[drtalon123]

Hi all,

Posting this up for informational purposes, as I haven't found a good single source of information related to this topic.

I spent a significant amount of time the last 2 days researching the approaches others have attempted, in order to move from the M10x1.25 head stud size to the larger M11X1.5 found on higher performance Honda 4 cylinders (B Series, K Series, etc). I am wanting to modify my engine to accept these, and figured I would share the process of what I come across along the way to try and help others interested in doing this.

From what I've gathered, a few things need to happen in order to complete successful modification to accept the larger head studs:

1. Properly sized M11x1.5 head studs need to be sourced, that are similar in length to the typical D Series M10x1.25 ARP kits that are offered.
2. Block threads for the head bolts/studs need to be modified to accept M11x1.5
3. Cylinder head bolt/stud pass-through holes need to be widened
4. Head gasket bolt/stud passthrough holes need to be widened

1. Sourcing Head Studs

This process took a bit of comparison via Google, along with contacting ARP to verify the kit bolt length average sizes.

SoulEngineering was kind enough to inform me that DOHC ZC engines run M11X1.5 cylinder head fasteners. After a little bit of Google time, I was able to confirm this. I also found that ARP doesn't officially offer ZC bolt kits, but there are many aftermarket companies that create kits for these engines using hardware from other ARP kits OR directly sourcing individual pieces of hardware direct from ARP to offer complete plug and play head stud kits for the ZC.

**Because of the nature of these DOHC ZC kits being pieced together, I did not spend the time contacting companies that offered these pieced together kits for the ZC, to ask about stud lengths used in those kits, so I have no idea if they are comparable or where they fall in the below table I put together. If you have size or length measurements for the DOHC ZC bolt kit lengths, I would love to know about them to add them to the table!

From what I've researched, I found the following:

EngineMake	ARPKit#	StudAverageLength	StudDiameter	ThreadPitch
B18 GSR	208-4303	7.250”/184.15mm	7/16"/11mm	M11x1.5
B16A	208-4601	7.100"/180.34mm	7/16"/11mm	M11x1.5
D16Y8	208-4305	5.700"/144.78mm	3/8"/10mm	M10x1.25
D16Z6	208-4301	6.450"/163.83mm	3/8"/10mm	M10x1.25
SRT4	141-4204	6.300"/160.02mm	7/16"/11mm	M11x1.5

For the D15B, D16Y8 and D16Z6 engines at least, the best M11X1.5 stud length bolt kit that has been CONFIRMED to work on more than one build variant is ARP's SRT4 bolt kit offering.

Both D-Serious's D15B (YouTube channel D-Serious) and DSO's own Jvtec8K's D16Z6 have utilized the SRT4 head stud kit in their builds.

**Another FYI when purchasing the SRT4 stud kit: Apparently around 2007, there were reports of ARP mis-packaging these kits with washers and nuts that were too small for the application. The result in high performance applications was that the head aluminum would sink/depress around the nut/washer, causing loss of clamp load. The recent kits should have appropriately sized fasteners, just putting this out there in case someone is offering abnormally cheap SRT4 stud kits, be aware!




2. Modifying Block Threads

There are typically 3 ways to do this:

1. Drill the existing threads out of the block, and retap the aluminum with an M11x1.5 tap
2. Purchase a Helicoil kit (and appropriate drill bits) that uses M11x1.5 inserts
3. Use the official Honda TimeSert repair kit (P/N 7111) to install solid bodied flanged M11x1.5 inserts

Out of the three above, numbers 2 and 3 are the best approaches in comparison to number 1.


#1 lacks the ability to provide full, proper thread engagement with the stud, because removing ALL of the M10x1.25 threads from the bolt holes will leave very little aluminum exposed to properly allow an M11x1.5 tap to cut with. The threads will be shorter than ideal, and chances are they won't properly engage the stud threads.


#2 is a better alternative than #1. The HeliCoil inserts are not the "Cadillac" of inserts by any means, but you can typically stack them together inside the blind hole to provide full thread engagement for whatever fastener you are trying to use. The HeliCoil inserts fully engage the aluminum, and offer a steel interface for the studs to latch on to. Since the HeliCoil insert is going larger and wider into the aluminum than stock, there is more surface area engaged against the block aluminum, so I would definitely trust these style of inserts with the larger studs, even in a performance application, if nothing else was available:

#3 is the most recommended process by far, and is Honda's OEM method to repairing block thread strippage. Every Honda dealer should have these kits in their service departments, so if you work at a Honda dealer, f*** you ya lucky bastard lol. If you DON'T work at a Honda dealer, then acquiring the TimeSert kit might be a challenge. It was for me, as every machine shop in my area did NOT have this kit, and Honda dealerships I contacted would not let me use this tooling even if I provided my own insert refills. I ended up breaking down and purchasing this kit myself, just so I could perform this modification. I will also offer this tool for rental here on DSO for fellow members wanting to go with larger head studs, as a sad attempt to recoup my own costs of buying this kit lmao. I will post up a link to the thread I will add to offer the rental and conditions. This is what the kit looks like:

3. Modifying Cylinder Head Bolt/Stud Passthrough Holes

The cylinder head passthrough holes will need to be enlarged to properly clear the wider diameter of the head studs, these guys:

Choose the smallest possible drill bit that goes slightly larger than the stud, and I would spring the cash to buy this drill bit brand new so it cuts cleanly, and not use the worn out bits from the general set of bits in your toolbox

Jvtec8k used a 29/64" bit.

