Jkdmag,
Pat is correct about the dartons. I would certainly go this route rather than machining away to a slim wall to fit a dry sleeve.
Dartons are centrifugally cast ductile iron and they certainly know what they are at when it comes to making them.
They have a VERY large selection, but if you cant find one to suit, you can design your own on the site.
Be warned, if you are machining out the deck and all, get_a_good_machinist, otherwise your beautiful sleeves will be wasted.
I have no idea how may cylinders you've got, but if its just one, you could easily get a sleeve with a wide top flange and bore this flange for your coolant routes. Your original routes will have got machined away with the large rebate required for the top lip of sleeve.
Or, if you have banks, you can machine in a pocket to take a frame with coolant holes that darton also do that locates down over the top of the wet sleeves to hold them all in place. This locates both around the sleeves, and into an accurately cut pocket in your original deck.
As for dry sleeving, and the min you need for support, this is not as easy done as you think due to the water jacket sand core shifting at time of pouring.
Ive cut up a lot of engines to study casting details, and every one of them has shown some signs of core shift.
Sometimes the core will shift to your favour, ie, forward, leaving a ticker portion of bore where the most trust force support is needed during ignition. But, with other blocks, the core can shift to the back, or sides leaving you with thinner portions where you least want them.
Alloy blocks do seem to display less water jacket shift. Im guessing because of more modern foundry tech, and the alloy having less inertia than cast iron, but, it is still present and different in all blocks - even ones with the same p/ns.
Since as Pat mentioned, its at the top you need the most support boring out the existing to fit a larger dry sleeve may not seem a problem. But, by boring, and if the cores have shifted, you may run into very thin wall sections as you go down.
In cast Iron Id like to see 3mm of metal min.
In alloy, 4.5mm.
Obviously, you have no way of telling how much you have left, but chopping up a block the same as it will give you an approx Idea.
Be warned, that you may hit chaplets in the adjacent bore walls also when you go thin. These chaplets are used to stabilise the sand cores before the metal is poured. Exposing them can lead to very unsightly areas that bad things can originate from. Be it cracks, or water/coolant ingress to gasket interface.
Another time, I cut up a honda block that had been dry sleeved. The wall was very thin in one spot and there also had been some casting porosity there. The porosity would normally have been fine, and watertight, but since the tight metal had been machined away behind it, water had crept in, and entered the space between dry sleeve, and original bore. The water found its way to the sump, and the engine was binned. How it did creep between them I dont know, perhaps the sleeve moved a little with the extra thin support.
Obviously, both the casting guy, and later, the guy that bored the engine to fit the sleeves were not at fault. But, the machining guy could have been more careful, a simple check by filling the water jacket with penetrating oil or something thin would have showed up the porosity.
Im probably going a bit too far with this, but I feel its all worth a mention for the above reasons.
If I was you, Id wet sleeve it. They are not too bad money-wise either, 90euro will get you any one you want. I never saw the point in getting it all jigged up to fit a thin dry sleeve, when, with a small bit more work, you could hog it all out and fit a proper sleeve that the devil could not destroy.
See attached Image for both bore wall thickness deviation and chaplet position between bores. Granted, its cast Iron, but Ive seen the same with Al blocks too. Sometimes the only way to learn is to cut stuff up and have a proper look.
Brian,
ps, Im in no way connected to Darton, but they make amazing sleeves.