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

[GTJIM]

Originally Posted by jeff denton I did the "piston stop method" of finding TDC when I built my engine My machinist opted to keep my head mill amount a secret even to me, as he would never be involved in any kind of cheating at the racetrack, or at least rumor of it... I like his attitude... So, how much head milling can be done, and how much angle milling has been accomplished successfully in your experience, never mind any silly rules?

The "piston stop method" is nice and certain - bring the piston up to a stop bolted across a couple of head bolts so the piston stops a bit down the bore then rotate the engine al the way back to the stop from the other direction - and split the diference.

Angle milling? Hell no! It is just that the machinist was a clutz who could not get things square - and I don't have another head. Honest to Mergatroid!
....and we just had to keep cutting to get it flat. You mean you want to disappoint the fans by stopping me racing - be it on your head!

I remember Bob mentioning that he ran pistons 0.005" ABOVE the block face to get the clearance down to 0.035" to 0.040" with a stock gasket.

"If you ain't winning then the other guy is cheating better than you!" S.Y.

[RallyBob]

Originally Posted by jeff denton Bob, my block was decked only to "clean up", by the rules, but, should we skip the rules, how much decking could be done, or in other words, how much piston top to deck height would you consider to be minimal? I never saw a spec on this...

Most stock flat-top pistons are factory installed at anywhere from .004" to .007" below deck. I like to bring the pistons above deck .005". Better compression, improved quench area, and lower emissions to boot.

So, how much head milling can be done, and how much angle milling has been accomplished successfully in your experience, never mind any silly rules?

I regularly mill heads .050" in conjunction with decking the block. Stock flat-top motors, although rated at 9:1, are in truth closer to 8.4:1. Milling the block and head the amounts mentioned gets you to just under 9.5:1, which happens to be the amount that is legal for SCCA Improved Touring for an Opel GT (listed compression plus 1/2 point).

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). That said the most I ever flat-milled was .105". The most I ever angle-milled on a running engine was .080", but I had my machinist angle-mill a junk head (one cylinder's worth) by .125" and it seemed like it would work. Valve angle changes a bit over 1 degree and of course the head bolt holes must be spot faced but it could be done. It also drops the plug a bit closer to the piston, don't know if that hurts or helps though....

Bob

[baz]

i have split this from another thread as 1 it had no relation to the question asked and 2 it is to good to lose in the wash

[jeff denton]

Thanks baz, sorry we did it again... It's impossible to keep our gears from turning even when a monkey wrench was thrown in. It is so incredible what wisdom and experience abounds here, a perfect example that anything can be done if you try. Everybody please keep in mind that I, myself, am truly an Opel Newbie, trying to have fun with a very unordinary little German car built thirty years ago...
Bob, I should have measured the head gasket thickness when I had it in hand. I know it is a pretty thick one as they go, but, even given that you like five thousandths of piston sticking up, I still don't know how much clearance the piston has with the head.

[soybean]

Ok, I'm coming on to this thread late because I didn't want to mess up the good ideas I was reading. I've got to ask a stupid question though. Jeff in post nos. 10 you said "After milling a head, the timing will be so screwed you have to "jump" the chain a tooth for nine degrees adjustment." My question is "jump" the chain which way? Thanks, I'm learning, slowly but surely. Jarrell

[jeff denton]

It's not a stupid question, Jarrell, it is good to be well advised and plan ahead before making any major and irreversible modification!
When the block is decked and /or the head milled, the camshaft is then located closer to the crankshaft, right? So the timing chain needs to be shorter on the side that is pulling on the upper gear, the side without the tensioner. Otherwise the timing is late. Way late in my case. With the hydraulic tensioner unit removed you can "work" the chain on the upper gear, it easily moves UP a notch at a time on the right side of the engine, that is retarding the timing so you have to do this quite a few times to go almost all the way around. I found at the time I built my engine that advancing it one tooth made the timing two degrees advanced from spec on the cam sheet which might be okay for street use (lower rpm) but not ideal for wide open racing (6500 rpm sustained) power. The alternative would be to have the timing seven degrees retarded, the stock timing marks put it there, way too much!
Using the "master link chain" is a huge help in all this, it makes it easy to remove the upper sprocket. I would never use a non master-linked chain again, believe me!
I think on my next engine, or next time I have the head off, I would grind a bit more chain clearance into the left side of the head, then I think you could
"work" the chain the other way, too, to make it simpler.