Tape off the machined surface around the holes on the block facing side of the head to prevent damage to head surface.

Drill from the valve cover side of the head, down to the block side, to keep potential damage to the head surface as minimal as possible.

Drill STRAIGHT and SLOWLY, trying to keep from cutting off center and removing too much material.

Make sure to lightly touch a deburring tool to the ends of the holes in the block side of the cylinder head after drilling, to remove any burrs and/or to lower any raised spots of aluminum that might have been pushed outward due to drilling.





4. Modifying Head Gasket Bolt/Stud Passthrough Holes

This process is the same as above for the cylinder head, but now you need to use the same drill bit, and drill out the stud/bolt holes in the head gasket to accept the larger stud diameter.

Put painters tape across the gasket surfaces top and bottom to prevent knicking any of the Viton sealant if using an MLS gasket. This is just good practice, regardless of the gasket material.

It is CRITICAL to verify that there are NO burrs or shavings that fall between the MLS inner layers! Take your time here and verify that there are no burrs around these drilled holes. Compressed air and a flashlight is your friend.

Remove burrs around the drilled holes lightly using a deburring tool if needed.












Reassemble and torque studs according to the ARP kit instructions you decided to go with to accomplish this.





Thanks,
Talon.

 

[drtalon123]

So I have some updates to this process of going big studded that I feel are important to those going this route.

I actually shot myself in the foot slightly going with the TimeSerts instead of Helicoils in this case, I will explain.

The TimeSert kit is a very specific kit designed for Honda block's that already have M11x1.5 threads. Defining characteristics between the D series block and my B series are the depth of the bolt holes in the block (deeper than the D), and the thickness of the cylinder heads.

Another defining characteristic is length of threads along the shank of the bolt/stud are different. The length of threads on the M10x1.25 are longer than the M11x1.5 fasteners, this is actually significant to the point of this post:






Why this matters? Well, the TimeSert kit drill bit is designed with a taper to cater to the actual flange on the insert. The bit is also designed to not cut down further than the depth of the hole, so when the drill bit bottoms out in the OEM depth hole, the taper is where it is, this can't be changed. What ends up happening is the insert stops at the taper and is suspended above the bottom of the hole about 1/4" from true bottom when installed to the block:






And because the SRT4 stud block thread length engages the entire TimeSert, no more, no less, the stud stops threading at the insert flange point, meaning you lose the ability to lower the stud the extra 1/4" into the block due to the physical insert installed limitation.

This adds 1/4" total height of the SRT4 stud sticking up above the block than normal since it can't bottom out, coupled with the fact that these studs are already longer than the D series studs, the studs become excessively long.

If the D series block hole was like 1/2-3/4" deeper (can't do this without risking puncturing through to the crankcase), and the head was thicker like their B series brother, this whole thing would be a non issue, there would be plenty of depth and length everywhere to fully utilize the entire length of the stud.

So, what to do in this overly long stud situation? If I would have went Helicoils, I could have drilled a bit further down below the stock hole depth, and put inserts all the way down to the bottom of the hole since Helicoils are not restricted by being flanged. I probably could have made the SRT4 studs work as they are going that route, in order to make up the required unthreaded portion sticking up out of the hole:




Because I was now limited by the TimeSerts and their installed depth, coupled with the stock hole depth, I had no choice but to modify the SRT4 studs to just work for my application. I swear, nothing is ever easy haha.

Oh yeah, to top it off, the SRT4 kit washers don't work on the D series, they are way too big. You need to use the old D series washers and drill them out. Hell, the SRT4 nuts barely fit in the head recesses lol


Please enjoy my struggles below for your benefit

Drilling the head:










Modifying the SRT4 headstuds:












Just a little bit longer:




Perfect:




Aaannndddd x10 for the remainder of the head studs and 1.5 hours later lol. Also needed to drill the washers. It helped to flat spot the washers to stay in the drill press vice:









3 hours later, one fully complete custom head stud kit for M11x1.5 TimeSerted D series blocks:




Installed height of custom studs (on right) compared to normal M10x1.25 studs (on left):













Bottom line, this process is honestly not for the lighthearted individual. It can get pretty involved, and you need the tooling to recover when you hit a roadblock, otherwise it will take forever to complete.

