J engine ring end gap

Could really use some help on this one.

Putting together the top end, bored 72mm with MTC 10.5:1 piston kit.

OEM end gap spec is .2mm to .4mm (.0078" to .0157") all rings.

MTC instructions ( www.mtceng.com/images/pdf_files/piston_kit_installation.pdf ) for high performance street gives me .0127" top and .0155" second.

With cylinders bored to 72mm and new rings I have .011" top and .020" second.

Can't make the second ring bigger, and how could the top ring be at .011" if bored too big. I assumed these rings should have correct gap on a true 72mm bore out of the box, seeing 10.5:1 kit is for performance street application.

Any ideas?

Overly large ring end gaps, even quite a few thousandths larger than max printed specs, will never hurt a thing... especially on a street bike.
This and always has been a red herring.
Main thing is that gap is not smaller then the minimum spec!

Good to hear. Just don;t understand why so far off on the second ring. It's even out of OEM specs. I understand Wiseco makes the rings for MTC. Gonna give them a call.

For what it’s worth... I’ve seen this with quite a few Wiseco piston kits too.
Anyhow, don’t panic about it...

Was pretty happy with my 700 Kit ..........had 3 top rings at .0085 and one at .0055 and the 2nd rings were between .0115 and .0135 so had to only open that one top ring .003......... remember asking Jay if I should open them up a few more and he said no you were lucky...........usually they come a little looser and you get what you get

So I guess the theory is the tighter the better, as long as it's not too tight. The biggest thing bothering me is that .020" on the second ring is significantly out of OEM specs for used rings in a used bore, while I'm looking at brand new rings in a fresh bore. Normal wear can only make it bigger. Haven't had a chance to call Wiseco yet.

VTEC wrote: So I guess the theory is the tighter the better, as long as it's not too tight. The biggest thing bothering me is that .020" on the second ring is significantly out of OEM specs for used rings in a used bore, while I'm looking at brand new rings in a fresh bore. Normal wear can only make it bigger. Haven't had a chance to call Wiseco yet.

I've had rings that were getting close to twice the minimum gap recommended and the engine ran fine with virtually no compression loss or oil consumption.

Keep in mind that you want to measure for the gap at the tightest spot in the bore.... it's the minimum gap that is really important.
Measure three or for spots up and down the bore...by pushing the ring down into the bore with an upside down piston... again, at a number of spots.
If the bore is perfect, the gap will always be nearly the same.
And also... don't go over the top with the notion that all the gaps, from top to bottom, MUST all be 120 degrees apart.... they can spin all over the place when the engine is running.

I only checked one spot about a 1/3 down the bore setting it true with the top of the piston. I also checked the same ring in another bore and got the same reading. I'm assuming the bores are straight since they were bored and honed by APE, but I will check in different positions to be sure. I know the gaps will move but I'll use the MTC/Wiseco pattern when I install. I have a cone ring compressor so I'll go with the install method I used last time. Install all 4 pistons from the top with the the wrist pin holes extended past the bottom of the bores. Then slide pins and caps through the rods as I lower the block down on the studs. Works best with a helper.

And also... don't go over the top with the notion that all the gaps, from top to bottom, MUST all be 120 degrees apart.... they can spin all over the place when the engine is running.
Bruce

Yes, assuming they are not gummed up, they move around at about 1 rpm, the cross hatch hone causes this I think. The reason to space 120 degrees apart is for a good ring seal for break in on first start-up, where the first few mins running are critical (in my opinion)

Agreed on the ring gap spec, seems the max clearances are a bit conservative.

Spoke with Wiseco. They said the ring set out of the box in a true 72mm bore should be correct. Meaning about .012" top and .015" second. He also said .020" is border line. Like .021" would be too much, which will be the case after they seat.

He said you can get a batch that is off, and suggested calling MTC and asking them to go over a few ring sets with a ring gauge and try to find 4 seconds with a better fit.

In my experience, the top ring gap is the critical one. You are correct – gaps are best tight as possible, but never too tight. If you can get 2nd rings that will gap in spec, great. If not, I don’t think 0.005” over on the 2nd rings is a problem.

APE is good – REAL GOOD – but anyone can make a mistake! I suggest you take your pistons and cylinder to a local automotive machine shop and have the cylinders checked. The shop should number and measure all the pistons at the skirts (to precision of 0.0001”) in a few locations per piston and record the diameters. Then they should use a proper cylinder dial bore gauge and setting fixture, like a Sunnen, to measure each cylinder to check that each cylinder is bored and honed straight, round, and to the correct piston to cylinder clearance. The dial should read increments of 0.0001”. Piston clearance (minimum at any point in the cylinder) should be 0.0015” to 0.002” for air cooled engines for street use. I prefer closer to 0.002”. Ask APE if they used a fixture to simulate head stud clamping forces while boring and honing your cylinders (often called a “torque plate”). This isn’t likely for a street engine, but if they did – you have to tell the person measuring your cylinders, or it will throw the cylinder measurements off around the stud holes.

I have a CBX cylinder on my shelf that was over bored many yesteryears ago by a machinist who had never made a mistake before (that I was aware of). When the ring gap was checked, all the new rings were on the extreme high end of the specs. It wasn’t the rings. When the cylinders were checked, the bores were on average 0.007” over the maximum piston clearances! Have your parts checked before assembly. I always do, now.

I hear what you're saying. everyone makes mistakes.. But I don't think it's the bore because there should be .003" difference between the top and second ring gaps.. There's .009" difference in the same spot of the same bore. So it only makes sense that it is the rings.