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

[GTJIM]

THe first thing done with most other motors is to hack and slash at the cylinder block/head surfaces to ensure flatness. After a couple of years discussion with "Nobody" in particular I am utterly convinced that this is the VERY LAST thing to contemplate on a CIH Opel motor. The unique positioning of the camshaft just ensures that ANY removal of metal on these surfaces in the Opel CIH series of motors results in serious disruption of the cam timing - unless an adjustable cam sprocket (expensive!) or offset cam dowel bush (tricky!) is used to re-establish correct cam to crank timing.
Also, if either of these surfaces is not flat the block or the head have been seriously overheated at some time so it is likely that the components you are trying to fix are seriously compromised - get others that are "in spec" or risk the ones you have cracking in service. Horrible but true!

As far as using anything but an Opel CIH motor in your first GT - after careful consideration, backed with YEARS of engine swapping experience with other cars - DON'T DO IT! Far better to get a good running CIH motor in there and running so that you can fully enjoy your GT. Then carefully plan and look into an engine swap at a later date - while enjoying your GT!
Mine has sat in the shed with the bodywork all complete for a couple of years while I have "played around" with various (expensive!) motor options. I am rapidly reaching the conclusion that a STANDARD 1.9 lo-comp motor would be the best bet to getting it back on the road. Who has any idea what is under the hood - when it is closed!

Rant OFF!

[spdkilz02]

I agree with everyone, I was going to do an engine swap and after talking to everyone they have convinced me to keep the 1.9 and rebuild it. Im just going to bore it out to a 2.0 and put new internals. I also hope to find a good 5-spd tranny to replace my leaking 4 spd. Then I plan on making a header and whole new exhaust system. I already have the brakes and suspension done to the car. I always believed that those are the first things to do because who wants a car that it fast when you cant stop it?

I know when I got my GT I was a Kid, only 15 and thought that I knew it all and could do anything. Boy did I learn quick about that, I'm just glad that my dad owns his own shop and I have the ablity to use his shop to do all the repairs.

Adam

[jordan]

Couldn't a thick copper head gasket be made to compensate for head or block milling?

[greensmurf20]

they are referred to as "shimstocks" in these part of the woods. you can use them INSTEAD of headgaskets in some cases to bump up the compression, or use them in conjunction with the headgasket to compensate for material removed by milling and decking the block/head surfaces.

[GTJIM]

Originally Posted by jordan Couldn't a thick copper head gasket be made to compensate for head or block milling?

That just removes the proper head face to piston top distance and reduces the "squish" which leads to detonation .....
Also copper head gaskets tend to be harder to seal on high mileage road motors plus their cost is prohibitive as they are custom made items....

[jeff denton]

The cam timing problem created by milling the head is, as I found out, for real. The fix for it, as I found out, after doing a little tinkering and brain straining, is so incredibly simple it just obviously evades even the intelligent enthusiasts. It doesn't take ANY custom parts. You don't even need a degree wheel any more. I described all this recently, finished it just last week. Yes, it goes a little deeper into engine building than most ever thought of, but we've discussed the importance of knowing what your valve timing is and not trusting any so called "timing marks" to get it right.

[GTJIM]

Originally Posted by jeff denton The cam timing problem created by milling the head is, as I found out, for real. The fix for it, as I found out, after doing a little tinkering and brain straining, is so incredibly simple it just obviously evades even the intelligent enthusiasts. It doesn't take ANY custom parts. You don't even need a degree wheel any more. I described all this recently, finished it just last week. Yes, it goes a little deeper into engine building than most ever thought of, but we've discussed the importance of knowing what your valve timing is and not trusting any so called "timing marks" to get it right.

Went back and reviewed your cam timing thread Jeff - had not picked up on the drilling of two extra dowel holes in the cam drive sprocket with the sprocket rotated on to the next bolt hole line up.
As you say "Incredibly simple"!

[jeff denton]

Yeah, see what I mean? I stumbled on to it after I had traced the upper gear on a piece of paper and noticed what happened to the position of the teeth when I rotated the gear to the next alignment of the bolt holes.
The tool made out of the old cam is a must for drilling the new holes, but they should be abundant. The biggest problem would be how somebody would time the engine later if he didn't know how it had been done previously, as none of the timing marks would be usable...

[jordan]

is this just a cam sproket with different holes drilled in it?

[jeff denton]

Yes, an ordinary upper sprocket with a couple extra tiny holes drilled so that the index pin sticking out of the cam will go into the sprocket in either the correct location, or two other locations wherever the bolts for the sprocket line up with the bolt holes in the cam. It just happens that the teeth are moved a couple of degrees different with each location. After milling a head the timing will be so screwed you have to "jump" the chain a tooth for nine degrees adjustment, then my little trick fine tunes a couple more degrees of adjustment. Well, it sure worked slick on Speedway GT, anyhow. I am amazed at how much difference four degrees cam timing makes.
Basically, the message in all of this is, when building a modified engine, even just putting in a different cam, timing marks should not be taken literally. You MUST properly degree-in your timing.

