Vintage ADA Head Dome Identification

[Carrera911]

I recently pulled the crusty old model ADA head off of my project SJ. The cylinders were both at 150 PSI which I though was strange for an A/M head but I thought maybe they're stock sized domes or at least very conservatively milled. Well, this is what I found etched into the domes.
YA2133 LTD with .030" squish. From what I can see on ADA's site, YA21 is their part number for 701 domes and the 33 I can only assume is 33cc (200 PSI Comp). They also list the squish as .015". I don't have a clue why the 33 is scratched through. So my question is this really a 33cc dome and I need to refresh the top end, or was the dome somehow modified and thus the 33 was scratched through? Also why is the squish different than what ADA offers now? Was it custom ordered or did they change to .030" for whatever reason?

 

[Big Kahuna]

33cc dome unless it has been cut afterwards. The YA2133 is ADA's labeling when they produced that dome. The other is by someone else.

 

[Carrera911]

33cc dome unless it has been cut afterwards. The YA2133 is ADA's labeling when they produced that dome. The other is by someone else.

I don't have any pictures of the cylinder side of the dome but it doesn't look modified as far as I can tell. I guess I could measure the dome with some water to determine the volume. The cylinder walls look to be in decent shape, no scoring that I can feel with my finger nail. I might just go ahead and order a new head from ADA and see where the compression is at with some 35 or 36cc domes. Worst case, I'm hoping I can get away with just some new rings unless the rods feel loose on the crank. Thoughts?

 

[Big Kahuna]

Well, you need to figure out is this a stock stroke motor? Has the cylinder been decked? All of these could be reasons why the domes were modified.

 

[Carrera911]

Well, you need to figure out is this a stock stroke motor? Has the cylinder been decked? All of these could be reasons why the domes were modified.

Wow I didn’t even think of that. The previous owner said he was going for a “freestyle setup” so it may have been setup as a stroker. However, he didn’t use it as a selling point so maybe not. What would I need to measure to confirm it? Piston at TDC vs BDC? All I have is a set of china spec calipers.


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[Big Kahuna]

@Jr.

 

[Vortex]

Is your cylinder ported? Some builders machine the cylinder to lower the transfers. If so you will have the piston poke out the top and you must use custom domes. You should check squish band with current set up to find out what's going on. I would guess you have excess squish Clearence due to the modified domes which would offer some explanation to the low compression

 

[waxhead]

whats the squish clearance on that engine

 

[Carrera911]

Thanks for all the input guys. I’ll have to check when I get home this weekend. I just generally inspected the cylinders and I don’t remember the piston at TDC looking too out of the ordinary, maybe a mm or so below the head. I haven’t looked enough at stock sj ports to know what they would look like. I’ll grab some pics this weekend.

What do most people use to measure squish? Put a ball of silly putty near the edge of the piston, install the head and turn over past TDC?


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[Big Kahuna]

Solder...... Bend to an "L", stick through head, roll coupler around until it compresses solder. Measure.

 

[waxhead]

Solder...... Bend to an "L", stick through head, roll coupler around until it compresses solder. Measure.

yes, just one thing extra to add. face it towards the opposing piston this will keep it in line with the gudgeon pin and eliminate piston rock in the equation

 

[Storbeck]

If you really want to be an overachiever lay a piece on top of the piston parallel to the wrist pin and measure both sides at once, eliminating piston rock. Requires removing and re-installing head with each measurement so I have to admit I often cheat and just do what Waxhead described above.

 

[Vortex]

Stock sj transfer ports are easy to spot usually a horrible mismatch between sleeve and cylinder. Thanks Yamaha! Lol

 

[Jr.]

Cumming? Have we met? I ride Lanier Beach South fairly often.

That is a 33cc std ada dome. At some point in time it was custom cut to match a built motor.
With your comp at 150#? It doesn't sound to me like its still sitting on that same cyl?
Being we are about a half hr apart? Please feel free to contact me directly. Im happy to evaluate it for you and give you the straight scoop.

Ski ya, Paul

 

[DAG]

If you really want to be an overachiever lay a piece on top of the piston parallel to the wrist pin and measure both sides at once, eliminating piston rock.

I've been doing it this way ever since Sensei Briggs scolded me for doing the one sided L method.

 

[Storbeck]

I've been doing it this way ever since Sensei Briggs scolded me for doing the one sided L method.

Some day I will measure both ways and compare how different the results are.

I've found that I typically get a few thousandths difference from one side of the piston to the other and from one piston to the other piston, most recent motor I built was ~.005" difference from one cylinder to the other, so I've never been very concerned about it. I'm not exactly winning world championships here though.

 

[Carrera911]

Got into the engine today and did the measurements. I used the fattest solder I had on hand (.061") and laid a piece across the piston. Torqued on the head and turned the motor over and felt 0 compression and sure enough it didn't even touch it. I then coiled 2 pieces to double layer it and laid them across from one another, parallel to the wrist pin. I got .069" and .0785. I'm sure this isn't as accurate with it coiled but obviously the squish is way off. What does this mean from here as far as what’s the correct dome for this motor?

When I pulled the head off, I didn't see one of the pieces of solder and after quite a few cuss words I started pulling the girdle bolts to remove the cylinder. Man what a pain in the ass since not one was anti-seized in the case. After getting 4/6 out, I glanced at the head and noticed it stuck to the dome so crisis averted lol. But on the bright side I got the cylinders far enough off to see what rods it has. The rods are 62T with an E on the opposite side and the cylinders and cases are 61X. I also took a closer look at the ports and grabbed some pics. I see where it looks opened up a little on the exhaust port but maybe not.
Piston at TDC

Cylinder walls

Domes

My ghetto measuring technique.


Thanks again for everyone's input and let me know what you think.

 

[Carrera911]

Cumming? Have we met? I ride Lanier Beach South fairly often.

That is a 33cc std ada dome. At some point in time it was custom cut to match a built motor.
With your comp at 150#? It doesn't sound to me like its still sitting on that same cyl?
Being we are about a half hr apart? Please feel free to contact me directly. Im happy to evaluate it for you and give you the straight scoop.

Ski ya, Paul

I appreciate the generosity, I might have to get in touch with you at some point during this build. I usually ride at the north end of the lake at 6 mile creek and with a group of stand up guys out of Vann's Tavern. I remember seeing a group of stand ups down by lanier islands a while back but other than that, stand ups are few and far between on Lanier.

 

[Vortex]

That pretty much indicates you don't need those custom domes and could benefit from some standard off the shelf domes. However there is no substitute for proper measurements to confirm this. For that you could consult an engine builder.

 

[Carrera911]

That pretty much indicates you don't need those custom domes and could benefit from some standard off the shelf domes. However there is no substitute for proper measurements to confirm this. For that you could consult an engine builder.

Thanks. ADA is running a 20% off sale right now so I'll pick up a new head with 35cc domes for 185psi. Anyone want a used head with custom domes? lol