Scuffed pistons and tight wrist pins

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2016: Scuffed pistons and tight wrist pins
Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Elliott, Tigard, OR on Monday, November 28, 2016 - 12:12 am:

I have an engine that needs rebuilding that I don't know the history of. It has .080 over pistons that are scuffed up. I have measured the bores and the pistons and there is .004 clearance. I have read that piston scuffing may occur if the wrist pins are to tight, which they seem to be. The questions I have are:
1. Can I use some emery cloth to polish the wrist pins bores to loosen them up a little bit?
2. How can I clean up the scuffing on the pistons, before I re-use them? Can I polish them out.
3. is there a way to tell if the piston rings are still good?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les VonNordheim on Monday, November 28, 2016 - 12:47 am:

Have the wrist pin holes honed for proper fit. Do not use emery cloth!
You should be able to remove the high points on the piston scuffing with fine emery cloth/fine file.
Hone the cylinder bore to remove scuffing and gain a little more clearance.....use new rings. If scuffing in bores is too deep, have block sleeved to standard bore size.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Monday, November 28, 2016 - 12:54 am:

Scott
.004" is not enough clearance for your pistons. .005 is the absolute minimum!! This was the actual source of your problem.

A good automotive machine shop should have a "pin hone" machine. They could likely help you with that. If you are determined to do it yourself, a brake cylinder hone could work. It will only take about 30 seconds per piston hole to polish them up.

A few gentle swipes with a fine smooth-cut file can be used to remove any raised material on the pistons. Actual clearance increase should be accomplished using a sizing type cylinder hone.

Rings; the condition of the ring grooves is the first concern and consideration. Can the rings move freely around the groove BUT with no obvious slop? How used are the rings? I will suspect not very, given the lack of piston clearance. I assume you know that the rings have a top and bottom? Rings are relatively cheap


Add a Message


This is a private posting area. Only registered users and moderators may post messages here.
Username:  
Password:

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration