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help piston to bore clearance

cornishgs

cornishgs

Forum Apprentice
Hi all having gs650 block bored for o/s pistons what piston bore clearance should i go for . Does .002" sound okay or should i go .0015 or different.help appreciated. Pistons are from cruzin image no instructions.
 
.002" would be as tight as I would go. You might want to message the CI guys for more info.
 
.003 will be safe. .002 will be tighter than I would recommend unless they are specifically made to run that tight. Which is RARE!!
Ray.
 
Nessism said:
.002" would be as tight as I would go. You might want to message the CI guys for more info.
Click to expand...
Have told machine shop to do 0015" might have to get them to hone a bit more .but dont want to end up with the ring end gaps too big .as i dont know what they have allowed.

Cruzin image not to hopfull of them getting back to me
Have heard good thngs about their pistons on kettle club for 2 strokes! And kz riders

I cant find the reccomended piston bore clearance for the genuine gs650 only that the wear limit is 005"
 
Leaning towards 0025" now will call mchine shop tomorrow. If rings allow for extra might go for closer to 003" last thing i want is piston seizure or huge ring gaps.
 
cornishgs said:
Have told machine shop to do 0015" might have to get them to hone a bit more .but dont want to end up with the ring end gaps too big .as i dont know what they have allowed.

Cruzin image not to hopfull of them getting back to me
Have heard good thngs about their pistons on kettle club for 2 strokes! And kz riders

I cant find the reccomended piston bore clearance for the genuine gs650 only that the wear limit is 005"
Click to expand...

If they're cruzinimage pistons then Ray's right - closer to .003in is needed.
It also depends how careful the machine shop is - the block should be cooled off before measuring. A lot try to do it while it's still too warm....
 
The "magic" is not in the clearance number. It is in the area of the piston where the measurement is taken. Pistons are not straight top to bottom. After having numerous bore and hone jobs done locally by "machine shops" that were not acceptable, I finally sent my block and pistons to a very reputable motorcycle shop to be done. After receiving the parts from them, I lowered a piston into the correct hole to find out it would hang in the bore. Cleaned the bore and piston and tried again. The piston would not drop through. Having spent some time in a precision machine shop myself, I knew the clearance must have been around .0002" (two ten thousanths of an inch). I was ****ed. Made a call to the shop and they said we will let you talk to the machinist. His name was Jose. He informs me that his measurement was not at the fattest part of the piston, but rather at the thrust face. He said to run it and let him know if I had any problems. I had to grind the ring end gaps as there wasn't any to, speak of. So now I had custom fit rings (to my spec) and pistons that seemed too tight to feel comfortable with. This turned out to be the best job that I had ever had done. No blow by (16:1 compression) and the catch can never had oil in it. Lasted for many years at the drag strip. This was not done by a "machine shop" but rather a company called Vance and Hines Racing. Dont get caught up in the number but rather the knowledge of the person doing the work.......Billy
 
Generally (talking automotive here) if you have a piston for a 4.030" bore and you finish the bore at 4.0300 inches the piston manufacturer has designed the clearance in to the piston, so clearance is magically correct regardless if is is forged, cast, whatever. Not sure that applies to Suzuki motors though....
 
Nessism .On honda forum had a look some one had used a 836cc kit 0010 to 0012" clearance!!!
 
Last edited:
bobgroger said:
Generally (talking automotive here) if you have a piston for a 4.030" bore and you finish the bore at 4.0300 inches the piston manufacturer has designed the clearance in to the piston, so clearance is magically correct regardless if is is forged, cast, whatever. Not sure that applies to Suzuki motors though....
Click to expand...

The last set of cruzinimage pistons I put in an engine had each bore finish honed to suit that piston. While a number of the top aftermarket piston kits are made on top quality machinery with effectively no variation, there's a little variation in these ones. Sufficient that individual fitting is worthwhile.
Pistons are usually measured across the thrust faces, about 1/2in up from the bottom of the skirts.
 
Cruzin image got bck to me and said the gs650 pistons i bought from them should have a bore piston clearance of

0.035mm to 0.045mm thats 0013"---to 0017" acording to the piston manufacturer

Dont know what suzuki recomended on their gs650 pistons.
 
Last edited:
cornishgs said:
Cruzin image got bck to me and said the gs650 pistons i bought from them should have a bore piston clearance of

0.035mm to 0.045mm thats 0013"---to 0017" acording to the piston manufacturer

Dont know what suzuki recomended on their gs650 pistons.
Click to expand...

I just scanned that SOHC 750 site and they say the pistons have "micro grooves" on the skirt that will break in and add about .0004" extra clearance, that's why they bore them so tight to begin with.

The GS650 factory manual has the stock clearance. Basscliff has a free download.
 
Nessism said:
I just scanned that SOHC 750 site and they say the pistons have "micro grooves" on the skirt that will break in and add about .0004" extra clearance, that's why they bore them so tight to begin with.

The GS650 factory manual has the stock clearance. Basscliff has a free download.
Click to expand...

Thanks for all replies all good thanks
 
cornishgs said:
Greg T what cruisin image pistons did you fit and what clearance.
Click to expand...

GS1000 and they finished up with .0025in clearance. They did not appear to be microgrooved either...

The 650 is quite a bit smaller in the bore so I'd go with the top end of their recommendation - but again, that clearance figure needs to be measured cold.
 
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