Slant build / pistons

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vitamindart

vitamindart

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ok, so I'm finally going to build a slant. Have wanted to and started once before but, life got in the way. I have a ported head with oversized valves, performance cam( don't remember the spec's ),hurricane intake, header. Now the questions begin. I have a later cast crank block ( milled .120 ) with stock pistons and new rings in old bores with a quick hone job. The ring gaps are way over the standard .004 per inch of bore. Do I tear it apart, bore it and run it? What pistons do I use? Is it worth buying th longer rods and forged pistons? Or do I look for a short block? Would really like some pep out of it. It's going to be my summer cruiser and might see a supercharger down the road ( 5-10 psi max ).
 
The cast crank is good......light, too. Make sure you have the right rods, as cast crank rods are different, I believe. KB makes a nice hyper piston that fits the 2.2 4 cylinder that will work in the slant with the 198 length rods. again, make sure the rods used will work with that cast crank.
 
I think the cast crank rods are a little harder to find. I have seen aftermarket ones for the forged crank in a few places. Just not the cast.
 
You need to be carefull, if you plan on using the 198 size long rods. With .120 milled off the deck, they may not work. Measure before spending money. The factory 198 rods were only for the forged crank, but K-1 and Molner had aftermarket rods in the 198 length for both the forged and cast cranks. The 198 length rod (7.005) cannot be used with a stock type piston, with a 225 crank, as the rod is .305 longer then the 225 rod (6.700), and the piston will poke out the top of the block. With .120 milled off the deck, you will probably need a custom piston (not the Wiseco PT112A), if you use the 7.005 rod.
 
Charlie, any idea on how crazy my compression would be with that blocked decked so much already? the head is an earlier ( has the spark plug tubes ) with 1.70 & 1.44 valves. it only was milled enough to clean it up .005ish. I realize with out cc'ing the head and getting actual measurement of the piston @tdc its just a guess.
just don't want to be a race gas trailer queen. premium pump would be ok.

sorry, just read your first post. was really hoping to avoid a custom piston if possible. maybe I am better off rebuilding with a different block.
 
There are two versions of the cast crank engine.
The first generation uses narrower rod and main journals than the forged crank, but the crank itself is the same configuration and weight as the forged.
The later one , from 81-up uses a crank that is between 20 and 22 pounds lighter. The blocks used on these engines are cast thin, and are approximately 16 pounds lighter.
In my opinion, this is the golden child of all Slant Six engines.
These can be quickly identified by a 5/16s distributor hold down bolt hole vs the earlier 1/4 inch.
The rods are interchangeable between all cast crank engines.
Going with a longer rod is the exact opposite thing to do if you are looking for any low end torque. The stock 225 rod is a half inch too long already.
I would keep the pistons you already have, and just source out a set of .010 over rings, then file to fit.
 
What's wrong with using that block, 225 rods (easier to get and cheaper), and a stock configuration piston? Use your head. Might have to notch whatever piston you use. That would depend on the cam. You would mostllikely be near about 10 -1 CR. Would have to measure to get a closer estimate. If not enough, mill the head more, if too much, use a thicker head gasket.
 
Nothing wrong with it, just wasn't finding any aftermarket pistons. Just one style replacements.
Wasn't sure that would be strong enough or get me the little extra pep I'm after.
Guess I will measure the bore, see how much taper there is and decide if I just need rings or a reborn and pistons. Probably the rebore
and pistons as I would like this rebuild to last
 
vitamindart said:
Nothing wrong with it, just wasn't finding any aftermarket pistons. Just one style replacements.
Wasn't sure that would be strong enough or get me the little extra pep I'm after.
Guess I will measure the bore, see how much taper there is and decide if I just need rings or a reborn and pistons. Probably the rebore
and pistons as I would like this rebuild to last
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Remember, the slant was designed in the late 50's,, the internal recriprocating components are plenty tough and will take a doubling of the stock HP without issue
newer pistons such as the Wiseco and KB 2.2 L pistons offer new technology such as shorter skirts and thin metric piston rings,, and there is some advantage there, but unless you either got a smoking deal on the new technology parts or are planning an 'all out' slant six racing motor,, you will never measure the difference in the real world.
Along with Charrlie I do some slant six drag racing,, excluding the folks that race slants at the very highest level,, I don't remember anyone loosing a rod or piston without it being due to a secondary lube or timing issue,, if you want to talk about head gaskets,, that is another subject.
 
As said above, you don't really need special pistons, in a slant, except for all out racing. I have used stock pistons in all my engine, except for my 170 turbo. That one had TRW forged pistons, and was built in 1979. And I did hurt some of them, due to my "tuneup" not being correct. Back then there was not much info on turbcharging available, and I was having trouble staying out of detonation. My 66 Cuda with a 170 and 66 Valiant with a 225 Have both been in the low 8's in the 1/8 and the Cuda 12.90 in the 1/4 mile. I have sprayed as high as 225 shot of nitrous (risky) on the 170. usually spray about 150-175 shot. Both cars have bone stock short blocks (except for cam), with std bore and stock used pistons.
 
Ok, I pulled the head today and measured the bores. 3.401 to 3.404 granted I was measuring with a caliper. So what kind of gaps do I want? The standard .004 per inch? Any suggestions on rings? Not seeing any .010 rings only .020.
Or am I being overly worried about the larger ring gaps?
 
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vitamindart said:
Can I file the .020 rings to work? Or is that too much?
Click to expand...
Are you asking about using .020 os rings on standard pistons going into standard size bores with some wear in the bore? You could file the rings to get the end gaps about right, but to manufacture a piston ring so it has a .020 larger diameter, the ring is processed on a larger mandrel, that results in a larger ring with a ring tension constant with a standard sized ring. By filing a .020 os ring to fit a standard sized bore, the end gap could be in spec but the ring tension ( pressure on the bore od) will be high,, will it be a disaster, probably not, will it be optimal, certainly not.
 
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You should also check the clearance between piston skirt and bore. If it is not in spec, you can get "piston slap". Ideally, a newly machined cylinder is honed to match each piston. But, you are dealing with honing of a worn cylinder. As I understand, the biggest problem is that the cylinder has worn oblong, so you will not get good sealing, regardless. People have long thought the main leak is thru the ring gap, but I read a recent article (Engine Builders or such) which said that has been found to be not true. Indeed, a current recommendation is to have more end gap in a new build since the biggest concern is the ring ends touching if they get real hot and jamming in the bore. In the same vein, they claim the expensive "gap-less" rings (overlap at the gap) give minimal benefit and are a waste of money.
 
thanks
my68, that's what was thinking. .020 over rings were for a .020 bore and would have higher tension.

bill, I think I read the same or a similar article last night. so I believe I will just run what I have and see what happens.
the bores are not badly worn. the larger than normal gaps just had me nervous. I cant remember the actual numbers since
it has been a few years since this was assembled.
hopefully I will have good news for everyone in the next few weeks when I fire this thing up!
thanks to everyone who helped.
 
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