Milling late 70s large log

So I hate to ask without doing at least preliminary numbers on my own, but with the NorCal fires I packed all my records and performance handbooks. I have a head with ~62cc chambers, it was supposed to be milled for compression but the shop flaked. Since I need to give guidance again I wanted to verify.

For a rebuilt engine 200ci 30 over I think, stock cam, is 60 thou milling my target, or should I take more for aftermarket gasket height?

1st which "late 70s" & what do they CC at?
(0h, wait U say 62 cc, coupla beers here) we look to .050 off in many cases as safe~
let's C what the experts say.

U Go Mr. Bronco !

Hi Invectivus, sorry to hear that your machine shop flaked out on you . Here are the specs for a stock 200 short block for a bit of comparison and it was a very decent combo in its day.

This is for an early 1965 to 1968 200 7 main stock short block.
3.680 Bore Size
3.126 Stroke
1.511 Piston Compression Height
6.5 CC's Piston Dish
.019 Deck Height (Down the hole)
.022 Thickness for the original Ford steel shim head gasket
.041 Quench Distance
3.810 Aprox. Ford Gasket Bore Diameter
52 CC's Chamber on stock Ford Head.
8.7 to 1 stock Compression Ratio

All specs above except for now a
62 CC's Combustion Chamber 1970's Log Head Swapped on using a FelPro composite head gasket
.050 Crush Thickness of the Head Gasket
.069 Quench Distance
7.71 to 1 Compression Ratio

From this we find the CR drops 1 full ratio point from what the early stock 200 six was and would be a significant loss of horse power and some torque too.

Some other items to note there was another set of stock cast Pistons that Ford used on some of the California Emissions 200 six'es that had a 10 CC's Dish Volume and plus there were the 250 Pistion's which had a 13 CC's Dish Volume. Note that most of replacement Pistions are only a 1.50 Compression Height droping the piston down the bore to .030 so the blocks deck should have a cleanup cut on the deck surface to square it up and reduce this deck height without this the NA engines compression ratio will be considerably less than original stock 200 engine. What is your goal compression ratio and do you know what the piston dish volume and compression height of your Pistons is?

A Typical Stock 200 Rebuilt Short Block's Specs

3.710 Bore Size (.030 over bore)
3.126 Stroke
1.50 Pistion Compression Height
6.5 CC's Piston Dish
.030 Deck Height (if the block is has not been decked / milled)
.050 FelPro Head Gasket
3.810 Gasket Bore Size.
62 CC's Combustion Chamber with A 1970's Log Head Swapped on
.080 Quench Distance
7.66 to 1 Compression Ratio
203 Cubic Inches

Using the 1969 to 1983 200 or 250 Log Head milled to a 52 CC head volume brings the compression ratio up to 8.69 to going to 50 CC chamber you get 8.78 slightly more than stock, using a .044 thick Victor head gasket brings the CR to 8.91 to 1 and still might be okay. The bad thing is that the Quench Distance needs to be in the .035 to .050 range for best results with a Zero decked block and a FelPro head gasket its at .050 or better yet .044 when you use a Victor head gasket. You can even have the pistion + .010 or more above the block then you could use a 9.0 to 9.2 to 1 CR depending on your location and still use 87 pump gas.

You can ball park the mill cut by using a .010 cut for every 2 CC of combustion chamber reduction and be real close, still it's better to CC the head if possable. So if you have a starting 62 CC chamber now then roughly a .050 cut will bring your head CC's down to 52 CC. Another .028 mill will compensate for the differance in head gasket thickness for the Felpro head gasket. But I am assuming that the block hasn't been milled any or zero decked to compensate for that extra .011 the pistons are down the hole. Additionally if your head dosnt already have atleast a 1 3/4 inch carb mounting hole opening its a good do it now so you can use some of the better late model carb's if you want in the future. Better yet is to go to a 2 to 2 1/8 inch carb base hole and radius the bottom edges of the carb hole leading into the Log for either size holes is worth a little power. The 2 to 2 1/8 inch hole will make it easy if you want to use a 2V to 1V carb adapter. Have a good good 3 angle valve job done with a 30 degree back cut on the intake valves and a back cut on top edge of the exhaust valves is also good idea. Also consider doing some valve bowl porting / cleanup and a center exhaust port divider. Hope that helps you some in figuring it all out, best of luck on your 200 build up

Man, I do NOT know what is going on with my engine (or my brain).

So it's .040 over, not 30, which should have been easy to tell because it's like stamped on the piston face for all to see. What's really weird though is that using a dial indicator, my piston deck height looks like it's .040 down. That seems really super wrong (unless they botched the rod reconditioning?).

So if that were true:
3.720 Bore Size (.040 over bore)
3.126 Stroke
1.50 Piston Compression Height
6.5 CC's Piston Dish
.040 Deck Height (weird)
.050 FelPro Head Gasket
3.810 Gasket Bore Size.
62 CC's Combustion Chamber
.080 Quench Distance
7.59 to 1 Compression Ratio
203.85 Cubic Inches

If I had the head shaved .070, that would get me a 48cc chamber (8.89:1 SCR), but demolish my quench distance down to .010. That deck clearance is really throwing me for a loop. If I'm wrong about the deck clearance, 48cc chamber gets me a 9.09CR which is high. I'm around sea level in coastal California (351'), which I guess makes it more of a concern than at a higher elevation.

