Don Terrill’s Speed-Talk

Typical sbc 350, 4.030" bore.
KB pistons recommends an end gap factor of .0065" making the gap about .026". They suggest this is necessary for the top ring because of spacing. They fail to suggest a factor for the second ring so most would probably use the same factor for both rings.

Hastings suggests a minimum of .0035 which would make it .014".

I have read where allowing a difference of a few thou. is a good idea to reduce flutter. Most suggest the larger gap on the bottom ring.

So if you are fitting Hastings rings on KB pistons, what would you do?

rcull wrote:Typical sbc 350, 4.030" bore.
KB pistons recommends an end gap factor of .0065" making the gap about .026". They suggest this is necessary for the top ring because of spacing. They fail to suggest a factor for the second ring so most would probably use the same factor for both rings.

Hastings suggests a minimum of .0035 which would make it .014".

I have read where allowing a difference of a few thou. is a good idea to reduce flutter. Most suggest the larger gap on the bottom ring.

So if you are fitting Hastings rings on KB pistons, what would you do?

The KB pistons requires a wider top ring gap than a regular piston would use.

II would do whatever KB tells me to do ...

I've always stuck with KB top ring directions with zero issues on those pistons. 2nd ring remains the same as other ring pacs. They are a good budget piston.

Close up the gap on a KB and watch the top of piston come off at the top ring----oh yeah guaranteed.
reed

The brand of rings makes really no difference in the gaps needed.

You need to know the engine, the piston, and what the engine will be subjected to.

To get really specific what the ring is made of could make some difference, but I think it is a small factor.
Also the design of the second ring could change the ideal gap for it, but also it is a small factor. Most all high performance stuff the top ring does the sealing and the second ring is a scraper type, so there is no reason to make the second gap smaller than the top, should be the same or even larger, in some cases HUGE.
but some engines the second ring is a compression ring, there is no such thing as a universal rule.

certain pistons because of material hold the heat more so you need a larger end gap to prevent butting

pamotorman wrote:certain pistons because of material hold the heat more so you need a larger end gap to prevent butting

This piston material reflects the heat (not absorb the heat)and as a consequence, the ring runs at a much hotter temp, thus closing the gap. In my opinion. I think this holds true for most if not all hyper pistons. If the piston absorbed heat, it would expand at a greater rate and u would have to have much more clearance---I think.
reed

racear2865 wrote:

pamotorman wrote:certain pistons because of material hold the heat more so you need a larger end gap to prevent butting

This piston material reflects the heat (not absorb the heat)and as a consequence, the ring runs at a much hotter temp, thus closing the gap. In my opinion. I think this holds true for most if not all hyper pistons. If the piston absorbed heat, it would expand at a greater rate and u would have to have much more clearance---I think.
reed

Hyper does not expand like a forged hence the bigger gaps..

I had a problem with ring butting when the kb's first came out years ago. This was in a sprint boat with a 400 sbc. According to kb the ring expansion problem is because of the high top ring position heating the ring from combustion. All other hyper pistons I just run normal ring gaps and have never had a problem.

rcull wrote:Typical sbc 350, 4.030" bore.
KB pistons recommends an end gap factor of .0065" making the gap about .026". They suggest this is necessary for the top ring because of spacing. They fail to suggest a factor for the second ring so most would probably use the same factor for both rings.

Hastings suggests a minimum of .0035 which would make it .014".

I have read where allowing a difference of a few thou. is a good idea to reduce flutter. Most suggest the larger gap on the bottom ring.

So if you are fitting Hastings rings on KB pistons, what would you do?

Whatever rings you use ,,, follow the KB guide for top ring gap then follow the ring makers spec for everything else and you will have no problem at all.

Another vote for following K-Bs directions. Have used those pistons for years on budget builds never had an issue. Seen lots of engines come into the shop with wrecked pistons when the instuctions weren't followed.

I don't buy the rings being higher up causing damage. Most K-B pistons have the rings .200-.300" down and they will still give problems if the rings aren't gapped right. Like was mentioned I think its the material.

i think you still should go wider on the second ring!

englertracing wrote:i think you still should go wider on the second ring!

the gap on the second ring is there to make sure pressure does not build up between the top and second ring preventing to top ring from seating properly.

"Running Clearance" ... it is all about originally preparing the ring end gaps so they will all be correct when in a running engine at temperature.

Running clearance and initial build clearance is nowhere near the same and different piston designs and material will require different end gaps.

KB Hypereutectic pistons locate the top ring high on the piston, closer to the combustion chamber, thus the rings run in a much higher temperature environment than most other piston brands. The higher temperature causes more ring expansion, hence the need for more gap. If the ring gaps butt together the rings will severely damage the cylinder walls and ultimately the piston grooves.
Yes, the second ring should still have more gap than the top ring, for the reasons that were addressed in a previous post.