Technical Flathead valve to head clearance?

A quick question..... I had a pair of old high compression weiand 8ba heads repaired and was planning to use them on my just rebuilt merc flathead in my coupe.

Well when claying them, some of the valves just squish the clay out on the back edge of the combustion chamber with the headgasked installed.....aka zero or minimal clearance at the very edge.

So how much should I have the heads cut above the valves? 0.020? Or should I go more? Piston clearance was fine.

How much meat do theses have above the valves?

I am running an isky max 1 cam on new stock spec valveprings.

 

How thick is your head gasket? And how much clearance do you have at piston dome height. You can use a thicker head gasket but you need to know all your clearances. It might be cheaper to get new head gaskets.

 

0.075 at the dome

I am not sure on the gasket....it is at the machine shop with the engine and heads and I didn't measure it. It is a stock felpro gasket

 

I just measured my old felpro gaskets and they are around 0.050

And I just ordered a slightly thicker copper set to use insead of the felpros....they a supposed to be 0.062 compressed.

So I would gain 0.010. There but still would like to know how much I should cut off?

Part number

91015895

 

No input from anyone?

I guess I will cut them .025 and with the extra 0.012 from the gaskets I will have 0.037...........

 

You are looking for some performance with that cam change, so piston squish clearance should be closer to .045 or .050 to work better. Gary

 

There have been a lot of threads on the valve to head clearance for Ford flatheads on here & on the Fordbarn.
Bored&stroked is a member who specializes in flatheads that you could PM.
http://www.jalopyjournal.com/forum/threads/valve-to-head-clearance-on-a-flathead.48666/
http://www.jalopyjournal.com/forum/threads/flathead-valve-clearance-ok-pistons-close.197285/

 

Agree...mill for proper piston clearance, a very profitable improvement, then find room over valves. On valve clearance, 040 is an easy answer, less ir probably fine. A secret HAMB researcher said that there is a tiny amount of flow from there so he left around .020.

 

Thanks Bruce!!!

I did read those other threads plus a bunch more and didn't find anything saying valve clearance.

Now as far as piston clearance that 0.075 is right at the top it tapers to around 0.050 or 0.060 out from the top of the dome. So isn't really ideal.

From what I read these weiand high compression heads a a very thin casting.. So you really think they have enough meat to safely mill another 0.020 or 0.030 off the surface. And reshape the dome plus cutting the valve area a total of 0.050.
I am thinking that I may end up punching though to water or at least be close.

Or am I better to just scrap the heads altogether and go with stock iron heads and mill those?

 

I would cut a little more off gasket surface (.010) with felpro then do the valve relief. I would be more concerned about a thin deck than a few spots around valve reliefs being thin. I would check piston clearance on all 8.can u get heads sonic tested?

 

You will get the most power with a 0.040 piston dome to head clearance. The valves could be as close to 0.020 with high end valve springs, but 0.030-0.040 is a safe way to go. You will gain more power by piston dome height than you will with bigger valves. I don't know anything about your heads so I didn't want to tell you what to do and then you go mill the heads and cut new valve pockets just to bore/mill into the water jackets. Good luck and keep us posted.
Btw what does your machine shop think????? If they can't tell you anything good go get your shit out of there.

 

Also you say your running a isky max 1 cam. That's a 0.364 lift cam. I would use the isky 185g springs or Lincoln v-12 springs. If you can use a better spring and stay in your budget it could be a cheap insurance plan if you are going to run it up in the higher rpm range that we all want too.

 

The machine shop has never seen these heads before so have no experience with how thick they are and seem concerned about cutting too much. I have used this place for 2 other motors and trust them but they arent dedicated flathead builders. Though they have built a lot over the years but mostly stock rebuilds. We are just trying to make the right decisions and I am trying not to go broke....which i am already at that point!!!

I don't even remotely claim to know what I am doing so any input is welcome.

But at this point I already bought the copper gaskets and really don't have the cash for new valvesprings at this time.

 

maybe just run the stock heads until you get some cash together. Get it on the road. Once you get some extra money get the heads worked over.

 

It is highly unlikely that taking .020 off the heads will hit water - can you send some pictures of the chambers as they are now? Normally these heads will have at least 1/4" thickness in the dome and valve areas. Now if somebody has been milling the crap out of them over the years - who knows how thick the deck areas are???

I can usually tell if they've already been milled - just by looking at the chamber diameters. On the valves, since they are at an angle, the first and probably only place they'll hit is at the top of the valve pocket - on the edge of the valves. If you need additional clearance there, then 'MAYBE' they can fly-cut the valve pockets - but they should do it at an angle to match the valves (don't just hog out the whole pocket, where you don't have clearance issues). If they can't do it this way (at an angle), then you/they can do it by hand with a high-speed air grinder with an aluminum cutting bit (small flame shape is what I use). I've done a ton of valve pockets by hand - not a big deal. Then you'll just use a sandpaper roll to smooth things out. Just make sure somebody knows how to use the tool and doesn't give the heads a 'root canal'.

