Stuck with cam timing issue-is it me?

[efhughes3]

I'm trying to time my cams. 1984 3.2L, DC19 cam profile, John recommends overlap of 1.8-2.0mm. So, I'm going with 1.9mm, which works out to .075".

I think I get the process, and know what I'm supposed to do. I set the crank at TDC, and the valve for #1 intake is adjusted to .004". I then turn the crank clockwise until the dial reads .075" of load, which is just past TDC, in other words I've spun the crank about 363 degrees or thereabouts.

My problem is that when I remove the cam sprocket bolt, and then pull the pin, the dial indicator drops about .060-.065" of the load. I first thought maybe I had too much tension on the chain (using Stomski tensioners), but after trying about 4 progressively lower tensions, I still get the same issue.

Should I just not look at the gauge when I un pin the sprocket? Just hold the cam, turn the crank back CCW a couple of degrees to TDC to pick up my overlap, pin it, bolt it and then spin it thru a couple of revolutions to see what I get?

EDIT: See below, I think I found the problem and a resolution...

[efhughes3]

I need to add two more points-

I've only got the #1 intake rocker in.

I've got Aasco racing valve springs.

Maybe it is the stiff valve and the fact I've only got the one rocker in, allowing the valve spring to push the cam? Maybe I should install the other rockers to put tension on the cam surface?

[911quest]

ok

[gigem75]

" then turn the crank clockwise until the dial reads .075" of load: correct me if I'm wrong but you zero the guage with preload on it, at TDC on the firing stroke, with your .004, then rotate the crank clockwise back exactly to TDC with the cam just having opened the valve, and THEN turn the cam until it reads the value you are looking for, then put the pin in. You want your desired overlap to occur at TDC for that cylinder. Check, check, then check again, repeatability is the key to sleeping well at night.

[Jeff Alton]

The measurement comes at 360, not 720 degrees.

Ed, more rockers will make the cam rotating issue worse. I would adjust it so that you reach the desired lift before TDC overlap, pull the pin and rotote the remaining degrees to reach TDC overlap, insert pin and bolt and check again.

Cheers

[efhughes3]

Originally Posted by gigem75

" then turn the crank clockwise until the dial reads .075" of load: correct me if I'm wrong but you zero the guage with preload on it, at TDC on the firing stroke, with your .004, then rotate the crank clockwise back exactly to TDC with the cam just having opened the valve, and THEN turn the cam until it reads the value you are looking for, then put the pin in. You want your desired overlap to occur at TDC for that cylinder. Check, check, then check again, repeatability is the key to sleeping well at night.

Gigem: That's not my issue, you're explaining what needs to happen. See below.

Originally Posted by Jeff Alton

The measurement comes at 360, not 720 degrees.

Ed, more rockers will make the cam rotating issue worse. I would adjust it so that you reach the desired lift before TDC overlap, pull the pin and rotote the remaining degrees to reach TDC overlap, insert pin and bolt and check again.

Cheers

Thanks Jeff, I think I did a version of that. I'll post below.

[efhughes3]

OK, I spent a bit of time on this, and tried "by the book" numerous times. I think the issue is a combination of several issues:

1. Higher lift cams (Dougherty Racing Cams DC19)
2. Racing valve springs
3. Larger overlap than normal (1.8-2.0mm)
4. "New style" cams with bolted sprocket instead of crows foot setup

While trying this, as noted above, my cams would turn when I pulled the pin. Not the sprocket, the cams themselves. Items 1, 2 and 3 above contribute to this condition, I believe. Then, since I can't hold the cam in place with a crows foot, or any other way (to my knowledge), I was hosed.

So, what I ended up doing, is pulling the pin and letting the cam settle. Then, I'd backtrack the crank counter-clockwise to where I "thought " it would need to be to sync with the proper overlap on the cam. I'd then pin the cam, and rotate the crank clockwise to see what I'd end up with as far as overlap.

After a dozen or so "trial and error" settings, I finally got the cam pinned to where when I put the crank @ TDC, I had just over .072" of overlap. I cycled thru 6 or so 720 degree evolutions and had the same measurement at TDC every time. This is within the 1.8-2.0mm tolerance (Gauge was counting down, and I'd started at '0', so this was .072" of travel):



Then, I went to the RH side, and experienced the same thing. Since I was better at guessing the correction I needed, I only took 6 or so times to guess where I needed to start the crank at, pinned the cam again, rotated CW to get just under .073" of load. Again, I ran thru several cycles of 720 degrees, and got repeatability:



So, I ended up with less than .001", probably more like .0005" of difference between the 2 sides. I think I got it all right......TDC, #1 intake "slack" with its .004" of clearance. Rotate crank 360 degrees CW, and I have .072" of overlap on #1 intake, #4 intake "slack". Rotate another 360 degrees CW, and I then have .072" of overlap on #4 intake and #1 is slack again. This is correct, right?!?!

I used the Stomski tensioners, which are nice items to have. I also got one of his pin pullers, which is basically a mini slide hammer. In light of how I had to do this, this tool paid for itself many times over considering how many times I had to pull pins today. I also got one of his TDC locating tools, and my marks were right on the money.

A timed engine (I think ):

[KTL]

Not only is gigem explaining what needs to happen, he's explaining something you can't do with the late-style cams which have the "bolt end" on them. Meaning, there's nothing to grasp the cam end when the bolt is removed, so you can't rotate it independently of the crankshaft. I had similar problems when timing my cams (DC20 Super C2 cams which spec at 2.2-2.4mm) but I did not run into the problem of the cam moving when i'd pull the pin- I also have different "performance" springs from John Dougherty.

I would pull the pin and rotate the crank the desired direction to gain or lose lift. Problem was, the cam would usually continue to rotate with the chain sprocket -even with the pin removed. I would continue to rotate the crank ever so slowly and slightly, and bump the wrench as I turned, to get the cam to not spin with the chain sprocket. Once the cam would stay put I could then rotate the crank the desired direction to gain or lose lift on the cam. Put the pin in, go back to TDC overlap for #1 and check the lift again.

Very tedious process when the cam doesn't want to release from the chain sprocket without the pin in it!!!!! It would be much simpler if there was a way to manually rotate the cam, independent of the crankshaft! This is very easy to do with the old 46mm nut cams due to the snout on the end of them.

So I finally got smart and did this:

Cam timing with DC20's

I found it helpful to set the cams at the start such that they were deficient in lift at TDC overlap. Then I could use the cam bolt bottomed out in the cam bore to rotate the cam in the clockwise direction to gain lift. This is much better than guessing if the chain sprocket has slipped enough like I did before. Since you can rotate the cam, you can watch the dial indicator move to the desired lift measurement.


Ed,

You'll also want to check your piston-to-valve clearance. I do not know what pistons you have so forgive me if your pistons are different than stock and have valve reliefs machined into them. I have stock 3.2 USA 9.5:1 pistons. When I got my cams set to my desired 2.3mm setting, I found that I did not have ample piston-to-valve clearance on the intake side- only 1mm, recommended is 1.5mm intake, 2mm exhaust I believe. I ended up having to back off my lift @ TDC overlap to 1.85mm in order to get sufficient valve clearance on both banks of cylinders (checking only cylinders 1 and 4).

[Jeff Alton]

Ed, sounds like you have got it!

Kevin brings up a good point. I would just use the adjustment screw method to check the clearance. 1 turn=1mm. You can do it .25mm increments.

Cheers

[efhughes3]

KTL- I'm glad it isn't just me. As you explain and as I noted in my list of contributors (#4- "new style" cams) not being able to manipulate the cam is really the issue here. To be able to hold the cam stationary would make things SO much simpler.

Yes, I'll be checking piston-valve clearance. I've got a lot of piston to dome clearance-I'm on the upper end of the tolerance-I've got stock pistons and the lighter cams, so I should be OK.

[2.7RACER]

I used the longer bolt bottomed out in the cam to adjust the cams in my son's '86 Carrera. Worked fine.

[gigem75]

I see what yall are saying now. Thinking out loud... wouldn't putting the exhaust rocker in #'s 1 & 4 help hold the cam in the desired overlap positon as it counteracts the tendency of the the cam to slide off the intake profile?

[911 tweaks]

Ed- Are you using the Stomski tool to only aid the timing process, OR. are you going to use them in the engine?
Stomski claims "racers" use them but would they last w/o the oil feed or oiling to keep the sprockets and all lubed & cooled?
Oh, the engine is looking great! Keep up the posts & fun!!
Bob

[1982911SCTarga]

Subscribed as the owner of a very late SC. Thanks, Ed.

Brian

[efhughes3]

Originally Posted by 911 tweaks

Ed- Are you using the Stomski tool to only aid the timing process, OR. are you going to use them in the engine?
Stomski claims "racers" use them but would they last w/o the oil feed or oiling to keep the sprockets and all lubed & cooled?
Oh, the engine is looking great! Keep up the posts & fun!!
Bob

I'm going to pull the mechanical tensioners and put my pressure tensioners back in. But, I'm going to make the safety collars that Aigel has detailed elsewhere for insurance. I was going to sell the Stomski stuff at a good price to recoup my investment, but who knows? I may need them in the future.

[Jeff Alton]

I will buy the stomski tensioners if you sell them!

Cheers

[JeremyD]

Originally Posted by 2.7RACER

I used the longer bolt bottomed out in the cam to adjust the cams in my son's '86 Carrera. Worked fine.

That's what I used too - It helped to hold the cam steady. Check you piston clearance - as Jeff said - you can tell by adjusting your rocker at TDC - thats the only downside of performance cams with stock pistons...

Congrats on getting this far Ed - it's high on "pucker factor" - if you are like me - it will wake you up at 3:00 in the mornin just thinking about it....

[KTL]

Don't just check your clearances at TDC. I found that my closest clearance was substantially past TDC.

[efhughes3]

Originally Posted by JeremyD

it will wake you up at 3:00 in the mornin just thinking about it....

That's funny Jeremy, I've laid down the last two nights to go to sleep, and all I could think about was the motor. The first one was the cam timing. Actually, I was able to grasp what I needed to do while tossing and turning, kind of a revelation.

Last night, I just kept going over checklists in my head. Went to Zim's today and got 3 oil filters, a new (rebuilt) alternator, new plugs and fan belt.

[JeremyD]

That is funny - and yes, Kevin is right, not just at TDC - through the range to be safe. I too like your tenioners - and when I do this again, I will be getting some solid tensioners.

I was befuddled reading the book on timing - and I must have read it 10 times. Once you start doing it though you do sort of get a revelation - ohhhhh that's how it works........

It's even easier to see once you get all your rockers and valve gear on - a couple of turns on the engine and you see how it all comes together!