Hi Folks,

I will be rebuilding my /6 this winter. I have noticed that Summit has pistons for only about $10 each.

My question: What are the odds that a 130k mile 225 (1968) will need an overbore to clean up & round out the cylinder walls?

For the price, it seems like I should just as well plan on a .40 or .60 overbore, and order the pistons with the kit, even before I remove the engine...

-Mac

well if it was me and i was gonna tear the motor apart anyways why not add some extra boring to your slant. I was gonna bore my slant and build her up but my car was tourched, the motor is good but why build it if i have no car

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Cuda Progress
The dart as it sits now

If it is already straight and round don't touch it. The slant is a very stout and solid block that doesn't have some of the problems of other engines. The only reason you should ever bore any engine is to correct a problem since the displacement gain of a .010 overbore is tiny. I don't remember the exact gain on the 225 but it is something like 4 cid which hardly makes it worthwhile plus it removes metal that might be needed at later date for a real reason like a broken ring scratches a wall.

At 130k, personally I would bore it if I had the time and money, but it really depends on what it's like now. Is the compression good and consistent between cylinders? If you want the motor to take some abuse, I would also suggest getting the rotating assembly balanced.

0.060" is a fairly modest overbore on the Slant and gives you 233 cubes total. Not a huge gain, but it doesn't really hurt anything anyway. 0.100" and 0.130" overbores are pretty common with race motors.

Lou

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Home of Slant6-powered fun machines since 1988

I'm with McNoople... if it doesn't need it I wouldn't do it. The displacement gains are minimal and an overbored engine is not as strong as one with stock bores. If boring is required to clean up cylinder problems I would do the minimum necessary to correct the issues. There are much larger performance gains to be had with even modest head work than you'll ever see form the 7 or so cubic inches you'll gain by overboring.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

If it has 130k on it then it will undoubtedly have a serious ring ridge at the top of the bores not to mention all of the bearing wear and oil gunk clogging the oil passages. It would be a waste not to bore it 0.040" while it's apart. Strip it all the way and do the Doctor's block prep to the oil galleries then have it decked and hot tanked. Go back up with new bearings and a fresh paint job and you'll have a better than factory fresh block to put a re-worked head down on top of.

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"Former Owner" of '65 Barracuda, 225, Auto, MP 2bbl intake, MP cam, Dutra Duals. Presently Moparless.

That really depends on how well it was cared for over the years. You'll have to assess it when you get it apart. I've seen 200k mile Mopars that didn't have a ridge and had visible hone marks, and I've seen 100k mile engines that were worn so bad that rings were breaking from all the taper in the block.

I'm not a big fan of jumping to a huge overbore, either. The minimum overbore for which a) you can get the pistons and rings you want, and b) that will clean up the cylinders is all you need. If you jump straight to .060 over, you've thrown away one if not two whole "lives" out of the block (iow, you might have rebuilt it once at .030 and again at .040 before going to .060)


My rule of thumb is that if the ridge at the top of the cylinder can "catch" a fingernail as you drag your nail upward on the cylinder wall, then it should be bored and not just honed because there's going to be too much taper in the cylinder. Measuring the block is the best way, but the "fingernail" test comes in handy when you're looking over a bunch of blocks without measuring tools.

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I had a 225 in a Valiant, more years ago that I care to count, that had about 130K on it when I did a basic ring and bearing job on it; I went back together with everything standard and the original pistons. I drove it another 100K hard miles after that. I traded it in and got $50.00 for the trade and have regretted it every time I have thought about it since.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Hm... I was thinking that since I'm putting in the oversize SI valves, that going 40 over would help minimize shrouding. Assuming the bores are currently good, will this be a waste of my money?

-Chris

I don't think .020" (1/2 of the .040 overbore) will make much of a difference for shrouding..............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes