65 Dart 273 Engine Rebuild

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I took the new pistons out to L&R engines so they could hone the cylinders to the final bore. They do that with a torque plate to simulate the strain caused by the cylinder heads torqued down.

The next day, I went back out to cc the dome volume of the pistons. I put a piston in a bore and adjusted it so that it was 1/2" down, measured from the lowest part of the top of the piston. I smeared a tiny bit of wheel bearing grease around the perimeter to prevent the liquid from leaking out between the piston and cylinder wall. Then I cc'd the volume above the piston, which measured 74.5 cc's.

A cylinder with a diameter of 3.655" and a height of .5" should have a volume of 5.25 cubic inches or 85.97 cc's.

The difference, 11.47 cc's is the dome volume of the Kanter pistons. Given the accuracy of the process, I'd say the dome volume is approximately 11.5 cc's.

Since that's bigger than I was estimating, I told L&R to take a minimum cut to square up the block. That should be about .005" leaving a deck height of 9.605"

Once the engine is assembled, we'll measure exactly where the pistons set relative to the deck, and then decide how much to mill the heads.
 

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I want to have the Crankshaft machined to accept the larger snout of a later torque converter. I've spent some time Googling to find the diameter, which I believe to be a 1.815" bore to accept the 1.810" snout. Can anyone confirm this number?

Also, just in case the crank isn't bored for a manual transmission, what's that diameter?
 
65DartGTConv said:
I want to have the Crankshaft machined to accept the larger snout of a later torque converter. I've spent some time Googling to find the diameter, which I believe to be a 1.815" bore to accept the 1.810" snout. Can anyone confirm this number?

Also, just in case the crank isn't bored for a manual transmission, what's that diameter?
Click to expand...

Stay tuned for about an hour... :D

I'll check one of my 340 Cranks for those measurements when I get to the shop this morning.
 
1.800" is the snout measurement I got from my 71 340 crank (originally in a 340/727 car, later swapped for a 4-Speed) with a digital micrometer for the Snout/Hub.

1-3/4" is the depth for a crank that's drilled to accept the input shaft of a 4-Speed
 
273 Rule. Cant wait to here that thing run. I did a compression test on my 273 after it was broke in. 155 psi in all cylinders. I'm curious what yours will be.
 
John! Your work is outstanding! I hope that I can listen to it some day in person or hear it on Youtube. Awesome build!
 
FYI youl will love the kanter slugs! got my 273 runnen sunday! ( post a few pick shortly) its very torquey for a small motor i also slapped on some crane iron 1.6 iron rockers on top of the e-4 cam aswell & put in 318 thin wrist pins to take off 40gms per piston/pin combo & reballenced it. She pulls rite to 5800-6000 ish & runs very strong no ping on 91 eather:cheers:
 
Sounds like it's a runner. Great tip on the 318 wrist pins. tmm
 
After the block was assembled I went out to L&R to measure where the pistons ended up relative to the deck. Most of the pistons were about where we expected them to be based on previous deck height and piston measurements.

The lowest pistons were .059" in the hole, but the highest piston was only .048" in the hole. A difference in piston height of .011" causes a quarter point difference in compression ratio!

I asked Derrick to swap around the pistons and rods to try to improve the situation. After 2.5 hours of musical pistons, he got everything to within .004" of one another.

Part of the problem is that the tops of the Rebuilder's Choice pistons from Kanter are as-cast, instead of machined. Advantage Egge.

Based on these measurements I told Derrick to make a cleanup cut on the smaller head and then mill the larger head to match. I'm expecting a chamber volume of 62cc's.
 

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This weekend I painted the Exhaust Manifolds with POR15 Manifold Gray.

First I had them media blasted professionally. They're large, and my air is not all that clean or dry so it was definitely worth the cost to have them done.

Then I sprayed them with the POR15 product. I bought a pint, and used maybe 1/3 of the can. It's really thick paint and you're only supposed to thin it with their thinner which I did not buy. So I cranked up the pressure to my $10 Harbor Freight gun and it sprayed OK. I didn't take the gun apart until the next day and there were quite a few chunks that I had to dig out. I don't take that gun apart after every use, so I can't say for sure if it was this paint that made the mess. But my advice would be to clean your gun really well after spraying this stuff.

I let them dry for about 27 hours before baking. Instructions say 24 hours minimum. They looked really dark before they went into the oven. The instructions are pretty vague about baking time. They just say to get them up to 300 degrees. I baked them for over an hour, starting at 300 and gradually working up to 450. Then I turned off the oven and let them cool down slowly in the oven.

The smell was not that bad and I wouldn't hesitate to use the kitchen oven again. Not as bad as the smell if you painted some walls inside your house. Just run the exhaust fan above your stove and maybe open a window if you're fussy about that sort of thing.

After they came out of the oven, they looked a bit lighter to me, which is the opposite of what others have posted online. The photos are not directly comparable since the lighting is different and probably accentuates the lightening effect. But they are definitely lighter than before they went into the oven.

The real test will be after they get good and hot on the engine.
 

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I got the short block and heads back from the engine builder last week. Need to decide which head gasket to run. First step was to CC the heads and see where the chamber volume ended up.

