Valve guide ID question - k241
 

I am at the very beginning of taking the measurements for the repair/rebuild of the engine on my cub cadet 108 fixer upper. The first ones I have taken are for the exhaust and intake valve guide ID's. Here is what I have come up with:

Intake valve guide ID
top of guide = .3125
mid-point of guide = 3125

Exhaust valve guide ID
top of guide = 3125
mid-point of guide = .3110

Now, what I don't fully understand is why the mid-point of the exhaust guide is under specs as given in the manual (.312/.313). I suspect it has something to do with overheating on the exhaust side of the top end. The fins there were packed with dirt when I took the engine out and cleaned it up and I believe this guide does show an issue that would probably cause the valve to stick. I would like to know how to address it (preferably without replacement). I have attached pictures of the general work, but the first pic is the main one. It is of the inside of the exhaust guide and it shows (as best I could) some kind of blemish at the mid-point of the guide. It appeared to me like cracked chrome.

Replace the Guides. Not expensive nor hard to do.

:IH Trusted Hand:

In a nutshell, good advice from Roland.
First off,
a caliper, while reasonably accurate most times, leaves a lot to "feel"/operator expertise.
You were able to read the difference between the worn part @ the top/bottom/center of the guide, but a mike will give you a more accurate reading.
Also throw in the variable factor of a telescoping gauge, read by a caliper.
and you get accumulation of error.

If you were to use that method on a freshly bored and accurate cylindrical hole,
and compared a mike to a caliper you would see a difference.
Then set a dial bore gauge in the cylinder, you would be surprised at the variance.
Never use a caliper to check a crank diameter except get an idea of if it has been turned, same for cylinders

My Mitutoyo DRO caliper and an old 16" Starrett vernier caliper as old as me, while having their place in the shop, are not as accurate as
my complete set of Starrett mikes.

Now as far as the appearance of an undersized Ex guide @ midpoint,
if you slide in a hand reamer, you will prolly find carbon on it when you bring it out,--- it happens.:biggrin2:
If,
your readings are accurate, the guides are usable once you get the carbon out of the Ex guide.
How worn are the valve stems ( using a mike)??

ream the guides to .312 5/16 and call it good you can put new guides in and ream and be right back where you started.Ream and put in new valves grind the seats if worn and lap in

Roland, ol'George, MikeMasheris, Thanks for your insight. time for me to invest in more tools (micrometer set, 5/16 reamer) before I go any further.

Do not get an adjustable reamer, just a regular hand reamer
( straight or spiral)
Example: ebay #
143147990500

OK, just bought it. Too bad there isn't an emoji of someone throwing around money like a drunken sailor...:Thanks: