Ring gaps any suggestions

[MJTru]

Hello everyone. Merry Christmas in advance.

Well it's been a while and all my parts are coming together to build 2x rb26 blocks. I thought I would post up my ring gaps results as I just got the blocks back from getting bored. Seems like this new company does a way better job. Here goes

Piston 1

First. 010

Sec, 018

Piston 2

First. 011

Sec. 018

Piston 3

First .011

Sec. 018

Piston 4

First .010

Sec. 018

Piston 5

First .010

Sec .15

Piston 6

First .011

Sec. 018

From what I see piston 5 is a problem on the second ring. The formula from wisco is to take my bore 3.4 inch (86.5mm) x by a given number. Which all depends on what I'm using the motor for. I went with

Street moderate turbo/nitrous

Top ring is .0050 and second ring is .0055

So my bore in inch system 3.4 x .0050 =

.017 isn't that big??

Second ring would be 3.4x .0055= .0018

So .017 top and .018 2nd. Rings. Fro. What I see on my results all my second rings are there already. Just my first rings have to be adjusted. At least it wasn't like my last machine shop that was to big. Side note piston to wall clearance is .003 is what I asked for. The spec sheet said .0025 so after it wears in i should be abit loose at .0033 or .0035.

Any advice would be greatly appreciated.

[MJTru]

I rechecked my gap on cylinder 5 and I don't know what went wrong. But it came out to .018
I'm sorry for using this form of measurement instead of metric system. I have ordered a ring grinder and as soon as it arrives I'll start my assembly, as crank and bearings all checked out.
I have also rechecked all 2nd rings at the bottom of the bore and every last one checked out at .018 and according to wisco spec sheet that lines up perfect with what I need. Thanks again. Feels like I did something wrong g no one has commented.

[GTSBoy]

Hi Marcus,

I think the only thing you did wrong was not do your measurements twice the first time!  "Measure twice cut once" applies equally well to engine building as it does to carpentry.

As to the large gap worry for your top rings....If Wiseco recommend a gap that looks big for engines with lots of combustion heat, they must be allowing for a bit of thermal expansion in the top ring.

[MJTru]

Hi Marcus,
I think the only thing you did wrong was not do your measurements twice the first time!  "Measure twice cut once" applies equally well to engine building as it does to carpentry.
As to the large gap worry for your top rings....If Wiseco recommend a gap that looks big for engines with lots of combustion heat, they must be allowing for a bit of thermal expansion in the top ring.

Thought you were missing for a minute there mate. Well thanks,first off, for the reply. And happy holidays. Christmas and all.
From what I can remember I thought running the cp pistons I was looking for a top ring gap of about .008.
That seemed good to me, but from that to .017 seems 2 times as big, so I thought I would ask. Especially when RB'S are known for oil issues and this is my time to control blow by. I went with this piston combination because it offered the upgraded pins and +625 bolts along with armor coating on the piston, with bc rods. I don't know how grate the rods are, but over all it was a great price. I'm sure wisco was contributing the gap via expansion, but just want to make sure. Today I measured like 5 times lol and all 2nd rings are .018 and top rings are all around .010 to .011. As I'm doing 2 engines I may try one at .010 and one at .017 as wisco recommend. See what happens.
Thanks again mate

[GTSBoy]

I am kinda missing.  Sitting in SFO airport again after 2 weeks in the frozen wastes of Utah.

Merry Christmas yourself.  Is that your lounge room or the waiting/office area of the workshop?

[MJTru]

Kml. Your just to damn good. Yes it is. Lol we wheel them in there rip off all the saran wrap and start measuring up. But really it's only because it has air conditioning that we do that. As well as very clean. As an added bonus I had two new head fitted with new brass guides and seats cut to accommodate the new valves all new supertech stuff. The shop also showed me all there machine. And as next year nears we are planning on buying up a few. Here my problem with the heads as I do most of my assembly myself. All the shims need to be cut down about .010 each. I have yet to find a good small machine or a very clever trick to cut them down. Last time I used glass and sand paper I sanded down my finger tips. I can say it works but there has to be a better way, or a machine that can do it. Google showed me a few monster of machine for this little task. Know off any other tricks.

[doo doo]

Don't cut the lemon shims down, they don't have the case hardening thickness for it. Once you know what size shims you need you can order them from here in Aus (precisionshims). They can be rubbed down as required and come in .02mm increments, and cost much less than oem. 

10 thou is too small for your top ring gap. It's better to be a bit too big than too small as rings butting will do damage. There's a reason wiseco (and piston ring manufacturers) recommend their gaps, follow their recommendations. Make your second ring gap a little larger than the top if you like, or the same, but not smaller. If you're running extra boost you can open the gaps a bit more, the wiseco recommended gap will be the minimum. 

 

Once you've redone seats in the head (and faced the valves) don't forget to check spring installed heights. The same shim place will do shims for the valve seats if needed. 

[doo doo]

Meh, 'oem shims' 

Edited December 29, 2016 by doo doo
Spell check

[MJTru]

Don't cut the lemon shims down, they don't have the case hardening thickness for it. Once you know what size shims you need you can order them from here in Aus (precisionshims). They can be rubbed down as required and come in .02mm increments, and cost much less than oem. 
10 thou is too small for your top ring gap. It's better to be a bit too big than too small as rings butting will do damage. There's a reason wiseco (and piston ring manufacturers) recommend their gaps, follow their recommendations. Make your second ring gap a little larger than the top if you like, or the same, but not smaller. If you're running extra boost you can open the gaps a bit more, the wiseco recommended gap will be the minimum. 
 
Once you've redone seats in the head (and faced the valves) don't forget to check spring installed heights. The same shim place will do shims for the valve seats if needed. 

Thanks mate. I just was thinking of precision shims. As I couldn't remember there name. Decided to search and saw this post. Thanks I have done all the head work on the intake side and exhaust side.018 and 015 sorry for standard figures. As that what my gauge is in. I have them all written down on a sheet and will place an order for new shims, as everything in the first head is new including the head and buckets. What I noticed with the new tomie buckets is they have a bigger bump inside that contacts the shims. This made all the shims be off by quite abit. Where as the oem ones were a bit more flat allowing for a thicker shim. Is this normal, and what's the advantage of running tomei buckets if any. I have poncam, as I didn't want to much aggressive ride/idle. Max head will allow without head mod.

[doo doo]

Tomei buckets are 1mm thicker (as you've noticed) so that you can run tomei procams (or any other camshaft with a 30mm base circle- standard base circle is 32mm so the extra 1mm in the bucket closes the distance down to stock-like spec). To run Poncams with tomei buckets you'll need shims that will be 1mm thinner than what stock buckets would need. The only need to run tomei buckets is when using smaller base circle cams. 

My advice would be to run stock buckets with the poncams however, so the shims aren't getting too thin. 

Running 30mm base circle cams with standard buckets requires 1mm thicker shims to make up the extra clearance, and people find that doing this can mean you spit shims out under high rpm, so the tomei buckets are the solution to that issue by using stock thickness (ranged) shims. 

Out if interest, JUN uses higher walled retainers to stop potential spitting out of shims when using cams with smaller base circles, and there's a a couple of different options. But they're pricey. 

[MJTru]

Tomei buckets are 1mm thicker (as you've noticed) so that you can run tomei procams (or any other camshaft with a 30mm base circle- standard base circle is 32mm so the extra 1mm in the bucket closes the distance down to stock-like spec). To run Poncams with tomei buckets you'll need shims that will be 1mm thinner than what stock buckets would need. The only need to run tomei buckets is when using smaller base circle cams. 
My advice would be to run stock buckets with the poncams however, so the shims aren't getting too thin. 
Running 30mm base circle cams with standard buckets requires 1mm thicker shims to make up the extra clearance, and people find that doing this can mean you spit shims out under high rpm, so the tomei buckets are the solution to that issue by using stock thickness (ranged) shims. 
Out if interest, JUN uses higher walled retainers to stop potential spitting out of shims when using cams with smaller base circles, and there's a a couple of different options. But they're pricey. 

Wow holly shit. I wish I had know this a few days ago. So I'll have to go back to the standard buckets that's the problem here. Wow. I just finished up my first head. Here are my results
First intake front/first being valve one.
1.10mm,1.42mm,1.47mm,1.50mm,1.17mm,1.27mm,1.24mm,1.27mm,1.17mm,1.40mm,1.32mm,1.24mm
the intake is thin. That's all gunning for
.45mm clearance.
Exhaust side front/first being valve one
1.93mm,1.88mm,1.85mm,1.80mm,1.93mm,1.85mm,1.85mm,1.80mm,
1.83mm,1.88mm,1.88mm,1.80mm
These aren't as small. But still smaller than factory set. Clearance of .38mm

I agree with you doo doo, I will go back to the stock buckets and order shims from precsion shims. I spoke to him and he offers the smallest shim at 1.50mm
I'm sure with the thinner oem buckets I will gain way more shim thickness. I guess to help get a close to the right clearance I'll measure each bucket and add that to the current value I have now from my shim thickness to get the difference I need. So in short shim thickness now, plus bucket thickness measured individually will give me my new shims thickness once added.
Damn what an ordeal.

Oem bucket thickness 2.97mm
Tomei bucket thickness 3.91mm

I see the 1mm differance right there well close enough.

[MJTru]

[MJTru]

Whats the proper range of shim size.

[doo doo]

The range of oem shims available from Nissan is from 2.275mm to 3.325mm. Anywhere within that range will be fine.

[MJTru]

Damn so I finally had some time after work to pull the cams off. We then swapped back the buckets to oem ones. The exhaust side lines right up to normal nissan size. Like .110 to biggest being. .115
the intake shims were so thin that when we installed the oem buckets on the intake side. We were around smallest .056 to biggest . 086 something was wrong. Numbers wasn't consistent. So we stopped and think. When the valves were open I could push the valve up. Problems shims to thin. Oem bucket touching the retainers on the springs and not the top of the valves. Test shims were ordered. But from the difference. We guess we will be in rang. Just food for thought.

[MJTru]

[doo doo]

Yep I keep a stock of used oem shims so I can get base measurements for shim clearances.