[RallyBob]

Originally Posted by jeff denton Bob, I should have measured the head gasket thickness when I had it in hand. I know it is a pretty thick one as they go, but, even given that you like five thousandths of piston sticking up, I still don't know how much clearance the piston has with the head.

Most gaskets are in the .039"-.041" thick range new. Compressed they're usually about .031"-.032". So that gives .026"-.027" of clearance with the piston .005" above deck. Even with forged (loose tolerance) pistons I haven't 'slapped' the head yet with a piston, but it does leave a cool combustion chamber carbon imprint on the piston top!

Bob

[nobody]

I've read this idea a number of times and it has been brought up I forget how many times. Jeff, Bob, Keith can you at least give a disclaimer that this is a bit over the top for the average Opeler? I know this is common on other motor types but with a CIH you have a different set of rules.

How about listing the indicators used and cost as well as the price to have the gear degreed and machined. Tell the whole story is all I ask. I bring it up so it can be followed and no motors are wasted thinking it's easy.

[RallyBob]

Originally Posted by nobody I've read this idea a number of times and it has been brought up I forget how many times. Jeff, Bob, Keith can you at least give a disclaimer that this is a bit over the top for the average Opeler? I know this is common on other motor types but with a CIH you have a different set of rules. How about listing the indicators used and cost as well as the price to have the gear degreed and machined. Tell the whole story is all I ask. I bring it up so it can be followed and no motors are wasted thinking it's easy.

Dave is correct in that you need to have a certain degree of ability, knowledge and tools to properly degree a camshaft.

>You need to have a cam card (assuming you're degreeing a performance cam) and you have to kow how to read it!
>You will need a magnetic-base dial indicator capable of traveling at least as far as your maximum valve lift.
>You will need a degree wheel, a pointer, and a crank hub adapter. (the latter two you need to make)
>You need some form of adjustable cam sprocket or offset crank keys. The bushing method I described is really very simply to do.... with nothing more than a drill press, some drill bits and ten minutes the cam sprocket is all set. The bushings themselves are easy to install, plus they are color-coded to indicate degrees. You still have to check to be sure however.....

Lastly, this subject is specifically posted in the high performance forum for a reason. It is not for everyone, otherwise it would be in the engine forums. Like building a header, porting a head or blueprinting your oil system, you need some background in automotive engine work and a good head on your shoulders.

But as an option it does exist, and for the racers in particular it is a necessity when the rules decree you must run stock pistons and you're trying to get every ounce of compression you can get out of your engine. Or in my case I use head milling in conjunction with small-domed pistons to get maximum compression with greater efficiency than a large-domed piston can offer due to flame front issues. So it's not for everyone....if you have trouble setting ignition timing or jetting a Weber then cam timing *might* be a bit of a stretch.

Bob

[nobody]

Thanks Bob

You can get a 1 inch travel indicator at any harbor frieght and a mag base for around 50 bucks.

Do a search on this site for "free degree wheel".

a good magnet sanded to a point makes a good pointer or if you've marked the front pully and checked it against TDC your set.

I'm not opposed to the idea but just wanted some truth in that it can be a drag to do and not to be taken lightly.

[soybean]

I understand the complications involved and am trying to learn what I need to take along to the machine shop, to advise them as to what has to be done. These people build engines for the circle track and drag racers in the area, so they have the necessary ability, knowledge and tools to properly build an engine. Maybe not all the intricacies involved for the CIH engine, which is why I was asking Jeff for more clarification. I am slowly but surely collecting parts, and knowledge, so that when the engine is taken to them, I will have what is needed to make a good running, performing, engine. I don't profess to understand all the things that have to be done. Building engines was never my forte, I know enough to get by, but not at the level Bob, Dave and a few others do. A lot that has been discussed is way over my head and out of my range. I do know you don't go to a Dentist for Brain surgery and vice versa. So you ask hopefully, intelligent questions. Besides I have 6 engines/transmissions on the floor, 2 of which are High Compression engines and 1 Gt to rebuild that needs a "good" engine. What has been posted is a good starting point to ask the machine shop " have you, and can you do this?" Gotta start somewhere. Way off the topic now so, I will be content to read. Thanks,
Jarrell

[jeff denton]

As for the average Opeler, I have no idea what his talents and skills are. I'm just a farm boy who had to fix everything that broke and break everything we fixed...
When you get good at that by the age of fourteen the next challenge is hot rodding and racing and somewhere along the way you become the neighborhood Mr. Fix It...
My race car was totally built in my backyard shop, an oversize one car garage. The only outside work was boring/decking the block and grinding the valves and seats.
Sure, I've invested well over fifty grand in tools and equipment in the last twenty five years, but I had to, I'm a mechanic. My race car could be built by someone with just a welder, a cutoff saw, a drill press, a sawzall, electric drill, and some hand tools and a couple common measuring tools like a vernier caliper and a dial indicator. This should not be unreachable by the average Opeler.
I'm just a gearhead, you see. I need to know how everything works so I can use the knowledge to make my stuff work. Everything can be improved, made better and stronger and faster!
I think anybody could do any of this if they want to, first step is study and learn. I read every word of every Hot Rod magazine printed during my teenage years, believe me, everything you need to know about building engines is covered there, even still! And all you need to know about doing it to an Opel is right here at gt.com, when you get stuck or confused, ask. You know I do!
Dave, the entire story IS here, and in the thread about using the flywheel as a degree wheel. It is that simple! There was no machining cost, the most impressive tools used were a cutoff saw, drill press, and dial indicator.
The cam instructions from Isky explain the basics and even show some tricks I didn't know, like using valve lash instead of a dial indicator which was how I did it first, it's in my post, the dial indicator was used to double check.

[nobody]

I understand completely, I was told by Smitty at age 16 my first high power Opel motor would probably explode because I went too far in too many directions. My only concern was a casual reference to milling the head or block and no disclaimer of what is involved to get it right again. Your right on the money of not knowing what others are capable of or what tools they have or if they know how to use them given a chance.

There are some 6000 readers here and you have to watch what advice you give. Not everybody looks to see if it's in a forum about extremes or just a general topic.

[kwilford]

I revised the thread title a bit to better reflect where the discussion has gone.

This has been VERY useful in discussing the effects of milling on cam timing, and has shown some really neat solutions. But most of the discussion (as has been pointed out) relates to significant milling, and really is only relevant to those few folks who are clever enough (or just plain brave) to tackle a seemingly complex problem as cam re-timing. But most folks just want to re-build their engines to enjoy as a daily driver. Sure, we all want more power, if it is free and easy, but few things in life are...

Now, without wading in TOO deep, I just want to make ONE point. Dave, back away from the keyboard

I have it from a VERY reliable source (and one that is impeccable in his reputation) that Opel CIH engines CAN tolerate a very slight re-surfacing of either the block deck or the head, WITHOUT adjusting the cam timing. But remember, the issue here is that ANY reduction in the distance between the centre-line of the crank to the cam WILL retard the cam timing. All the above discussion is fascinating if you have purposely (or cumulatively, or even accidentally!) milled the head or the block more than a "small" amount. I will leave the definition of "small" for a moment.

Here are a couple of facts (at least as they were presented to me):

1) each .025" of milling retards the cam timing about 2 degrees

2) A good rule of thumb is every 2 degrees of cam retard will move the power band up 500 rpm. The torque will be a bit 'softer' at low rpm, and cranking idle pressure will be lower.