[RallyBob]

Jeff, you've 'stumbled' across a technique that was actually used and documented in the early '70's in the Opel 'Dealer Opel Team' rally car preparation manual. It shows drilling two alternate dowel holes and describes the changes possible (either 6 degrees advanced or 6 degrees retarded) by using the alternate dowel holes. It is ideal for heavily milled heads. One particular engine I built has so much milled from the head the cam was retarded 7 degrees! So I set it with 6 degrees advance on the upper gear and let it run at 1 degree retarded, which ironically is what a stock Opel cam is ground to.

Bob

[GTJIM]

This could be "finessed" even more by tweaking the position of the new dowel holes and slotting the three mounting screw holes slightly!
Or even driling the holes out to fit an offset dowel button to give almost infinite variation.
..... wait a minute! The new owner of a motor "finessed" like this would probably make disparaging remarks about the "Previous Owner" Unless the actual cam advance/retard was stamped on the sprocket by the holes......

And Ihave just paid out GBP25 for a Kent Vernier Cam Sprocket too.

[jeff denton]

Yes, in the process of solving my problem I had oblonged the bolt holes in a spare sprocket and drilled the pin hole out to 5/16, thinking I would install the gear, finesse the timing, and then drill another pin hole through the sprocket and into the cam to lock it. Then realized there was this simpler way.
Darn, Bob, here I thought I really found something only to find out it's old hat. :o

[Betta Carotene]

Does anyone got any pictures of this? Im understanding what you are saying but a visual would be better.

[RallyBob]

Originally Posted by Betta Carotene Does anyone got any pictures of this? Im understanding what you are saying but a visual would be better.

I'm working on taking pics of all the options. Redrilled stock gear, offset-bushing modified stock gear, Kent adjustable gear (shown here http://www.opelgt.com/forums/showpos...8&postcount=19 ), Piper adjustable gear, and TG Motor adjustable gear (I don't own one but can get a pic). All of them have their ups/downs, but they are capable of returning the cam timing to stock if excess material is milled from the head and/or block. When the milling gets very heavy it's a good idea to shim out the hydraulic tensioner or your timing chain will have too much slack as well. Like this:http://www.opelgt.com/forums/showpos...8&postcount=48 and this http://www.opelgt.com/forums/showpos...9&postcount=49


I have used these methods and it worked perfectly on a circle track Opel that had .015" milled from the block and .105" milled from the head. That's almost 1/8"!

[GTJIM]

As "Stroker" McGurk replied when asked how many "thous" he had removed from his Flathead V8 heads: "Thous be F----d! I took off an 1/8th of an inch!"

You guys watching this exchange will now be seeing all the ramifications of hacking & slashing at Opel blocks and/or cylinder heads - OK for cunning old sods like Bob, Jeff and my humble self BUT if you can get away with out touching those surfaces then you will not have to sort out all these cunning methods to put things back where they should be in the first place!
Sometimes it has to be done when engines are modified away from 'factory stock' but if you can avoid going into this mine field then do!

[nobody]

Jim you sound like somebody I know. . I truly like the idea of the multiposition front gear however the issues I see right off are the extra chain length and the idea of trying to get a X degree fix based on what some machinist has decided to remove. The math alone is staggering. Then your talking indicate in a round hole VS a round gear to be able to accurately coordinate rotate it to + or - what the math determined to bring it back should be. Me personally I wouldn't trust it unless I saw the numbers off a CMM to check it all. Head block and cam gear based against a known stock. Ok in just setup and checking it to be right, that cost is higher than another block and head. You haven't machined it yet so brace yourself. Now you need to be able to drill and ream on a rotary axis with a fairly tight tollerance. Ok raise your hand if this all sounds easy or cheap. Keep in mind a 1/16 of an inch is equall to more degrees of cam timing than it takes to screw it up or not fix it but make it worse. I've bit my tongue on it but even the stock flywheel has a few degrees of play. How many motor builders indicate in the flywheel position to be absolutely true to TDC?

[RallyBob]

Originally Posted by nobody How many motor builders indicate in the flywheel position to be absolutely true to TDC?

Very true, I've seen some flywheels off as much as 7.5 degrees. I always index off the front pulley/timing cover after checking #1 piston exact TDC with a dial indicator at the center of the piston. Even piston rock at the edge of the piston will throw you off a degree a two!

Bob

[nobody]

Bob, one of these days we need to actually meet, sit down and discuss quantum physics or just Newtons laws of motion as they pertain to short cars. Maybe you can explain to me why a 300 horse wagon with fake wood siding has had me so captivated.

[RallyBob]

Originally Posted by nobody Bob, one of these days we need to actually meet, sit down and discuss quantum physics or just Newtons laws of motion as they pertain to short cars. Maybe you can explain to me why a 300 horse wagon with fake wood siding has had me so captivated.

I'll bring the keg....

Hey if you ever want that wood siding to be real, I still have access to my old man's wood shop. Maybe some walnut veneer with ash surround-trim?

Wagons with killer engines ARE pretty cool. It's so unsuspecting....

[RallyBob]

This is the DIY method of allowing cam timing to be dialed in. Far cheaper than an adjustable 'vernier' cam gear from overseas. It entails either enlarging the three bolt mounting holes (I drilled mine to .400") or slotting those mounting holes, buying a set of Chevy offset bushings (About $15 for a set of 5), and drilling a hole the diameter of the bushing from the backside of the gear (but not all the way through the gear).

'All' that remains it to actually dial in the cam timing and choose your bushing offset.

[Gary]