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View Poll Results: Double Stack Gaskets?
No 2 25.00%
Yes 1 12.50%
Only on certain connections 5 62.50%
Gaskets are part of a conspiracy to squeeze out a few extra dollars from us and are unnecessary 0 0%
Voters: 8. You may not vote on this poll

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  #1   IP: 45.49.35.172
Old 03-10-2020, 12:44 AM
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Stacking Gaskets...Do any of you do it?

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.
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Old 03-10-2020, 07:46 AM
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Only when instructed as in the case of our head gaskets - - 2 required.
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Old 03-10-2020, 08:36 AM
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Quote:
Originally Posted by ndutton View Post
Only when instructed as in the case of our head gaskets - - 2 required.
+1 .
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Old 03-10-2020, 11:11 AM
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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.

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Old 03-10-2020, 04:14 PM
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Quote:
Originally Posted by Dave Neptune View Post
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.

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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?
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Old 03-11-2020, 12:33 PM
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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.

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Old 03-11-2020, 04:41 PM
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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.
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Old 03-12-2020, 01:54 PM
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Lightbulb 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.

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Old 03-12-2020, 02:14 PM
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I did not mean to correlate compression with bearing wear but rather our unsupported crankshaft's vulnerability to added stress.
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Old 03-12-2020, 03:02 PM
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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
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  #11   IP: 71.201.94.254
Old 03-12-2020, 03:56 PM
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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.
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Old 03-12-2020, 11:40 PM
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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...
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Old 03-13-2020, 11:49 AM
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Lightbulb 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.

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Old 03-13-2020, 12:10 PM
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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?
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Old 03-13-2020, 01:16 PM
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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!

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Old 03-13-2020, 02:22 PM
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Got it. I'm almost to the assembly phase of the build (painting now) and I have a late model. I was going to mark TDC on the flywheel and punch a hole in the sheet metal cover and TDC reference on it. Now it looks like I need a 34 degree mark as well.

Where do you get the correct lightweight advance springs? MMI?
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Old 03-13-2020, 03:52 PM
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OK, my Google-fu just found this thread:

http://www.moyermarineforum.com/foru...ead.php?t=2998

Looks like Indigo and just contacted Tom and he had only sold the springs... plus he still carries them.
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Last edited by ronstory; 03-13-2020 at 03:53 PM. Reason: typos
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Old 03-14-2020, 09:19 AM
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Dave -
34° of full advance? Twice the specification?

ref: http://www.moyermarineforum.com/foru...ead.php?t=2324
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Old 03-14-2020, 11:28 AM
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17* in the distributor is 34* on the crank.

Dave Neptune
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Old 03-14-2020, 12:00 PM
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Quote:
Originally Posted by Dave Neptune View Post
17* in the distributor is 34* on the crank.

Dave Neptune
Yes but you'll notice the pdf curve Don attached in the link I provided is in degrees BTDC. TDC is a crankshaft position so wouldn't the curve be crankshaft degrees? As best as I can recall, the only time distributor degrees came into play was with the old school distributor machines that measured distributor function off the engine.

Thatch's extensive timing work from a few years ago provided timing mark measurements for both the flywheel and the accessory drive pulley, 1.71" and .56" BTDC respectively. Using the flywheel marks, with an 11" diameter flywheel, 1.71" on the circumference calculates to 17°.
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Last edited by ndutton; 03-14-2020 at 12:14 PM.
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Old 03-14-2020, 12:37 PM
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Neil, same distributor machine I used.

I don't know how to copy and post from one post to another so check out Don's post in Engine timing advance 5/2/08 post #2 by Don on his findings.

I used Tom's springs and Bruce's machine to set the springs for 17* or as close as I could get. Against the stops full advance was achieved at 1550RPM's. I set the timing at 1900 to 34* on the crank which pinned the weights. I let the engine come back to idle and it hovered around 0* or near TDC.

I don't remember the measurement for "max timing" on the accy pulley where I mounted the pointer. No more A-4 so I can't check the dia of the pulley Tom & I used nor the measurement of which we concurred from TDC on the pulley. Those numbers are lurking on the forum somewhere around a decade or more ago.

Full dist timing of 17* against the stops to set the timing. The idle moved around slightly as idle was controlled by the springs IE no stop.

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Old 03-18-2020, 08:45 PM
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not a displacement hull comparison

As to rpms and head gaskets:
I am only using one head gasket, and last outing turning 3600rpm direct drive.
In my tuning process in my planning hull, I got an increase in rpms with headgasket removal.
I also tuned the timing until I got max response and top rpm.
I haven't tried spring changes yet.
The cubic inches are so low per cylinder in the A4 as well as the intended rpm, I think we have more than enough flow available, given since we are under .240 valve lift.
I built kart racing flathead engines, and turned them 10,000 rpms. They were 13 cubic inches stock and about equal valve diameters. We cut the heads, ran thin gaskets, and cut the decks down a lot.

Now that I gave that comparison, I have ruined the performance of a basically stock 5hp Briggs & Stratton flathead. The early wives tale was to run a 4hp
head. It had a way smaller chamber. Lots more compression......But basically killed airflow. I cut on a 4hp head a lot and installed it.
It sounded killer running and revving. But basically would not move the kart and instantly over heated.
Swapped back to 5hp head, and good to go.
We also cut "fire slots" into the head to carry more flame front pressure over the piston.
Fun stuff to test. I had a dyno in the garage, and I wore my racing helmet while testing the high rpm motors...lol
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