Compression imbalance after rebuid

Adidasandy · Jan 31, 2020

Right, Changed domes back to my 35's and now have even 180psi. Going to perform another leak down test - CORRECTLY this time.

Storbeck · Jan 31, 2020

So it was an o-ring? Why are you changing domes?

Adidasandy · Jan 31, 2020

JC-SuperJet said:
That's Good News, we'll make a good Engine Builder out of You haha

Leak down test in progress. Sitting at 8psi for 20 mins now so fingers crossed.

Adidasandy · Jan 31, 2020

Storbeck said:
So it was an o-ring? Why are you changing domes?

Don't really want 200psi comp TBH. Would rather 180 psi to play it safe.

Adidasandy · Feb 1, 2020

JC-SuperJet said:
TIP: Grease the O-Rings before installation. Grease protects the O-Rings and helps to hold them in place.

If you install the O-Rings dry, they can easily be pinched, cut or damaged.

View attachment 388786 View attachment 388787

Yeah they were greased before install. Water test went good, just need to dial on the carbs now.

joelake · Feb 5, 2020

Nothing wrong with 200psi with 98 octane fuel (aus octane, I am in aus too). I have run 200 210 approx for years.

Pro-pulsion · Feb 17, 2020

Sounds to me like the new domes may have been tagged the same but are actually not physically the same. 200 compression is what my 31cc 760 domes produce on my 701, 175 is about the range of my 35cc domes on a first over 0.5mm bore. I would be having a good hard look at the shape of those new domes to see if there are any noticeable differences like depth of cut, shape of cut, squish band length, even try putting an old plug in both domes and pour water in to see if they hold the same volume. They might not even be 701 series domes when thinking about my 760 domes.

Adidasandy · Feb 17, 2020

Pro-pulsion said:
Sounds to me like the new domes may have been tagged the same but are actually not physically the same. 200 compression is what my 31cc 760 domes produce on my 701, 175 is about the range of my 35cc domes on a first over 0.5mm bore. I would be having a good hard look at the shape of those new domes to see if there are any noticeable differences like depth of cut, shape of cut, squish band length, even try putting an old plug in both domes and pour water in to see if they hold the same volume. They might not even be 701 series domes when thinking about my 760 domes.

Never even thought of that TBH. Will take a hard look and thanks.