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

[soybean]

Originally Posted by jeff denton The main thing is, you must not have any gasket material hanging over into the combustion chamber. 9-1/2 to 1 compression ratio should make for a nice peppy engine, will need 91 octane gas.

Jeff, that was what I was wondering about, "gasket material hanging over into the combustion chamber." That said, the 1.9 gasket being 2mm under, wouldn't it be prone to fail?

Originally Posted by nobody , 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.

Too much compression with 91 octane gas with the 1.9 head? or should I step up to a 2.0l head with the 43mm intake valves and 36mm exhaust valves. I'd also looked at thread http://opelgt.com/forums/showthread....ht=S-10+clutch which discussed some of these questions here.Thanks, Jarrell

[markandson]

Well, Git Er Done!, I just took apart a stock 1.9 yesterday and I didn't throw out the old head gasket yet . So here you go.... The crushed piston seal diameter runs between 3.736" (94.894mm) and 3.741" (95.021mm) and the crushed thickness at the piston seal area is .038" (.965mm). HTH

[GTJIM]

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.

This is a perfect excuse to "unshroud" valves out to the edge of the new bore size as it helps in two ways - better air flow and slightly reduced static compression ratio.

[kwilford]

Originally Posted by soybean Okay here comes a dumb question. Assuming you use the combo the Keith posted, in item 2 , he has 30 over flat top pistons (93mm). One uses the 2.0 l (95 mm) pistons, do you use the regular gasket set, or go with 2.0 l gasket set since you're over 02mm? or does it matter. Jarrell

Jarrell, I believe that you need to use the 2.0 head gasket for either the 2.0 pistons, or any similar size (such as the "economical" SBC 265, or stroked-crank with the 305 pistons). Call and ask Gil at OGTS, he will say for sure (or Bob or Dave could just chime in) and he also sells them of course. But as I recall, he was out of stock a few months ago...

[greensmurf20]

about a month and a half ago i took the last felpro headgasket he had and said he was just about out of even the "normal" ones.

[GTJIM]

In a previous post Bob mentioned that the standard 1.9 head gasket can be used as the diameter of the holes is 94.8 - 95.0 mm in a compressed gasket.
So it looks like you can sneak by with a 1.9 head gasket on a 95mm - 2.0L bore.

[nobody]

The problem you get into using a 1.9 gasket on a 2.0 is that the inner edge of the metal to seal the combustion chamber is now in the combustion chamber. A stock head gasket is meant to be between the block and head and is actually above size for a standard bore. 2.0 0r 95mm is just over the working limit of stock so you run the risk of burning up a stock head gasket or piston hitting it if your pushing the compression limits. When I did the 2.0 I had gaskets galore and I found that the chances of one sealing and staying good were pretty slim. Use the right one and save the headache and worry.

[azopelnut]

Originally Posted by RallyBob When I used to build a lot of 2.0 litre circle track engines, I could get around 10.5-10.7:1 compression with flat-tops if I decked the block .010" and milled the head .085" with flat-tops and Chevy valves (1.85/1.50).

How did you correct the timing with that amount of milling? Did the profile of the cam make up for the milling?

[soybean]

[QUOTE=azopelnut]

Originally Posted by RallyBob When I used to build a lot of 2.0 litre circle track engines, I could get around 10.5-10.7:1 compression with flat-tops if I decked the block .010" and milled the head .085" with flat-tops and Chevy valves (1.85/1.50). How did you correct the timing with that amount of milling? Did the profile of the cam make up for the milling?

Check out post 42 and a couple of earlier ones that Jeff posted, on how to change the cam timing. HTH, Jarrell

[azopelnut]

Right
I didn't think that that much milling could be compensated with the modified cam gear. Like Keith and Rallybob said 2 degrees retard for every .025 milled so if Rallybob milled a combination of .095 then that would be nearly 8 degrees retard and the modified gear would only be 6 advance leaving the engine at 2 degrees retard..right or am I missing something?

[soybean]

You are correct. Check out Bobs post 44 near the end, and from what I am able to gather that 2 degrees will give you some good low end torque. HTH, Jarrell

[kwilford]

Paul, the "6 degree" fix is just the modified cam gear. The vernier cam gears that Bob describes has much greater adjustment, and much more precise.

[Travis]

Don't be afraid to combine the 6 degree dowel pin trick with the offset bushing and even skipping teeth on the sprocket. You can get any adjustment you want this way.

For example, if you advance the cam one tooth(18 degrees if I remember correctly) and then retard the cam 6 degrees with the extra dowel hole, you'll end up with 12 advanced. You can then use the offset bushing to fine tune in either direction...

