I picked up an A12 engine and the cylinder walls have a slight rust near the tops. I plan on honing out the walls but how much would be too much?

Hi Dave, for rusty bores, use steel wool and naval jelly to remove the rust If the bore then measures in-spec, go ahead and use it. If it doesn't clean up all the rust, go ahead a hone it

Use a flex-hone (ball-type hone) instead of a stone type hone. The re-check the bore and if it is still in spec you are good to go. If after honing it is now too large, you can either use a different block or rebore it for larger pistons. The advantage of overbore is that you get more HP than most other mods, for example adding compression. You can also upgrade to flat-top pistons at the same time for even more HP increase

If the flex hone doesn't clean it up use a regular stone type hone, The stone hone will remove more of the wall. This is a traditional hone, and usually this is fine for an overhaul, but it can be overdone and enlarge the cylinder too much, so just do it enough to clean it up then re-measure

For the newbies, honing mean finishing the cylinder walls to receive new rings:
* After a cylinder bore, to fine-smooth the walls out
or
* At an overhaul, to re-smooth the wall to correct minor issues -- for example to clean up very light rust. It is not designed to repair damaged walls. If there is pitting then a rebore is needed

As always when rebuilding, first check the cylinder for trueness and straightness. If out-of-spec it will need to be re-bored if any measurement is larger than spec

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Funny there has been over the years many a heated discussion on the Society of Automotive Engineers about whether or not to hone a used cylinder when re ringing, The Jury is still out as they post up various real world oil consumption and power figures for both methods.

I work on the theory that if there is a wear lip that can break new rings do the rebore and plateau hone method to bring it back to the factory specifications and therefore only use a bottle brush flex hone for the plateau finish after a run through the sunnen machine to hone to size that gives increased lifespan over conventional honing

Hi If a rebore would require a new set of pistons what oversizes are available for the A12 engine? and the cost for an oversize set?

Which A12 the original 71-73 1200 1171cc motor or the later A12A installed in some 79-82 210s?

Rockauto still has some of both in stock .20 over is available. They run about $110 a set.