Chevy Nova Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
103 Posts
Discussion Starter #1
I am helping a buddy who is computer literate rebuild a carbureted motor with 250,000 miles. The motor is in very good condition but going to be installing new cam bearings, rod bearings and main bearing and finally new piston rings. As you can see by the pic, the cross hatch marks are still there. Not sure if they are from the factory.

I also came across this on Hastings website:

http://www.hastingsmfg.com/ServiceTips/cylinder_bore_refinishing.htm

CYLINDER ROUGHNESS
Substantial controversy exists on the correct cylinder roughness for proper seating of piston rings, whether chrome, moly, or plain cast iron. It has been our experience that the use of 220-280 grit stones and achieving proper cross hatch angle produces a finish compatible to all three types of the above rings.



My question is after re-honing, should I use cast, moly or plasma piston rings and why?

Thanks

Waid
 

·
Registered
Joined
·
1,009 Posts
The cylinders shoud be honed with a torque plate installed and use a good hone as that what your rings see for roundness once the heads are bolted on.

Most shops don't understand what it takes to achieve good ring seal.

with that many miles its hard to believe the ring lands are not worn.
 

·
Registered
Joined
·
103 Posts
Discussion Starter #3
There is a tiny piston bore ridge there. Since I dont have a dial bore gauge, I took a straight edge and placed it in the piston bore against the ridge. I was not able to get a 0.0015 feeler gauge under the straight edge next to the ridge.

Thanks

Waid
 

·
Registered
Joined
·
332 Posts
With that many miles and all that work with a few key parts that are surely past their prime-new pistons and likely an overbore would be money ahead.

But to answer your question...I vote for the same material that came out of the engine...it already worked for a quarter million miles!

Good Luck!
 

·
Registered
Joined
·
103 Posts
Discussion Starter #5 (Edited)
The circumference of a circle is: c = pi * d or the diameter is: d = c / pi.
Since I am only interested in the difference in the diameter and I don’t know the exact diameter of the piston bore at the top and bottom, the piston gap itself can be used to calculate diameter. Even if assume a piston bore diameter of let’s say 4.000 and subtract the piston bore gaps, the answer remains the same.

Piston bore diameter at the top:
The piston ring gap at the top is 0.045”, therefore, the diameter at top is: d = c / pi. Which is: d = 0.045 / 3.14 = 0.014”

Piston bore diameter at the bottom:
The piston ring gap at the top is 0.035”, therefore, the diameter at bottom is: d = c / pi. Which is: d = 0.035 / 3.14 = 0.011”

Therefore, the difference between top and bottom is 0.003”. This will not tell me the exact diameter of the piston bore at various palaces, but it is a very good indication that my piston bore taper is acceptable.

According to Hasting (Which I am no were near and that my calculation is correct - I am at 0.003" and looks like I can go up to 0.012"):

For this reason, Hastings recommends a MAXIMUM of .003" wear per inch of cylinder diameter, not to exceed .012" in any case for successful reringing. If a cylinder is worn in excess of this it should be rebored and the proper oversize ring installed.

DIAGRAM BELOW SHOWS EFFECT OF.012 CYLINDER TAPER ON RING GAP IN FOUR-INCH BORE.

http://www.hastingsmfg.com/ServiceTips/ring_gaps.htm



Thanks

Waid
 
1 - 6 of 6 Posts
Top