Blairm
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| posted on 27/2/09 at 07:41 AM |
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Maximum Advance on Crossflow
Hi,
Last week at the track my crossflow started running like a dog. The points had closed up a lot. I quickly opend them up a little before the next
sprint race and it ran a little better.
Decision made to put a electronic trigger in and I pulled the distributor out to check it to find one of the springs had come off.
Anyway, Spring fixed and Pertronix kit fitted. Lined up roughly and fired first pop.
Borrowing a timing light tommorow and I need some advice on the best way to sort out the timing.
The Dizzy has been altered to have no vacume and the top plates welded together. I read I should be looking to get around 34 deg advance over 3500
rpm. How do I measure this when the marks do not go up this high?
Also what should I set it up for at idle.
It has a 234 cam and twin 45's
Thanks Blair
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02GF74
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| posted on 27/2/09 at 08:24 AM |
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40 degre BTDC springs but I need to check my graphs at home.
obvously the exact number will vary accoring to engine spec.
typically 10 degree BTDC at idle
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britishtrident
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| posted on 27/2/09 at 08:29 AM |
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IF you were running the Ford/Fomoc/Autolite distributer the point gaps were well known for closing up -- the trick was to set them to the wide end
of the gap tolerance (eg 0.027" and make sure the distributer cam had a tiny ammount of grease onit.
As to your ignition timing on Xflos unless you have a modified distributer with more centrafugal advance the ignition timing tends to be limited by
the maximum static ignition advance you can set without the engine kicking back against the starter..
Try using crank 10 degrees static this should give 30 crank degrees total advance, if the engine dosen't kick back against the starter or pink
try adancing the ignition 2 degrees at a time. About 38 degrees at over 3000 rpm is probably the maxium total advance you can usefully use but
unless you mod the distributer for more centrafugal advance this probably won't be practical.
The test for pinking is to fully warm up the engine and try accelerating from low RPM in a high gear ---- ideally up a hill. if you hear a tinkling
sound from the engine retard the ignition 2 degeres at a time until the sound stops stops.
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Blairm
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| posted on 27/2/09 at 08:30 AM |
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Thanks 02GF74,
The distribitor was built up by a professional rebuilder so I assume the curve he used is suitible for the engine spec the builder gave him. I assume
the spring (the light one) that came off was not damaged so all should be OK. The weights have 17deg on them. Is this standard or modified for the
removed vacume setup?
How do I check teh 40 Deg when it is of the marks (12 deg max from memory)
Thanks Blair
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britishtrident
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| posted on 27/2/09 at 08:37 AM |
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Good If you 17 degrees distributer adavance then intially just set the idle timing up to line up with the 6 degree line on the timing chain case.
(17x17)+6 = 40 degrees.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Blairm
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| posted on 27/2/09 at 08:37 AM |
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The distributor is a Lucus 25D4 as I was told not to bother with the FOMOCO unit i had originally.
Can some one explain static this should versus crank degrees total advance?
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britishtrident
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| posted on 27/2/09 at 08:53 AM |
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Each time the crank shaft turns 1 full turn the dizzie only turn 1/2 a turn ---- so 1 degree on the distributer = 2 on the crankshaft.
Total advance measured on the crank pulley = static + centrafugal
ie 6 + 2x17 = 40
If using a strobe you line up the 6 degree mark at idle speed this will probably give about 37 degrees total advance if it runs ok you can then
try advancing it 2 or 3 degrees and test the engine for signs of pinking. -- but don't go beyond 40 degres total.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Blairm
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| posted on 27/2/09 at 08:57 AM |
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Thanks Guys, much appreciate the help.
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