HKS Exhaust Install Issues
 

Just installed an HKS Hi-Power exhaust on my 2014 Nismo. It fits perfectly and was a snap to bolt up but I do have one leak I can't seal properly by tightening the bolts.

The older model had an all welded h-pipe crossover:
Attachment 96509

The newer models have a bolted flange:
Attachment 96510

Unfortunately there is no way to put a socket on the nut or bolt head to tighten it. I can barely get an open end wrench on by angling it 45 degrees on the bolt head and using a box-end on the nut side. I even added another washer to move the head away from the rolled flange but it's still difficult.
Attachment 96511

I tried unbolting the flanges after the crossover to allow the pipes to be drawn together more easily but no luck - it still leaks. Furthermore, the flange bolts are torqued to 50 ft lbs and water still drips from them although I can't hear or feel any air leakage.
Attachment 96512

I can only get it so tight with the open end wrenches and the crossover still leaks in the center between the bolts. I think my only option is to remove the entire exhaust and reassemble it using high temp RTV.

Anyone else had to deal with this issue and how did you resolve it?

On a positive note I didn't have to remove the shield to clear the muffler. The shield on my Nismo is thin sheet metal, not plastic, and I simply bent it slightly to provide clearance.
Attachment 96513

The hanger for the driver side muffler (the one in front) needed to be modified. It has an extension that lowers the muffler hanger but that has to be removed. The bolt that attaches the rubber must be either replaced with a shorter bolt, trimmed shorter to clear, or a spacer used to prevent it from hitting the horizontal damper mounting bracket.
Attachment 96514

After I get the leak corrected I'll add a stack of washers as a spacer to properly tighten the bolt.

Any suggestions are appreciated.

To bolt the cross over pipe I would recommend using a combination wrench to go around the bolt head. Then use a 3/8's torque wrench with a crows foot to tighten the nut to spec.

And that is a fvcken retarded new H-pipe section!

It's a great suggestion but the crows foot is thicker than a socket and there is not enough clearance between the bolt head/nut and the pipe to allow the crows foot to turn. It'll fit partially on the nut (as far down as the flange will let it) if it is rotated to the opening but it can't be turned because the pipe is too close. In addition the pipe flanges extend and cover most of the bolt head/nut so any tool that cannot be angled to fit will not work.

You're also right in that it's a very poor design. I assume they did it to separate the parts and make them easier to handle and a smaller package to ship. If the flanges had been rotated vertically the bolts would be clear of the pipes and a socket would fit. If the flanges were flat plate like the others and the bolts further from the pipe a crows foot would work to torque the bolts. The way they are the bolts are completely inaccessible.

From my perspective here are my options:

1. Return it for a refund
2. Take it apart and reassemble with RTV
3. Weld the flanges together
4. Trim the flanges to allow access

and my thoughts on my options:

1. I don't want to return it - what a hassle. Besides I like the way it sounds.
2. What a pain! And placing the RTV in a confined space in proper manner and sequence will be a formitable challenge for me working alone with multiple sections of pipe without smearing it and ruining the sealing bead.
3. Sounds simple but it would have to be removed and without a jig to hold the pieces in place a challenge to align properly to fit. I guess it could be tacked in place then removed and welded but again, what a hassle. I shouldn't have to do this.
4. The flanges are what gives the thin metal its rigidity. Trimming the flanges would make them very flexible and probably make it impossible to seal, so really not a viable option.

I would just trim the edges of flanges to allow access.

Followed by contacting HKS and let them know their current is design is flawed so they could possibly either rotate the flange or make it a normal open flange.

Wow that $hit is stupid. I'd probably just ask for a refund. But if I really want to keep it, I would find a competent shop to cut that stupid flange out and weld in a new open pipe piece to make it like the old version. I would also contact HKS to inform them of the terrible design and the hassle gone through and asked for them to pay for part of the work done (not greedy, just like $50-100 depending on what it cost me).

Hopefully this works
 

Unfortunately the loss of the flange would remove the stiffness they provide and would allow the then metal plate to flex so I'm not considering that as a viable option.

I have one box end but I went and bought an offset box end wrench to hold the other side so I didn't have to use the open end. I unbolted the pipes from the resonator section and unbolted the crossover so I could move the sections apart to apply the RTV.
Attachment 96540

I applied a bead around the flange, positioned the gasket and snugged up the bolts till the RTV started to squeeze out.
Attachment 96541
Attachment 96542

Now I have to wait one hour then fully tighten the bolts. I have to wait 24 hours for it to cure before I test it.

That's probably my next option but I'm hoping it is not necessary.

What a pain in the pooper lol. I'm still eventually going to buy this exhaust. Hopefully I can request the old style H-pipe section.

Notes on bolt torque values
 

I read in another thread to use 45 ft lbs as the torque value. The bolts provided are M10 x 40 pitch 1.25 grade 4.8 and the torque values per Nissan service manual is 21 ft lbs/28 Nm (without lubricant). I found this out after I broke one of the bolts over torquing it.

Attachment 96543

Attachment 96544

The values in the service manual are general per bolt size and not specific to any particular assembly, nevertheless 21 ft lbs seems too low since I had originally used 45 lbs and the flanges at the front of the resonators were still leaking water. Since I had to remove the bolts several times I kept upping the torque to get compression on the gasket and when I reached 60 ft lbs one of the bolts broke. When I replaced it I used a grade 8.8 and 60 ft lbs which is still way over the recommended value of 30 ft lbs.

I'm not sure one could achieve a complete seal at only 21 ft lbs with the provided bolts but I would recommend to use that value, then start the car on the lift or stands and check for leaks and upping the torque only if necessary. If a much higher value was required it might be prudent to replace the supplied bolts with a higher grade to prevent any inconveniently timed leaks or issues with CO as a result of the bolt snapping from being overstretched/overstressed.

The manufacturer really should provide this kind of basic information with installation notes for their product.

Wow. I'm glad I have the original design HKS

Hey sandersd, is there any way you could call whoever you got the HKS exhaust from and see if requesting the old H-pipe design is possible?

If you do, I would tell them to let HKS know about this issue.

Tech support? What tech support...
 

Yes, I emailed Z1 Motorsports and linked to this thread. Maybe I'll hear from them next week. I also went to the HKS USA website but there is no contact info for the manufacturer, just the distributor and authorized dealers. I called Jotech Motorsports since they were one of the dealers and was told Tony would call me back but he never did. I emailed him but he hasn't responded but maybe next week he will. Went to HKS Japan for contact info but it just sent me back to the USA site.

I guess I could write them a letter...

lol!

First drive...
 

Try to listen on good speakers!

I installed the washers as spacers to prevent the bolt from hitting the horizontal damper as described earlier.

Attachment 96609

Another shot of the shield that I decided did not need to be removed. There seems to be plenty of clearance from the muffler.

Attachment 96610

I've read in other posts people say the factory Nismo exhaust is not a true dual exhaust and narrows to a Y pipe like the standard exhaust so I wanted to post a pic for any confused readers or doubters. The Nismo is a true dual exhaust with an H pipe crossover underneath the heat shield.

Attachment 96611
Attachment 96612