3) It is pretty routine to surface the head and/and block during a re-build. Most engine builders/machinists want that piece of mind. Imagine building the engine, the owner pays to install it, then you find out it has a head gasket coolant 'seep' which they must now pay for (removal, machining, gaskets, and re-installation). It just makes sense....

4) A street engine will not notice much difference if the amount removed isn't more than 10 thou. This causes less than 1 degree change. The stock cam is already retarded 1 degree. You'll start to feel it at around 3-4 degrees unless it's a very modified engine. Stock engines benefit more from the compression increase than anything.

5) You asked if, on daily drivers, 1 or 2 degrees of cam retardation is really noticeable? If it is being milled less than .015" I don't even check the cam timing (although before milling I measure the block and head to see if it was previously milled...tolerance stack can be a bitch). But any milling intentionally done to increase compression warrants a cam timing check IMO

One of the issues that is pointed out above is the CUMULATIVE effects of milling. While the first 5 thou from each of the head and block shouldn't cause much grief, when the second machinist decides that another 20 thou of EACH the head and block is required, then cam timing is a REAL problem. And since the factory spec for the head and block height is NOT published (and will not be, due to some concerns about racing sanctioning bodies limiting what a poor, under-dog Opel racer can do to even run at the back of the pack), it is very difficult to know how much has already been removed. One obvious solution is to look at a known, un-milled head and block, and then use that as a reference. Or ask one of the more knowledgeable Opel engine re-builders, off-list, so that appropriate guidance can be given to the machine shop.

JM2CW and let the discussions ensue....

[jeff denton]

Excellent, Keith! You have done some serious research. I like your point about the little 1.9 needing every trick in the book thrown at it to keep up with the Fords at the racetrack, at least that's my take on it!
If there is no published deck height or head thickness and the racetrack tech inspectors would need to check a supposedly "untouched" engine to determine if one has been excessively cut, we racers therefore must ask that EVERY owner of 1.9 engines RADICALLY cut them down for more compression.
After considering Bob's spec on deck height, it seems that the most effective way to get the most compression (utilizing stock pistons) would be to deck the block, at least when abiding by rules such as ours that allow no more than .020" removed from the block OR the head, but not both. Am I thinking correctly?

[RallyBob]

Here's the Dealer Opel Team cam timing method, which Jeff recently 'rediscovered' on his own. Note there are two additional dowel holes, which allows for three total possible cam timing positions. I added the two other timing marks on the outer perimeter for easier identification. Hope this clears things up a bit for those who wanted to know a bit more about this method.

Bob

[kwilford]

OK, if I understand this, the original dowel hole gives stock (retarded one degree) cam timing. The other two gives either 6 degrees of advance or retardation (I assume actually 5 and 7 degrees respectively). I assume this is simply due to how the bolt holes line up to the cam gear teeth in each of the three positions. And I presume that this is "cam advance", versus "crank advance" (two degrees at the crank only gives one degree at the cam). Do you mark which cam mark is used for which dowel hole? I get confused enough with CIH cam timing without having two extraneous cam timing marks!

So, two questions, if I may.
1) Is it as simple as using a template from a cam face to locate the two new dowel holes (or just one, presuming you only want the advance or retard option)?
2) If a person has a slightly milled head and block (say, 25 thou total for 2 degrees of cam retard), and a somewhat HiPo engine (30 over flat top pistons, OGTS 0.430" lift Combination cam and hydraulic lifters, 38 DGAS, Sprint manifold) and this is a street engine, so low end torque is more important than high end power, is it a "good thing" to advance the cam timing the 6 degrees? Well, actually 3 degrees, since the cam started off one degree retarded, and the milling retarded it another two degrees.
3) Conversely, what kind of engine benefits from the "retard" option? One that is pretty much exclusively a rev-machine (such as Jeff's) and seldom sees less than 3000 rpm except to idle into the winner's circle? Jeff, did you say that you got better performance when you ADVANCED the cam timing?

Thanks Bob.

