How to read ADA domes sizes?

[ItsRixter]

I just purchased a set of 40cc ADA domes for a 760 motor. The etching reads: ya7640 which makes sense YAmaha 76o 40cc
I have a set of used domes that read ya7640- 50. Any ideas what this means??

 

[SUPERTUNE]

I just purchased a set of 40cc ADA domes for a 760 motor. The etching reads: ya7640 which makes sense YAmaha 76o 40cc
I have a set of used domes that read ya7640- 50. Any ideas what this means??

Yes you are correct the 40 in the part # stands for 40cc, 76 stands for a 84mm bore 760 engine, the -50 or any # after a L stands for squish depth.
A 701 Yamaha 35 cc dome has a part # Y2135L, The L is a term meaning 'LIMITED' which is .015 standard squish depth.
A Kawasaki big bore 85mm piston (flattop) in a Yamaha or in a Kawasaki...
A part # of K8526L18 would stand for 85mm bore, 26 dome cc's, and a squish depth of .018.
ADA domes are made to suit most over bores up to 1.5mm (.060) with the squish O.D.
A Y7640L could be used up to 85.5mm oversize piston. A K8528L15 would handle up to 86.5 mm bore.
This is most of the time a system ADA follows. As ADA will make custom domes for any application.

 

[ItsRixter]

Thanks Chuck! I was thinking you would reply. Your pwc knowledge is endless....perhaps I should have just PM'd you :smile:

I forgot the "L" in the etching. The two domes types I have are: ya7640L and ya7640L50.
So is squish = bore? Looking at the two domes the ya7640L seems deeper than the ya7640L50.
Which dome will give me lower compression? What is the worst case if the ya7640L is installed on a 86mm bore motor?

 

[SUPERTUNE]

OK, Your not quite getting this...The YA7640L domes have .015 step in the dome for piston to dome clearance, with a stock engine the piston is approximately .030 negative deck height (piston in down in the hole a TDC) this will yield about .045 squish clearance.

If you try and use the YA7640L50 this dome has the squish cut step .050 and not the normal L spec at .015. This dome was custom cut for a stroker crank (with a positive piston deck height) OR like I like to do with 760 cylinder to make a lot better freestyle power is to mill the bottom of cylinder to lower the port timing. This makes the piston a positive deck height, so you need to use a cut out deeper squish in the dome.
When setting up domes and heads, you must set the squish clearance 1st, then figure in what squish ratio you want, then compression last with machining the bowl to final compression ratio.
It's not quite that easy, but gives you the idea what it take to design and build domes.

 

[ItsRixter]

ahh...okay I understand now. Chuck you are the greatest!