-Travis

[RallyBob]

Originally Posted by azopelnut Right I didn't think that that much milling could be compensated with the modified cam gear. Like Keith and Rallybob said 2 degrees retard for every .025 milled so if Rallybob milled a combination of .095 then that would be nearly 8 degrees retard and the modified gear would only be 6 advance leaving the engine at 2 degrees retard..right or am I missing something?

I also often have the cam ground with some advance in it too. So you can not only return the timing to zero but you can gain some cam advance as well.

[jeff denton]

There's way too much worry about all this. This is about doing all the decking and milling you want to get max compression and then just fix the timing problem. Forget timing marks. Degree in your cam according to the spec sheet that came with it and you're done. The nice expensive vernier sprocket is beautiful, the way to go, no doubt, but I'm talking about STOCK parts just kind of "messed with" for ULTIMATE performance. On a budget, may I add... I can drill two little holes in a gear pretty cheap... Was not surprised by Bob's finding that Opel racers had my trick figured out long ago. It's too simple to overlook once you get focused on it, just re-read my post about how I found it and do the experiment yourself. Trace the sprocket on paper, teeth, bolt holes, dowel hole, and all, then rotate it to the next bolt hole. Look at where the teeth land. Rotate it again to the next bolt hole, look at where the teeth landed this time. Do this and you will see the obvious simplicitity of the whole situation! If you are fretting about any of this topic you do not yet understand it, trust me, but keep looking, it will hit you eventually. You could have the cam ground a bazillion degrees off and still fix it this easily, it is all about degreeing in your cam. When do you want the valve to open, make it happen. Skipping the chain a tooth on the sprocket changes timing nine degrees, as I recall from my first attempt at making an angle milled head degree in at all... that's all I did at first, and won a (trophy dash) race even, against 2.3 liter Mustangs

[Washout]

Guys, I've read this post a couple of times now and still need a little help. I've never had to degree a cam before but this engine I'm building now had been decked and I have no idea how much since there is no published factory height. All that said, I've installed a degree wheel after making a mounting hub out of an old pulley and I built a piston stop for insuring that I have absolute TDC set on the degree wheel. I set the cam using the old timing marks as a starting point and using the .050 reading provided with my ISKY cam spec sheet I started taking readings.
In my case the spec sheet says the intake should be open .050 at 4 degrees Before TDC and closed to .050 at 44 degrees ABDC. My measurements indicated the the cam was opened to .050 at 3 degrees After TDC and closed to .050 at 45 degrees ABDC. How can the ABDC reading be so close to correct (45 actual vs 44 planned) and yet the BTDC reading is off by 7 degrees(BTDC 4 planned vs ATDC 3 actual)? Is this attributable to timing chain stretch? I've only got the rocker arms installed on two cylinders to provide some tension on the cam, is that enough or do I need them all installed for a more accurate reading?

[RallyBob]

Originally Posted by Washout In my case the spec sheet says the intake should be open .050 at 4 degrees Before TDC and closed to .050 at 44 degrees ABDC. My measurements indicated the the cam was opened to .050 at 3 degrees After TDC and closed to .050 at 45 degrees ABDC. How can the ABDC reading be so close to correct (45 actual vs 44 planned) and yet the BTDC reading is off by 7 degrees(BTDC 4 planned vs ATDC 3 actual)?

Quick question... Are you checking with zero valve lash, and at .050" lifter rise?

By my calculations, you are supposed to have a cam with 228* @ .050" and with 110* intake centerline. You are only measuring 222*@ .050" with a 114* intake centerline.

This shows two things:
One, the cam is 4* retarded.
And two, it has 6* less duration than what the cam card says it should have.

This is not entirely uncommon! Some cams are wayyy off from the cam cards, but sometimes it has to do with how you measure it. Some things that can affect it:
Is it truly at zero valve lash?
Is the dial indicator at the center of the lifter?
Is the dial indicator rididly attached, or does it move around?
Is the dial indicator perfectly perpendicular to the lifter?
Does the degree wheel spin when you rotate the engine?
Does the degree wheel pointer move around?
Did your 'positive stop' in fact move during the measuring process?

So it could just be a 'tolerance stack' of any one or all of these things. I am overly cautious when degreeing a cam, I will perform the same check 3-4 times until it's consistently the same, because I've had the same issues in the past!

HTH,
Bob

[RallyBob]

Originally Posted by Washout I've never had to degree a cam before but this engine I'm building now had been decked and I have no idea how much since there is no published factory height.

Missed this before.
Factory deck height is A+T mm, this is measured from the top of the block to the crankshaft centerline.