[RallyBob]

Originally Posted by kwilford OK, if I understand this, the original dowel hole gives stock (retarded one degree) cam timing.

Well, the original cams are ground one degree retarded. So theoretically an aftermarket cam ground 'straight up' with an OEM gear will be at '0'.

Do you mark which cam mark is used for which dowel hole? I get confused enough with CIH cam timing without having two extraneous cam timing marks!

I have a little sketch for my own use with the locations marked. But once in the engine I can tell if it's advanced or retarded just by looking at the cam. It's pretty easy once you know what to look for.

1) Is it as simple as using a template from a cam face to locate the two new dowel holes (or just one, presuming you only want the advance or retard option)?

The Dealer Opel Team manual suggests bolting two stock gears together back-to-back as a pattern. But there's a lot of slack in the bolt holes, so I made my own jig from a cut-off front snout from an old camshaft. I use it like a rotary table in a drill press, using countersunk-head bolts to hold the cam in place (they're self-centering).

2) If a person has a slightly milled head and block (say, 25 thou total for 2 degrees of cam retard), and a somewhat HiPo engine (30 over flat top pistons, OGTS 0.430" lift Combination cam and hydraulic lifters, 38 DGAS, Sprint manifold) and this is a street engine, so low end torque is more important than high end power, is it a "good thing" to advance the cam timing the 6 degrees? Well, actually 3 degrees, since the cam started off one degree retarded, and the milling retarded it another two degrees.

6 degrees is a lot of advance unless the engine is very modified. But for example, C & R used to sell all their cams with 3 degrees of advance. This was partially to compensate for incidental head and block milling during a rebuild, partially to compensate for a stretched timing chain, and partially to give a bit more bottom-end torque.

However an advanced cam can really make a 'hot' cam really torquey for the street. I ran a 6 degree bushing (actually measured out to 5.5 degrees) on one street 2.0 litre and after head milling was figured in it had 3.5 degrees of advance. Well, this 242 degree cam had torque up the wazzoo.....crack the throttle at 1500 and it pulled clean even with the bored out 38 DGAS and the 3/4" plenum spacer, but from 2500-6500 it was pretty vicious for a 2.0 litre engine. I attribute the characteristics of the engine not to one single thing, but to the entire package. The headwork, the compression, the cam choice, the lobe separation angle, the cam degreeing, the carburetor, the spacer, the ignition timing, etc. Sometimes the sum of the parts is better than the parts, if they are chosen wisely. So cam timing is not an end-all, but it can make a nice cam that much nicer, or it can turn a nice cam into a piece of s**t in regards to power and driveability.

3) Conversely, what kind of engine benefits from the "retard" option? One that is pretty much exclusively a rev-machine (such as Jeff's) and seldom sees less than 3000 rpm except to idle into the winner's circle? Jeff, did you say that you got better performance when you ADVANCED the cam timing?

This option will probably never be used for most people. Ya really gotta be willing to give up a lot of low end power in exchange for top end. That said, if your cam on your racecar is borderline 'too small', then retarding it a degree or two might delay the purchase of a bigger cam by extending the rpm range a bit.

HTH,
Bob

[jeff denton]