Replacement pistons have a different pin height than stock to compensate for head resurfacing, ironically. That's why you now have increased deck height.

Invectivus, yes something dosen't seem quite right on the pistion to deck height should be about .030, unless your block had an extra high deck height from the factory. With the Piston .040 down the bore and using a .050 head gasket this equals a .090 quench distance the milling of the heads combustion chambers to reduce the CC's dozen't change it any only raises the compression ratio. These are the ways to change the Quence Distance first is by using a thinner head gasket, next is milling the block deck height down, using a longer Connecting Rod (Custom), using a piston (Custom) with a different compression hight, increasing the crankshafts stroke slightly (Custom off set ground), or by combinations of them will change the Quence distance. Did the machine shop cut the block deck any and rebuild the rods?

yeah, no quench ina head...
even if a bronk !
8^ )

Get .40"under rod bearings if your crankshaft rod journals are stock & have not been previously ground.
Have the crankshaft rod journals offset ground .015". This will bring the piston up .015" closer to the deck & the piston will go down .015" more for a stroke increase of .030".
It will also add 2 cubic inches.
If you bore it .030" that takes a 203" engine up to 205 cubic inches.
Then you will not have to take much off the block deck to "zero" deck it.

So some history for accuracy. I didn't have the engine rebuilt, I bought it from someone who was doing a v8 swap in their 1966. When I bought my 67, the engine was out and left in the rain, even a 40 overbore left a possibly excessive amount of texture on the walls of cylinder 2, so I bought a running replacement. Over the intervening years I only drove it about 40 miles, and when I finally got it back together after a t5 swap, my head gasket blew and started dumping water into the #4 cylinder (it's so clean now!). When I disassembled it to evaluate it, all the cylinders had really fresh looking cross hatch, so I knew a rebuild was recent, but I don't know anything more than the crosshatch and the 40 over.

I decided to get another head rebuilt for the larger log/carb options, and because one of my exhaust bolt heads broke off. Without getting into the weeds on the horrible service, the quote for services reads:
-multi-angle valve job, including 30* backcut on intake.
-new intake valves and stainless exhaust
-port divider install
-Machine and CC head (48cc)
-machine and install nitride seals

I know the seals and port divider was done, I know the chambers are stock, I would need to disassemble the head to check on the valve job (I have a good compressor, I just need to do it).


Back to the engine, one of the reasons I bought a dial indicator was because at TDC, I was able to get .042 feeler gauge between the top of the piston and a straight edge, but not a .044. But not being experienced, I thought I might be doing it wrong and wedging, so I wanted something that had less force behind the test. I took multiple measurements, and repositions the base and recalibrated it multiple times, like 90-95% of the time I came out with exactly .040 deck clearance. A few times I came out with .042 or .043, but that was in a real minority of cases. I can be relatively confident that I don't have a 30% error in my measuring. I made sure to rotate the base, not the pedestal, so I shouldn't have rotating mast threads changing the height on me. The reason for the extra 10 thou is technically moot (though I should clean the other pistons and check each one), I can't know without breaking it down and measuring everything, so I guess I'll clean/remeasure each piston, I'll cut the head for stock deck clearance (60 cut / 8.79CR) so it can be used on another engine if I rebuild one without raising the CR too high, use a slimmer victor head gasket and call it better than the 62cc stock chamber volume.

X2 wsa111, brings up a good plan that's made to order for your situation, by off set grinding the crank you would solve much of the problem of the Quench Distance plus give another benafit of a couple more cu. inches.

So if you paid to have the head milled so you have a 48 CC a Chamber that's what they should give you they likely didn't check it and only gave it a light cut. As far as measureing each piston height that's fine normally I just check the #1 and #6 to see what they are then you now the deck height matches front to rear so the block can be squared and true. When the head gasket was blown did you check that the blocks deck was flat? On average with the later 62 CC heads it takes a .050 cut to get them to .052 CC and another .028 to make up for the extra thickness of the FelPro composition head gasket, not to mention the extra .021 lower deck height of those pistons. So with the 48 CC head you could be very close on the compression ratio at 8.85 to 1. A 200 at sea level zero decked does good with 9.0 to 9.2 to 1 running 87 pump gas and a good tune up. Edited

Hi, I read your post and I'm surprised no one asked why are you sticking with a stock cam? I think there are some good cams that would make you happier. Good luck

+1

I'd recommend a 256/256 from Schneider. The 256H for your 200. I put a 256/262 in my 250 for the van and I couldn't be happier. The only reason we went with the 262 on the exhaust was b/c of compression concerns with my build b/c it was designed around a different cam. Jerry recommended the 256H off the cuff before we got into why I needed to bleed compression @ 9.6:1 SCR in an iron log head 250 long stroke. 255. Dynamic compression was pushing 8.3 or more with the cam change iirc. I was shooting for 7.7 to 8 with the first cam. My house is somewhere less than 50' above sea level. Pinging was still a problem but it turned out to be an overly aggressive advance curve and weight's that allowed 30 deg of mechanical advance. I altered the weights gap from 15L specs to 13L by welding, filing and measurement and the problem disappeared. I'm running 87 right now, no problems. 9.6:1 in a 250 at and near sea level. And it still shits and gets grins all day.