Help--Cam Timing

Groesbeck Hurricane · 06-08-2002, 12:38 PM

Really confused and have many questions, but to start:

'83 SC, original motor and cams, etc, re-building due to broken studs and going for everyday driver

I set everything at TDC. I turn the crank ~360 degrees, the cams are now 180 degrees opposite direction, and Cylinder 1 intake has started its travel about 5 degree earlier.

Is it possible that I somehow switched cams? do I need to switch them? Do I need to rotat bank 1,2,3 cam 180 degrees?

When I am going for the .061" (don't have metric tool) setting, is this what the reading should be when I am top dead center on the cam?

Thanks,

Peterfrans · 06-08-2002, 01:28 PM

I think that the no 1 intake valve should start to open somewhat sooner (but not that much) than 5 degrees on the crank. At least that is what mine does on a 70-S.

When you look at the cams from the nut end, the left cam has the first two lobes that you see spread out as wide V. The right when viewed from the nut end will have its lobes closer together (looks like a rabbit whit its ears up in the air (R)).

Procedure is as follows:
1. turn crank to TDC (Z1 on the pulley)
2. adjust the cams to also the point which is impressed on the nut end piointing up. This will give you the basic setting for cam timing.
3. adjust valve clearance on No 1 and No4 intake valves to 0.004 inch (.1mm)
4. install dial indicator in no 1 intake valve.
5. turn crank 360 degrees
6. read dial indicator. Compare to correct value.
7. in case the lift is wrong, remove the cam nut, pul out the pin in the sprocket and turn the cam so much as to obtain the correct value. Install pin and cam-nut.
8. turn engine 2 times 360 degrees and read dial indicator.
9. in case value still not correct, go back to 7 etc.
10 if value is correct, install dial indicator on no4 intake valve
11. turn engine 360 degrees, read dial indicator etc.

May take a while to get there, just went through the procedure yesterday. Also be sure to check the values again after properly torquing the cam nuts.

Good Luck,

Groesbeck Hurricane · 06-08-2002, 01:46 PM

Peter,

Thanks for taking time so late in the evening!

It appears I did not mix up the cams.

I do want some clarification though:

I have 1-4 as you state.

5. Turned crank 360 degrees. Cam has moved 180 degrees.

6. Take reading and compare to value (I am low)

7. The lift is wrong, remove the cam nut, pul out the pin in the sprocket and turn the cam so much as to obtain the correct value. Install pin and cam-nut.

8. Turn engine 360 degrees twice and take reading on dial indicator, etc.

Thanks. My confusion is in the expectation that the valve will be moving in the first 360 degrees, not just prior to the second, although as I think about it, this just makes more sense.

Wayne 962 · Wayne 962's Garage

This whole procedure can be confusing and complicated (the SC/3.2 engines are the easiest to time). This is Project 15 in the 101 Projects book - it's tough to explain without the pictures...

-Wayne

Wayne 962 · Wayne 962's Garage

Also look at Page 130 in Bruce Anderson's Performance Handbook, 2nd edition. This diagram will answer your questions...

-Wayne

Groesbeck Hurricane · 06-08-2002, 07:29 PM

Thanks, just had difficulty visualizing the process (can visualize whorled peas, but timing on a horizontally opposed engine....) but have now muddled through. Got #1 without any issues, went in wonderfully. Now I have to get #4. I will need to retard #4 in order to obtain .061" clearance at TDC. Shaft keeps hanging up on rotation and then slipping slightly more than I wish. Thinking about turning the entire motor 710 degrees and then replacing the pin. I'll get back on it in the morning when I have a little more of the proper religion and maybe a little less.....

Superman · 06-08-2002, 09:11 PM

All the above seems true and correct, but I'd add this: If, after rotating the crank 360 degrees, the correct lift is not achieved, turn the crank to where the correct lift is. THEN remove the cam nut and the sprocket pin. Rotate crank back to TDC, and then reinstall the pin and nut. Repeat. The procedure is pretty quick this way.

You are correct in that the intake valve will not move through most of the 360 degree rotation. but toward the end, it will move. Plenty. And it will begin to move well before 5 degrees BTDC

Oh, and you won't be able to move the crank 710 degrees with the pin out of the sprocket. You'd get piston to valve interference.

Thomas Owen · 06-09-2002, 04:50 AM

David - Super has it right: you need to think of the rotation of the crankshaft in terms of placing it where you get the correct dial indicatior reading THEN loosen the nut, remove pin and rotate the crank slightly ahead or behind to TDC. It will go quickly this way.
Good luck-

Groesbeck Hurricane · 06-09-2002, 10:30 AM

Thanks again! I went though the process and was able to get the following settings: #1 at .060" #4 at.058". Both were repeatable and stayed the same after application of torque. I have taken a lunch break and we are installing the fittings on the new tensioners and then bolt back on everything. Pray for installation in three hours!!! Man am I overeager/wishful thinking or what?

sand_man · 03-27-2006, 12:12 PM

Quote:

Originally posted by Superman
All the above seems true and correct, but I'd add this: If, after rotating the crank 360 degrees, the correct lift is not achieved, turn the crank to where the correct lift is. THEN remove the cam nut and the sprocket pin. Rotate crank back to TDC, and then reinstall the pin and nut. Repeat. The procedure is pretty quick this way.

