3.9 timing

bones · Post by **bones** » Fri Apr 24, 2009 12:43 pm

Hi all, at the moment static is 10 btdc, what should the other timing marks be for the higher revs,

rich

CastleMGBV8 · Post by **CastleMGBV8** » Fri Apr 24, 2009 1:01 pm

Rich,

For the 3.9 34 deg. is the recommended total advance all in by 3-3400RPM
which ever suits your engine best. Opinions vary and others may suggest all in as early as 2700 RPM.

I would run without vacuum to be on the safe side. The vacuum cans (Lucas) give far too much advance especially with the Edelbrock carbs.

Kevin.

bones · Post by **bones** » Sat Apr 25, 2009 6:27 am

Hi Kevin, its got a mallory dizzy in it, i know some have a higher static than 10 btdc but the hyfire cd box doesnt go any higher than that. So 34 degrees at about 3000 rpm ,Thanks for the reply.

rich

bones · Post by **bones** » Tue Apr 28, 2009 10:36 am

timing for dummies answer needed. at 3000 to 3500 rpm using a strobe light should it show 24 deg on timing marks.Static is 10 btdc as total should be around 34 deg. Ive never understood this stuff, i should stick to fishing and give up on cars,and that sounds a pretty good idea at the moment,

sidecar · Post by **sidecar** » Tue Apr 28, 2009 3:56 pm

bones wrote:timing for dummies answer needed. at 3000 to 3500 rpm using a strobe light should it show 24 deg on timing marks.Static is 10 btdc as total should be around 34 deg. Ive never understood this stuff, i should stick to fishing and give up on cars,and that sounds a pretty good idea at the moment,

Nowt wrong with fishing! (and that can get bloody complicated if you want it to be!)

As to timing for dummies:-

The static timing is the the timing of the spark if the engine was turned round very slowly by hand. If you did manage to turn the engine and the timing was set to 10 degrees BTDC then number one plug would fire as the piston came up to 10 degrees BTDC. The static timing is usually set at 1000 RPm or less as it is eaier to do it this way. The low RPM ensures that the bob weights have not started to have an effect. The vacuum system should also be disconected and plugged for this test.

The advance that the bob weights can add will always "go on top" of whatever the static is set to. So if the bob weights can add 20 degrees at the crank (This would be 10 at the dizzies rotor as the dizzy spins at half the speed of the crank).

This is example the max, total advance shown at the cranks damper wheel would be 30 degrees. (10 static + 20 mechanical advance). Some strobe guns have an adjuster on them so that they always show the timing marks at TDC by the use of a inbuilt delay system. I can not stand doing the timing this way so I have set my adjuster knob to zero and taped it up! You can only do this if your damper does have all the other marks that will be required.

What RPM is required to get the full advance is depends on the bob weight springs.

The other thing that effects what the advance figure is as at any particular time is the manifold vacuum if you have the vac system fitted.

As to what the static, total and RPM that all this stuff happens is a subject that could and has filled many books!

My 4.6 runs 12 static, 32 all in at 2700 with NO vac system.

The link below is some info that I obtained from reading and testing out stuff on my own engine:-

http://how-to-build-a-pilgrim-sumo.wiki ... by-members

Pete

vaultsman · Post by **vaultsman** » Tue Apr 28, 2009 6:23 pm

sidecar wrote:Some strobe guns have an adjuster on them so that they always show the timing marks at TDC by the use of a inbuilt delay system. I can not stand doing the timing this way so I have set my adjuster knob to zero and taped it up!
Pete

Hi Pete,

Is this a personal thing? Or do you reckon errors can creep in with the advance dial?

===============

Not wanting to hijack bones's thread, but I'm running a 3.5 with Lucas points dizzy and SU's in a P6B.
AFAIK the advance rates are:
10-12 @ 2800
7-9 @ 1300
1-3 @ 600
0 @ <300

I know you've ditched the vac, but if I were to keep mine what static would you start with?

Stan

sidecar · Post by **sidecar** » Tue Apr 28, 2009 6:52 pm

vaultsman wrote:
sidecar wrote:Some strobe guns have an adjuster on them so that they always show the timing marks at TDC by the use of a inbuilt delay system. I can not stand doing the timing this way so I have set my adjuster knob to zero and taped it up!
Pete
Hi Pete,

Is this a personal thing? Or do you reckon errors can creep in with the advance dial?

===============

Not wanting to hijack bones's thread, but I'm running a 3.5 with Lucas points dizzy and SU's in a P6B.
AFAIK the advance rates are:
10-12 @ 2800
7-9 @ 1300
1-3 @ 600
0 @ <300

I know you've ditched the vac, but if I were to keep mine what static would you start with?

Stan

If I was going to keep the vacuum I'd only let the full mechanical advance be all in between 3000 and 3500 RPM.

I'd start with the static at 8 degrees at 800 RPM and then keep advancing it 2 degrees, each time go for a test drive, you want to be on the look out for any jerkyness just as you start to apply a very small amount of throttle, especially at the sort of revs that you know all the mechinical advance will be in by. When it jerks it is basically at least one piston trying to go back down its bore BEFORE it has passed TDC. As you can imagine this is not good for the piston or the big end bearings.

Once you have found the 'jerk' setting I'd retard the static setting 2 degrees just to be safe. I'd then check that the total advance is something reasonable with the vac system disconnected. Around 36 degrees for a 3.5 lump.

Without the vac system the static should be around 14-16 @ 800 RPM. With the vac it might end up around 8-12 @ 800 RPM. (I know you have figures for as low as 300 RPM, I would not know how to set the figures for such a low RPM, my engine will stall at 600 RPM, it is only smooth at 800 RPM) My mechanical advance starts to add advance at approx 1200 RPM.

Having said all that, my tests with the vac system were with an Eddy 500, It may well be that they create too much vacuum for the vac system, an SU carb might be OK!

Really I'd just not bother with the vac at all, on a 3.5 I'd go for 14 static, 36 all in by 2700 RPM.

As to the strobe timing knobs, it's just a personal thing, I can't be arsed working out how to use one really!

Pete

vaultsman · Post by **vaultsman** » Tue Apr 28, 2009 10:03 pm

Many thanks Pete,

I've just rebuilt the top-end and there's a few more jobs to do before it's back on the road (isn't there always?

)

When it is, I'll try it with and without the vac and see how it feels. The vac unit starts at 5 and ends at 17 in Hg, and yields 8 deg advance. I've heard Eddy's give higher vacuum than SU's.

Looking through the Rover WSM then I can see that the advance curve I gave, are dizzy speeds not engine rpm i.e. the 300 rpm equates to 600 crank rpm.

The manual gives total engine advance figures for this distributor of:

8-12 deg @ 1200 rpm
15-20 @ 1800
20-24 @ 2600
25-29 @ 4400

Pretty conservative!

Cheers,

Stan

sidecar · Post by **sidecar** » Wed Apr 29, 2009 4:38 am

vaultsman wrote:Many thanks Pete,

I've just rebuilt the top-end and there's a few more jobs to do before it's back on the road (isn't there always? )

When it is, I'll try it with and without the vac and see how it feels. The vac unit starts at 5 and ends at 17 in Hg, and yields 8 deg advance. I've heard Eddy's give higher vacuum than SU's.

Looking through the Rover WSM then I can see that the advance curve I gave, are dizzy speeds not engine rpm i.e. the 300 rpm equates to 600 crank rpm.

The manual gives total engine advance figures for this distributor of:

8-12 deg @ 1200 rpm
15-20 @ 1800
20-24 @ 2600
25-29 @ 4400

Pretty conservative!

Cheers,

Stan

29 degrees at 4400 will be when all the mechanical advance is in, a bit of a guess but I reckon that you will get another 15 BHP by pushing this up to 36 degrees.

The other thing is that running the ignition in this retarded state actually makes the engine run hotter!

bones · Post by **bones** » Wed Apr 29, 2009 9:59 am

cheers Sidecar, so this is what ive been adviced ,using a edelbrock 500 and unilite dizzy, total 34 deg 2700 to 3000 rpm, and can adjust vacuum by small allen screw in cannister,does this sound right. But another ?? how much effort is needed to move the bobs when sucking on the vacuum, because when i tried it i nearly ripped my throat muscles up so i took the bar off the bobs and tried again and the bar still didnt move.

rich

sidecar · Post by **sidecar** » Wed Apr 29, 2009 3:26 pm

bones wrote:cheers Sidecar, so this is what ive been adviced ,using a edelbrock 500 and unilite dizzy, total 34 deg 2700 to 3000 rpm, and can adjust vacuum by small allen screw in cannister,does this sound right. But another ?? how much effort is needed to move the bobs when sucking on the vacuum, because when i tried it i nearly ripped my throat muscles up so i took the bar off the bobs and tried again and the bar still didnt move. rich

You can suck until the cows com home, you will NEVER move the bob weights that way!

The bob weights are moved out by the fact that the dizzy is spinning round and round quite fast!

The base plate that the pickup coil is fitted to will move when you suck on the tube attached to the vac canister. You will have to suck quite hard, the base plate will move about 5mm.

Go for the timed port on the Eddy 500, if you use the other port you will be in a world of 5hit!

JUST DITCH THE VAC!!!

In fact you will have to restrict the amount of advance that the vac system can supply if you have all the mechanical advance all in by 2700.

The allen key on your system will allow you to do this. How much I don't know, you will have to mess about. Just bare in mind that a kick back is a piston getting the crap knocked out of it!

mgbv8 · Post by **mgbv8** » Wed Apr 29, 2009 5:05 pm

"JUST DITCH THE VAC!!! "

Thats exactly what I have done Rich.

bones · Post by **bones** » Thu Apr 30, 2009 6:16 am

even with the vacuum canister off ,the bar doesnt even move,which is what i meant by the bob weights

can move it by hand but thats not easy, say goodbye to the vac, i cant check things till the weekend as its got some water leaks know,

rich

bones · Post by **bones** » Sun May 03, 2009 12:54 pm

ok, vacuum disconnected 800 to 850 rpm, it flutters between 800 and 850 ,static is 10 btdc use strobe light shows 16 btdc connect right port vacuum goes upto 36 btdc. I have adjusted the to 34 with vacuum connected, the engine isnt running smooth at idle and seems to have a slight miss

rich

bones · Post by **bones** » Sun May 03, 2009 7:00 pm

Been out and checked the timing this is how it was, STATIC 10 deg, IDLE 16 deg, 1500 rpm 26 deg, 2000 rpm 36 deg, 3000 rpm 40 deg, so total advance is in way to early, tried to adjust the vacuum ,and no joy, adjusted dizzy and got the timing down to 34 deg at 3000 rpm ,it seems abit better but runs lumpy on tickover, so is the allen key screwed right in when running without vacuum??

rich