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Ring Size ?

2K views 22 replies 9 participants last post by  yzair 
#1 ·
If my cylinder bores are 4.0495 would the rings be .30 over on sbc 350 ?
 
#5 ·
I used a telescopic bore gauge and quality digital micrometer and they were all around 4.050 average the cylinders have very little piston ridge also the motor had less than 10,000 miles on engine bearings were ok same with mains. so ok obviously it's over bored between .030 & .060 thats why I asked seemed odd but thats what it is.
 
#9 ·
I'm going to re check the cylinders again maybe I made a mistake? yes I have the pistons I'll check one as well. The motor had just been rebuilt but unfortunately it was left with open exhaust ports and no distributor and when I pulled the pan there was a bunch of rat **** in motor, so I tore it apart there was rat turds everywhere. I'm going to thoroughly clean it and wanted to re-ring and new bearings hell the cylinders are still cross hatched. Just don't get the bores. motor had new acl tri metal main & rod bearings @ .010 which looked like they sucked some dirt but very very little.
 
#13 ·
Was this engine used as a hot rod motor? Many moons ago, people used to build them 'loose' because it was believed to help them run more free. True to a point. Had an engine once that had .009 piston clearance and it ran pretty good but it surprised me that it had so much when I tore it down at the end of the drag racing season.
 
#14 · (Edited)
Sure it's an N? Zollner was a Canadian piston manufacturer. Great products and a circleZ. Too bad their automotive pistons are no longer produced like those.

It was somewhat common to run excessive clearances on the old style "Forged" racing pistons. The material and skirt designs were not near as good as present stuff.. Used to run .008"+ on bbc race stuff. Cast pistons, as these are, very rarely run more than .0025" anymore..
 
#17 ·
A .030" piston will require a .030" ring and a .030" hole. There is no way you can run a .030 piston in a .050" hole.

The required piston to wall clearance is built into the skirt.

I run into similar situations with old retired guys that decide to repair small engines.. Repeatedly having to tell them that you have to run the correct oversize piston in an overbored cylinder. NOT just put oversize rings on a standard piston..They get a bit noisy that way! Plus they smoke profusely...
 
#20 ·
I used a telescopic bore gauge and quality digital micrometer and they were all around 4.050 average...

Well the piston mics out @ 4.030

Checked the piston clearance is .009
You sure this engine wasn't built as a demo derby mill? But if the p to w is 0.009" and the pistons are 0.030", the bore can't measure 4.050".

If you keep this block, have it checked for bore diameter by a shop and sonic'ed and if it's OK to take out to 0.040" or 0.060" over, do that. There's no way you will get a satisfactory rebuild out of it the way it sits, IMO.

So could I use .20 rings and check ring end gap clearance since the bores just under 4.050 or would this be an issue
I think you mean 0.020" not ".20", but either way, no- this will not work.
 
#22 · (Edited)
Again, the bore is 4.055" and the piston is 4.056 that won't work.

Measure the skirt directly across from the pin bore.It has to read at least .001 less than the bore.

Try this. get an inexpensive set of feeler guages. use the .001 leaf and place it alongside the piston with the end of the leaf at the pin area of the skirt. then place this in the hole. it should have light drag but pass up and down. Repeat this with the next size till the assembly locks up. next smaller is your clearance.

Probably a .060 bore..
 
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