My upper sprocket looked just like the one Bob shows. It was drilled using a bit of an old cam cut off as a template. It is important to note that once you are using a degree wheel (or the flywheel made into one as I did) that stock Opel timing marks are not used, forget them, they are gonna confuse you if they aren't already! The only thing that matters at this point is the crankshaft degrees from true top dead center that the cam opens the intake valve .020" in the case of my ISKY cam and its spec sheet. So there are no relevant upper sprocket marks to be concerned with, do you follow me? Forget marks.
I wasn't trying to come up with a specific amount of change, couldn't say that my mod would change it one degree. I knew when I traced the sprocket on paper that there were three different settings available, to find the right one would be trial and error. I was lucky, I liked the difference on the first try and that was it!
A possible additional reason my timing was way retarded at first was that I was using an old timing chain. Hey, we were on a budget! I had only intended to get some test laps done before the track closed for the winter... This mod required the new chain with master link, even I can't figure out how to get the sprocket out any other way short of pulling the head.
As stated before, my engine sounds different now. It idles kind of sometimes at 1200-1500, you rarely can fire it up and turn your back on it. I can't really feel any low end torque difference, it only putt-putts around the pits in first gear, then when we get lined up and motioned to take the track it's a drag race up to third gear, we back off to about 4000 rpm to get lined up bumper to bumper two cars wide and anticipate a green flag as we come out of turn four. Then it's wide open throttle, let up a bit just before the apex of turn one, and hammer down again to accellerate through turn two. A very different driving style, let me tell you! It is a rush. I'm learning to be very aware of anything that appears in my peripheral vision, it is the only indication you get that you better hold your line, no lane changing! There is no time to actually look, and we are not allowed to have rear view mirrors...
So to answer the question, no, I don't think I noticed any difference, I think you would really need a dyno to see it. Running the retarded setting is, as far as I know, just how you do it in a high rpm (who needs low end) racing engine. But the first time I ran the car with this retarded timing I timed in third fastest in the field! Wow, freaked everybody out. We did also have the Sportwagon spring in, no doubt that helped...
Keith, get down here and check it out, come on you're just a few hours away!
You are welcome to be on the pit crew, I think you could handle setting tire pressures and reading tire temps!! Or should you prefer to participate in the beer drinking festivities you may enjoy the grandstand side of the track, join in in on the ever-growing #00 cheering section!
Let me comment on Bob's thoughts about a cam being "too much" or "not enough". Hot Rod mag showed a brilliant way to find out. Requires a dyno, yes, but they are getting plentiful all over America. They say to get a baseline reading with the cam set at minimum lash, and then a reading with the lifters set at maximum lash. Which made more power? If it was better with minimum lash, you need more cam. If it liked maximum lash, you have too much cam.

[davegt27]

just get one of these

http://www.needforspeed.co.uk/pages/...ehicle=OPMAN01


davegt27

[jeff denton]

That would be ideal, Dave. It might not be allowed, may not pass inspection as being factory stock, could fall into the rule not allowing "aftermarket or motorsports parts" as they say in our rulebook. In our class the only thing not required to be stock is the camshaft itself, the carburetor, and the exhaust manifold IF it is a tubular header. The ignition can be fudged a bit, they had no problem with my Motorola electronic. Other goodies are allowed if home made and they resemble stock.

[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

[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.

[jeff denton]

I wish I had a used head gasket I could measure, or at least lay on a 1.9 block to see how close it comes to the bore. 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.

[davegt27]

Sorry Jeff there is know way i can know the rules that you have in your racing class

I was directing my post to the original poster GTJIM in an effort to help out.

i just dug up my old Receipt from Kent Cams the "Opel/Vauxhall Vernier cost
59 pounds p.n. S14 that was in 2000

I ordered a Piper ADJ Vernier just to see the difference the piper was not as nice as the Kent cams one but what was cool is i ordered the Vernier and i got the whole kit

ADJ cam sprocket (Vernier) timing chain and the lower gear. what a deal i thought

in this day and age i consider an ADJ Vernier a must
Maybe if enough people get together they can try for a group buy?

The other thing I would like to add is -- People have been milling Opel Heads and blocks for years and years (just ask rally Bob what's the Max he has milled off an Opel Head) don't even worry about it.

i have a Mrgasket offset bushed upper cam gear laying around but i would get the piper or Kent cams setup

(click page 2)
http://go.mrgasket.com/ProductsListB...2&selection=10

cam bushing kit Chevy
This 4 bushing kit can be used to advance the cam for more low end torque and midrange horse power. They can also reduce excessive low end torque and increase top end horse power by retarding the cam. Fits Chevrolet 283-454 cu.in,all Chrysler B-Block. 1,3,5,7 degrees plus 0 degrees.
Part Number: 85B

HTH
Davegt27