Boring a flathead

[steve tansy]

thanks, i thought that it could be done on engine likes the engine is not tore down, do you have a measurement from a 239 stock piston that you could give me from the center of wrist pin the top edge of piston, by the way the the new 3 3/8 pistons are three ring pistons tell me and tell me if your measurement is to top edge or at the slight dome thanks so much, steve this would help so much

[scooder]

Just measured a stock 3 3/4 stroke piston (239) from the top of the wrist pin hole to the edge of the crown, not the top of the dome, but the start of it. I got 1.179".
For a 4" stroke you should have about 0.125" less.
Hope that answers your question.
Martin.

[steve tansy]

yes, that is what ron said to do i understand this i my problem right know i have not disassembled my engine i was hoping someone out there could please measure a 239 piston for me from middle of pin to top edge to the top edge of piston or crown thanks. steve

[scooder]

You can use the measurement I gave you. You have the 3 3/8 pistons Sat there, measure them from the top of the wrist pin bore to the edge of the crown. If it's the same, they're 3 3/4 stroke, if they measure close to 0.125" less, they are 4" stroke.
Get it?
Martin.

[scooder]

Your reply has disappeared! Where did that go?
There must be ghosts.
Martin.

[Ol' Ron]

There are several kinds of pistons, basically street and racing. And among these there several types available. For street they're the 4 ring thermal strut pistons like the stock ones and hypercritic3 ring like the Egge and others. These can have tight piston to cylinder wall clearance for better oil control. For racing they're the inexpensive cast pistons or the more expensive forged pistons. These require much larger piston to cylinder wall clearance due to expansond caused by heat. However there is a very nice forged piston of material that allow them to be fit very tight, but expensive. You must check with the piston manufacture what clearance they recommend.

[steve tansy]

THANKS, Martin, sorry for the mix up on my end your right .125 less than from .179 is .1054 4 inch stroke right on.Thanks again you have help me veary much .Steve

[Walt Dupont--Me.]

Originally Posted by robert dick

used to run a 3 7/16 x 4 flatmotor @ Sanford Maine back in the mid 50's, always wondered if i met Walt at one of these meets-- i had purchsed the block from a fellow named Garvin Cooper @ new england speed--he used to run @ Norwood Arena.

CRS, Robert, what was the name of that guy that ran at Sanford back in the 50's, his name was on the back of 32 4dor? I believe he was in a wheelchair and built that engine. He had a young fellow drive the car. I remember standing behind that car when it took off down the 1/4 mile. It had wicked torque, I remember he usually turned 103-104 mph. I always wondered what he had it that engine. Walt

[scooder]

Originally Posted by steve tansy

THANKS, Martin, sorry for the mix up on my end your right .125 less than from .179 is .1054 4 inch stroke right on.Thanks again you have help me veary much .Steve

No problem bud, glad to help.
Martin.

[chuck stevens]

Hey, as long as we have some of the best minds on flatheads present answer one question for me. What purpose does having the center lines of the valves not the same on each bank? It must of been intentional, because the 85 and 60HP both have a three degree difference. Also the cam CL isn't lined up with the Crank CL. Thanks Chuck S.

[Tim Ayers]

Originally Posted by chuck stevens

Hey, as long as we have some of the best minds on flatheads present answer one question for me. What purpose does having the center lines of the valves not the same on each bank? It must of been intentional, because the 85 and 60HP both have a three degree difference. Also the cam CL isn't lined up with the Crank CL. Thanks Chuck S.

I am not pretending to be an expert and I'm curious about this as well. If I recall correctly, I thought I read that it has something to do with the crank or cam not being 100% centerline in the block.

I can be way off, but has something to do with the way they cast the block that caused the need for the valve angles to be different from bank to bank.

Experts, please enlighten us.

[Ol' Ron]

The definition of EX-Spurt is: An EX, is like an Ex wife or Ex president. A spurt is a drip under pressure. So an expert is just a drop.

[JWL]

The cam being slightly shifted on the X axis required adjustments to be made so all the same valve parts could be used for each bank. Ford engineers decided on differing valve angles to be designed so all the components within the valve group can be the same part #--length--height--etc.

Maybe I am just a "drop". But a rather large one.

[Ol' Ron]

Atta Boy John. I can just picture you with a coupla Beagles. Did the Alagator ever come back?

[Pete]

As a side note, when Ford moved the valves farther away from the cylinders in 1946 to alleviate cracking between the valve seat and cylinder, they elected to go cheap and did not change the indexing on the cam.
The technical explanation for this is long and involved but the basic reason was tooling cost because they knew there were going to be major changes to the engine in 1949.
The cams from 1946 to 1948 were ground on the same index as the 1942 and earlier ones.

[Tom Walker]

Originally Posted by Pete

As a side note, when Ford moved the valves farther away from the cylinders in 1946 to alleviate cracking between the valve seat and cylinder, they elected to go cheap and did not change the indexing on the cam.
The technical explanation for this is long and involved but the basic reason was tooling cost because they knew there were going to be major changes to the engine in 1949.
The cams from 1946 to 1948 were ground on the same index as the 1942 and earlier ones.

Why does moving the valve head make any difference? if your not moving the stem in relation to the cam, the timing will remain the same wont it?

[russcc]

Walt, sent you a PM. That was Carroll Sleeper's Fordor.

[Ol' Ron]

I think the lifter bores went with the valves

[Pete]

Originally Posted by Tom Walker

Why does moving the valve head make any difference? if your not moving the stem in relation to the cam, the timing will remain the same wont it?

The valve timing to the engine will remain the same but the angle of the valves between the 2 banks changes. (bank separation) Therefore, the bank separation has to be changed on the cam.

[4tford]

hope this pic works