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Old 01-03-2020, 05:35 PM   #1
elwood
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Default Valve to head clearance

Hey guys, Im wanting to put a little cam in my 8cm Merc engine, how much lift cam I get under a stock iron 8cm head ?
Thanks ...
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Old 01-03-2020, 06:54 PM   #2
Black Fifty
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Default Re: Valve to head clearance

Elwood, the group is going to hit you with all kinds of questions about street or strip, gearing, trans, other engine mods etc.

In all honesty, you should check out JWL's book called Flathead Facts and the Tilden Technologies website.

My two cents. Mike
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Old 01-03-2020, 07:07 PM   #3
JSeery
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Default Re: Valve to head clearance

Quote:
Originally Posted by Black Fifty View Post
Elwood, the group is going to hit you with all kinds of questions about street or strip, gearing, trans, other engine mods etc.

In all honesty, you should check out JWL's book called Flathead Facts and the Tilden Technologies website.

My two cents. Mike
The references are good, but not sure I totally understand the comments. The clearance above the valves is mostly a fixed amount without modifications. So the available lift with proper clearance is likewise fixed. Don't see how usage or gearing or anything else has much of anything to do with it.
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Old 01-03-2020, 07:46 PM   #4
Black Fifty
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Default Re: Valve to head clearance

I guess I never realize that no one else can read my mind.
Elwood is talking about changing the cam Lots of lift and duration might be good at the track but not on the street. Ford got it right with the 8CM camshaft.
Just an opinion of course.
Mike
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Old 01-03-2020, 07:53 PM   #5
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Default Re: Valve to head clearance

Basically, there are a few variables here....how much have the current heads been planed already throughout their life, how high in the block are the valve seats, how thick are the valve heads, etc. Only real way is to measure....
Easiest way would be to clay with what you've got at present, that'll tell you how much clearance you've got at present. Then, knowing your current lift, current clearances, you can calculate how much additional lift you can get by with, and order your new cam with some degree of knowledge that you'll not entail any extra clearancing work by fitting it.
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Old 01-03-2020, 07:59 PM   #6
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Default Re: Valve to head clearance

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Brian nailed it. I would suggest you listen to his advice.
Cheers
Tony
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Old 01-03-2020, 08:19 PM   #7
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Default Re: Valve to head clearance

You are dealing with a 70 year old engine. No telling how much the heads have been milled.This being said I would probably check valve clearances with clay before I choose a cam. I think stock lift on a 8BA cam is about .310 and a Merc. is maybe .025 more lift. You would also subtract valve lash from that. Isky makes some good garden variety cams like the Max 1 which is about .0364 lift which is very popular. Also the Isky 77B is very popular with a little more duration and less lift. About .0325 (very close to stock lift)
Brian nailed while I was typing.....
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Old 01-03-2020, 10:30 PM   #8
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Default Re: Valve to head clearance

If the heads have not been previously milled, you can get quite a lot of lift to fit. Probably more than you'd ever want. But checking actual clearance is a must.
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Old 01-03-2020, 10:35 PM   #9
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Default Re: Valve to head clearance

I always thought .050 head cleaance was the rule or sweet spot. granted if it has a blower more is better.


Can always work milled heads when porting.

Last edited by Tinker; 01-03-2020 at 10:53 PM.
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Old 01-03-2020, 11:12 PM   #10
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Default Re: Valve to head clearance

There must be a reason for any modification to the engine, or any part of the vehicle. Now why do you want to install a cam with higher lift?? You must have a reason. Maybe there is a different way to accomplish the same thing. For a stock engine, milling the heads for a tighter piston to head clearance, improver combustion . this improves low speed drivability and fuel economy at a reasonable cost.
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Old 01-03-2020, 11:19 PM   #11
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Default Re: Valve to head clearance

Elwood, further to your initial request, I think a more important consideration, when selecting a camshaft, is the use the vehicle will be put to. At what engine revs will it be mainly run at, weight of vehicle etc, gearing.....All too often, I feel that people 'overcam' their engines and get some wonderful sounding cam at idle. Then find that, for example, in a street driven car, predominately used on the hiway at 60-70 MPH, the engine is turning 2000 RPM and the cam comes in strong at 3500.
edit, Ron was typing much the same as me at the same time; beat me to post.
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Old 01-03-2020, 11:42 PM   #12
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Default Re: Valve to head clearance