Bob

[Paul]

Yea... what Bob said....

On the cams I've bought, I've found the lift and duration to be a little LESS than advertised. When dergeeing the cam, I did not try to get the @ lift numbers to match the cam card. I carefully measured and charted several lifts vs angles. I probably did more than a skilled tuner would have to do to understand the result, but sometimes the more information the better.

First, use Bob's guidelines above and be sure of your set-up. I found my dial indacator was moving slightly due to the tiny vibrations of the process. Next repeat 3 or 4 times, writing down the numbers each time and then check for variation. If you bought a big wheel then by all means record to the half degree.

I measured lifts on the lift side @: .005; .010"; .013", .025; .050"; .100"; .150"; .250 and then on the way back down again at each corresponding lift height.

Then, using the math I calculated Centerline at each lift: .005, .010" etc.

You may find the opening ramps and the closing ramps to NOT be symmetrical causing the C/L to be skewed. On one cam I found the numbers @.050" to be off slightly, so the numbers I took higher help to confirm the @.050 trend.

The numbers are still in a notebook, but it is in my desk at work. If you need, I can scan them in early next week and you can see exactly how I did it down to my calculations.

[Washout]

Bob,
The Piston stop is solid, I made it out of 1/2 inch thick by 1 3/4 wide 6061 aluminum, reamed the bolt holes for close fit and then threaded and installed a 3/8 bolt in the center. The 3/8 bolt is completely threaded into the stop all the way to the bolt head... it's solid, no flex. The Degree wheel is solid as well, I cut the pulley off of an old opel pulley then machined a face on it that the index wheel could fit over. Then I made a washer with a face to pinch the index wheel in place. The pointer on the block is simply a piece of welding rod but it too is solid.
I have the dial indicator directly on the lifter, perpendicular to the lifter (no rocker arm installed) and the magnetic base seems to be very solid. The results I've been getting are very consistant. I just don't quite understand them. You say the cam is 4* retarded, I thought it was 7 degrees retarded since it was suppose to be 4* BTDC and instead its 3* ATDC? The inaccuracy in the grind would explain the second reading though. Thanks for the information.

[opelnut10]

The measurments that are on the cam timing card are based on 1.5 rocker ratio, Opel is 1.44 and that is why you get a different reading than the advertised lift and duration. The fix that Rally Bob came up with (using the Chevy off-set dowel bushing) works very well in degreeing the cam, If you get the cam grinder to put in a chevy dowel pin insetead of the opel one. As far as milling the head to gain compression it should only be done as a angle mill and you also have to angle mill the intake manifold to get the correct port alignment.

[RallyBob]

Originally Posted by Washout You say the cam is 4* retarded, I thought it was 7 degrees retarded since it was suppose to be 4* BTDC and instead its 3* ATDC? The inaccuracy in the grind would explain the second reading though. Thanks for the information.

Remember that the second number (3* ATDC) is based on only 222 degrees, not 228 degrees. The amount the cam is retarded is based on the centerline, not necessarily the intake opening.

Bob

[Washout]

Originally Posted by RallyBob Remember that the second number (3* ATDC) is based on only 222 degrees, not 228 degrees. The amount the cam is retarded is based on the centerline, not necessarily the intake opening. Bob

Now I got it I see where I was going wrong, Thanks for all the help guys.

Gregg

[Paul]

Gregg,

To improve the resolution of reading the numbers, did you sharpen the welding rod to a point?

Is the Dial indicator on a Magnetic base? If so is it supported? If not it will vibrate and move, no kidding

[jeff denton]

Fun, huh? You just have to go through it again and again and it gets clearer all the time. You probably know that you can't rotate backwards, ever, or the chain slack will mess you up.
Try my "flywheel tooth" method of keeping track of the degrees, you'll like it. There's plenty of room on the machined surface of the flywheel to make marks and write notes like "intake open" and "exhaust closed" if you use a nice fresh Sharpie. Some numbers of teeth ATDC are also marked in parenthesis as numbers BTDC and ABDC to help keep track of where you are. Knowing that each tooth= 2-1/2 degrees, half a tooth is a little over a degree, go slow and think about it, it works well for me time after time, with the engine in the car even. With my marked flywheel I don't need the degree wheel any more.
Yes, measure lift from the top of the spring retainer, and have zero valve lash or less first! Your dial indicator doesn't really care if the valve is open or not, you are reading what the cam told the rocker arm to do to the valve.
I don't recall ever seeing the block's deck height from the crankshaft centerline being given before. Please keep this dimension a secret, OK?