decking a flathead

cuzncletus

cuzncletus

Senior Member
I finally had an engine built by a professional engine shop. It was an obsolete version of one of Ford's V-8 jiggler motors that had been gone through twice. All I can say is it was expensive but worth it. Before I had always used what we call "garage motors"; get the basic machine work done and bolt 'em together yourself in the garage. The difference between that and having it all done correctly is 'seat of the pants' unbelievable.

Next up is an 8BA. I'm considering having it decked. Questions: I know the decks on flatheads are thin. Does this compromise the little strength there is? (Heads will be studded.) How far out are these blocks normally? It seems with the rather cavalier casting Ford was doing the chance for these engines to be fairly out of square is high. This is on a street rod engine with Merc crank and typical mods. Heads are Edelbrock 1115's. Lift will be .368. Is there plenty of clearance in the combustion chamber?
 
cuzncletus said:
I finally had an engine built by a professional engine shop. It was an obsolete version of one of Ford's V-8 jiggler motors that had been gone through twice. All I can say is it was expensive but worth it. Before I had always used what we call "garage motors"; get the basic machine work done and bolt 'em together yourself in the garage. The difference between that and having it all done correctly is 'seat of the pants' unbelievable.

Next up is an 8BA. I'm considering having it decked. Questions: I know the decks on flatheads are thin. Does this compromise the little strength there is? (Heads will be studded.) How far out are these blocks normally? It seems with the rather cavalier casting Ford was doing the chance for these engines to be fairly out of square is high. This is on a street rod engine with Merc crank and typical mods. Heads are Edelbrock 1115's. Lift will be .368. Is there plenty of clearance in the combustion chamber?
Click to expand...

Hi Cletus, it's good practice to have a nice flat surface for a new build!

Assuming the decks are NOT damaged, taking a "flat-cut" will have no adverse effect on the performance! If the decks are in fairly decent condition you will only need about a .005"/ .007" pass to make them "new"!

Have the same amount removed from both sides, although this is not "etched-in-stone" either, it's good practice to follow.

(Add) Ford's machining is not as bad as you would believe, even back then!

I have been placing the following "tips" up on most forums: first, make absolutely certain the shop doing the boring/honing can produce a "block-plate" to finish the bores. I realize these blocks have some high nickel (making the block fairly strong) but the plate is necessary to "maximize" the HP numbers and second, have the guides lined with bronze liners, keeps the valves from "hanging" open during storage periods. This was a major issue over the years with the "Flatties", haven't had a single valve "hang" in ages! This procedure also maximizes valve/seat life by allowing tighter valve-to-guide clearances! We also use the new green "Viton" seals on ALL 16 guides, which we pre-machine also while doing the liners!

Thanks, Gary in N.Y.

P.S. The cam lift should not be an issue, but check it anyway. Also place a spark plug in each hole and make certain the "tip" is not buried in the threads, we "fire-slot" almost every aftermarket Flathead aluminum head for the best flame travel!
 

Attachments

  • Flathead Fire-Slots.JPG
    Flathead Fire-Slots.JPG
    63.1 KB · Views: 171
  • Flathead Fire-Slots-A.jpg
    Flathead Fire-Slots-A.jpg
    76.6 KB · Views: 137
Most blocks do not require a deck cut to be acceptable. It is impossible to advise you without first checking the condiitions as they currently exist. Removing the same amount of stock from each deck is not important and should never be done to maintain them equal unless the deck height is first accurately measured. Cutting the same from each deck might only perpetuate the use of inaccurate deck heights.

If accuracy is your goal the first step is to validate the main housing sizes and alignments. Next, with the block located on the main housings, the decks can be cut so as to be square and perpendicular with the main housings while maintaining equal heights at each deck.

Having said that, a perfectly "accurate" engine is not necessary for the average street car and decking need not be done unless it is necessary.
 
I built a 59a many years back. Had it bored and the valve seats cut but didnt have it decked but it was checked for straightness and was O.K.. The problem came when I got it all put together and had spent all that money and time it ran and sounded great . Put it in my 40 and noticed after the engine got up to temp I could here a thump thump at idle . Pulled the heads off and noticed on the pass side the pistons were just touching the head .Wound up running two head gaskets on that side . Aparently that block had been decked sometime and too much was removed from the right bank. Flathead cranks are off center so that might play into the equaistion.
 
It's hard to believe you can deck a block so much a piston will hit the heaed. Most stock engines have an excessive amt of piston to head clearance and require .030-.040" head milling to get the .050" desireable clearance. Many shops and customers don't bother to check this. After spending all this money on balancing, porting, relieving and other unnecessary operations. Why not get the combustion chambers tightened up. This one operation is more important than the other mods for making a good running street engine. IMHO
 
I have a 8ba that have been decked, and my advise is to be careful.
I put on a set edelbrock heads and studs, and got in big trouble. The block cracked around one of the center head bolts, there was not enough material left to keep it strong enough. I will try to take some pictures soon.
Yngve N
 
I always check clearance before installing heads regardless of the situation. Clay or tin foil whatever. You never know what has been done during all those years.......
 
Check it for square if it is why deck it? You can check it for square with a minimal amount of tools and time.You need the crank main brgs one rod and piston assy that you are going to use and the rod brg.a depth mike and a good thick strait edge and a dial gauge to locate tdc and away you go on all 4 corners record your measurements and you are done. Probably not worth the time but some guys do split hairs.I wouldn't worry too much on a stock street engine.

Ronnie
 
You must log in or register to reply here.
Back
Top