here we go again... does anyone make 3 7/8

[Charlie ny]

Bored and Stroked does with cad what I attempt with laborious hand die grinding. The
method I use takes, on average,6 hours per head but exactly matches the comb
chamber to the piston crown. His statement is so correct.....'in many cases the head
head doesn't match the piston anyway'. After milling the heads I actually apply a thin
coating of grease to the piston crowns and valve heads then rotate the motor by
hand. The points of contact are readily apparent and are then carefully relieved.
Each head is hung on 4 studs to insure repeatability. The optimum .040 clearance
is sort of built in when the head gasket is in place at time of assembly.
Charlie ny

[Bored&Stroked]

Originally Posted by Ol' Ron

When I built the Bville engine I used a 3 3/4 stroke piston on a 4" crank. The Heads had been domed by Grancor for this. Had very good flow with 9.2 CR. I used .060" piston to head clearance to protect against rod stretch at Hi revs.

Probably a good idea to have some 'wiggle room' for rod stretch in a high rpm race situation. What type of rod were/are you using?

[tubman]

I'm going to make one last stab at trying to get you guys to understand me.

"JWL" said "OFFSET" grinding moves the centerline of the rod pin away from the main line requiring shorter compression height pistons to avoid the pistons extending above the block deck".

This does not have to be so. Depending on the side of the journal on which the "OFFSET" is ground, it can move the centerline of the rod pin either farther away from the crankshaft centerline or closer to it. The amount to be removed from the 8BA crankshaft to use the earlier rods is .140. Half of this is .070. Since a 1/8" stroke results in a .0625 increase in stroke, which is less than this amount, "OFFSET" grinding the crank and biasing the "OFFSET" to the side of the rod pin away from the crankshaft centerline will accommodate this increase in stroke. I imagine one could obtain optimal piston crown to combustion chamber clearance using this method after some careful measuring.

[JSeery]

"This does not have to be so."

Sorry, yes it does! An increase in stroke will increase the distance between the centerline of the piston pin and the centerline of the crank throw (and crank centerline) by definition. To maintain the same piston position you have to move the piston pin location or use shorter rods.

[tubman]

Originally Posted by JSeery

"This does not have to be so."

Sorry, yes it does! An increase in stroke will increase the distance between the centerline of the piston pin and the centerline of the crank throw (and crank centerline) by definition.

Sorry to disagree with you, but do your diagram over taking the offset off the other side of the pin and see where the rod pin centerline goes.

[flatjack9]

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Remember, he wants to have a 3 7/8" stroke crank. Thus JSeery's diagram.

[JSeery]

Well, sorry tubman, not sure where your confusion is, but this is a well established process, don't think everyone is wrong on this one. Sure you can de-stroke the crank by offset grinding toward the crank centerline, but this will decrease the overall stroke. The objective was to increase the stroke.

[tubman]

OK, I finally see it. While what I am suggesting would work fine, what I'd end up with is a small journal 8BA crank with a 3 3/4 stroke. Doable, but why bother?

[JSeery]

Originally Posted by tubman

OK, I finally see it. While what I am suggesting would work fine, what I'd end up with is a small journal 8BA crank with a 3 3/4 stroke. Doable, but why bother?

Or you could de-stroke it. That has been done to meet class requirements in racing.

[GreenMonster48]

Originally Posted by tubman

OK, I finally see it. While what I am suggesting would work fine, what I'd end up with is a small journal 8BA crank with a 3 3/4 stroke. Doable, but why bother?

Exactly my thought. Lots of hoop jumping and machine work for what? A couple extra cubes?

[JWL]

In case you missed it, the subject was 3 7/8 stroke. My comments were aligned with the original subject. Now, if we just want to argue about something let's discuss the wonderful job our president and congress are doing. But, not on this site. There is plenty of extraneous stuff already.

[chuck stevens]

Bored & stroked, and Ol Ron, this has me pretty excided. The standing rule for flatheads has been- anything you do to increase compression hurts flow, and vise-a-versa. By take some off the head it should help flow in the transfer area. Thanks Chuck S.

[Bruce Lancaster]

The 3 7/8 stroker mod was largely obsoleted when the new Merc crank in '49 allowed a cheap over the counter 4", and then 4 1/8 with the same labor as making the 3 7/8...
but stock car racer types with stroke limits frequently cut the big journal cranks concentrically (no change on stroke) in order to slightly cut friction, add a bit of safety, and lower weight of moving parts by using the small journal floaters. Just another old-timey mod trying to get the most with stock Ford parts and restrictive rules...

[40 Deluxe]

What kind of tooling is needed to re-dome the head to match the piston dome? I have access to a mill but very little machining experience. Are there companies that make custom tooling? Or is there something available off the shelf? CNC and CAD are out of my reach-need old school.

[Bruce Lancaster]

Search dome or doming or maybe fly-cutter under Ol' Ron's name...he posted how to make the cutter!

[scooder]

Chuck,
If you do a search on here the 3 7/8 piston question has come up before. I stated in that thread that using stock Ford 3 3/4 pistons and stock Ford uncut heads, as in OEM, will work. From the combinations I've measured, it'll just bolt together. I've dry assembled a 99A block, 8CM crank (4"), OEM 3 3/4 pistons, stock head gasket and uncut 81A heads. The pistons literally just kissed the heads. Now remove the 4" crank, swap in a 3 7/8" crank now you've got 1/16" clearance over the pistons.
The dome on the pistons I had and the dome in the 81A heads matched perfectly. These heads could also stand cutting 0.010" to give 0.050" clearance without cutting into the dome. The dome on these here heads is kinds counter bored into the head, so a 0.010" cut won't actually contact the dome.This would give you a nice uniform quench area, nice. This combination obviously ups the compression ratio aswell, as the combustion chamber now has another 1/16" of piston Sat in it. I think this would be a lovely combination. Higher compression with stock heads with there relatively deep transfer area.
Martin.

[Bruce Lancaster]

Redoming tool, by Ron: here and next page of that post!
http://www.fordbarn.com/forum/showth...ghlight=cutter

[Ol' Ron]

I used 29A Rods with floating bearings on a 4" crank. I like using EAB heads on big inch engines. The give all the CR you need for the street, In my case the 280 in my truck has EAB heads Milled .040", which is a ttad too much, but as Charley NY said alittle work with a die grinder gives the deaired clearance. However I also increase the angle of the exit of the transfer area to improve flow. You don't have to remove much materal just brake the edge. My compression measures 8.2. Engine also has an EAB cam with valve rotators, 2GC carb and a distributor by Richard.
I just got the truck regestered yeaterday and have 3 miles on it. now I have to get it inspected.

[Ol' Ron]

btt

[scooder]

I think I've said it before, incase I haven't, that sounds like a real nice street engine Ron.
Good luck with the inspection, looking forward to some real street use feedback.
Martin.