What to do if Your Head or Block is Milled? (was "what to do with a decked head?")

[Washout]

Paul, The dial indicator is mounted on a magnetic base and attached to the head but the surface is uneven. I think I'll make a plate to attach to the head that will give me a more stable platform for the dial indicator.

Jeff, I'm going to re-read your flywheel procedure and cross-check my current readings with that.

This just doesn't seem like such a difficult concept until you try to apply it!

Does anyone know if OGTS still sells the split timing chain? That sounds like a good investment.

[Washout]

OK Guys I worked on this most of the day and here's where I ended up. Using Jeff's re-drilling of the cam gear I was able to move things around until I got the following readings. All these numbers are based on .050 valve lift.

Exhaust timing ended up open 44* BBDC and close 3* ATDC

Intake timing was 1* open BTDC and close 41* ABDC

The cam is an isky OR-66 and claims duration at .050 will be 228* although Bob pointed out it is more like 222* I made these reading with all valves adjusted to ensure that there was a good load on the timing chain to remove all slack. The head was snug but not torqued down. I repeated the checks three times for each valve with complete repeatability.

From these numbers am I correct in believing I have the cam accurately timed and is there any reason I would want to further advance the cam?

[RallyBob]

Originally Posted by Washout From these numbers am I correct in believing I have the cam accurately timed and is there any reason I would want to further advance the cam?

Right now, I have it figured as 222* intake duration @ .050", and 227* exhaust duration @ .050". Intake centerline is 110 degrees, while the exhaust centerline is 110.5 degrees. That means the lobe separation angle is actually 110.25 degrees, and the cam is now advanced .25 degree.

I would advance the cam 2-3 degrees if you do mostly city driving and prefer low-end power. Otherwise, leave it as is!

Nice job, the first time is always the hardest!

Bob

[jeff denton]

Way to go! That's kind of a strain on the brain, huh? Next time you'll be able to do it much quicker.
You may have noticed in your efforts, and I mentioned this somewhere in a discussion, if you grind a little extra clearance in the head around the timing chain, it makes messing with it a LOT easier. And the chain with master link is virtually a MUST, now you know.
Am glad to see the sprocket drilling method worked again. The Kent adjustable one is a dream, but not really necessary.

[Washout]

Can someone give me the formulas that you're using to make these calculations? I've looked on the web and i've not been able to get a detailed results as you guys are getting. I may not be the only one here that needs the formulas.

Gregg

[baz]

what formula's are you after Gregg ?

[Washout]

The formulas for determining camshaft timing. In the earlier posts based on the readings I was getting Bob was able to determine that the cam was either retarded or advanced and where the centerline for each lob is. I don't quite understand how he's reaching these numbers.

Quote" Right now, I have it figured as 222* intake duration @ .050", and 227* exhaust duration @ .050". Intake centerline is 110 degrees, while the exhaust centerline is 110.5 degrees. That means the lobe separation angle is actually 110.25 degrees, and the cam is now advanced .25 degree."

I understand where he got the 222* and 227*, what I don't understand is how the centerline of 222* is 110 and not 111 or how the centerline of 227 is 110.5*. Clearly, I'm missing some step in this calculation. This is my first attempt at timing a cam other than just lining up the marks and I'm trying to understand the formulas for making the type of determinations he was able to make here. Thanks

[Paul]

Okay, lets see if I can remember... It always helps to draw the picture diagram...

Intake opens 1* BTDC and Closed 41 ABDC Therefore,
1+180+41 = 222 / 2 = 111 - 1 (since its BTDC) = 110 CL

Exhaust opens 44 BBDC and closes 3 ATDC
44+180+3 = 227 / 2 = 113.5 - 3 (since its ATDC) = 110.5 CL

As Bob said the actual is half way between the two, so 110.25

[Paul]

Draw yourself a "plus sign" about 2-3 inches tall on a sheet of paper. Now draw a cicle centered on the intersection of horizontal and verticle lines about 80% the size of the plus sign. Now draw another...Label one intake and the other exhaust.

