1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

[Richard M.]

What is acceptable? I cannot find specs anywhere or info via searces here.

A machine shop left me with a mess. I got the hardware 3rd party of a takeover project. Using a gauge block I'm seeing apx 0.003" to 0.005" difference between upper and lower "Y" between several cylinders. Both sides. I also measure 0.010" difference between the front cylinder deck area flats to the intake manifold angled walls(ears), and the rear cylinder flats to rear walls. Both decks.

Unfortunately this was after assembly, start up and cam break in after 20 min at 2000 rpm, running fine, went to idle and coolant overflowed within seconds. Reran after cool down and water refill 3 times. Ran fine up to 180. When 180 thermostat opens, coolant forced out the overflow. Coolant proved to be pressurized by combustion leaks. Leak down test proved 3 bad cylinders(6,5,7)at 18 to 22%, combustion gasses in coolant using dye test. Tore it apart. Both heads are a problem. I find out later heads were NOT decked, just cleaned up. Magnafluxed and pressure tested post failure and passed. Heads being redone 100% at different shop, now I'm checking block and have concerns.

Using Felpro composition gaskets which help the cause, but I don't like the variations I'm seeing on the block deck measurements. Please.....Lectureless technical opinions welcomed.

Thanks,
Rich

[Loren L.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Have you measured deck height relative to top of the piston on all cylinders? Might even think about doing both sides of each.....the horse might be too dead to rise again.

[Richard M.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Good idea Loren, thanks. I'm heading out to the shop shortly and will post results......

but just another thought......... Would it be best to measure parallel to wrist pin on each side of the pistons, as opposed to top/bottom of pistons? (piston tilts vertically by design, correct?)

[Dick W.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Good idea Loren, thanks. I'm heading out to the shop shortly and will post results......

but just another thought......... Would it be best to measure parallel to wrist pin on each side of the pistons, as opposed to top/bottom of pistons? (piston tilts vertically by design, correct?)

Use one rod, one piston for your measurement. Make sure the piston has rings. You can use a depth mic to square piston up. Take your deck height measurement from the center of the piston. Do not be surprised if you see as much as .010 from front to back, side to side.

[Richard M.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Here are some of the numbers. I'm not happy. I measured the deck clearance on #1 and #6 and #7 @TDC 4 sides. 1 & 6 when the balance at 0. 7 was by eye/feel. Main objective is to see left to right delta.

I also took spot measurements where the tool would fit. I can see why #5 and #7 were bad, I'm not happy.

Pics of written results below.
"Star" is where I set the block on the deck, small "dots" are where the dial indicator landed.

I rolled crank and took #7 msmnt after pic. Gauge block set at near lower left of cylinder. Throttle lever and firewall obstructions there.
I measured:
top- 070"
left- 062"
right - 065"
bottom- 055" (rechecked....it's 0.055, not 0.065)

I have to go to the new machine shop and will review these numbers there as well.

Rich


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[Timothy B.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Richard,

With deck clearance like that you almost have to question the piston compression height, I wonder if the correct pistons are installed for a 283.

[Duke W.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

The way I determine any deck warp is to us a machinist's bar and .0015" feeler gage. If the gage pulls out with equal effort all along the bar, the deck is flat. As a minimum the measurements should be made with the bar across the top of the deck (near the lifter valley), the bottom of the deck, and diagonally.

If the .0015" gage can be freely removed anywhere along the bar, then use thicker feeler gages as required to determine the depth of the low spot.

If I understand your measurements, you have up to .008" variation (warp), but you used some kind of tool. Can you post a photo of the setup with the tool? I'm not too concerned about the greater variation on the deck "ears" at the front and rear of the block because they don't have to seal combustion or water pressure.

Your deck clearance (not height) measurments are very large, which indicates you have very low compression pistons - probably no more than 8:1. I believe the nominal 9.5:1 OE pistons should yield a deck clearance of .025" on a nominal deck height (9.025") block, and many of those engines will run satisfactorily on 87 PON fuel, so you are leaving a good amount of torque, power, and fuel economy on the table by not running up to 10:1 assuming it is a base cam engine.

Deck clearance should be measured on all 8 pistons and if you use the same piston/rod in each cylinder there will be no variation due to differences in rod length and piston compression height. I measure at the top and bottom of the piston, and rock the piston as required to achieve the same measurement on both sides. The variation is slight on snug fit cast pistons, but can be a challenge to get right on loose fit forged pistons.

Once you have all the measurements, you can determine how much, if any, "slope" the decks have front to rear and left-right average variation. A little slope does no harm other than resulting in compression ratio variation, which can be equalized with chamber grinding, but it's a time consuming process because you have to measure each chamber, then run the data through a CR calcuator and determine how much must be taken out of each chamber and then remeasure the chambers to verify that you removed the correct amount of material.

This issue was discussed in much detail in the "Compression Ratio Explained" article in the fall 2009 Corvette Restorer.

If the block deck passes the .0015" gage test, then it's okay to use a shim type gasket, and my rule of thumb is that most composition gaskets will seal with up to .003" variation, so if your block has .008" variation, I don't see how you can get it to seal up without taking at least a .010" cut on a properly fixtured block to eliminate the deck variation, achieve deck parallelism with the crankshaft centerline, and increase the depth of the cut on the highest deck to eliminate the side to side variation.

If you find the above to be a "lecture", just ignore it, but others might find it useful.

Duke

[Loren L.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Richard, at this stage I KNOW you don't need another question, but what is the discoloration on the top of the pistons in holes 2 and 4? Best of luck, BTW.

