Piston to cylinder wall clearance.

G_YamTech_314

XS650 Junkie
Top Contributor
Messages
854
Reaction score
1,794
Points
143
Location
Lancaster Pennsylvania
I took a look at my cylinders, and I think I may want to bore them out... How do I do this and get the most power out of the motor? I know that it isn't all about the bore... I also am aware that I should only bore if necessary, but I'm tossing up the ideas of going 1 over just to start fresh. This being said, can I buy specifically sized pistons? How would I do that? And where would I buy them?
 
I got a great set off ebay.. think pair was $90.oo.. with rings and pins/clips.... made in Japan... I always go with 2nd over... because... my machinist said it's much easier bore'n cylinders 2nd over then 1st over..... clearance usually 2 thou
 
Last edited:
+1. If you decide to bore, get the pistons first and take them to the machinist with the cylinders. Check around for a shop with a good reputation; you don't want the job done by some outfit that does 2 or 3 jobs a year on a clapped-out boring bar.
 
+1. If you decide to bore, get the pistons first and take them to the machinist with the cylinders. Check around for a shop with a good reputation; you don't want the job done by some outfit that does 2 or 3 jobs a year on a clapped-out boring bar.
There is a family friend that has been machining for decades. He does all the work for my cousins race cars so I trust his reputation.

If I were to buy pistons, where would I find a QUALITY oversize piston and ring kit? Or how does this work...? In school I just rebuilt with same parts for practice.
 
Lots of sound advice here. After initial measuring, I would look at Hoos Racing (pricey) and I would see if there are Wiseco pistons available for your application. Maybe you can score OEM parts. I would avoid Asian aftermarket unless it's Japanese. Only forged pistons will do. I understand the "affordable" part but you get what you pay for.
 
Hovel, I disagree. Oem pistons are often cast even in performance applications.

I wouldn't hesitate to run a good cast piston.
They grow less with heat usually. Are quieter, lighter...

Got nothing against wiseco pistons but they were 3x the cost of the nice Japanese cruzinimage ones and I don't see piston failure as the weak link on our low revving engines.

Probably better to spend the money on good valve springs! Lol
 
So I heard back, he wants to see if he can even secure it in his boring machine, if he can, I'll have him mic it, then bring a piston along for him to measure just in case it needs nothing! (Doubt it... Had some good vertical scoring going on.)

Then as far as I've heard, I can just have him bore it out, AFTER I buy a specific size piston set. Then when I get it bored out all I need to do is get the hash marks in it (unless the machine takes care of that...) And oil it up before installing?
 
The "hash marks" as you call them is what's known as honing. Many times the machine shop will bore the cylinder to very close to the size they want, then finish it with honing. Honing can remove a small amount of material if done long enough. It also gives the cross hatch finish to the cylinder wall you want for oil retention and ring seating. Usually when you have a cylinder bored, they do the honing too as a final step, so it's ready for assembly when you get it back (but do clean it well first).
 
"Clean it well" means hot soapy (detergent) water, quick dry and oil the walls immediately. You won't believe how fast they will flash-rust or oxidize.
 
When "measuring" the cylinders to find out if it's been bored out or not, would I be able to use primitive tools such as vernier calipers? Or would I really need a ball gauge, mic set, and the whole 9. The problem is that I know how to do it the right way, but the right way is expensive.
 
When "measuring" the cylinders to find out if it's been bored out or not, would I be able to use primitive tools such as vernier calipers? Or would I really need a ball gauge, mic set, and the whole 9. The problem is that I know how to do it the right way, but the right way is expensive.
Oversizes are in 1/4mm increments... or .25mm. Do you have a vernier that will measure down to that?
 
but the right way is expensive.
25 bucks for a 3 function caliper ain't bad. I've had this one from Home Depot for about 3-4 yrs now and found it to be accurate enough for engine work. I'm sure a "T" gauge that size could be had for much less. Consider them an investment for the many engines to come. ;)

general-tools-calipers-147-64_1000.jpg
 
I do have a blue point one that I got in my school tool kit. It measures down to that.

If the motor were stock would it be in the 75.10 mm range?
 

Attachments

  • 15984899112825668017384573155263.jpg
    15984899112825668017384573155263.jpg
    63.4 KB · Views: 82
Cool, So then my next step is goi g to be ordering pistons for 1 over, and having my machinist match the clearance. In that order... I think? Lol. I haven't set foot in my garage in weeks or more... Been too busy.
 
Back
Top