std. bore size

[thomd51]

need to know the std. bore size of a wisc. robin ey27w engine. I measured it and it's 2.914 in the worst spot parallel with the wrist pin and 2.919 in the worst spot
90 degrees from the wrist pin. if I took out the piston I could measure the cyl. at the bottom. .004 over is reject size on kohler k series. this one has .005 out of round compared to the other worn side. can you imagine ? the owner said it smokes and he's been starting it with ether for years. people are awful.
this engine was on a vibrating tamper. valves are loose in guides and piston wobbles in cyl. did leak down test VERY bad. just want to know the std. bore size
so I can show the guy how bad it is. TOM.

[RoyM]

That is an old engine, he has gotten excellent service out of it. What is the taper? Measure the bore at the top of the ring travel and at the bottom at the cylinder, if more than .003 difference it needs a rebore. From the sound of it that beast is completely worn out.

[KE4AVB]

74mm (2.910")

[madmantrapper]

74mm (2.910")

74 mm is actually 2.91338, that makes some difference.

[KE4AVB]

74 mm is actually 2.91338, that makes some difference.

Just quoting the service manual; didn't do the conversion.

[bgsengine]

You would think a specification would be much more precise - 1 millimeter, when it comes to cylinder bores, is a HUGE difference.... Isn't there a more precise "reject" spec in the manual? Or is that the reject dimension? in which case the OP's bore is WAYYYY out of spec and at 2.919 at the largest dimension, that is nearly .010 oversize already, if the reject spec was 2.910

[KE4AVB]

From correction table all in mm.

Std Bore 74mm Tolerance .019 Limit .15 with service limit 1.15

max out of roundness .01
max taper .015

[bgsengine]

From correction table all in mm.

Std Bore 74mm Tolerance .019 Limit .15

In other words, maximum diameter in inches would be 2.9129" , bored out oversize would be maximum 2.9586"

with service limit 1.15

max out of roundness .01
max taper .015

So his engine would definitely be way outta whack by at least .007" beyond limits at the greatest dimension

[madmantrapper]

From correction table all in mm.

Std Bore 74mm Tolerance .019 Limit .15

In other words, maximum diameter in inches would be 2.9129" , bored out oversize would be maximum 2.9586"

with service limit 1.15

max out of roundness .01
max taper .015

So his engine would definitely be way outta whack by at least .007" beyond limits at the greatest dimension

I'm not following your math. 74mm is already larger than 2.9129" so how could the maximum diameter be 2.0129"? If it is all in mm the tolerance would be .00075" and the limit .0059".

[madmantrapper]

OP: Here is a link to the service manual if you are interested.
http://www.subarupower.com/media/manual ... 098750.pdf