4C Cam install 1200

M

mizike77

Junior member
Hi all, I have been working on refreshing a 78 1200 Jota America that I picked up a while back. It has been an enjoyable project and I am getting down to the end here before firing it off. I swapped out the old A11 cams for a set of C4 from Wolfgang and had my cam wheels redrilled and stamped professionally from drawings that he also provided.. When putting the cam chain back on is it normal to have to manually turn and hold the cams on the timing marks while looping the chain over the cam wheels  as they are putting tension on a few of the valve springs . It makes it a bit difficult to hold everything in time while assembling and I just wanted to ask those who have done it before .
Thanks for the help-
 
Use a screwdriver pushed down the camchain tunnel (between chain and head casting) so that the handle jams the chain at the front of the engine if you need to stop the exhaust cam from turning.  A spanner on an inlet camwheel bolt head will enable you to turn the camshaft against valve spring tension (turning cam forward so as not to inadvertently start loosening the bolt!!).  Once you've got the cams aligned & chain correctly positioned then as Hamish says, a pair of thin-nose or circlip pliers helps to pull the chain ends together whilst still leaving space to partly slip the split link into place.  After tensioning the chain carefully recheck camwheel marking alignment - easy to get things one tooth out when the chain is slack. Turn the engine over by hand to ensure nothing hits & all OK.  With practice, some of the foregoing steps can be omitted.

Noting your redrilled camwheels, and for complete peace of mind, I'd check valve timing is correct with degree disc/dial gauge(s)
 
Is2 said:
What Rob said, works for me.
Click to expand...

Until, the ring spanner slips, hits the garage roof and and comes down ....... right down the cam chain tunnel. Leaves you and your mate questioning what the odds where, while trying to fish it out with a length of wire. :-[
 
Thanks guys. Exactly the info and reassurance I was looking for-
In regards to the degree wheel and cam timing : That will be my next series of questions. I have been doing a fair bit of reading and I am sure I will have some questions. I will note that my exhaust  cam has elongated hole for wheel adjustment while my intake does not.
 
I will note that my exhaust  cam has elongated hole for wheel adjustment while my intake does not.
Click to expand...

...so someone has had a go at retiming it.  Not a problem in itself, but does mean that you can't be certain about the situation now, depending on where the bolt sits in the slot.  And as has been pointed out, even using original timing marks doesn't guarantee that the timing is 'correct' (to factory spec).
 
Well, all is installed and its on to the timing wheel. I must say it is a bit confusing having never done it before. The wheel is on, true TDC has been found using a piston stop. I have a dial indicator mounted on the right cylinder intake valve and have zeroed it out at full open.  But as far as numbers and where to go from here I am just not sure. I have read a few articles on it but am having a hard time wrapping my head around it. Maybe it was the the beer in the shop fridge? I will do more searches today to try to educate myself . C4 Cams in an otherwise stock 1200 180 engine.
 
Cam timing can take a bit of effort to get your head around. If triples are the same as 99.99% of other motors, the assumption is that full lift occurs exactly halfway between open and close. So this full open position is your ref. Using the spec sheet, determine what half the open-to-close duration in degrees is, then use that figure to tell you at what point in the 360 degree cycle the cam should be at full lift (ie at the halfway point). repeat for exhaust. try it on other cylinders to confirm if you want.
 
To get your head around it a bit easier...

1) Print yourself a degree wheel off from the internet, grab some colored pencils and scribble on the degree wheel - with the 'to be expected' positions and phases. That way you can have a guide right by your side as you spin the engine for real.

2) Give a valve phase diagram a good dose of thinking about. This kinda thing...
stroke-1.jpg


Sorry if I'm teaching granny to suck eggs

Good luck, Paul

 
Cam timing is well worth the effort. On a DOHC engine you can get cute with the numbers too. From the Laverdamania page. I have not done this so others may have some advice: Advancing the intake and retarding the exhaust shifts the power curve upwards to the detriment of low-end power.
Delaying the intake and advancing the exhaust gives a greater power range, but affects power at high revs.
With dual overhead camshafts, you can afford the luxury of independently adjusting the cams.

