4AG head porting - OST-030: a case in point

[oldeskewltoy]

Got this via FedEx yesterday....



I've gotten heads in all kinds of containers/packaging. But this one is unique, and lead to the title.....

It has very interesting latches....





I wish all clients would be able to do this.......




Safe and secure with plenty of protection around it




the head is clean, and it comes with all the hardware....



..... along with a set of Pon cams!!!!



More to come.......

[oldeskewltoy]

hmmm...military owner by any chance?...we use those cases for equipment/parts

That's a flight case, often used by musicians and such.
The latches are very similar to those used in Military cases (non Peli type) as they have a high latch strength and low profile

Now I (we all) know about this kind of case/latch


While OST-031 is being cleaned and pressure checked, it gives me a few days to work on OST-030...


Besides the Poncams, my client is using a piston with a 3.2cc dome. He has to check, but believes he has .005" of positive deck - piston slightly ABOVE the blocks surface. He wants to run a squish of .040".

What chamber volume does he need for a 11.3 to 1 compression ratio?


My clients said his head had been already run through the mill once... .008"




Seems pretty close to me....

btw... look at the "round" exhaust port...


All the cam journals look pretty much the same as this...


Since MR2tailbreaker noticed a "small" problem in his cam and journal clearances using the Poncams, I'll be checking these journals for similar issues.....


Work begins on the bowls and seats of chamber #1




More to come....

[trdee]

lol at the "round" exhaust port. factory quality

[oldeskewltoy]

lol at the "round" exhaust port. factory quality

The gap between original design and finish casted part is what allows me to do this... the exhaust port on OST-030 isn't nearly as crappy as the combustion chambers 2 and 3 in OST-031

What do you do about bad cam journals and caps?

not ignoring you... not quite ready yet to show that part of the process

Is this a CA customer? 11.3 on 91 octane, better have clean chambers, and management dialed in nicely, my recommendation from experience... I would even worry that improved breathing/VE would skew things even more toward a little less CR. If this is 93 octane, probably it's fine, but potentially close to incipient detonation.

Other side of the country..... Part of the issue is opening the chamber to accommodate the piston. With the clients deck, and the piston volume, the chambers may need to be "opened".


Most pistons can be milled a few ten thousandths, which could drop the piston volume under 3cc

example of piston milling


The piston I designed could be milled .030" and drop the dome volume from 2.5cc to about 1.8cc.

[oldeskewltoy]

#1 is almost finished...




Here is #1 exhaust bowls/port in transition




And a closer view of the short radius, and the port in the background





More to come.......

[oldeskewltoy]

2 down.... 2 to go.....

Chambers.....




exhaust ports.....




More to come.......

[oldeskewltoy]

further progress... 3 down 1 to go....


this time the intake view - first short radii...


followed by the view down the ports



The exhaust...




And the chambers... 3 panel this time so you can see the progression





More to come.....

[oldeskewltoy]

4 down......








Next stop valve job and resurface... and then we set chamber volume....




More to come.......

[oldeskewltoy]

Besides the Poncams, my client is using a piston with a 3.2cc dome. He has to check, but believes he has .005" of positive deck - piston slightly ABOVE the blocks surface. He wants to run a squish of .040".

What chamber volume does he need for a 11.3 to 1 compression ratio?


My clients said his head had been already run through the mill once... .008"

Here is what is now known....

82mm bore or 3.229"
77mm stroke or 3.031
.012" piston sticks out of the bore
.052" Cometic gasket
3.2cc piston dome

So I ask again what chamber volume does this build need to have a static CR of 11.3 to 1???

Now how do I achieve that target volume on a head already cut .008", and will be cut an additional .002"????

[roadsailing]

Here is what is now known....

82mm bore or 3.229"
77mm stroke or 3.031
.012" piston sticks out of the bore
.052" Cometic gasket
3.2cc piston dome

So I ask again what chamber volume does this build need to have a static CR of 11.3 to 1???

Now how do I achieve that target volume on a head already cut .008", and will be cut an additional .002"????

are these questions you are asking yourself out loud? if you know how to work chamber volume out with the pistons flush with the deck then just add 12 thou times (bore X bore X pi)/4.

oh, and account for the gasket too. so chamber volume will need to be

so swept volume is 406638.3mm^3

so your desired theoretical chamber volume will be 35985.7mm^3, just add or subtract the various volumes from this, no? is the "dome" of the piston convex or concave?