Note: If you're not really good with a air porting tool, then make sure you tape up the the deck surfaces on the heads - around the valves . . . so when you slip with the grinder, you don't cut into the sealing surfaces. Now ask yourself - how would I know that is bound to happen???

I normally run .050 head gaskets (compressed). There is no reason to run thicker ones - and then mill your heads more - that makes no sense. I'd aim for .040 to .045 or so over the piston domes. If the dome profiles don't match your piston domes - then you'll either have to redome the heads (and that takes a special tool or a CNC mill and a 1/4" ball mill or expert hand work with an air grinder). On your setup - just makes sure that .035 is your tightest clearance on the piston to head clearance . . . will be more in other areas.

On value to head clearance, as long as you have .020 or more . . . you'll be fine. If you ever float the valves a bit - what is the worse that can happen?

Obviously all these clearances are based on final assembly - with a compressed/installed head gasket. Just make sure you're doing the math correctly - it surely isn' thard. LOL

 

On the piston clearance...biggest issue is to generate max turbulence for quick flame travel, resistance to detonation, etc. Benefits are more power, great resistance to pinging allowing more compression, responsiveness.
Remember those SBC powered cars of the late '70's and early '80's pinging their wretched ways down the road? Chevy had cleverly destroyed the quench area and turbulence by going to 360 degree dish in piston...shorty thereafter. maybe 1985, they hired an engineer and rediscovered the quench area and soon were producing 10:1 smog motors that went fast...

 

As usual, Bruce knows what he is talking about! Flow, quench and turbulence are key to making HP in most engines - and the Flathead needs all the help it can get! Now the full-Hemi chambered engines of the past . . . different deal altogether . . . but they sure are good for blowers and nitro!

 

Thankyou all so much for your help!!!!

My phone was dead when I picked everything up yesterday so I didn't get a pic of the heads. They still have them and are going to cut them deeper and mill them,a bit more..... I probally won't end up with 0.050 quench but will be closer than 0.075.

Here
is a few pics of the motor once I got it home and a pic of it partially assembled and painted.

 

It is hard to imagine you having that much quench - unless somebody domed the heads before. Post some pictures of the chambers and also of a piston at TDC in the block - just want to 'visually see' what you have going on!

 

Here is the block... Pistions are just shy of the deck.

I will get chamber pics as soon as I get them back.

 

watch your plugs to valve clearance too. I have a set of those heads and have to put 2-3 spark plug washers on certain plugs so the valves don't 'kiss' the electrode. I'm using NGK B6HS plugs.

 

Do those plugs require washers as well?

 

Well - your pistons are just a bit 'down in the hole' - so that does increase your piston to head clearances. Depending on how deep the dome pockets are in the heads, you may want to take some off of them . . . but I usually don't deck/mill heads unless it is necessary (warped, corrosion, etc) - but in your case, you might want to tighten up the piston to head clearances if you can. It will probably be somewhat of a compromise - but it will still run well.

 

And - try to get a plastic bag around that motor . . . you don't need to get a bunch of crap into it! LOL

 

Ha ha. Will do.

 

The washers will depend on the lift of your cam. Just something to watch out for. Sounds like you dont need another headache. I had trouble when I changed head gaskets. the new ones must be just that little bit thinner.

 

I was probally going to run autolite 216s like I did with the iron heads before rebuild... They are a tad shorter reach wise.

Yesterday was nice (cold but not raining or snowing) so I got the motor in the car and everything hooked up except for the heads put on....still waiting on them.....

 

You probably won't have a problem in general - but the 216's are about the shortest ones. Keep us posted when you get the heads back.

 

Well I stopped at the machinist and checked out the beds again and got some pics... He hasn't cut yhem,yet he is hoping to get to them Friday.

216s are really down,in the spark plug hole but may be unshrpided when he cuts the valve pockets. I ordered some of the nkg plugs too in case I need extra length.

Here is a shot of one of the chambers.


You can,just see a shiny spot where the very edge of the valve touched on the bottom of the 2nd pic.

 

Well, given that the head has been milled a decent amount - don't believe you'll have too much piston to head clearance - might come in "about right" (just hoping for your sake). On the valve pockets, have him do them on an angle (that matches the valve angles - which are different side to side) - this will help you not take too much off of the spark plug area. It is a bit harder to do it this way - but the right way to do it.