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Username Post: Let's talk about head gaskets        (Topic#349555)
Junkyardwarrior 
Contributor
Posts: 305

Loc: Yuma AZ
Reg: 02-25-15
02-07-18 01:40 PM - Post#2723664    

So, as I've noticed a lot of people have an opinion on how to pick a head gasket. I personally am wondering about PTFE Coated Kevlar for an iron block with aluminum heads in my case, but I'm curious as to other opinions as well. So 1) Would it be safe for my heads if I used previously stated gaskets and 2) anyone want a general head gasket discussion block?

"8 cylinders of why the f&@% not" - me


 




IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-07-18 07:01 PM - Post#2723696    
    In response to Junkyardwarrior

Discussion sounds great, as long as it includes correct and proper quench distance input.



 
Junkyardwarrior 
Contributor
Posts: 305

Loc: Yuma AZ
Reg: 02-25-15
02-07-18 08:30 PM - Post#2723707    
    In response to IgnitionMan

I agree completely. I think quench distance is far too misunderstood and way too important to overlook. Actually I think that's been the issue I've been fighting with my motor not wanting to cruise without surging and popping the whole time. I never considered my block may have been decked and I ran a .028 head gasket. Hence why I'm replacing them.

"8 cylinders of why the f&@% not" - me


 
IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-07-18 09:07 PM - Post#2723709    
    In response to Junkyardwarrior

Well, with that gasket thickness, and the piston down in the bore between .011 and .017, the quench would have been right in the good zone.



 
Junkyardwarrior 
Contributor
Posts: 305

Loc: Yuma AZ
Reg: 02-25-15
02-08-18 07:45 AM - Post#2723736    
    In response to IgnitionMan

It could be right to be honest, I'm not sure. Part of why I'm tearing it down. I have to verify my piston deck clearance to make sure I had the proper quench distance. One question I do have is on a dish piston, I measure from the high point of the piston correct? On the outside edge?

"8 cylinders of why the f&@% not" - me


 
IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-08-18 12:57 PM - Post#2723765    
    In response to Junkyardwarrior

If you look at any piston, you will find a flat deck on it, pop-ups have it circling the raised areas, dished, around their outer edges. This is the place to measure between it and the gasket deck for the piston down in the bore, or if it is zero, or positive deck.

There is a method to check quench with the heads in place, and results should be taken with some questions. The method goes like this,

Pull both push rods from the cylinder you want to measure, to keep the valves closed, pull the spark plug.

Turn engine, BY HAND FROM THE BALANCER, to get the piston up, but not to full TDC. Through the spark plug hole, insert a section of SOFT plumbing solder so it can be flattened by the piston deck when the engine is rotated, with the rest of the solder left outside the plug hole, so the quench will flatten the solder, and it can be removed easily after the flattening.

HAND TURN the engine to get the piston to, and past TDC.

Remove and measure the flattened solder, this is the quench distance, and is fairly accurate.

The ONLY questionable issue with this method is what if the engine has been in service for decades, and has severe carbon buildup on the piston deck? Most engines we work on that have been rebuilt, modified, done not so many miles ago, should not have a large carbon buildup, if any at all.

Only other fool proof method is to do as you thought, pull the heads, clean, measure.



 
Junkyardwarrior 
Contributor
Posts: 305

Loc: Yuma AZ
Reg: 02-25-15
02-08-18 01:02 PM - Post#2723766    
    In response to IgnitionMan

I'm tearing the intake off anyways to replace my lifters so I might give that a shot since the push rods will be out anyways. Replacing the spark plugs too. If it measures good I won't pull the heads because, let's be honest, who wants to take the heads off their motor? Either way, I'll have a set of gaskets in waiting so I can swap them if need be. Even if it's in the questionable range 1/100th of an inch won't kill that much compression so better safe than sorry I say.

"8 cylinders of why the f&@% not" - me


 
IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-08-18 05:50 PM - Post#2723803    
    In response to Junkyardwarrior

Lets clear up just what quench is, and what it does, and doesn't do.

Quench is tasked with the holding of, and directing end mixtures of fuel/air into areas that can have catastrophic results if the mixture is not present in the area. I

Examples:

Too little quench, mixture is literally blown out of the quench area, leaning out the area.

Too large an area, same result, with the area being so large, the mixture migrates out of it.

Benefits of retained end mixtures in the quench area, leanness is reduced significantly, to eliminated, and when the mixture is retained, piston edges run cooler, as do top piston rings. Proper quench also promotes more complete mixture burn across the top of the piston.

The one objective in getting as complete a burn as possible is to get the largest "push" possible across the most piston top area as possible, to push the piston down in it's power stroke as efficiently as can be done. Proper quench does help do just that.

So, we need to make sure the mixture isn't blown out of, nor migrates out of the quench area. If allowed to lean out from lean quench areas, very serious issues will result.

Quench has really nothing to do directly with cmpression ratios, but proper quench is vital to getting the compression ratio to work correctly, without detonation frm end areas running too lean, and overheating.

With the proper quench, compression ratios can usually be run between 1/4 to 1/2 a point higher, simply because the end areas are not running detonation level lean.

Ever take heads off an engine and see carbon on the piston top, everywhere but the edges of the pistons? They are still clean, and can be pock marked with small holes from detonation. Tihs is the quench areas running lean, quench very seriously incorrect.

