Stacking Gaskets...Do any of you do it?

[Ando]

I'm asking bc the only gaskets I have seen are very thin...until I happened upon and used a really cool and thick metal/resin type gasket for the manifold/exhaust connection that I had to remove when removing the manifold for inspection. Now I only have the thin Universal factory gaskets that seem thin and flimsy compared to that other one.

[ndutton]

Only when instructed as in the case of our head gaskets - - 2 required.

[GregH]

Only when instructed as in the case of our head gaskets - - 2 required.

+1 .

[Dave Neptune]

Gskets

When doing an A-4 or some "flatheads" I decide on how many head gaskets for proper deck clearance for air flow through the plenums. On the A-4 I always recommend 1 gasket for a direct drive and 2 for the reduction units. I have found that the little extra compression helps the slower turning direct drives and 2 for the reduction units to maintain enough flow for the higher RPM's. This is also common on many flathead applications.

As far as stacking other gaskets "no WAY" unless the additional "space" is to get things to line up after machining. If extra gaskets are needed to get non flat surfaces to seal then fix the parts so they seal properly with the specified gasket.

Dave Neptune

[ronstory]

When doing an A-4 or some "flatheads" I decide on how many head gaskets for proper deck clearance for air flow through the plenums. On the A-4 I always recommend 1 gasket for a direct drive and 2 for the reduction units. I have found that the little extra compression helps the slower turning direct drives and 2 for the reduction units to maintain enough flow for the higher RPM's. This is also common on many flathead applications.

Dave Neptune

Whoa, one gasket? A fundamental shift in A4 physics. I love this forum.

Cool idea and theory. How much of a compression ratio does a single gasket provide vs. the "traditional" two?

[Dave Neptune]

Sorta on subject

Ron, I don't think it is the additional compression that increased performance slightly although it did not do most of it. The performance I found was in the middle slow cruise ranges up to a fast cruise not WOT. At WOT the gain on my engine was just over a hundred RPM after getting the carb re-jetted.

The performance was gained through the working range of the motor by the increase of velocity through the plenums allowing the engine to work harder at higher manifold vacuum settings. It gives velocity to get to the cylinders and the velocity eliminates any fuel puddleing in the plenum and creates a better fuel atomization to the cylinders for a better burn. This puddleing can be a problem in an updraft which is part of the reason for the scavenge tube.

The engine ran on regular as I could not fined a lower octane rated gas.

Dave Neptune

[ndutton]

Don't forget when tweaking compression that our flathead isn't like other flatheads. We have 4 piston rods between crankshaft main bearings whereas most other engines have only 2 or 1. This long unsupported crankshaft design did not fare well on my spare engine. When I tore it down it was missing the #2 rod bearing shells explaining the deep, sickening knock when it ran. As a result, the crank was also bent.

[Dave Neptune]

HP and load factors

The compression should have little to do with bearing wear. The bearing wear is due to HP load and shock loads on the engine. Timing being advanced will cause a pre-ignition condition which will kill bearings from the shock load of the pre-ignition. The HP gains from very little compression should have no input to bearing wear. The gains are very slight and only noticeable when well tuned.

Do not forget that the direct drives are reduced to less HP from the limitations of RPM's to about 18~20 HP at 2500 (if attainable) or so RPM's and the reduction units can make the 35 rated HP at 3500 RPM a whole different application of available HP to the crank shaft.

I ran my direct drive with one gasket for over 25 years after testing and it is still running as far as I know. I only use regular gas and never any Hi-test as it is a complete waste and makes less torque and HP in an A-4!

Timing and lugging from to much prop are the bearing wear factors not a fraction of a point in compression. What you need to pay attention to is a machined head, this machining also raises the compression slightly but MOSTLY restricts the "amount" of fuel/air that can be "flowed" through the plenums due to the reduction of plenum area. It's just how flatheads work! It is not compression that makes a good flathead it is how much you can get to the cylinders through such a restricted "breathing" process.

Dave Neptune

[ndutton]

I did not mean to correlate compression with bearing wear but rather our unsupported crankshaft's vulnerability to added stress.

[Dave Neptune]

Neil, I understand completely. I am trying to point out that poor tuning practices have more to do with bearing/crank related wear and failures than trying to gain what just is not there. These engines probably ran better in the "time of design" because of lower octane fuels being the "NORM".

The fuels today are far better but not designed for such low compression as in the days of yore. The lead being removed really has little to do with the A-4 as the block is "hi nickel" and does not need the cushioning of the lead for the valve seats and rings, so no need to do the traditional upgrades of the pre 70's engines. What these engines need is lower octane. This "higher octane" has lead to engines running with way to much advance, thus shock loading the crank with no pre-ignition noises (pinging) as we don't have enough compression to make these pre-ignition noises (unless way off) leading to the exaggerated bearing loads. This is why I say never use premium in an A-4, yeh it runs fine but does not make as much torque since most of it is burned before the piston is done being pushed by that burn.

The A-4 is a great marine engine and well proven over the "decades", a testament to it's engineering. However 50+ years later we need to keep in mind the fuels and oils available at the time of the A-4 are no longer there. The A-4 needs lower octane fuel and the oils today are so much better that the cheapest krap is superior to anything available then!

This would of been a good overall post to tuning instead of gaskets.

I hope this helps some or all to understand the simplicity of the A-4.

Dave Neptune

[Sam]

Wow, thanks Dave for a great explanation on the "lead" and octane issues. It has been years since I have read anything about leaded fuel vs unleaded and then the comments made were that the "cushining" was needed and a lead substitute fuel additive was beneficial. Years ago I bought a large container for off road/marine engines and have used few oz per year possibly without harm but probably w/o real benefit in my early model A4??

The torque loss with the higher octane was also thought provoking.

[ronstory]

Dave--

Because I have that pesky curiosity gene that I seem to have acquired (or mutated), with the higher octane fuel we have today does it make sense to retard the timing after TDC?

My elementary logic is is the fuel is going to burn faster than what the A4 was designed for back in the 1940s... could we mimic the effect of lower octane fuel with different timing setting?

Random thoughts...

[Dave Neptune]

Octanne

Ron, the need is for lower octane which would be a faster burning fuel for low compression.

Hi-compression engines require a much slower burning fuel as it is compressed much more IE denser fuel/air mix. This denser mas of air fuel needs to burn slower in such a compact state so it can burn steady and push the piston down not go bang causing a lot of stress on the related parts. The hi-compression engines are designed for higher RPM and hi RPM power.

In the low-compression engine the compressed air/fuel mass is not as dense so it needs to burn faster so the piston is not already heading down the cylinder before the burn is really pushing. The low compression engines also operate at far less RPM's.

The timing of these burns is most important. Our A-4's seem to like a total of 34 degrees of advance (that's 17 degrees in the distributor). This advance is controlled by the centrifugal advance in the distributor. You want this full advance by 15~1700 RPM's. The available spring kits work very well!!!

By using "premium" fuel you may be able to run more advance but this will make less torque and run rougher. A duty type engine as the A-4 likes to work all day when running smooth with no pre-ignition shocks on the crankshaft. This preignition or "pinging" as it is commonly called can be happening in a low compression engine and not be heard like in a fussier hi-compression engine. The engine may seem more responsive when reving or at low throttle settings but when loaded up you will have less torque.

Case in point. I drive a DP Hemi Challenger with a manual trans. This S/B Hemi has over 10:1 compression and is tuned for premium fuel and is quite lively to play with. Now this is a computer controlled OB-2 system and is a premium fuel engine. I run regular gas in it when on trips or just cruising around and the computer handles the timing. Now when I give her some 91 or 93 octane fuel she really livens up. This engine will make far less HP on regular however the computer manages the timing when doing so. The A-4 runs at 3500 max and the Hemi at 5800. To make power at higher RPM compression is needed thus the fuel restrictions.

Dave Neptune

[ronstory]

Dave, thanks for the detailed explanation. I've never really owned an engine that I worked on with a compression less than 8:1 (IH Scout) so I'm in new territory. The great thing about that IH engine was any old gas I had in the shed I would just run through the Scout, it didn't care.

So the takeaway is use the lowest octane ethanol-free gas you can find and check the disti advance mechanics for healthy operation.

Is static timing at 0deg BTDC sill the best rather than adjust the disti for max RPM under load?

[Dave Neptune]

Ron, if you have TDC marked the timing can be set with a timing lite. Many of us have marked TDC on the accy drive with a made to suit pointer. This TDC mark will be close enough for most applications.

I don't remember the fraction nor the diameter of the accy drive pulley. Tom may remember for sure. I think it was 11/16"~.6875"( may of been 13/16" I just don't remember as it has been many years). From the TDC mark measure 11/16" from the TDC and put another mark. The fractional measurement represents the 34 degrees of full advance. Now bring the engine RPM's up with the timing lite on the new mark while revving the engine to around 2000 RPM's so the advance is now solid and not moving this is full advance, so now set the distributor at full advance. This full advance should happen around 15~1700 RPM's.

If the timing now at idle is not around TDC then adjustment or cleaning of the C-advance is due. This is where the new "lighter advance springs" really shine!

Dave Neptune