 

[robgoof]

would the hole depth be different on z6 and b7 blocks?

also fuck, labor much?

 

[EFB055]

Ridiculous, but great.

 

[rabid]

This post is very informative, thanks. However, I would warn everyone not to cut threads into critical parts like a head stud. The threads on these are formed and super strong. Cut threads are not nearly as good. I would recommend leaving the stud alone and get a machinist to make a "thick washer" to take up the extra length.

Also, check out NS300L thread inserts. They are beefy and cost a bit less for the kit and you can use any size with the same kit. This stud only has about 1" of block thread. The insert is made with only the bottom 1-1/4" of thread which would sink the stud as deep as possible. The insert could be put at the bottom of the hole if needed. I don't think the stud would be too long for this.

Use ARP washer number 200-8530. It will fit the stud and keep inside the limited washer area on the head.

Question. Your chart says the d16z6 stud is 6.450"/163.83mm and the SRT4 stud is 6.300"/160.02mm. But your pictures show the SRT4 stud is much longer? I called ARP and confirmed that the z6 and SRT4 are indeed these lengths so I assume you are showing y8 studs here?

 

[drtalon123]

This post is very informative, thanks. However, I would warn everyone not to cut threads into critical parts like a head stud. The threads on these are formed and super strong. Cut threads are not nearly as good. I would recommend leaving the stud alone and get a machinist to make a "thick washer" to take up the extra length.

I cringed just doing it, but the guy on my shoulder popped up and was like "You still have half the threads that are original and strong, adding a few more with a die shouldn't hurt" lol. Yeah, they are cold rolled originally so they are super consistent, straight and strong... my version of cold rolling doing this mod was using a die and an ice cube haha.

I actually considered this. I was going to get some thicker washers made with the same steel quality as the ARP's, but I was stupid pissed at all the time and money that already passed over the whole process, my machinist telling me it would be another 2-3 weeks made my shoulder demon pop up and reason with me into taking a shortcut. If I was out to break records, I would have made the effort, but honestly getting to 350whp shouldn't have been this hard lmao.

Also, check out NS300L thread inserts. They are beefy and cost a bit less for the kit and you can use any size with the same kit. This stud only has about 1" of block thread. The insert is made with only the bottom 1-1/4" of thread which would sink the stud as deep as possible. The insert could be put at the bottom of the hole if needed. I don't think the stud would be too long for this.

This is exactly the insert my original machinist attempted to repair my first block with! But he f***ed up, used a super shitty tap that made the inserts super loose in the aluminum, and then tried to compensate with an excessive amount of blue loctite to hide how loose they were, and then lied to me telling me they were an inch long... took them out and they were only half an inch long. I waited for 3 months to get this process done, paid for it, got it home, inspected it, got super pissed at what I found, pulled another block on my lunch break, and bought the timesert kit lol. I'm sure those inserts the right length, installed by a competent individual, would have been bitchin.

Use ARP washer number 200-8530. It will fit the stud and keep inside the limited washer area on the head.

Already bought a 10 pack lol. Next time I rebuild the engine or pop another HG (whichever comes first), I will swap them out.

Question. Your chart says the d16z6 stud is 6.450"/163.83mm and the SRT4 stud is 6.300"/160.02mm. But your pictures show the SRT4 stud is much longer? I called ARP and confirmed that the z6 and SRT4 are indeed these lengths so I assume you are showing y8 studs here?

Yup, showing the Y8 studs in comparison. Sorry, thats a good clarification point! The work I did to make this work went into a Y8 block and head combo.

 

[rabid]

FYI, I am doing this job on a z6 engine with the NS300L kit and I'm almost done. It was a real bummer to find out the head bolts had really tore up the threads after I spent the time and money on a CSS block. So I figured I would go 11mm if I'm taking the time to do inserts.

An interesting bit of information is the SRT stud the same length from the block thread to the top as the 10mm arp studs. So the stud bottoms out on the block thread at the same height as the z6 10mm studs. The SRT stud has 11x1.5 thread at the bottom and 11x1.25 at the top. The nut barely fits in the head. I'm going to have to grind a 14mm socket to thin up the walls or find a thin socket.

The only down side to the NS300L kit is they use a 5/8" x 11 tpi tap and that sucker takes a lot of room. I tested on a junk y7 block for thin spots. The water pump boss is really thin but I don't expect problem because the insert is 1.75" tall and deep in a z6 block. I would be more worried in a y8 block but with all the thread engagement, it's probably fine.

I am surprised the studs actually aligned with the head after all this work. The red loctite is curing now.

The holes in the gasket are 11mm and even a few thousands off on a stud or the gasket holes will make the gasket not go flat. I had one gasket go flat and one not. So enlarging the holes is a must. I'm not looking forward to that but after drilling the head and block, this is nothing.

Not for the faint of heart is an understatement. I have been stressed out for a week with this. I would not be doing this if I didn't already have so much into this block.