Valve guide clearance & reaming

[Pintopete]

Hi all, we have a Cub that we rebuilt including new guides and valves two or more years ago. It was a thorough rebuild, but soon after, we observed what seemed like missing and to make a long troubleshooting story short, have attributed it to sticking valves. My Dad feels that we should have reamed the new guides. It is also possible that one or so got a bit mushroomed during the install. My question; do the guides usually need reaming when replaced? When I tear the engine apart, what diameter reamer should I use to either enlarge or remove irregularities in the guides from install? We have tried oil additives and all the easy tricks that I know of.

All input and ideas appreciated.
Thank you, Peter.

[Gary Dotson]

Hi Pete, Welcome to the forum! Generally, the guides will not need to be reamed, although checking clearance, after install, is important. Nominally, the C-60 valve guide would be .3125" bore diameter. Valve stem clearance is made up by reduced diameter of the stem, itself. If your clearance is too little, a good shop will have reamers in +.001" and +002" sizes. You'll need to measure, to see what you need. I haven't looked at the specs. but you'll probably want about .002" on the intake stem and about .003" on the exhaust. Over the years, I've seen quite a few engines, with new valves & guides with valve sticking problems. Since all aftermarket parts are not created equal, carefully measuring during assembly is more than just a good idea.

[Slim140]

Gary has you in the ballpark on the clearances. The spec shows stem diameter on the valve .3095"-.3105" on both intake and exhaust. It shows clearance in guide---intake .001"-.003" and exhaust .0015"-.0035".

You should be able to run a reamer through the guide by hand to get it to size, be careful not to get started crooked and use a lubricating oil of some sort on the reamer. Most reamers will cut .001" over size but not sure what will happen with a valve guide already being close to size and it depends on how hard the guide is so be careful not to make them to big.

[ntrenn]

The key point is “by hand”. I one time used a drill and the old man came unglued.....

New guides should always be resized irregardless of the installers skill.

[Glen]

Hi,
Below is the Cub service manual, the engine is in section 1, it has much info about measurements.
The valve guide specs are on page 1 - 7.
More info is on page 1 - 21.

http://farmallcub.com/rudi_cub/www.clea ... index.html

[Pintopete]

Guys, thank you all very much. If time permits, I may pull it apart this weekend. I borrowed a couple readers from a buddy. Planning to study the situation before I leap into reaming.

Thank you all again for your help and advice.
Peter