If I'm going to go. 080 over with I'll be bore be.I want to make sure I don't have any piston slap.is it going to be exactly 68mm or bigger like i sead before I just want to make sure before I put it all back together I won't have any slap
bore ?
- Thread starter blastblast
- Start date
Dose anyone know the spec right off so I'll have it the person doing it dose mostly car motors and I'm not sure if he has any way of knowing the specs on ATV motors.if I wasn't posting off my phone I would down load the manual for the blaster.
If you're going with a cast piston (namura, stock, ART) the spec is .0015" piston to cylincer clearance. If you're going with a forged wiseco the spec is .002" piston to cylinder clearance.
If you're getting someone who normally does vehicles to do it, MAKE SURE you take the piston with you to have it fit perfectly. Don't tell him to bore the cylinder XXXXXX size and then hope that it fits the piston...
Also, you need to chamfer the ports after the bore is done. Most automotive folks don't know/do this and it will cause premature ring wear/short bore life and worst case is it can actually snag a piston ring.
If you're getting someone who normally does vehicles to do it, MAKE SURE you take the piston with you to have it fit perfectly. Don't tell him to bore the cylinder XXXXXX size and then hope that it fits the piston...
Also, you need to chamfer the ports after the bore is done. Most automotive folks don't know/do this and it will cause premature ring wear/short bore life and worst case is it can actually snag a piston ring.
Ports, after boring all have sharp edges on them. Sometimes even after honing the port edges are like razor blades. They'll wear down rings (and sometimes even the piston) to the point that you'll start to lose compression (or worst case scenario, break the piston skirt off) and then you'll be back at it again with a "low compression, 10 hours on the top end WTF?!?!?!" thread.
Chamfering involves physically "breaking" or removing the sharp edges on the ports backwards into the port just a tiny bit so that the edges aren't so sharp. It's usually done manually using a grinding stone VERY carefully as not to damage that fresh bore.
Chamfering involves physically "breaking" or removing the sharp edges on the ports backwards into the port just a tiny bit so that the edges aren't so sharp. It's usually done manually using a grinding stone VERY carefully as not to damage that fresh bore.
I would do a little research on your local guy to make sure he knows what he's doing when it comes to boring 2 stroke cylinders.
I had never heard of chamfering the ports either (I've learned ALOT here in the short time I've been here, thanks everyone) but I had a well known well respected bike builder bore a cylinder for a CR250 I have and when I looked at it, it wasn't chamfered. Just because someone is even a bike engine builder don't assume he will know (or take the time) to do this. I takes a little more time and maybe a little more money but from now on my stuff will get sent off to someone I know will do it right.
It's not that a non-chamfered 2 stroke engine is going to grenade the moment you start it, it's that rings are designed to wear the crosshatching off gently as they break-in. Sharp port edges can cause the rings to bounce badly and wear the edges off the rings reducing ring life. If there was something you could do that would take 15-20 minutes (or $10 extra if you get someone else to bore it and don't have the tools to chamfer yourself) but you KNEW would extend piston ring life another 50 hours of run time, why wouldn't you do it!?
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