The first number is concerning. I'm guessing it's because the valves are not recessed as far into the head as the other chambers. I put a straight edge across the tops of the valves, but couldn't see any significant variation in the stem heights.

Chamber Volume​
60.4​
63.2​
63.0​
63.4​
​
62.7​
62.7​
63.0​
62.3​
 
Before taking the head back to have more work done, I thought it was a good idea to cc each of the cylinders to see what kind of variation I'm getting in the piston height and dome volume.

View attachment Dome Volume.JPG

I previously posted a dome volume of 11.5 for these pistons. That's very close to the average of these measurements, but the variability is concerning. I think in hindsight I might have been better off waiting for the Egge pistons which have fully machined tops and probably are more consistent.

Some of this variation in dome volume could be offset by variations in compression height, but since the pistons are in the bores, I can't measure compression height of each piston.

I can tell you that the variation on how far down the pistons are in the hole is not within .004" as the builder told me, but actually within .009". No way to know the cause of this variation at this point.

View attachment below deck.jpg
 
Here is what happens when we combine the chamber volumes with the cylinder volumes.
View attachment CR1.jpg
The head gasket volume is for the Felpro gasket with 4.180" diameter and .039" compressed thickness.

The column labeled "Below Deck" is the volume in cc's above the piston, but below the deck. Most of these values are negative which means that the part of the dome that is above the deck is larger than the empty space below the deck.

Obviously, the heads can go on the engine two different ways. These numbers are for the optimum configuration which puts the smallest chamber on top of cylinder #1 which has the largest volume below deck. I was lucky in how this worked out. Even though #1 has a much smaller chamber volume, it's CR is near the middle of the pack.

If I swap the heads, the numbers get worse with max compression on #8 of 9.52:1, while #1 drops to 8.94:1.
 
So I guess the term for what I'm trying to do is called "Compression Balancing". You can definitely get some big spreads in CR when tolerances stack up in the same direction.

The question is, how close should I try to get these numbers? It seems to me that 4/10ths of a point of CR is too big a spread. It forces me to use a thicker head gasket and/or burn premium fuel to avoid detonation in a couple of cylinders, without the benefit of high compression in the others.

As far as remedies, I can think of the following:

  • Swap pistons and rods between the cylinders
  • Have the valves cut lower in the chambers with high CR
  • Grind some material from the chambers with high CR
  • Grind some material from the piston domes with high CR
This last option, would effect the balance of the engine. Aluminum weighs 2.7 grams/cc and I think were talking about 2 cc's of material. Would I notice 5 cc's removed from a piston/rod assembly that weighs something like 1500 grams?

The builder told me that each piston and rod assembly was balanced to the same weight. So I know that if I don't separate the pistons from the rods, I will stay in balance. He also told me that in his experience the rods are extremely consistent in weight so that it would probably be OK to swap rods between pistons. Does this sound right to you guys? How consistent is the weight of factory rods?
 
Never sink the valves, Grind some material from the chambers with high CR. Just for grins I'd swap rod 4 with 8 and /or rod 5 with 7 to see if it is the rods or pistons. You can weigh the rods to make sure they are the same weight when swapping.
 
I'd be willing to bet factory engines of the era had as much if not more variance than what you've observed.

The only way I can think of to properly fix all the issues, would be to equalize your chambers to the highest volume, mill if desired to reach a given number; machine your piston crowns to the lowest common dome volume, and rebalance as necessary. Or you can start playing mix and match again if the numbers you see are that disconcerting.

You had your decks equalized, right?
 
txstang84 said:
You had your decks equalized, right?
Click to expand...

The block was decked and checked for square. It started at 9.610" and was supposed to be milled .005". I can't tell you the final measurement or exactly how close to square it ended up.
 
65DartGTConv said:
Time will tell.
Click to expand...

I did the same procedure and they have rusty spots after a few years but what the heck, I made them look better than new and I can do it again. Eventually I will pull the drive train to paint my car and they will be done over. Keep up the good work. I enjoy seeing your progress. tmm
 
65DartGTConv said:
Isky E4. Intake closing event at 48 degrees. Doesn't bleed that much pressure.
Click to expand...

Nice cam! Wish it had a little more rumble but it makes the
273 run very good. A little too much duration and the stock 273 looses bottom end. tmm
 
I noticed in your pix that the measurement of the .5" below deck was done at the thrust faces, where I wouild expect pistons rocking in the bores a bit would make that vary. It would best to measure at 4 points around the piston top (above both thrust faces and above both pin bores) and then average. I suspect that unless you followed procedues like that in the measurments then there is some variability in the measured data.

BTW, some study and engineering work has been done years in the past and found that effective octane varies as much as 4 points when going from dry 40F air to high humidity 90F air. So you have significantly more variability in that factor in operating your motor with backoff to avoid detonation than in the CR variations as you measured. And besides, your CR's are not all that high anyway. Perhaps just grind some chamber material off to avoid the highest CR in a corner cylinder, since mixture variations are a big contributor to cylinders being lean, and that is not being controlled by balancing CR's.

Lots of hard work there, and all very interesting.
 
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