8ba block decking

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mercuryray

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I am having an 8ba reconditioned and they have decked the block on the left side and the valve seats are allowing the valves to stick out to far and when I put the head on the valves and the pistons touch the head is there a fix for this. Thanks Mercury Ray.
 
mercuryray said:
I am having an 8ba reconditioned and they have decked the block on the left side and the valve seats are allowing the valves to stick out to far and when I put the head on the valves and the pistons touch the head is there a fix for this. Thanks Mercury Ray.
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Hi Ray, sounds like they may have "over-decked" it somewhat!

You should not have to do any "extra" machine work due to milling the decks??

In any event you're going to have to start "hand-fitting" the components on a piece-meal basis! We have on occasion fly-cut the valve pockets, see the photo below, but it was more to work around the chamber volumes.

(Add) Both decks have the same angle and hgt, however, the valves are installed at two different angles from the factory. This explains why they sit at different hgts when in place! If I recall correctly one side is 50*, the other is 53* (nominally).

Thanks, Gary in N.Y.

P.S. Have been milling these Flatheads for some years now on our CNC mill, have never really taken any more than .010" off to get them "flat" and the correct finish?? These decks are "thin" going in, better to leave as much original as possible.
 

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If the shop that did the machine work was not familiar with flatheads, they could have machined the decks as if they were both at the same angle. I know of a block that was ruined this way.
 
deuce roadster is right, machine shops that are not familiar with flatheads are usually not aware that the angle on the flathead blocks are not the same on both sides, and have to be machined accordingly. your block may be able to be saved, but I think I would find a different machine shop. like goes fast said , the decks are alredy thin. do not take off any more than is absolutely necessary.
 
deuce_roadster said:
If the shop that did the machine work was not familiar with flatheads, they could have machined the decks as if they were both at the same angle. I know of a block that was ruined this way.
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Alaska Jim said:
deuce roadster is right, machine shops that are not familiar with flatheads are usually not aware that the angle on the flathead blocks are not the same on both sides, and have to be machined accordingly. your block may be able to be saved, but I think I would find a different machine shop. like goes fast said , the decks are alredy thin. do not take off any more than is absolutely necessary.
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Always thought that the decks were the same 45° angle but the valves are different from each other??
 
Couple more question
Do you have hi lift cam , do the piston pop up at TDC . I would grease up the top of the valves and piston and place head on top loosely and roll engine over by hand checking for hi spots
Who’s piston ,some dome are taller .180 to .220 .8BA heads have been milled , try another set of heads for mock up .
 
Yes, of course both decks are the same angle and height. Regarding the problem decks, steel shims were once available and I even saw one example where the steel outer shell of a head gasket was stripped off and added to the gasket package for clearance. However, I do not like that approach and agree you are now in a "cut and try" fitting situation.
 
Did they not deck the right side also? That would bother me as you would have different compression on each side. Ten thousandths might not mean a lot but they should be symmetrical, no?
 
How I deck a block and mill heads. The machike we use is called a Broach, not sure why and can't remember the brand, It has a flat area where the block/head is put on and clamped. The head then travels over a 10/12 cutter. with the block over the cutter, it's brought up until it that's the surface. The block is pulled back anr 2/3 thou is added to the cutter and the machine is put to work. after about 5 minutes the block is done. with a mirror you ca see if it got everything. Most of the time that's all it needs.
Angling heads:
Mlace the head on the flat surface and place a shim the thickness of the amount you want removed from the opposite side and clamp the head to the machine. For the stock cars we used a .07" shim and took 2 passes of .035 and one of .010 for a total of .080". Now after this you have to check valve and piston clearance. On an 8BA head to took an 80cc chamber down to 68cc's but not all heads are the same, I will soon do this to a set of eab heads which hove more valve clearance.
This may sound complicated and expensive, however, 800 bucks foe a fancy aluminum head might be cheaper.??????
 
deuce_roadster said:
If the shop that did the machine work was not familiar with flatheads, they could have machined the decks as if they were both at the same angle. I know of a block that was ruined this way.
Click to expand...


The decks are BOTH at a 45 degree angle, but the valve angles are asymmetrical. The passenger side valves are at 49.5 degrees, whereas the driver side valves are at 52 degrees. Cam and cylinder bores are centered in block....crankshaft is offset 0.265" to the passenger side of center. The crank offset has to do with the DeSaxe principle. DD


64986
 
Actually the cam is offset from the crankshaft .021 plus or minus .002 on the 46-53 engine block.
 
Given that he is talking about a 49-53 engine, it is very common for the Driver's side valve seats (at the top) to be flush with the deck - or even barely touched/machined on the top edge. Due to the different valve angles (side to side), the Driver's side will be the one where the valve seats (and valves in general) are "highest" as compared to the deck. This is normal.

If somebody is decking a block, it needs to be done with the main crankshaft bore in a "saddle", such that one can accurately machine the deck height (side-to-side) to be square to the crank centerline and the same height. Rarely are flathead blocks that accurate - so usually one side is decked more than the other (usually less than .010 difference).

There may be nothing wrong with the machine work on this block - one can only know if the deck height is accurately checked (side to side). The easiest way to do this is with the crankshaft in the engine, two rods and two pistons --- then checking the piston crown to deck height on both sides. (There are other ways to measure - most folks don't have the jigs, tooling, mics to do so). If you don't have the right dial-indicators, magnetic bases, etc - and know how to use them, then bring it to a machine shop that does.

If the machine shop correctly setup the block (as noted above), then there is no reason to have in accurate deck heights . . . though by looking at them, one can easily think something is wrong (due to the valve angles and height above the deck on the Driver's side).

Here is a correct drawing of the dimensions on a 59X to 8BA style flathead block. I did these for the purposes of determining CNC valve pocket work for custom head designs.

FlatheadFordCrossSection-59X-8BA.jpg
 
JWL said:
Actually the cam is offset from the crankshaft .021 plus or minus .002 on the 46-53 engine block.
Click to expand...

The original 8BA drawings show the camshaft offset to be from .0192 to .0292 offset from the crank, so I "split the difference" and went with .0242 in my cad model. There are some minor differences in the 59x versus 8BA drawings - with the 8BA ones being easier to read.

I will have to test the cam offset at .019 to .023 and see what it does to the valve angles - will be an interesting 3D experiment. ;)

The valve angles shown on the 8BA drawings are 3.38 degrees and 6.23 degrees - though obviously they change depending on the true CAM centerline offset. When I did my CAD model, I let the specific dimensions of the CAD models (off the prints) drive the final dimensioned values - so there will be some variance, due to the various variances in the drawings.
 
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