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Ignition timing, have I got it right? - Engine/Ancilliaries - The Lotus Forums Jump to content
Steven162

Ignition timing, have I got it right?

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Hi people,

 

I adjusted my ignition timing today, I need some confirmation (or otherwise) I  did it correctly! I have never really adjusted timing before and have nightmares about melting pistons etc.

 

Its an 87 Turbo HC.

 

Hot engine, all vacuum connections plugged in. I adjusted it to 12 degrees BTDC at tick over (about 900rpm by the dashboard gauge) using my timing gun which has a knob that can be set to the required angle BTDC so that the TDC mark can be used instead of other marks. Before adjustment, it was running about 25 degrees BTDC at tick over, found by moving the knob on the gun until the TDC mark on the flywheel aligned with the pin in the clutch housing and looking at the position of the knob.

 

As I adjusted the timing the idle slowed a little so I had to adjust it up a bit.

 

The car feels crisper, and has a bit more popping on the overrun.

 

Have I made a fundamental mistake or not?

 

Thanks

 

Steve

 

PS. I did make a schoolboy error, I didn't understand how the clamp works on the distributor so after adjusting the timing I tightened the horizontal nut that holds the clamp to the oil pump housing and thought after a blast up the road to see how it drives I will re-check the timing and then tighten the vertical clamp bolt. I turned out of the drive, gently through first gear, changed into 2nd, booted it and at about 6000rpm there was huge bang and a flash in the rear view mirror that I saw even though I was driving in bright sunshine, and a dead engine. You all know what had happened......   

 

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Steve, real sorry to hear that. Couple of years back exactly the same happened om my S3 and that was caused by a reputable garage making the same mistake.

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I've had a look at the book. It says for 1987 model year onwards, the timing both for static and hot idle (850 to 900 rpm) should be 10 deg BTDC. There is a 28degree advance  available from the vacuum capsule and the centrifugal advance mechanism should give 11 degrees at 2000 rpm and 8 degrees at 5000 rpm. You should be able to check these figures with your trick timing light!!

 

I trust you got the distributor back in OK ?....(!) When I take the distributor out, I always remove the clamp with it...then when it goes back, it's going to be timed near enough already...the key drive being asymmetric and a one way fit!

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Yes, I got the distributor back in OK, after a battle! I really need smaller hands. I now understand how the clamp works. I am getting about 28 degrees advance maximum when I rev the engine, it must be somewhere near.

 

JohnP, I didn't blow the engine up, just lost drive to the distributor at full throttle/load/revs which caused a huge explosion behind the car but no damage, once the distributor was put back in and timed all was fine.

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My manual doesnt cover the HC engine but it would be highly unlikely that the timing spec is 10 deg at idle with advance connected.

 

10 deg without vac advance seems more likely and I would suspect you now have it mis-adjusted if you set it with advance connected.

 

For the pre-HC engines the book states the static timing (ie engine not running) but specifies the actual adjustment is made at 3500 RPM at 28 degrees.

 

If you have not checked and set the timing at 3500 you must do this because thats where it matters. The timing at idle is largely unimportant.

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I quoted exactly what the book said for post-1987 Esprits....which I believe are the HC cars. Vacuum advance is not going to be dependant solely on RPM....but on engine load...as the manifold depression will change with load and throttle opening. Here is the relevant section copied from the manual.

post-568-0-19928200-1431514801.jpg

post-568-0-23577000-1431514818.jpg

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Interesting.

 

They state the static timing is 10 degrees (ie no vacuum as engine not running) and the idle timing is still 10 degrees. At idle there will be high vacuum. So this does not seem to make sense.

 

They mention clamping off the vac pipe AFTER checking the idle timing, I think they mean before, ie all checking and setting is done with the pipe clamped.

 

Level of vacuum will indeed vary with a combination of engine speed vs throttle opening but will be high at idle as the engine is pulling against an almost closed throttle.

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Okay, then. The official Lotus manual is wrong....(!)

 

That is always going to be a very dangerous assumption. With the system on the HC engine, there are two sources of vacuum... one comes from the manifold and the other from a port upstream of the throttle butterflies. The change from one source to another is accomplished by a thermal switch...so that with a cold engine, the vacuum comes from the manifold. Below 60 degrees C engine temperature, this gives full vacuum to the capsule and thus fully advanced timing...intentionally, "to aid cold idle and driveability"... to quote page 3 of section EMD of the Service Notes. Once over 60 degrees, the vacuum source is switched to the one upstream of the butterflies. At this point, at idle it is pretty much at atmospheric pressure....so the capsule will be in exactly the same conditon as with the engine stopped. Thus, for an engine at operating temperature...read the bottom of the first page I copied...the vacuum advance will be ineffective. Opening the throttle will make a change, as the vacuum port will be exposed to the engine vacuum with the butterflies open. If you have the manual, the diagram on page 3 of section EMD shows the vacuum circuit.

 

Of course, without the thermal ignition valve, were the manifold to be connected directly to the distributor capsule, or the ignition set at idle with a cold engine with the thermal valve, then you'd be correct!! But it isn't....

 

That's been an interesting and useful exercise for me...not having this complication on my 1982 turbo!... I now understand it myself(!)

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That all makes sense. Its an unusual arrangement. In fact disconnecting the vacuum is still valid as it isnt doing anything when hot, as you say.

 

I dont have any of that in my manual, but thats probably because I bought it in 1984!

 

Its always worth checking the timing does fully advance to the figure given in the manual at higher RPM though.

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Yes...the Wunda Twiddly Timing Strobe should be able to do that...(!)

 

I suppose that if you follow the book method, it will reveal if the thermal thingy is working, too...

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This appears to make a lot of sense now, not near the car but I'm guessing the changeover valve is the odd thing inside the rear quarter pael near the fuel release solenoid. 

Pretty sure the hoses are correct. I'm guessing it is controlled by one of the temp sensors in the Alu pipe? Do all these switch at the same temp? Maybe I have the wire pairs to wrong switch?

you just have to admire the simplicity of an Esprit ?

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