An example for 4C a / c: To obtain a good performance at mid-speed ("problem" of the 4C) without losing at high speed, we can advance the exhaust by 4 to 7 ? and delay by 2 to 4 ? l 'admission. This can solve some issues of loss of efficiency at mid-range (especially with a 3-in-1 exhaust). Celma also gives a little more headroom between the two valves when crossing.

Note from the webmaster: Attention! Staggering the a / c can create big valve-piston clearance problems! The most critical moment is, upon admission, just after PMH. Only consider this type of work if you think you have the skills required. If so, always adjust in small doses and check the clearances each time. Never use force in case of resistance.

A Vernier (drilled full circle for adjustment as below) cam wheel is helpful.

l3JDCdPpZmC3neKb-YcL3wTpEpYnFi91W4IzRQnh1OWqELHbYt3b71pJcxZ3fSJjz-ncRrwzVud4Y0QtasuYm1nGjaoQVXUYFP7t9-FBH6RB2jI4IH-ufmzf1YNbqjyTVyfIwcCCiA
 
Well tonight I am attempting the intake cam. Using the formula in the article, I have come up with 99 max lift on the intake. Now from here I have no idea where to go. I am aiming for the numbers below :

"An example for 4C a / c: To obtain a good performance at mid-speed ("problem" of the 4C) without losing at high speed, we can advance the exhaust by 4 to 7 ? and delay by 2 to 4 ? l 'admission. This can solve some issues of loss of efficiency at mid-range (especially with a 3-in-1 exhaust). Celma also gives a little more headroom between the two valves when crossing."

I did it three times and came up with 3 different max lift numbers.  I feel there is a lot of room for error the way I am determining opening and closing times.  I am rotating the engine and setting the dial gauge at zero when it is fully closed. The just rotating back until it hits zero and recording the number on my wheel.
 
I am not sure what numbers you have. The specs for a set of 4C camshafts. Measure with normal running clearance with TDC at zero. Then look at lobe centers?

Optional / Jota UK
4C
Intake
opens 50* BTDC
closes 74* ABDC

Exhaust
opens 70* BBDC
closes 38* ATDC
 
Yep, totally confused for the night. Im looking at 69 degrees BTDC for the intake opening.  I must be doing something wrong. Im taking my valve readings off of the right cylinder. Perhaps I am on the wrong lobe?
 
mizike77 said:
I did it three times and came up with 3 different max lift numbers.  I feel there is a lot of room for error the way I am determining opening and closing times.  I am rotating the engine and setting the dial gauge at zero when it is fully closed. The just rotating back until it hits zero and recording the number on my wheel.
Click to expand...

Sounds to me like you're trying to determine ACTUAL opening/closing times. Are you using MAXIMUM open as your reference? Someone correct me if I'm wrong, but you won't get accurate figures trying to measure when the valves start to open or close - a miniscule discrepancy in valve clearance will give you errant numbers.
 
mizike77 said:
Im looking at 69 degrees BTDC for the intake opening.  I must be doing something wrong.
Click to expand...

It could be 69? which means your intake cam timing is a bit early, but don't worry too much about that yet. Opening and closing figures can vary quite a bit depending on valve clearances so it's not a useful measurement for cam timing.

You need to identify the lobe centre angle at maximum valve lift. As Quentin said earlier, the best way to do that is to measure the same lift position on both sides of the cam lobe and work out the centre between those two readings. Choose a point at about half valve lift to get away from the opening and closing ramps. It's exactly the same logic as you used to find TDC. For a 4C cam, lobe centres are: Intake 102? ATDC; Exhaust 106? BTDC.

I've attached a PDF file of a timing disk for 4C camshafts that shows the valve durations and lobe centre positions as measured at the crankshaft. It'll print out he same size as a CD, so you can glue it to a CD and use that as your disk. Or you can simply transfer the info onto your existing disk in some non-permanent way like coloured tape or whiteboard markers. It'll make it easier to figure out where you are in the valve timing cycle.

Once you've worked out where your lobe centres are, you'll know straight away if they don't align with the figures mentioned above.

If your valve timing is out (as you suspect from your inlet opening measurement) there are various things you can do about it. Let's leave that until you have some accurate figures.
 

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