| I still don’t know full advance on our 300 distributors or direct connection for that matter . They give you a data point at like ? 1900 rpm on the way up . You need to know full mech advance in distributor to know where you end up — and reading off damper any better than 3 -4 degrees does not cut it ? Even then most of us do not have a calibrated tape on damper ( a wise investment) or use dial back timing lights ( I hate those) Maybe one day Don has one on his sun machine and he tells us all! Every few hundred rpm . I bet stock 300 advance curve is perfect for high performance , as it was done pre nitrous oxides pollution issues . I know they backed J ignition from 15 at idle to 12.5 with service note due to knocking ( so it was “right there “ on tuning ) that says max advance mechanical had to be like 18 more , 32-33 ? (wedge ) . Hemi likes 29 total . love the set it at 12.5 . Right. Sent from my iPhone not by choice On 14 Feb 2021, at 8:26 pm, RICK AND DEBBIE CLAPHAM < rixpac@xxxxxxx> wrote:
More brain damage, one of the first engines I fully rebuilt was a 7 cylinder Jacobs air craft power plant. Figure out how the cams work, fire 1, skip 2, fire 3, skip 4, fire 5, skip 6, fire 7, skip 1 and so on.
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sorry it is two to one ratio , cannot be same degrees . wheel can be calibrated though any way you like . same as “distributor degrees “ And old mopar FSM uses both at times . you have to figure out no it’s
twice that. if reading damper . pretty hard to read distributor degrees they give the spec on . But everybody had a Sun distributor machine back then
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On 14 Feb 2021, at 6:12 pm, RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote:
Cam degrees are crankshaft degrees. Degree wheels go on the crankshaft.
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agree Henry , but exhaust has to be closed for a significant time rotationally after tdc or you will burn valve / lose power . Remember cam turns half as fast as piston crank , and cam degrees are not crankshaft degrees . So valve activity
has not commenced even just after TDC ignition especially given slower rotation of cam , the ramps are a small part of total exhaust event . but I am open to learn ..
At least as I understand it exhaust would open near bottom of power stroke , exhaust pushed out by pressure and then by rising piston on exhaust stroke . with some overlap /,early opening at bdc. yes. Maybe I will look at cam card .
Doing things without understanding the why is just a road to disaster “ cuz I’m the mommy” type stuff . No doubt it works , despite no obvious explanation... may just do it that way ..
thanks for chiming in !
John
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On 13 Feb 2021, at 11:44 am, RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote:
More brain damage, how about industrial 413 engines and marine reverse rotation engines. Fun to think about. But for your application your decal works on A, B, RB and RB Hemi… Rick
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John
This is a good question because it isn’t as simple as one would think. Lash has to be set with the lifter on the cam base circle. For example, at TDC on the firing stroke, the exhaust valve “is
getting ready” to open soon. So, depending on how the cam is ground, some of the “slack” may already be taken up.
How do I know? I looked at the 57 Service Manual lists which tappets are on the low side at two! positions (Cly 1 & 6 firing). Too easy! Silly me set the lash that way on my 300C when rebuilding
it years ago. However, before I finally put the valve covers on, I thought I should do a check and found the gaps were way off. Maybe the Manual’s advice was ok for a New Yorker cam but not for a 300C cam which has more duration. The adjustment chart below
is probably right – haven’t checked it. If you want to check the exact mid point on the base of the cam, split the angles between valve close and open from the specs.
NB I have a Mopar timing tape on my damper so I don’t really care if I have to move the engine multiple times. Still only turn it twice overall.
Cheers
Henry
Not sure if this helps..... but this was an old decal that was used and stuck under the hood of many a Mopar back in the day:
Without overly complicating it,I was starting to do this and laid out firing order 392 vs crank degrees. 413 the same firing order
, but distributor turns CCW other is CW . My new damper marked every 90 degrees.
392 and A block;( B may be in the same situation, but not there today). Starting with #1, at TDC firing (which position by the way
is 360 of crank rotation AWAY (forward CW) from where you align timing chain dot marks..(=confusing as hell , I have ever seen that fact talked about) . Yes , The piston is on TDC when chain marks are aligned ( at install ) , cam key points at about
4 o clock but that is not the compression or firing stroke. On firing stroke on #1 , the dot on cam sprocket is at top (180 more on cam--SO, on next full rotation of engine ---and firing , yes pointer is back at TDC----.and cam has turned one half turn.
#1 Piston went down and came back up. Fire!
So, I started overthinking again. ---- on a V8 , 4 firing TDC's happen per turn of crank, 360/4 = every 90 degrees. So, measured
degrees from the #1 firing TDC . 1,8,4,3. =0, 90, 180, 270 ; 360 position (start of next turn) is the start of 6,5,7,2 firing ,and yes #1 is at TDC again at 360 but not firing ; 360,450,540,630. So 720 is 0 again ,same as # 1 firing . 720 Crank degrees.
that is = 360 distributor and cam degrees , rotor is back pointing at 1. = 18436572
Now all through Mopar land is some kind of chart ( I have a copy) saying adjust I 2 and E 8 when # 1 is at TDC on compression /
firing stroke , = still requiring 8 bumps of crank by 90 each , to do 16 valves . I do not get this advice from on high at all. If #1 is firing on TDC by definition both valves are closed, that is when to adjust #1 valves ? Especially if moving it 8 times
anyway. There is probably some pattern where one could move only 4 times, and adjust say 4 at once, why this line of inquiry started in the first place (from me). But instead sometimes 40 posts in an online sequence with guys killing each other over how
to do this, but none of them advocate what I just said. They confuse themselves with the base circle and " heel" (??) of cam etc . Tangled in underwear? Base circle is a long time % duration of cam, certainly where both lifters are sitting when cylinder fires?
Wha???? is my reaction. Anyone with me? Thoughts?? "for those who do not understand, no explanation suffices" is my reaction to all
this, but maybe I am missing something important!???? If so, not alone..
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