Cylinder + Piston advise.

[350GUY]

Daryl:
It appears from the pictures that these cylinders have been modified.  We can't tell about the port timing, but it looks like the main transfer port entries, at the base of the cylinders, have been raised to improve mixture flow.  That doesn't really mean a great deal to
how you treat the cylinders but maybe you should evaluate the porting to see how much effort/money you should pay to restore them.  Joe has given you the only right way to approach this; bore them clean, determine the piston size needed, install the pistons/rings and you and done. 

As an  alternate you can use a Sunnen mechanical hone to clean up the bores and then buy a forged piston to see if it will fit the piston.  Forged pistons have looser clearances and might work.  I don't like them as they are noisy and they should be thourghly warmed up before you ride off, but that would be a cheaper way to get the bike on the road.  A ball hone, glaze breaking hone, will not work as you have to clean the bore or it is likely to seize. 

If you want to keep the cylinders, engine, and bike I suggest you get an expert to evaluate the cylinders.  Joe can do that.  Chuck Q can do that.  Maybe your local shop can do that but many shops don't have a lot of experience with two strokes and are not familiar with piston to cylinder clearances. 
Lyn Garland

Hi Lyn,

Hope all is well.
Good observation. The cylinders are lightly ported at the base. I checked the port timing and that seems to be untouched.

B/R,

Daryl

[350GUY]

Hi all:

I bought a pair of RD350 cylinders, the pistons were stuck/frozen in the bore. The cylinders measure at 64.08mm and 64.06 mm, each. I had to drill holes into the pistons to get them out of the bore as they just wouldn't budge even after 2 months in all sorts of oil, heat etc. etc.  New pistons will be required.....
From the looks of it there was barely any mileage done as the cross hatch hone marks are still visible along the bottom end of the cylinder skirt. However, the area around mid-cylinder wall and TDC had some rust from the pistons + moisture that effectively glued them pistons to the cylinder wall. I tried scrubbing the rust off with soapy water & scotch brite...... attached are some pictures.  What do the experts recommend, what are my options here since new pistons are required anyways?

- Light hone + new (STD?) pistons
- Bore to  (1ST o/s?) size pistons
-Just drop new (STD)pistons without honing
Thanks in advance!
B/R,
Daryl

Hi Daryl!
Glad to see you made it over to the new forum...

If needing to try to determine if the bore is good you need to use a ball hone first to knock off any rust on the walls for measuring with a dial bore gauge. (mine is a Sunnen Dial Bore Gage and is over $1000 new now)
The RD's have 2 places that have high wear in the cylinders...just under the exhaust port is one point from heat and piston rocking and the other point is just below the intake port where any dirty air comes into the engine and the bottom of the intake skirt rocking more there because off that part of the skirt is farthest point from the pivot of the wristpin.
Measure these 2 points and also check for out of round halfway up from top of exhaust port to TDC.
Most of the time a good indicator of what the original bore size was, is to take a measurement at the wristpin sides of the bore and 1/2 inch below the transfers.
This is a place you rarely see wear and is a good indicator point.

There are a few of us that are specialist's on 2 strokes and with RD's...
I had 3 of my engines in the top five last weekend at the AHRMA Barber Vintage Festival is the F-500 race!
Also dyno tuned a few RD's while there. (4)
Chuck

Greetings Chuck,

Glad to be back here, it's been a while. Hope all is well by you.
Congrats on the top 5 at AHRMA, way to go! Many thanks for yours below, as always, much appreciated.
You are correct, I measured the bores and there seems to be slight wear at the piston skirt area/bottom of the bore compared to the top.  At this stage it would only make sense to go in for the next O/S and I agree with you and Lyn's expert advise. There are not many folks in my neck of the woods out here that are able to attain the cylindricity and dimensional accuracy. Last year I had done my LC cylinders out here at the local shop and the fellow was way out of the minimum clearances I had requested, They did not even know what hone grit they used! I concur, when it comes down to the RD's it does take a 2-stroke specialist! Thanks once again and I'll holler at you.

B/R,

Daryl

[350GUY]

Bore to clean up then bore/hone to the next appropriate piston size.

Thanks Joe.