Hi Dave & Rich: Could you tell me what is piston gas port modification? What do you do to the piston? Thank you Bart Phillips

Hi Bart,
Long time no hear from.
We have been using 4 holes at 90 degree intervals down through the piston crown to the back edge of the ring groove.
#60 drill. I did this originally with 12 holes but 4 works just as well.

Good Flying,
Dave

Dave,
I am curious too as to the reason for such a
modification. I can only think that it might aid in
expanding the piston wring at high altitudes.
I am a stationary engineer and deal frequently
with close tolerance matters. Please let us know.

The gas porting provides a better ring seal. As you know the YS engines use crankcase pressure to run the regulator. If the ring seal leaks periodically while the engine is running and does not provide steady pressure in the case, the engine will surge while it is running due to fluctuating regulator pressure.
We used to build full size racing engines with this type mod and I decided to try it in the YS a couple of years ago. It has solved some nasty problems and as a benefit makes the ring last longer.

Dave

Dave,

Thanks for explaining GPM. I have always marveled
the YS engine since the original F-120 some 23 years ago.
By no means am I an expert but a true enthusiast of the
design. I know YAMADA MFG. prototyped a 120 twin just
before the release of the F-120. Do you think they might have
an answer to the 80cc &up Gassers?

They made a DOHC twin which I'm sure you will never see produced. Mr Yamada's passion is single cylinder stuff so I doubt we'll see anything else. I've been after them to make a 1.8 two stroke with the YS regulator system, but so far no soap.

Dave

How much does the gas porting cost?

We do the gas porting as a regular part of any repair if it hasn't already been done. Since the engine has to come apart to do this mod we usually replace all the gaskets and seals.and do an overall check. Shop rate is $30 per hour plus parts and shipping. Usual repairs are about 1 hour including test running the engine.

Thanks and Good Flying,

Dave

Dave,
Are factory engines already GPM? If so, when was this started and is there any chance my 91AC will already have this?

Thank you,
John

We started doing this in all production engines late last year. I doubt your 91AC has the mod, but if it is running OK, I would not worry about doing it until it's time for a rebuild.

Good Flying,
Dave

Thank you Dave. I bought the engine second hand, NIB and it still has yet to even be mounted in a plane. I was just curious..

Thank you again,
John

Is this service still being offered ? I noticed my early version 110 has the ported piston, my 120 FZ does not. I think the 110 came new this way because it's never been in for service. Funny thing is, my 120 FZ was in for service about a year ago and it still has the original non-ported piston. Perhaps the 120 doesn't need it ?

I don't think any of the 120 pistons were ported....Not that could not be but there were NO as in ZERO 120's in production when the gas porting modification started.

I'm sure that YS Parts and Service can do this work for you. It will likely be at a charge for labor. I don't know for sure the details on that.

The gas porting is not a requirement to have the engine run properly. YS made 4 stroke engines for 12-15years before they started gas porting the pistons.

Troy Newman
Team YS

See image...is this what your talking about doing?
Apologizing in advance for my graphic skills but the top image is looking at the piston from the top and the bottom image is the same piston from the side. And, the piston is just a basic (unfancy) one. I would need a drill press for this....

It is, but after reading your other post on the 63 and the amount of fuel you have run through it I doubt you need it. Probably a new ring.

Yes, that is how you do it, you just drill up to behind the ring
I happen to have 2 63's, one is older and doesn't have it and the other does, they both work fine
but a friend has a 53 which is a known troubleprone engine.
after we gas ported it the difference was dramatic, like night and day
we did it with a drill press, but I dont think it is necessary since the piston is aluminum and can be drilled slowly by hand
just make sure to cleanup the ring groove where the hole exits