Hey guys, thanks all for the replies, I guess I was kinda skirting the question knowing this is a restorers site,
The reason Im asking what I did, is because I want to run Merc heads on the blower engine Im building for my 34, Pete special ground the blower cam for me, and its big and nasty, without finding the specs, I think its 412 lift .
So, what I was wanting to know, is how much lift you can get under a 8cm head, will they take 412 lift ? Can I fly cut them to get the clearance ? or will they not even take that much cam ?
Am I making any since ?
Thanks again guys,
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Old 01-03-2020, 11:44 PM   #13
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Default Re: Valve to head clearance

It is a "restorer" site, but we flathead guys. Race to stock. You have to clay to find clearance on a head, you can grind heads also. Fly cut to my thinking would lower clearance. Too many variables to just say yes.

Last edited by Tinker; 01-03-2020 at 11:49 PM.
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Old 01-03-2020, 11:48 PM   #14
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Default Re: Valve to head clearance

I know I need to clay Tinker, I just want to know if the 8cm head is even capable of taking that big of a cam .
Guess I should have mentioned he engine is in the mock up stage still, and to clay to check for clearances Id need to have the cam installed and valves setup already.
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Old 01-04-2020, 12:08 AM   #15
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Default Re: Valve to head clearance

I'd be very surprised if the stock heads (if uncut) wouldn't have a lot f room. Given the 8CM's were 6.8:1, with the 4" stroke, there is a lot of room. I had over .100 on a set of 8BA Edmunds Custom heads and I had to have them milled to get the squish right.
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Old 01-04-2020, 12:53 AM   #16
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Default Re: Valve to head clearance

Guess I should have mentioned he engine is in the mock up stage still, and to clay to check for clearances Id need to have the cam installed and valves setup already.



Yes indeed! that is the way to go....yes, you can flycut, to a certain amount, you can also get Cometic gaskets in any desired thickness, can also flycut the piston clearance. Many ways to get the final clearances to suit ....
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Old 01-04-2020, 01:25 AM   #17
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Default Re: Valve to head clearance

The way to get your answer is to, measure the head gasket thickness that your going to use and then, with a depth mic, measure the depth of the area, over the valve, in the head. Add them together and subtract .050, for your clearance and that figure, will tell you the maximum valve lift that the head will take.

.050, is more than needed but, is used to allow flow over the valve. Needed because the back side of the valve opening, hits the back side of the head and then flows back forward.

With a blower, it would be beneficial to have more clearance, over the valve.
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Old 01-04-2020, 09:39 AM   #18
Ol' Ron
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Default Re: Valve to head clearance

Yes, the stock heads will clear the 400jr cam, in most cases. Now when considering this "FLY" cutting. Consider the fact that the head is at a 3 deg angle +/-. So this means that only the top od the valve hits the head. A small Dremet tool will do the clearancing, and this should be done with out the gasket.. Once the gasket is installed you'll have more than enough. But we still don't know why royr running this cam.

PS this should be done after you correct for pston to hea clearance.
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Old 01-04-2020, 11:31 AM   #19
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Default Re: Valve to head clearance

Keep in mind that the valves are at an angle to the deck surface - the highest part of the valve is the top-most part of it (toward the intake). I would clay this area with the .412 cam that Pete ground you - then you'll know.

In my opinion, the correct way to achieve additional valve clearance is not with a typical fly-cutter - running the cut parallel to the head surface (takes too much of a cut in areas that don't need it). The cut should be at an angle to match the valve - which is different side to side.

I tend to figure out the clearance at the top of the valve and use a high-speed porting grinder by hand to achieve the clearance . . . or use a CNC milling machine to do it. I keep the valve pocket at an angle - to match the valve.

Many of the early head designs accounted for the valve angle (like earlier Edelbrocks - which even had a right/left side head). If you're running a blower, you might need more combustion chamber volume anyway (depending on the static CR you're shooting for), so the above might not be as much of an issues (angle cutting the valve pocket).

Make sure you achieve a .040 squish area above the piston, then figure out how big your chambers need to be to clear the valves and to achieve the final static CR you're shooting for.

Best of luck!
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Old 01-04-2020, 12:40 PM   #20
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Default Re: Valve to head clearance

Here we go, these are the answers I was looking for, thanks all.
Im really wanting to run Ford heads, now I know I can with a little effort.
Thanks again all ...
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