[Richard M.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Getting pics and measurements and info for all ?'s, but let me answer a few while I'm taking a "back" break..... I don't have a machinists straight edge, but Starrett 12" and 18" from Enco in Nevada are in a UPS box on the way, in a few days unfortunately. I'm trying to borrow locally, tough to find. That's why I got the "Surface Gage" to get something going.

#2 & #4 is like #1 and #3(cleaned by me). It's from bad valves or seats or guides or ? I was given these 962 heads that were just "cleaned up". The heads were not decked as I found out later. I found out after above mentioned retest that.......
they were put on a industrial machine shop flat table machine belt sander. I saw it behind me there. I abruptly picked up the heads, loaded them in my truck, left the shop and brought them to a engine builder friends' recommended shop for opinions. They're getting fully rebuilt right now at new shop. I just went back earlier to discuss the cylinder block with the shop owner/machinist.

I'll get back shortly with more.
Thanks

ps it's a 270hp, and they used rebuilder pistons just like they weren't supposed to. We calculated the CR at apx 8.75:1. Yes I know what it means but I had no control as I wasn't involved with choices then.

[Richard M.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Thanks all,

Pics of the surface gage I used.

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Before each measurement on the deck surfaces, I placed the setup on my "flat" mill table and set the dial indicator to zero. Went to take each measurement, then went back to check "0" at the mill table for accuracy between each one.

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Ignore the large numbers for the deck clearance from before. My statement in post#5...."Main objective is to see left to right delta." was to show the variance, not the deck clearance. Sorry for confusion.

I just measured 4 cylinders after using a separate dial indicator on magnetic base to find TDC. #7, #2, #1 and #8 are all 0.030" DC. More later.

I am trying to get the straight edges and go over these areas again for accuracy. I feel my results will be very close to what I've seen with the setup I used.

I was wondering if the upper deck near the lifter valley being lower could exacerbate the problem. If the torque of the higher long bolts is slightly more than the shorter lower exposed bolts, could this cause a rocking effect of the head on the deck surfaces. There was evidence of the leakage coming from the lower cylinder areas near the spark plug cooling ports. Again.....the heads were never decked, just sanded.

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In the above photo, ignore the extra water on the head gasket. I forgot to pull the lower block drain when I unbolted the left side. Drained water for the right side removal.

I will get straight edge deck variance measurements before a final decision is made, but if 0.003" appears to be a max, I'm planning that the block must come apart. Felpro composition head gaskets were used on this originally in the assembly process.

I have to leave shortly for the evening and will get more info later or in the morning.

Thanks,
Rich
p.s.
Duke, I didn't feel lectured at all....by anyone. It all has been very informative and helpful. My lecture statement was just to try to head off the sometimes occurring statements about what I "should have done".

[Steven B.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Rich, if you are looking for an excellent machine shop with experienced builders Grimes Automotive machine in Alpharetta (Atlanta), GA is very good. Garry does restoration and racing engines. Garry did my RPO 469 2X4 283 and my L-82. Google Garry Grimes and Grimes Automotive Machine. He has done work for Zora and a number of aftermarket companies. If it can be straightened out Garry can do it while optimizing performance. Steve

[Richard M.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Steve, Thanks for the lead. However Atlanta is quite a hike from me here in eastern Florida. But..........

The new shop I'm working with has a good reputation for engine work. I felt very comfortable going over the head problems with the machinist the other day.

My friend Jay Howell uses this shop. He's coming over this weekend to go over my numbers and I'll have a machinists straight edge borrowed by then. I'll let Jay do the measurements, then correlate with my measurements using the dial indicator/surface gage to verify I haven't made a mistake. He's built a few engines in his day. He's presently building a replica of the Anglia he built in the '60's, so he's been pretty busy with his own project and going to give me a hand over the weekend.

You may remember the Prock and Howell F-Troop Willys, and the Little Red Wagon. He also built cars for Prudhomme, Logghe, and many others, Jay built the upgraded Hemi for the Little Red Wagon and was the first to get a full wheelie in it. When he tells the story of the day he did it, it's a scarey one!

Jay's info here.

Thanks,
Rich

[Steven B.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Sounds like you are in good hands Rich! It is great working with guys like this not only because of their expertise but the stories they have. Good Luck!

[Richard M.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

Between all of the guys here.......Loren, Dick, Duke, Tim, and you, and my good friend and member here Chuck McSheehey(sharp/lurker/hands-on helper) & very knowledgeable friend JohnB.......and Jay, it should work. The hardest part of all of this is the car was done, just break it in, a few adjustments, a little ride around the back fields, and the next one begins.

Delays like this hurt but Oh well, I'm taking it in stride and trying to make the best of it by looking at the brighter side......I'm learning a massive amount in a accelerated hands-on situation. Never had this kind of problem before. Fault insertion procedures at their best.

Rich

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[Duke W.]

Re: 1960 283 Cylinder Block Deck Surface Flatness Tolerance ?

It's tough to tell from the photos, but it appears your block has been previously decked, and it may require another cut.

Since you will have to disassemble the block you might want to consider increasing the compression ratio to gain the cross the range performance increase and better fuel economy.

KB makes two 283 pistons. The KB165 is a flattop with 6 cc valve notches, and the KB166 has a net dome volume of 4 cc. Given that your deck heights will probably end up at least .020" below factory nominal dimension the domed piston will provide about 10.3:1 compression with a composition gasket, which the Duntov cam will tolerate with premium fuel.

New pistons will require rebalancing, and if you still have the spindly original 283 rods they should be replaced with a better design. A used set of second design 327 rods would be okay if you're on a budget, but a new set of Eagle SIR 5700 rods would be best.

Other options include a "sort of" Duntov cheater cam - uses the Duntov lobes with a wider LSA and later phased POMLs. Crane can grind it.

Then there's the option of massaging the heads if you want a 7200 rev screamer.

Duke