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

[ronstory]

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?

[ronstory]

OK, my Google-fu just found this thread:

http://www.moyermarineforum.com/forums/showthread.php?t=2998

Looks like Indigo and just contacted Tom and he had only sold the springs... plus he still carries them.

[ndutton]

Dave -
34° of full advance? Twice the specification?

ref: http://www.moyermarineforum.com/foru...ead.php?t=2324

[Dave Neptune]

17* in the distributor is 34* on the crank.

Dave Neptune

[ndutton]

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°.

[Dave Neptune]

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.

Dave Neptune

[Ball Racing]

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