cam is out of alignment just a little bit?"

what is the ignition timing for the N/A I can't see where it says 16 o BTDC

the manual can be found here
http://www.lotusm100.com/manuals/

"Elan-M100-NA-Ign & MPFI-Section EML (Pdf)"
page 58 describes it as 16 degrees BTDC

Might I suggest that you try retarding the ignition see if it improves things start with say 10o BTDC.. just a guess!

I checked the timing a while ago and forgot what exact delay i ended up setting up. if memory serves me right, i got it to 2 degrees away from 16 btdc, i think was 18btdc, but may have been 14?

[dapinky]

I am one of those members here who are old enough to have cut our teeth on cars which had the simplest of control systems for the engines, and even something like the NA Elan would have seemed like black magic back in the 1970's - what with an ECU, Fuel Injection, and sensors all over the place - highly advanced stuff!

It is also stuff from an era which lasted only a comparatively short time (automotively speaking) and belonged to a small selection of cars (every manufacturer went their own way).

As such, I am somewhat in the dark as to the specifics of the system, and how the spark gets to the right place at the right time to meet the squashed petrol vapour in this particular car.

I would have a complete list of things to do/check/change on an older car (yes, I know, it's a very short list 'cos there was only points, plugs, condenser and rotor to look at until you got to advanced stuff like fuel pump, carb jets/floats and valve clearances.)....... but the theory *should* remain the same.

Most cars with a distributer were designed in such a way that the body of the dizzy would rotate through about 30degrees, whilst the shaft remained meshed to the camshaft (or other driveshaft) on a helical gear..... and if there was insufficient range to get the timing right, you simply lifted the dizzy out, rotated the shaft 1 tooth on the gear and dropped it back in - rinse and repeat.

The only thing that made anything more complex was when working on different engines, you needed to know what the firing order was, and which way the dizzy spins (yes, I've watched those masters of the universe who can fit all the leads on a V8 or V12 engine and get the HT leads right every time, whether it happens to be a Ford, Chevvy, Buick or Jaguar unit - as for me, I'd be into the Haynes Manual every time to find the right info).

The NA only fits in one location, so it *should* be straight into the right range of adjustment - and anything that stops this from being the case is relevant to this whole thread.

Now, whether it is a problem with the ECU (which basically adjusts the timing in the way an older system used balance weights and vacuum advance), or the rotor arm/cap I wouldn't like to guess - especially as I only really learned 'just enough' of these type of systems to get by, and on an individual basis.

Hence, my only suggestions have been to address the original question of checking the cambelt timing at the sprockets, and to see if the HT leads are int he wrong places...... anything to do with the spark timing (dynamically) is beyond my current knowledge.

So, with that in mind, I'll ask a question.......

....... with the timing light fitted to HT lead #1, and the engine off, can you find any position for the dizzy where the strobe activates? and if so, does it do so with movement of the dizzy, or only after the end point is reached and the engine is rotated further? (does that make sense???? it does to me, but I know what I'm trying to ask!).

Put it another way, with the dizzy advanced at full movement, how far out is the timing at the crankshaft markings - and is it the same with the engine running as it is with it static?

.... I ask to try to establish if it is a 'physical' limitation with a mechanical solution, or a 'timing' issue where it is part of the electronics.

[RonR]

As a guide, each tooth out at the Cam sprocket is 7.8 degrees rotation of the Cam (46 teeth), so it's worth checking if you have that amount of adjustment of your dizzy - so up to 24 Degrees if static timing is 16.

[Simon_P]

where it says 16 o BTDC
the manual can be found here
http://www.lotusm100.com/manuals/

(under the assumption the NA enters diagnostics mode the same way as the SE)

Same part of the manual says it does

Simon_P wrote:
no EST or wasted spark for you!

according to the manual there is EST.

no EST or wasted spark for you! (Am I wrong?)

please don't selectively quote me.

Anyway back to your issue of

"i have a surprisingly high idle speed"

I think that there's more than one issue at play here.
To increase revs significantly you need more air or more fuel.
For diagnosis 14BTDC is close enough being 2 Deg retarded would slow it down slightly.
One tooth out on the exhaust cam as described would make the exhaust valve open early and close late you might loose some power and burn the exhaust valve but I don't think you'll get an increase in revs.

[Simon_P]

As a guide, each tooth out at the Cam sprocket is 7.8 degrees rotation of the Cam

Thanks Ron I was wondering that. So 15.6 degrees Crank.

[Tuga2112]

Thanks for input guys.

unfortunately when i started this thread, i had 2 weeks ahead with time to investigate in the garage.. that plan was foiled before the end of the weekend. i now am waiting for a tripod bearing for a fiat driveshaft, then theres a saab waiting for rear shocks, disks and pads all around to get trhought.... oh yes.... also the NA is currently on its way to cambridge, my brother needed a backup car...

Dave.
Your comment made me realise theres more going on between the cam sproket and the rotor than just being a straight shaft all the way to the cap.

I Need to read about that in detail from the paperwork. its not been easy to get a moment lately to sit down and properly focus on technical material.

Ron.
thanks for the detail about the angle of each teeth, i can check how much movement in the cap i have in order to see if the theoretical adjustment would allow the spark to be roughly in the middle of the cap's range

Simon.
at this moment, theres only one thing that i know for certain, I cannot set the timing right.
my intention with this theoretical scenario was to find out "what side effects would be expected if a exhaust cam is out of sync", then decide how to continue the investigation based on the suggestions.

I think your right, theres a good chance theres more going on than just the timing, but i want to fully focus on this aspect of the problem before looking elsewhere, being this far out of range seems bizarre. when this is right, I Will then look at the next step (which im hoping its just a matter of adjusting the screw at the top of the throtle body)

just to re-iterate, do not recall if it was 2 degrees advanced or retarded, im going to ask my brother to take a picture of the cap. so that i can be 100% sure when i mentioned "clockwise" earlier i was correct.

[simonbuk]

Interested in what was the outcome of all this ?

[Tuga2112]

The exhaust cam was 1 tooth out of alignment. But there's still something else wrong, because after correcting it, I can get the timing correct but it's still extremely close to the limits of adjustment of the distributor.

Engine still running rich and fast idle.