Years ago, I did a Ford 302 engine over for a friend. It overheated, detonated and just plain ran bad. The shop that built the engine did a good job, save for the quench distances.

The engine had 400 miles on it when I got it, and we went through ignition tming, carb, all sorts of other issues before I checked the quench. .115 was the reading. The engine had "destroked" Silv-O-Lite pistons, they are made with the pin heights higher by .025 from stock. This was supposed to lower the comression ratio to help with pinging and detonation elimination.

The pistons sat down into the bores at TDC .055. Add to that, a head gasket that had .060 compressed thickness, not a winner.

Everything else on the engine was top notch. I simply had the block milled to zero deck, and the intake manifold cut to fit the head cuts, and a new gasket set with .042 head gaskets, WITH NO OTHER MODIFICATIONS, and it stopped detonating, stopped pinging, ran like it should have in the first place. It even got to use the 12 degrees initial, 36 degrees total, and the 10 degrees of vacuum advance on full manifold vacuum, with no adverse effects what so ever.

That Ford engine wasn't the only one I have "reset" to have the right, reasonable quench, many Chevrolet engines as well. All responded positively.

I also work on Japanese motorcycle road race engines, and their development. The Japanese have two "gaps" they consider esssential, one for ignition, the other for quench, which they call squish clearance.

The one for ignition energy is called "E Gap", related to spark energy for firing the ignition off efficiently.

The other is "I Gap". I Gap is "Ignition Gap". I Gap IS squish (quench) distance on their scale of speaking, and they consider it so essential, getting it right makes for running 1,000cc inline 4 cylinder, EFI injected, water cooled MotoGP engines to between 290 to 340 horsepower, and at FIM Racing Group limits of 18,800 rpm red line levels. These engines are not turbo, nor supercharged.



 
models916 
Valued Contributor
Posts: 4774

Age: 67
Loc: Addison, IL
Reg: 05-28-10
02-09-18 06:24 AM - Post#2723849    
    In response to IgnitionMan


Quench has nothing to do with the dome or bevel of the piston. Just flat spot on the head to the flat spot on the piston at TDC with an average on the rock in the bore.



 
IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-09-18 07:02 AM - Post#2723852    
    In response to models916

This is great, more excellent, factual info.



 
Shepherd 
Frequent Contributor
Posts: 1258

Loc: Lake George, NY
Reg: 11-11-15
02-09-18 09:52 AM - Post#2723872    
    In response to IgnitionMan

Back in the 70's I ran a 64 Ply Max Wedge race car, when blueprinting the engine the minimum deck height spec was.018 piston height below the deck, a steel shim head gasket measuring .022 was used, so .040 quench, someone at Chysler knew what they were doing. 12.5:1 compression with an 86cc head.



 
models916 
Valued Contributor
Posts: 4774

Age: 67
Loc: Addison, IL
Reg: 05-28-10
02-12-18 05:32 AM - Post#2724137    
    In response to Shepherd

1962 factory quench on the 409/409 was 28. I run mine there abouts. Piston rocks at TDC so you have to average a little and make sure it's not tighter than that.



 
IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-12-18 10:30 AM - Post#2724149    
    In response to models916

I've not seen that tight a quench in any Way engine I ever worked on. They have had the piston deck that uch below block deck, and to maintain that quench, there wouldn't be a head gasket in place.

I have seen both 409 & 425 engines with .005 down in the bore, with two .020 steel shim gaskets per side, though.

EDIT: finally got to my computer, and off my phone, easier to write. On the W engines I have owned and done, 409 - 409/425, and Z11 427, I have seen quench done a lot of different ways, and as mentioned, there is one glaring problem and one not so well known with super tight quench distances.

The pistons themselves do not have a flat top, they have a flat section, then an angle, so they will form a wedge chamber, and, part of the tops are very heavy as opposed to the angle side, which doesn't help piston rock over in the bores. With super tight quench. The result on rock over at higher rpms is the heaviest section of the flat top its the head, rather hard.

The second issue also aids the pistons hitting the heads, connecting rod stretch.

Add both the above, and run the engine up in RPM's, tight quench, recipe for instant disaster.

The late Lamar Walden, a noted W engine tech and developer, always set the quench no tighter than .042, even with his aluminum heads, and with all the sets of aluminum rods he did for them, even further open, because the aluminum rods stretch more than the steel ones at top RPM's.



 
models916 
Valued Contributor
Posts: 4774

Age: 67
Loc: Addison, IL
Reg: 05-28-10
02-13-18 08:43 AM - Post#2724246    
    In response to IgnitionMan

1962 only got a single steel gasket on the 409/409. 63, 64, 65 doubled up on the gasket on the 425hp. I'm going by what I was told by Paul Esterly of E&R racing engines, IL. They prepped a lot of famous Stock and SS Chevy 409s and Pontiac engines back in the day. Arnie the farmer was one of the Pontiac customers.



 
IgnitionMan 
Valued Contributor
Posts: 3306

Reg: 04-15-05
02-13-18 03:50 PM - Post#2724288    
    In response to models916

My experiences come from working on my own engines, directly, and also working at Chevrolet Engine Development.



 




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