028 AV Super project
- Thread starter flatsfisher
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I find this very interesting. this is only my 2nd saw overhaul, but I've done scores of 2 stroke dirt bike top ends, and it has always been that way, A is smallest diameter then B. etc.
I just measured my "C" marked cylinder this evening (piston is marked "C" also but is too damaged to get accurate measurements). using a snap gauge and a micrometer I took 4 measurements in the intake to exhaust port axis and 3 in the transfer-to-transfer port axis (less cylinder wall to measure with the double transfer ports). I also took 2 measurements diagonally each way about halfway up opposite the transfers. on each of the 9 spots, I checked the snap gauge with 3 instruments, micrometer, digital caliper and dial gauge caliper. most of the measurements were very close to each other. I added the 27 measurements together and the average was 1.8114" or 46.00956mm. let's call it 46.010mm.
if a worn, possibly 38-year-old, freshly ball honed "C" cylinder is 46.010mm (1.8114") diameter than I am curious what new "A" and "B" cylinder diameters would be.
I cannot find any info anywhere with measurements of Stihl A, B or C pistons. in fact, I can't even find a C piston online for this saw. I do find NOS AB and B pistons. btw, I would assume that an AB piston should fit between A and B in diameter.
as far as aftermarket pistons, I looked at them all as far as I know and the only AM manufacturer that lists piston diameters on their website is Meteor. their "A" piston is 45.96mm (1.809") and their "B" piston is 45.97mm (1.810"). and so far, I could only find the "B" meteor for sale. so, if my bore is 1.8114" minus the Meteor "B" piston diameter of 1.810 then I only have a bore .0014" (.039mm) bigger than the piston. that would give me a piston to cylinder clearance of .0007" (.0195mm). ain't workin. hope I'm missing something.
where did you find this?
emailed Ryan at Wolf Creek. he responded very quickly and told me that the Meteor "A" pistons run 45.90, not the 45.96mm that is shown on the website and that he could ship me an "A" piston set. hope to have it in a few days.
Saved this pic from this forum. It come from Stihl 041 service manual.
You're wrong with your clearance calculation. Piston to wall clearance = jug diameter - piston diameter
A 0.05 mm clearance is a usual value to look for.
So you need a 46.010 - 0.05 = 45.95 mm piston.
A 0.05 mm clearance is a usual value to look for.
So you need a 46.010 - 0.05 = 45.95 mm piston.
great. I guess if the piston I ordered is too small I will send it back. thanks.
piston just arrived. using my Japanese digital caliper and checking that with my Japanese digital micrometer the piston measures 45.96mm/1.809 in. when I drop it in the bore with the spark plug in it drops all the way in but slows down the last half from air pressure.
I measured again, this time just above the exhaust port and got a ring end gap of .010 so I think I'm good.
btw, 3-day shipping from colorado to florida. great job Ryan at wolf creek.
You want 0.002-0.0025" clearance. Differences in diameters.
Make sure you measure pistons at the skirt. They have significant taper, 0.005-0.006".
this piston actually measures slightly less diameter at the skirt. the 45.96mm I got was just above the skirt.
still waiting on one of the crank seals, the clutch drum bearing and the carb kit. funny, the crank seal was shipped from Louisiana to Florida. it went to Washington DC and is now in Maryland. our federal government at work.
How much did they get you for the seals?
you mean what did the NOS OEM seals cost?
one was 10.59 and the other was 8.73 shipping included.
ebay. use the part numbers to search. I couldn't find them OEM just searching using the model number of the saw. by using the seal part numbers I found out a series of Stihl backpack blowers uses the same part number crank seals. they are Stihl BR400 BR420 BR320 BR340 BR380. I looked up an IPL for the BR400 and sure enough. do your own research though.
