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BT7 Timing Advance

Drone Dog

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i checked my timing advance today... thought i had done it before but guess not....

anyway first i checked the vaccum at idle from the tube and got just over 6 inches of vac at idle. first question, does that sound about right? don't think i have any leaks. it is a brand new line so i assume it is correct and does not seemed plugged.

second thing i checked the vacuum advance. put a vac pump on it and gave it a few pumps. it moved the plate ok but the plate would slide right back. So it would not hold the vacuum.

then i did a check for total vac with the vac advance connected and got the following readings.
RPM advance
1000 15*
1500 30*
2000 34*
2500 41*
3000 44*
i should have done it again with the vac advance plugged but my partner was getting antsy to go someplace else. hard to get good help...haha.

what do you all see from the numbers?
get a new vac advance?
get stiffer springs for the mechanical advance?
have the diz completely rebuilt?

i started this wondering if the timing, even though it was set at idle to 15* with vac plugged, could be causing my engine to run warmer than it should? trying to control my engine temps as best possible. want to make sure i have everything working as it should before i spring for a new radiator. you know the routine... checked gauge, tried extra ducting, tried electric fan, etc. Nothing has seemed to make a difference. my engine runs really well, very smooth. but thinking if my engine is building extra heat at speed from poor timing, well idling is certainly not going to help it recover.
 
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Joe Schlosser

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Re: BT-7 timing advance

I am not an expert on big Healey but it does seem that you are over advanced.
Flat top motors generally do not go over 30-35 degree at full advance.
 
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Drone Dog

Drone Dog

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Re: BT-7 timing advance

just FYI
i have been emailing with Rob from British Vacuum unit about rebuilding the diz totally. Sounds like it might be a good idea to go ahead and have it done.
 

dougie

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Re: BT-7 timing advance

I run 37 degrees full advance on my 6-cylinder race motor, it's happiest there.
 
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Re: BT-7 timing advance

Too much advance, esp for a street engine. Forget about initial and shoot for 35 degrees at 3000 revs. Your car should run cooler and not knock.
 

RAC68

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Re: BT-7 timing advance

Michael,

Your suggestion to set the advance at 3K RPM to 35 degrees with or without vacuum advance connected?

Ray(64BJ8P1)
 

RonR

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Re: BT-7 timing advance

Shop manual is clear: maximum 36 degrees for 6-port head.
No rpm is mentioned.
I doubt you will see any difference in advance between 2500 and 3000 rpm.

Advance Distributor rebuilt the distributor for my car.
 
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Re: BT-7 timing advance

Ray--

Connected--in order to know the amount of advance under actual conditions.
My 100, in any case, is quite sensitive to the amount of advance and anything more than 35-36 degrees reflects quite quickly on the water temperature gauge.
Not that it matters but I run a non-vacuum advance Mallory Unilite distributor.
 
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Drone Dog

Drone Dog

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Re: BT-7 timing advance

So then this is what i kind of get from my reading.
yes my total advance it too high and probably hurts my engine cooling. ALthough some suggest you advance timing a little to help with cooling. even so my light throttle advance is also off and that can cause extra heating at lower and mid-range rpm's.

i could set my total advance back but then what is my idle at? so retarded it runs hotter at low or idle RPM?

So for this reason, i thought it best to just have the total dizzy rebuilt by someone who has a diz test machine. Also Rob says that they recurve them for modern fuels. he said even the original book settings are not set up best for today's fuels. i don't know what changes there but that is why i am sending to him.

i happen to have an extra complete diz so tomorrow i plan to mail it off to New Hampshire.

fingers crossed it will help with my engine temps.

i guess i never put the timing vs heat issue together because my engine runs so smooth; no knocking or pinging, no missing, starts great...

We shall see what happens. it is certainly cheaper than a new radiator... for now. i may have to have spring for a radiator also before it is all over. but even so it makes sense to get this done. from some things i read improper timing and advance can cause some other stresses on the engine i really don't need either.
 

Lin

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Re: BT-7 timing advance

Doug, if you use a connected vacuum, do you use ported or manifold vacuum?
Lin
 

DerekJ

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Re: BT-7 timing advance

He will be able to rebuild and recurve your distributor with new springs and weights but the problem is that itā€™s not on your car when he does it and it really should be adjusted to the engine it is controlling. I use the old school method of advancing it until there is knocking then back it off until it doesnā€™t.
 
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Re: BT-7 timing advance

I am a happy customer of Jeff Schlemmer at Advanced Distributor. He has done the disty's on all my cars and I recommend him highly.
 
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Drone Dog

Drone Dog

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i have my diz back in and timing is set.

i went with setting it all with the vac line plugged per the Rob's (British Vacuum Unit) direction. he has sent me some info on what the advance should be at various rpm's. And once i got the 1000 rpm set the rest were pretty darn close to what he wanted.

i ended up with this:
1000 rpm 17*
2000 rpm 25*
3000 rpm 34*

my 3000 rpm was a little more than what he said but i left the adjustment there since the others seemed right in line. i was trying to do this by myself so i did not get to see where it maxed at. when i can get some help, i will recheck and check for max advance and where it happens. i would expect around 3500 rpm.

took first drive today and car does run better. it actually ran fine before but now it seems to be more responsive. of course a working vac advance has to help some. the car also seems to rev easier and it definitely feels more powerful in the 2500 to 3000 rpm range. like i said, it ran pretty well before. very smooth and no misses or knocks. but i had nothing to compare it to so i did not know how it should feel. this is definitely an improvement.

i can't say for sure it helped the car run much cooler. but i felt like it was more stable with the temp. plan to do some more runs tomorrow so we shall see. just can't help but think there is a 4 core radiator in my future....
 
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Drone Dog

Drone Dog

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speaking of cooling... and radiator..

has anyone tried the one from Victoria British? Looks resonably priced compared to some others. they say it is a 4 core and 12 FPI.

good radiator?
look original?
fitting issues?
captive nuts there?

Thanks
TL
 

dougie

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Re: BT-7 timing advance

Dougie
Do you have a vac advance in your race car or is that all mechanical advance?

No, Jeff at Advanced Dizzy built me a Lucas race unit similiar to what was used on the D type without vacuum advance. In addition, I use a Pertronix II ignition with the Pertronix Digital HP management system.

57' 100-6 MM Race Motor 2018.jpg
 
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