Now on the Intake diagram draw a radial line from the center outward that describes 1* BTDC and the same for the exhaust 41* ABDC. The lobe center line is the distance (angular degrees from the top verticle line clock wise downward. Looking at my math above do you see what I did.

Similar for the exhaust, Top verticle axis CCW top down. Thats why I subtracted the 3* since its ATDC........

[Washout]

Thanks Paul,
I should have been able to figure that out for myself but I kept hitting a brick wall. I've got it now.

I had to use the Chevy eccentrics to finesse the setting but I finally think I got it. The final readings were:
Intake = 4*BTDC open and close 39* ABDC = 4*+180*+39* = 223* duration, making the intake centerline 109.5

Exhaust = 45* BBDC open and close 0* or TDC = 45*+180* = 225 duration, making the exhaust centerline 112.5

Subtract the two centerlines and I get 3* advanced, Wow this has been an education in formulas as well as how to convince the cam to move the few degrees I needed without buying the adjustable cam gear. That said, I can sure see the advantage to the adjustable. If I've made an error here please correct me now. I'm about to peen the eccentric into place.

[asdasc]

Originally Posted by nobody Jarrell with the 2.0s you will be over 9:1 to start. I think around 9.4. I'd be watching the finished compression with that combination.

I am FINALLY getting around to putting my new engine together and was doing some light reading to refresh my memory on things and came across this. I didn't realise (or remember) that with OGTS 2.0L pistons the starting compression is up to 9.4! I had my machine guy deck the block to bring the pistons up to +.005 over deck height.

I am running a stock 2.0L head with a mild Hydr cam. I was blessed to get a 'signature series' Jeff Denton modified timing gear, so I am not worried about getting it timed.

My only worry now is too much compression (is there such a thing?!). Will it be a problem for a street motor?

Thanks,

[opelnut10]

Originally Posted by asdasc I am FINALLY getting around to putting my new engine together and was doing some light reading to refresh my memory on things and came across this. I didn't realise (or remember) that with OGTS 2.0L pistons the starting compression is up to 9.4! I had my machine guy deck the block to bring the pistons up to +.005 over deck height. I am running a stock 2.0L head with a mild Hydr cam. I was blessed to get a 'signature series' Jeff Denton modified timing gear, so I am not worried about getting it timed. My only worry now is too much compression (is there such a thing?!). Will it be a problem for a street motor? Thanks,

Now is the perfect time to relieve the valve shrouding (ala Rally Bob) which will increase your combustion chamber cc's and thereby slighty reduce your compression ratio. You will most likely need to run 91-93 octane gas but that is streetable. You can also use a heavier dist. advance spring which will slow down your mechanical advance and allow a slower transition to full advance, and spread the rpm range to keep spark knock down.

[jeff denton]

Those of us who are into Serious High Performance want all the compression we can get! Sure high octane fuel is needed, but for the extra cost per tank of gas we enjoy the benefits.
Yes, do be sure your intake valves can flow efficiently, unshrouding the area discussed is key.
Remember that compression ratio, octane, and ignition timing all go hand in hand. This can be a problem for those who don't clearly understand why.
Continue taking your time, there's no rush, right?

[asdasc]

Ok, Up until now I have been pretty reluctant to do anything with my head, as it was new very few miles ago. This might be the excuse I need to actually put a die grinder to it.

As for the timing, I was going to use the LS disty mods and rivet the plates together to eliminate the advance.

Jeff, you really have to use it to remember it. When this project started last year, I read everything I could for months and had it all figured out. Six months have passed, and I am having to start the learning all over in some cases. Between the engine mods, timing, carb set up, exhaust - whew! If I get it done and it works right, it will scream! If not, it will rust....

[opelnut10]

Riveting the plate only solves part of the advance problem, you still have mechanical advance and that is where advance cam weight and spring tension comes into play, you can grind weight off the cams or use lighter springs to make the mechanical advance quicker or you can use heavier springs to slow the advance down.

