Jump to content
Sign in to follow this  

Piston/ring questions

Recommended Posts

Is reringing a piston on a modern 250f even worth it considering it costs 1/3 or more what a piston does when you factor in gaskets? Are the rings the main culprit for piston slap in a worn engine or is it the piston itself?

 

The last piston I had wore out a cylinder after only 70 something hours and had bad skirt wear. I did a bottom up rebuild and am now approaching 30 hours and am trying to decide if I am going to rering or go with a new piston when I hit 40.

Share this post


Link to post
Share on other sites

I think the best thing you can do is measure the bore in the places the service manual recommends, then compare those measurements to those of the piston to get your actual cylinder to piston clearance. This is the correct way to do this. If your previous piston had excessive skirt wear, and you did not replate the cylinder, you can bet the new piston will now be just as bad as the original was. The cylinder & piston have to be an exact fit, with the correct clearances. If one, or the other, is off, then you can expect accelerated wear on all parts.

 

Piston slap is typically a result of excessive clearance between the cylinder and the piston itself. So, one, or both, part(s) are worn beyond their serviceable limit. Please keep in mind that running the engine while it is experiencing piston slap is likely to cause more, expensive, problems.

Share this post


Link to post
Share on other sites

Coated cylinder?  Always a new piston and rings.  Also check the play in the crankshaft lower end rod bearing, Hondas wear out their cranks in a couple hundred hours in the 450s, the 250s are probably the same.  For the piston and rings I recommend Wiseco, OEM or Hot Rods for the crank.

Edited by cjjeepercreeper

Share this post


Link to post
Share on other sites

Yup its a honda... nikasil. When I did the rebuild I put in a new used cylinder that was in spec.So forget reringing it and just throw in a piston?

 

I guess I'm really asking if the rings wear out much before the end serviceable life of the piston or if the two are pretty close.

Edited by problem_child

Share this post


Link to post
Share on other sites

You shouldn't be guessing. The other previous post mentioned the cylinder and piston needs to be professionally measured.

 

The nikasil, unless it is scratched, will retain the bore size.  Obviously, if it is scratched a recoat is necessary.  The coating is so thin it really has no significant measure to it.

Share this post


Link to post
Share on other sites

 I am just asking if generally you can extend the life of a piston on these high revving 4 strokes by reringing it or if generally by the time it needs rings it needs a piston. I am also trying to gauge whether reringing is worth the time/effort and if there is a direct correlation between piston wear and the condition of the rings.

 

I always measure everything when I do a tear down.

Edited by problem_child

Share this post


Link to post
Share on other sites

The nikasil, unless it is scratched, will retain the bore size.  Obviously, if it is scratched a recoat is necessary.  The coating is so thin it really has no significant measure to it.

My opinion is there is certainly a measurement to hard chrome bores. Measuring it is the way it's done.

Share this post


Link to post
Share on other sites

I am just asking if generally you can extend the life of a piston on these high revving 4 strokes by reringing it or if generally by the time it needs rings it needs a piston. I am also trying to gauge whether reringing is worth the time/effort and if there is a direct correlation between piston wear and the condition of the rings.

I always measure everything when I do a tear down.

Since you are there, the way I look at it is why not replace the piston? It's not 8 of them, it's just one.

Share this post


Link to post
Share on other sites

Since you are there, the way I look at it is why not replace the piston? It's not 8 of them, it's just one.

yea that's what I am leaning towards especially considering an oem one is like 80 or 90 bucks

 

Still kind of curious about the correlation between ring wear and skirt wear/piston slap. I kind of figure as the rings wear the tolerances will change resulting in accellerated piston wear but that's just my theory with nothing to back it.

Edited by problem_child

Share this post


Link to post
Share on other sites

My opinion is there is certainly a measurement to hard chrome bores. Measuring it is the way it's done.

The reason you measure a nikasil bore is not really for wear, it's roundness. Nikasil is only.002-.003 thick. If there is any scoring or flaking it's time for a recoat, or if it is out of round. One thing about pistons, the 3 manufacturing processes they use to make pistons will have different piston to wall clearance because of expansion differences.

Edited by cjjeepercreeper

Share this post


Link to post
Share on other sites

yea that's what I am leaning towards especially considering an oem one is like 80 or 90 bucks

Still kind of curious about the correlation between ring wear and skirt wear/piston slap. I kind of figure as the rings wear the tolerances will change resulting in accellerated piston wear but that's just my theory with nothing to back it.

Your coated bore is many times harder than your piston.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...