[oldeskewltoy]

are these questions you are asking yourself out loud? if you know how to work chamber volume out with the pistons flush with the deck then just add 12 thou times (bore X bore X pi)/4.

oh, and account for the gasket too. so chamber volume will need to be

so swept volume is 406638.3mm^3

so your desired theoretical chamber volume will be 35985.7mm^3, just add or subtract the various volumes from this, no? is the "dome" of the piston convex or concave?

I ask questions to try and get involvement/discussion in my threads...

Without checking it..

stroke volume is 3.14x41x41x77=369.5
piston sticks up 3.14x41.41.0.3=1.6
gasket is 3.14x41x41x1.3=6.86

Let X be the head volume.

So the BDC volume is
369.5+6.86+X-1.6-3.2 which is 371.56 + X

The TDC volume is
X +6.86 -1.6-3.2 which is X + 2.06

For an 11.3 to one CR
BDC volume = 11.3(TDC volume)
371.56 + X = 11.3(X + 2.06)
371.56 + X = 11.3X + 23.28
371.56-23.28 = 11.3X - X
348.28 = 10.3X
so X = 34.83


..and can I have 25minutes of my life back please!

As to the chamber volume I'll need... I find to save time, and poor calculating skills on my part I use one of the online compression calculators..... https://www.rbracing-rsr.com/compstaticcalc.html or http://www.csgnetwork.com/compcalc.html



in both cases we come up with about 37cc (37.3 in the RB racing calculator)



More to come.......

[MorGo]

Well,I don't know how crappy fuel you have there but I would just worry how high I can make the compression!
My something like 11,5:1 4A-F run fine with Russian 95 octane.
You do something wrong if there is a problem above 11:1..
I haven't found how to make compression enough to knock!

[oldeskewltoy]

Well,I don't know how crappy fuel you have there but I would just worry how high I can make the compression!
My something like 11,5:1 4A-F run fine with Russian 95 octane.
You do something wrong if there is a problem above 11:1..
I haven't found how to make compression enough to knock!

I'm not so worried about my head work(the top of the chamber)... as the pistons my client is using(floor of the chamber)... has a less than ideal crown/dome...




I prefer a something a bit flatter, with a bit less volume - http://www.toymods.org.au/forums/thr...ew-4AGE-piston

[oldeskewltoy]

So with OST-031 now @ the machine shop getting its valve job and surfacing we delve back into OST-030


I've gotten the head back from the machine shop, they have provided a minimum resurfacing .003", to add to the previous clients report of a .008" resurfacing, the current surface is not quite @ .011, closer to .0102". This head is now 115.74mm thick, having had a total of .26mm removed.

Typically with a 10 thou cut you can expect chamber volumes to drop to about 35cc, the deshouding adds about .4cc, to gain volume I had the valve seats machined an extra .003" to gain 1cc in chamber volume, this lowers the valve on the seat allowing for a bit more volume in the chamber. The valve tips were cat an equal amount so use of more common shims sizes is retained.



So right now the chambers sit @ 36.4cc (1/10cc tolerance)

All the cam journals look pretty much the same as this...


Since MR2tailbreaker noticed a "small" problem in his cam and journal clearances using the Poncams, I'll be checking these journals for similar issues.....

The FSM(BGB) states the cam to journal clearance to be .035mm to .072mm, with nothing greater then .1mm




Using the Plastigage PL-X - The PL-X range is a bit on the tight side for measuring the whole range of the cam to journal - a bit too small for perfect accuracy, but in this case it works adequately.



This is one of the measurements, you can see it is quite a bit narrower then .045mm which is middle tight of the span in the FSM.

By carefully surfacing the cam cap "feet" we can get this dimesion closer to the center of the specification





Here is a 2nd journal going from a bit loose....




to middle of the spec




Of course the worst one I didn't get a photo of, that was #5 on the intake side... farthest from the oil supply, it was so loose that most of the Plastigage thread was intact when checked, and it too was brought into spec.


Now that the cam journals are all within tolerance, assembly can begin.....



More to come.....

[oldeskewltoy]

Showing off her angles....

Now that the cam journals are all within tolerance, assembly can begin.....

The head and hardware are all laid out, #1 cylinder already has the valves in....




Now half assembled...





sometimes during assembly you see something that you just don't like.... tossed the retainer on the left for the one on the right. There was no other damage, I just didn't like that kind of a flaw.





Fully assembled... now whats left is setting the valve clearances, and getting it back to my client.







More to come.....