exhaust port

[cardojr]

I was cleaning up a 6B cylinder prior to boring and noticed the liner cut out at the bottom of the exhaust is a good 1/8" (+) higher than the aluminum in the cylinder.This leaves a vertical lip.  All the other ports match from the sleeve to the cylinder as does the top of the exhaust port. From all I can see, this is a stock bore- I don't see any evidence of a re-sleeve.
I don't have any other motors open at this point to compare. Is this normal and have I the lost the powers of observation or is this an anomaly?
thanks- rob

[tomale]

I can not speak to what is normal or what would happen if you matched up this port but i will tell you that these motor and this includes anything that is mass produced is generally assembled to work with in stock specifications. The variance can be considerable when you realize that parts come from different suppliers etc. The concept of "blueprinting" is smiply cleaning up small inperfections to make the motor run at its best with in the stock specs. To know exactly what you need to do, consult the tuners on this site that can help you.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)
72'sixday (project bike)

[Ernie Phillips]

Rob,

I eyeballed 6 - 125 cylinders.  4 were pretty much "matched"  2 had a small lip, 1/32 - 1/16".  1/8" seems excessive.  For reference, the lower edge is ~53.9 mm from top of cylinder.  The link below has photos of exhaust ports.

The key measurement of the bottom edge of the exhaust port is that it is flush with the top of the piston at BDC.  However, the location of the bottom edge is also affected by the thickness of the base gasket.

With these old motors, who know what mods were done.  Maybe this is a replacement liner.  Use caution when altering port configuration --taking metal of is a lot easier than putting it back on.  good luck -- EP


http://www.pentonusa.org/forum/topic.asp?TOPIC_ID=9550&whichpage=2&SearchTerms=computer%2Csimulation

Ernie P.
Chattanooga, TN

[cardojr]

I knew that I'd seen those charts before. I'll print them out and have a look at the port locations. It might just be that someone hogged out the spigot. If things are totally out of whack I'll post a few pics.
thanks again- rob