|07-11-2003 08:52 PM|
Here's another version with pics:
|07-11-2003 12:39 PM|
|78 monte||Wow!! Can I get that post in a paper back version??|
|07-11-2003 03:02 AM|
cam timing / ignition
Heres a basic overlay, please use this for help, buy a build ford book of some discription, Ford performance book etc as there will be slight variations depending on exact blocks, cams etc.
I am assuming you understand the basics and have stripped the motor far enough to do the work.
With the cam mechanically installed but not connected to anything yet make sure the crank is in the correct position, this is number 1 cylinder at tdc, this will put the crank timing gear mark at 12 o'clock as viewed from front.
Fit cam gear only and bring cam gear round until cam timing mark is at 6 o'clock.
Remove both gears and refit all timing gear correctly now with the chain or required drive, on completion the crank and cam gear indicators should now be at 12 and 6 oclock (facing each other ) when at no1 tdc.
Rotate the assembly once the cam gear should now be at 12 o'clock *** should the crank gear.
Rotate once more and eveything should be back to where you started.
this is without any valve train attached so you can check the cam before you start lifting valves.
This is the cam timed with 0 degrees ofset. this is the normal set up for a standard or aftermarket cam with no other index available.
If you are using timing gear with offset dowels supplied for cam indexing use the o ofset dowel initially to set this up. if you are using these then you need a book, as you need to know how to dial a cam in correctly at 0.5inch lift etc to check for proper cam timing, this is not easily explained here. (this should be done any how but for most non race replacements follow the standard install and all should be ok)
you still need to check lift and clearances if possible but as long as not too radiacl to should install by the basic procedure and be ok.
Once happy all lines up and ok build up the valve train etc and re check rotation etc for any fouling or unusual operation, this is bassically the cam installed and timed as per the manufactureres spec (restricted by machining acuracy). the only way forward now is to check the cam timing with a degree wheel to ensure the specified lift is correct, this is where the offset dowels may be required. If you do not do this you are at the mercy of the cam grind acurracy. (this process is not too difficult but get a book if you want to have a go as I will be here all day tring to write it down so you can undertand what I mean)
Do not get overly concerned here I know of hundereds of cams fitted and never a degree wheel used, I know all the race guys will now be flipping there lids and suggest never, never install enything without checking everything twice but it at home some of these operations are not always practical.
(maybe you should start a thread on degree or not too degree that is the question).
back to the motor, cam in to FORDs build up procedure for a 302 obviously, valve train in and all rotating correctly.
Rotate assembly to number 1 tdc - make shure it is number 1 tdc and firing on 1 tdc, both 1 cylinder valves shut and on compression stroke, again assume you know how to do this.
Some would say bang the dissy straight in at this with it lines up at number 1 lead. This will work, it will fire - usually - the timing will be out but will easily be acomadated by turning the dissy to bring into correct index.
As cams need lubeing and running in (remember this), I prefer to try to aim for 10 Degrees before for initial starting on a ford, fire it hit 2K revs hold with plently of water in etc for at least 10min preferably 20, keeping it cool and have no vac unit connected and all the vac lines pluged for run in.
Stop the motor after this - cam should now be ok to run.
(have skipped all the getting oil up etc as assuming we are only talking about a cam change.
Oh yeah to get the 10 before, rotate as before line up and insert dissy dirrectly on 1 tdc, turn crank to 10 before on tabs and then reset dissy by turning to line up dirrectly with 1 lead again and approx timing will be set to fire motor.
try to have a timing light on hand as as soon as the motor fires with no vac advance on and on a strong fast idle if you check the timing you should be seeing over 10 degrees on the light and marks as you have some centrifugal advance now in as well.
turn dissy to make this so 2k revs = 20 degrees ish will be ok for now.
Run cam in, then let idle or get an idle with no vac advance connected. Run motor with light on at 1Krpm no higher, set timing on light to cam recomended spec or ford spec if in any dought use 10before as a base. (if this is a late emissions motor this could be as high as 20 at this stage)
Ensure all is ok and motor starts stops etc, do not try to snap rev at this stage.
Get a good clean 10 (or whatever) with no wandering (carb, dissy vac leaks, cam not run in etc.) 10 on the mark with the idle sounding correct to the ear at least, no misses etc, motor must be at operating temp - crusial point this for final setting.
Shut down now check again at recomended or desired idle speed, readjust to get correct timing.
Now fit vac advance to correct carb port and one timed motor is now available for you to go and play with.
If you now recheck the timing on idle you should have the 10 (or desired setting) ,when reving the timing should move due to the vac and centrifugal advance and these could add upto 50 degrees depending upon spring weight, allowed movement etc or as little as 20 but you should always get more than the 10 (base setting) if a vac advance is used.
Yuo now have an initial set advance (the 10 or speced setting) that will run and idle the motor, you need then advance for drivability (not racing full throttle) this is the vacuum part throtle advance and pulls timing up when accellerating to keep the spark following the charge density. finally when we are really rotating we need centrifugal advance to move spark away from the tbc possition as the pistons are coming round quicker so take less time (time as in time-ing) to get round - speed is quicker so from point of firing to compression maximium (tbc) the time is reduced so you need to move the spark further away from this point to keep the fire in the right place.
Easy isn't it. try tovisualise this its a good model if you can.
Think of a clock face with one big hand spining slowly (tickover).
At 10 oclock the spark lights the fuel (it takes a little while for the fire to spread to is maximium expansion - all the fuel on fire) as this fire spreads the clock hand is still heading toward the 12 o clock position the hand hits the 12 the fire is at is most compressed (because this is TDC and the piston has squashed the air fuel charge to a maximum.), and the fire is also fully lit. Bang round we go using the expansion energy to push the big hand round.
If we add fuel the fire is bigger so the hand goes faster - why? More fuel biger bang!
If we still ignight at 10 oclock the fire is bigger so we are still tring to light all the fire (more fuel takes longer to ignite) , as the hand passes 12 its not all lit, because its going quicker, it finishes the job afer the event (TDC) and some energy is wasted so we get reduced power.
If we move the spark to the nine o clock position so we are lighting off earlier to compensate for the faster hand movement so we hit the comprssion and full fire point together again and go faster again, we keep going until all the rods and valves can be seen from the outside of the engine through nice holes.
no really once you mknow what is actually hapening you can translate the timing light info and engine behaviour much easier.
We need to move the position of the spark in relation to the speed of the motor for the above reasons - understand this and the timing will follow.
The valves attached to the cam obviously are the mechanical doors that allow the fuel in, trapped and out again at the right time of the stroke.
I hope this helps I really do but heres the real thing, If you can not do this, don't. get a friend who can to work with you and llisten and learn from his experiance and mistakes made in the past. Alterativly put the job out to someone who can, its not a difficult job at all but they never are if you know how.
|07-11-2003 12:48 AM|
IGNITION and CAM TIMING
I got a 302 Engine..i got a cam in there with these specs http://dab7.cranecams.com/SpecCard/D...1=Display+Card
my distributor is vacum non electronic
and my car is non-computer controlled
...My question for you helpful experts..PLEASE EXPLAIN TO ME .....HOW do i set my IGNITION TIMING and My CAM TIMING.. .PLEASE HELP..im new at TIMING and not sure..so please be VERy descriptive..HELP