1st Time Flathead build-Need advice

GreenMonster48

GreenMonster48

Well-known member
Just got good news that the flathead block I bought last year checked out OK after a hot tank and mag.

It's for my old truck and I don't want to build a nasty street machine or anything. Stock stroke, 3/4 cam, 4 barrel intake and Edelbrock heads and probably a hotter ignition.

My plan is to get the surfaces cleaned up, bored out to the next higher number (.010, 020, 030), and new cam bearings installed. I was then going to bring the block back home and install one of H&H's stock 3 3/4 crank kits myself. Does this sound reasonable? The machine shop warned me that sometimes the aftermarket pistons/rings can be off by a few thousanths. Is it worth just having them do the install, or is this something I can do myself?
 
First of all, you need the pistons so the machinist knows how big to bore the cylinders. Why would you want to buy a 3 3/4" stroke crank? They are as plentiful and cheap as the day is long. Buy a 4", 4 1/8" or 4 1/4" assembly. Have you ever built an engine before? There is a difference between putting an engine together and building a proper engine.
 
If you are going to buy a crank kit go for the 4" at least ---and make sure it is all balanced ---had a 46 1-1/2 ton truck, going to 4" was the difference between --I think I can, I think I can to ---no mountain too steep
 
Stock cranks are 3 3/4 no need to spend big bucks to duplicate the original crank, I think everyone was just saying if you are buying new go a little bigger for the same money.
 
Understood. I just wanted to know if having a block punched out say, .030 over would mate up to .030 pistons and rings out of a catalog. I thought it was a safe assumption that they would. Some say yes, some say no. I thought I'd ask the flathead experts if tolerances were that important in a basically stock motor. This is my first build of any kind of motor.
 
Use the original stock 3 3/4 in. crank and save some money. Also, use adjustable lifters. Keep in mind that the OFFENHAUSER 4 bbl. intake offsets the fan carrier bracket 7/8 in towards the driver side which causes it to NOT line up with the crank pulley. That is a problem.
 
The answer I got on your question of matching machine shop bores to oversize pistons is this. If the pistons are of a new build the tolerances are so much better today in manufacturing it is ok to bore the cly before you get the pistons. If you are using old stock you should match the bore to the piston. Either way the person assembling the motor needs to check each fit and ring gap.
 
19Fordy said:
Use the original stock 3 3/4 in. crank and save some money. Also, use adjustable lifters. Keep in mind that the OFFENHAUSER 4 bbl. intake offsets the fan carrier bracket 7/8 in towards the driver side which causes it to NOT line up with the crank pulley. That is a problem.
Click to expand...

Do you know if the Edelbrock 4bbl intake has the same problem?
 
JonC said:
The answer I got on your question of matching machine shop bores to oversize pistons is this. If the pistons are of a new build the tolerances are so much better today in manufacturing it is ok to bore the cly before you get the pistons. If you are using old stock you should match the bore to the piston. Either way the person assembling the motor needs to check each fit and ring gap.
Click to expand...

Thanks Jon.
 
JonC said:
The answer I got on your question of matching machine shop bores to oversize pistons is this. If the pistons are of a new build the tolerances are so much better today in manufacturing it is ok to bore the cly before you get the pistons. If you are using old stock you should match the bore to the piston. Either way the person assembling the motor needs to check each fit and ring gap.
Click to expand...
You absolutely do NOT want to bore the block before you have the pistons. Anybody whos says you can, I would not want building an engine of mine. You also never take anything for granted, always measure. As far as these so called balanced assemblies, the one time I used one, one the connecting rods had never been sized on either the big or small end. How's that for precision?
 
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GreenMonster48 said:
Do you know if the Edelbrock 4bbl intake has the same problem?
Click to expand...
Don't believe the Edelbrock is offset. The only possible problem with the Offy is the location of the fan and gen./alt. ( in most cases, not really a problem )
I have an Offy on mine and didn't notice it until I tried to re-install a fan shroud. ( fan was hitting the shroud on the drivers side )
The situation was rectified when I fabricated a new fan mount with fan axle moved 7/8" to pass.side.
 
Well, I'm going to have the machine shop fit the pistons. I just called to let him know and he laughed and said "good idea!". Guess he knew I was out to prove myself wrong :)
 
Just a couple of last questions, why would anyone bore the block before obtaining the pistons? Would anyone purchase pistons without knowing what bore would be needed to clean up the cylinders?
 
All things considered, I think you'll be much happier if you let your machinist fit the bores to whatever pistons you purchace. It eliminates any question that the appropriate piston clearance can be made exactly the number you're looking for rather than 'pretty close'. OMO
 
I couldn't believe how noticeable the 4 inch crank is over the 3 3/4 in a stock 8BA. Terrific low-down grunt. A real stump puller - best thing you can do to a flathead in my opinion.
 
I purchased Frank Oddo's book..........and had a good read BEFORE i started my first flattie.............glad i did.......


oddo.jpg



.
 
One point and one question.

Point:The single most important modification in many folks' opinion is a set of headers. Save some time and call RED's.....

Question: What kind of 3/4 cam are you considering?
 
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