Posted: Sat Oct 25, 2008 11:45 am
Have seen a few piston issues lately. Of course proper breakin including AFR are important but first you have to give the assembly a good chance by properly checking assembly. So here are some tips. Feel free to add more here since there are many.
SLEEVE
Fit of piston:
Measure fit. If you don't have bore guage take it to a shop or a feeler guage will work. These sleeves are machined in a fixture so it won't be perfectly true or round but go by manual and follow the specs in it or provided by manufacturer. Here is a quick check. Stock piston and stock sleeve. Piston will fall right through but if you turn piston it will not fall through. I won't even bother measuring since it's no good and very good chance skirts of piston will sieze to liner. Maybe not permanently. But piston and liner will be scored causing loss of compression and performance. Measure you ring gap always.
In this pic stock piston and stock sleeve piston will not even fall through. I am holding in the air. Not good. Sleeve can be fitted but would require Hone.
[attachment=7328:Piston_s...tips_008.jpg]
Reason this happened is because some sleeves aren't machined properly. LOOK FOR CHAMFERS. Every corner on every surface should have a radius or chamfer if it doesn't pay attention it is THE BEST indicator of improper machining. If no chamfer or too small in corner indicated you MUST put one there. Grab a file and five minutes your done. Does not need to be as big as the other stock chamfer but won't hurt if big like that. It Must be bigger than the case chamfer. Can also cause case cracking etc.
[attachment=7329:Chamfer_Comparo.jpg]
The Dimple
If too deep sleeve can crack. Just tip of drill or none at all is best
[attachment=7330:Dimple.jpg]
SLEEVE
Fit of piston:
Measure fit. If you don't have bore guage take it to a shop or a feeler guage will work. These sleeves are machined in a fixture so it won't be perfectly true or round but go by manual and follow the specs in it or provided by manufacturer. Here is a quick check. Stock piston and stock sleeve. Piston will fall right through but if you turn piston it will not fall through. I won't even bother measuring since it's no good and very good chance skirts of piston will sieze to liner. Maybe not permanently. But piston and liner will be scored causing loss of compression and performance. Measure you ring gap always.
In this pic stock piston and stock sleeve piston will not even fall through. I am holding in the air. Not good. Sleeve can be fitted but would require Hone.
[attachment=7328:Piston_s...tips_008.jpg]
Reason this happened is because some sleeves aren't machined properly. LOOK FOR CHAMFERS. Every corner on every surface should have a radius or chamfer if it doesn't pay attention it is THE BEST indicator of improper machining. If no chamfer or too small in corner indicated you MUST put one there. Grab a file and five minutes your done. Does not need to be as big as the other stock chamfer but won't hurt if big like that. It Must be bigger than the case chamfer. Can also cause case cracking etc.
[attachment=7329:Chamfer_Comparo.jpg]
The Dimple
If too deep sleeve can crack. Just tip of drill or none at all is best
[attachment=7330:Dimple.jpg]