[asdasc]

Ohhhhh yeah! I can't believe how much I have forgotten in the last 6 months. Thanks for the correction... I will dig into that more when it comes time to finish the dissy. I better focus on the task as hand for now. Which is to assemble the lower end. Hopefully, that should be pretty straight forward, assuming the machinist did a good job.

[Paul]

Wow, took me a while to find this thread........

I've been trying to piece together some of the comments Jeff, Bob and others have made over the years about the "easy" way to modify the timing gear to correct cam timing... without enlarging the bolt holes...

IIRC the infered method was drill two new cam dowl holes 120 degrees cw and ccw from the original hole. So I found on Hiro's web site a drawing of the gear have modified it further, thanks Hiro

To me, it illustrates the possibilities to adjust cam timing by increments of roughly -6, -3, 0, +3, and +6. The new dowl new holes: ccw 120* would result in -6* and +3*. Where the cw 120*dowl would result in -3 and +6.... depending upon which direction the chain is jumped on the cam sprocket......


So what I need is someone to please check my math and tell me if I'm full of it or if I finally got it......

Also, if this drawing is correct, it will help others understand HOW to use the modified gear...

[jeff denton]

You got it Paul. It really is that simple.
To drill them I made a tool out of an old camshaft.
You can elongate the bolt holes a bit to get more or less than 3 degrees.
But once you drill the hole that's where it stays.
I really do like the Kent Adjustable sprocket, though. But the drilling method does work fine.

[GTJIM]

Be aware that Opel cams are also ground with differing amounts of retard in the actual displacement between the dowel and the cam lobes also. There was quite a bit of 'fiddling' with cam advance/retard by Opel in meeting emission and drivability issues. On a reground cam it all depends upon the way the grinder sets up the cam too - so all this knowledge is real useful to get a cam installed correctly!

[Paul]

Nevermind, I think I finally get it. Maybe......

The dowel hole CW 120 degrees can result in either -3.15 or +6.32 depending upon chain placement

The dowel hole CCW 120 degrees can result in either -6.32 or + 3.15 depending upon chain placement,

Now am I on the right track??????

[jeff denton]

Paul, your original last post appeared in my email notification and was, well, just too much math for this time of night... thanks for editing all that out
You're making it harder than it has to be, like I explain to all who are trying to "get it".
I discovered all this by just making a degree wheel out of my flywheel and playing with the timing. Jumping the chain around and seeing what happened. It's just all about where the piston is when the intake valve opens, and really more important at high rpm, where the piston is when the intake valve closes. To get real technical it's really more like where is the intake valve when the piston starts coming back up. All in theory, and numerous variables in how the engine is built, especially rod length and header effectiveness.
To try to figure this out in your head is difficult. You know this, you are driving yourself crazy already... Put a degree wheel on the crankshaft and a dial indicator on the intake retainer and the cam card taped to the windshield and just start rolling her over. If you like what you see, great. If not, you rotate my sprocket a notch and try it again. You'll have to move the chain around some, but you'll either end up with the timing better or worse. By a couple or few degrees, if it isn't perfect then get the error in your favor, for example a couple degrees advanced for street torque or retarded for high rpm power.
Trial and error. Which is why I so recommend a little extra chain clearance in the head and that wonderful master link timing chain! I teach myself the hard way...
The Kent gear is so nice.

[Paul]

Jeff,

I thought my edit actually made it simpler..........

I'm about 95% sure I've finally figured it out. Unfortunately, I don't have the luxury of having the engine on a stand so I can go through the degreeing process again. The head was pulled to fix a .... um a problem... but the rest of the engine is still in the car.

I modified a cam gear a while back to fix a "retarded" cam. I thought this would be the perfect opportunity to install it. It was just a matter of understanding which dowel hole / jumped chain position resulted in the effect I needed.

Now I got it figured out