You are correct in that the intake valve will not move through most of the 360 degree rotation. but toward the end, it will move. Plenty. And it will begin to move well before 5 degrees BTDC

Oh, and you won't be able to move the crank 710 degrees with the pin out of the sprocket. You'd get piston to valve interference.

I'm reviving this one. I'm pretty clear on the cam timing, but I have a question about the statement above. When you rotate the crank "back to TDC (Z1)" after the correct lift has been reached, can you actually turn the crank COUNTER CLOCKWISE once the cam bolt and pin have been removed? Or must you go CLOCKWISE all the way around again, being sure to stop on Z1? Sorry if this is a stoopid question...I just want to be sure.

Groesbeck Hurricane · 03-27-2006, 01:22 PM

Nothing is a stoopid question!!

Always clockwise, never tempt the devil... I'm sure smarter heads will chime in but that is my understanding.

sand_man · 03-27-2006, 04:20 PM

Quote:

Originally posted by Groesbeck Hurricane
Nothing is a stoopid question!!

Always clockwise, never tempt the devil... I'm sure smarter heads will chime in but that is my understanding.

Right, but I'm thinking that we're only talking about a few degrees. Anyone else?

sand_man · 03-28-2006, 05:01 AM

BUMP...I gots to know!

2.7RACER · 03-28-2006, 06:35 AM

Sand man,
The idea about always turning the crank clockwise is the layout of the cam drive chains. The chains pull the cams counter clockwise in a "straight line"
This is classic chain drive engineering.
When you rotate the crank counter clockwise you are pulling the chain against the idle tensioner. The chain is not in a straight line back to the drive sprocket. Some load is placed upon the idle tensioner.
Now this is ok to backup a few degrees and then go forward to TDC to look at timing. Better to just go around clockwise.
That said, I always rotate the crank clockwise at least 2 rotations to recheck timing and then I do it again just to be sure.
Bottom line backing up a few degrees shouln't hurt anything. Backing up complete rotations is not a good idea and really serves no purpose.
Now, tell us all about downtown "Cooterville"

sand_man · 03-28-2006, 06:39 AM

Cooterville thanks you, 2.7RACER! I got the same advice from Rennlist. I'll keep it going clockwise.

sand_man · 03-28-2006, 06:46 AM

Quote:

Originally posted by 2.7RACER

Now, tell us all about downtown "Cooterville"

Cooterville is an interesting place...:

HKZ Bob · HKZ Bob's Garage

Quote:

Originally Posted by Peterfrans

I think that the no 1 intake valve should start to open somewhat sooner (but not that much) than 5 degrees on the crank. At least that is what mine does on a 70-S.

When you look at the cams from the nut end, the left cam has the first two lobes that you see spread out as wide V. The right when viewed from the nut end will have its lobes closer together (looks like a rabbit whit its ears up in the air (R)).

Procedure is as follows:
1. turn crank to TDC (Z1 on the pulley)
2. adjust the cams to also the point which is impressed on the nut end piointing up. This will give you the basic setting for cam timing.
3. adjust valve clearance on No 1 and No4 intake valves to 0.004 inch (.1mm)
4. install dial indicator in no 1 intake valve.
5. turn crank 360 degrees
6. read dial indicator. Compare to correct value.
7. in case the lift is wrong, remove the cam nut, pul out the pin in the sprocket and turn the cam so much as to obtain the correct value. Install pin and cam-nut.
8. turn engine 2 times 360 degrees and read dial indicator.
9. in case value still not correct, go back to 7 etc.
10 if value is correct, install dial indicator on no4 intake valve
11. turn engine 360 degrees, read dial indicator etc.

May take a while to get there, just went through the procedure yesterday. Also be sure to check the values again after properly torquing the cam nuts.

Good Luck,

What can I do if my cams are regrind and I don´t have data for it?

BR bob

T77911S · 11-09-2010, 04:16 AM

you can only go around with the cam sprocket pin out if you only have rocker arms on 1 and 4. if they are all in, you cant go 360 degrees. and i would still be carefull if you have not done #4, or better yet, dont put it in yet. if you go backwards, go back enough so that you will have good tension on the chains.

i was just going through Tbelts with someone else. when i do timing belts, after i put the belt on, i back the crank up enough so that when i bring it back up to TDC, the belt is tight and both the crank and the sprocket move. its better than trying to go 360 degrees and find out at 180 that something is hitting.