Milling a flat head?

[Master Hack]

I know its been done. How much can a (Briggs) flat head be milled before causing problems? And will that produce any noticeable difference in performance? I’m sure .010 is ok, what about .020? More? Stock 5 Hp motor. No real reason for doing this, just cuz l can and want to see what happens.

 

[Russ2251]

Increase Compression Ratio/Eliminate Head Gasket

Increase Compression Ratio/Eliminate Head Gasket-NO MILLING Very straight forward. Three things are needed: 1.) A large workable surface such as safety glass and must be absolutely flat. The surface I use (accurate to a few millionths inch) is from a discarded wafer prober and is not readily...

www.diygokarts.com

 

[Master Hack]

A surface plate would work for that as well and is readily available for a few bucks. What I am looking for is how much material can be removed before it causes problems. Valve interference and or detonation or the like. Surely someone has done this, gone too far and screwed up a head?

Granite Surface Plate - Lee Valley Tools

www.leevalley.com

 

[Russ2251]

Eliminating gasket IS equivalent to removing .060" from head without actually doing so. There is 0 (zero) damage done.
No milling, no worries = win, win. No interference, No detonation.
Gasket can always be replaced if you want to change back to factory spec.
Difference in power is immediately noted.

 

[Master Hack]

I get it thanks! Thats kinda what i’m looking for.
.060 doesn’t cause any problems. Have ya tried going more? The compression ratio on an unmolested engine is what ? Around 8:1?
I’m playing around with a couple off the wall ideas. I don’t do much that would be considered normal anyway.
you did come up with a simple, quick and effective way to increase performance, brilliant!

 

[redflash]

how confident can one be that there will be no leak...without the head gasket, on an old flathead ?

Da Redflash

 

[Thepartsguy]

It’s not about compression anyway it’s bout flow. Look at the eyebrows on a stock 5hp then realize the muffler has a plate in it that the exhaust smashes into before going around the baffling. that’s of course with the swirl metal piece restricting the intake. And some terrible port casting leftovers that would pull fuel in the intake way Before allowing it to flow smoothly. take the eyebrows off and make a bigger combustion chamber. mill the head a bit so your compression stays the same and i imagine it would preform way better because the compression has not changed but it can flow sooo much better. Then putting The valve keepers and an exhaust spring in the intake valve to make a stock raptor valve train. throw a dyno cam in the mix and you can have a lot of fun. Edit: are you throwing away the oil bushing sidecover and going with a bearing side cover? I can’t be sure the exact number arc racing said but it was like up to 40% reduced crank flex? Maybe it was 60% crank flex? there are ways to get power other then just more compression.

 

[Master Hack]

there are ways to get power other then just more compression.

You are absolutely correct! But just for the purposes of this conversation, l’m interested the head milling only. There are probably better ways to get power than just increasing compression.
For now all l’m trying to accomplish is to help out a youngster with $0 and a badly honked up head. (Briggs head not the young’n).
And get him a small, cheap little bit more.
Perhaps l should have been more clear with my original query.
I have another head on a parts engine, but wanted to see what happens after milling some off, got nothing to lose at this point.
Not looking for any other mods right now.

 

[Thepartsguy]

And get him a small, cheap little bit more.

ohh ya! Exactly what I do. Found a junk drill with a mostly used up wire wheel Fixed the wire plugged it in and it worked! used it and a half can of paint I got from a yard sale bin and made a nice clean engine. Chucked a cutter bit in the same drill and did away with the eyebrows. the port castings almost needed no work for a change. if it’s a tank style carburetor pull the swirl piece out. A master hack can make a header. Traded the engine for a gokart with a 5hp engine on it.

 

[Master Hack]

The paint looks great, however l like the patina in the B4 pic!

 

[Denny]

Leave the eyebrows alone and relieve the block please! Flathead 101. You can mill the head just use some Play Dough to check for proper piston to head clearance and valve to head clearance that’s all. Heck you could use the Play Dough to check clearances first then mill the head. Flat head engines in general and air cooled engines in particular are susceptible to pre ignition compression ratios are usually around 7-1.

 

[Master Hack]

My engine experience has been only with engines having 3 to 7 more cylinders than these little things. I kinda like these things, cuz heavy lifting equipment is not necessary! So now l’m intrugued, where can l find info on releiving the block?
All this talk, l’m going to releive myself, l’ll be right back…..

 

[Denny]

I can tell your potty trained!! You could look on the H.A.M.B. For information and pictures.

 

[Master Hack]

Stupid old guy here, What is a H.A.M.B.? something for a sammich?

 

[Denny]

Hokey A$$ Message Board.

 

[Denny]

They are traditional hot rodders. All things old car related nothing newer than 1965 and no muscle cars or mustangs! Check out the Larry Farris Tempted Once thread. I’m SS327 on there.

 

[Thepartsguy]

They are traditional hot rodders. All things old car related nothing newer than 1965 and no muscle cars or mustangs! Check out the Larry Farris Tempted Once thread. I’m SS327 on there.

been a bit pretty sure my name has bin at the end on that forum board