V8S Distributor & Ignition timing

[Barkychoc]

First of all I've discovered (again) that my vacuum advance isn't working.
This time its the diaphragm thats died, new one ordered from Rimmer Brothers.

Also the bit it moves inside the distributor was pretty seized aswell, so I've had that apart & lubricated it & freed it off.

The question I have is when I put it back together what should I set the timing to ?
Steve Heaths Bible says 4 degrees BTDC for unleaded & 8 degrees BTDC for 4 star.
So where does this leave super unleaded ?
Wouldn't want to think I'm losing a bit of performance if I can run it at 8 degrees.

I have a timing light and have marked it all up prior to taking it apart so hopefully it will work when I put it back together !

All replies appreciated.

Chris

[GreenV8S]

I ran mine at 12 degrees with 10.5:1 CR on 95 octane without any detonation, 10 degrees ought to be quite conservative enough for the original engine (which would be around 9.35:1 originally I expect). Don't put too much faith on the timing reference marks though unless you have verified the position of TDC. Ultimately you will have to experiment to see how much advance your particular engine will tolerate.

[Barkychoc]

Thanks Pete.
Just a question - well at least with my exhaust - how the hell can you hear it pinking ?
Or is it more a case of making it labour & seeing if it pinks ?

I assume that if you can hear it pinking you should back off the timing till you can't hear it then a bit more ?

Chris

[GreenV8S]

Barkychoc said:

Or is it more a case of making it labour & seeing if it pinks ?

If it's bad you'll hear it, it'll be most noticeable at peak torque (probably around 4000 rpm). I do also have a knock sensor now, but I didn't have that when the engine was normally aspirated.

[Barkychoc]

I've fixed this.
O H - M Y - G O D !
How fast is this thing ?

Boy some of those horses were sure hiding somewhere, but its the low rev response thats most improved.
It was a bit lethargic pulling away before. I think overall the acceleration is probably similar to before, but because it responds so much better it feels loads better to drive.

Bought a snap on timing light off fleabay (£31) and its running at about 8 degrees BTDC according to the crankshaft pulley marks.
This is after just putting the distributor back at the marks I'd made.
Its running well so decided not to fiddle with it.

Anyway better go and pack for holiday.

Will miss SCH

Chris

[ed_crouch]

Sorry to butt in: Im a smelly 390SE wedge owner (**gets coat**). I have read that the timing marks present on the front crank damper arent always very accurate. To be honest, the pukka way of doing it is such a nause I havent bothered, but apparently you should:

take out no1 plug, and with a suitably secured extension (important, that bit!!) on a dial gauge, clock the piston up at TDC with both rockers closed. Very gently rock the engine back and forth to find the very top of the piston travel on the gauge, and mark it on the pulley. Gotta be done VERY carefully to be of any benefit, as around TDC, very little piston movement will equate to several degrees crank rotation.

Another thing Ive read is that the Rover engine is pretty tolerant of wayward timing. This is no excuse for those chasing the neddies, though...

Anyway, hope this helps, and sorry if the above is a sermon in the bleedin' obvious.

Ed.

[clarenceboddiger]

ed_crouch said:

take out no1 plug, and with a suitably secured extension (important, that bit!!) on a dial gauge, clock the piston up at TDC with both rockers closed. Very gently rock the engine back and forth to find the very top of the piston travel on the gauge, and mark it on the pulley. Gotta be done VERY carefully to be of any benefit, as around TDC, very little piston movement will equate to several degrees crank rotation.

If you want to be even more accurate, move the piston towards TDC as above and watch the DTI needle, as it stops moving mark the crank pulley in relation to the pointer on the block (or wherever it is)keep moving the crank the same way the needle will be static for a small amount of crank turning whilst the piston is at the top of its travel, then as soon as the DTI needle starts moving again, mark the pulley again against the pointer again, you now have 2 marks on the pulley, make a 3rd mark halfway between these marks. the 3rd mark is true TDC.

[ed_crouch]

Good point well made.

Ed.

[GreenV8S]

It's much easier to do this accurately if you fit a dead stop to stop the piston a few mm below TDC. Approach this from both directions and you have two positions, mid way between them is TDC. This will seem the same as the other approach using a dial gauge, the reason this way works so much better is the relationship between piston speed and crankshaft speed. As the piston approaches TDC it gets smaller and smaller, making it hard to read the position accurately on the dial gauge. With a dead stop it's very clear and you can get the TDC position very accurately without any guesswork.