High Compression 3.2L Engine Build

[Mac Attack]

Oh, my DLC-coated wrist pins are still going after nine years at 550 WHP and 9k RPMs in the OEM rods.

At the time, I had considered other items for DLC coating like you (cams, rocker pads), but decided not to as no one else back then had done much in street applications with these coatings.

 

[MotorMouth93]

Thanks for the helpful insights @Mac Attack! Nice to know there's a little more flexibility with material removal on the big ends than I thought.

I went back and forth with what I want to do with the wrist pins quite a bit but ultimately decided to stick to the original engineering and interference fit them, after all Honda used this approach up past 8500rpm in some of the Type R 4 cylinder engines, but with the DLC coating after talking to Calico about it. It also keeps me from having to guess at oil clearances and will make the engine a little more resistant to damage from pinging if I end up with a batch of bad gas with the high C/R I'm running, as that tends to beat the hell out of the small ends if they are floating since its such a small load bearing surface compared to the wrist pin bores in the pistons and rod bearings.

 

[Mac Attack]

Yeah, you should be fine looking at your pics.

Interesting idea about the interference fit. I overlooked that possibility when doing mine although I did consider going to a larger diameter wrist pin for the reason you noted. Wiseco made two diameters you could have their pistons spec'd for but ultimately I just kept their standard diameter.

I understand what you're going through! You're doing great!

 

[MotorMouth93]

Was that the 23mm option for the C32 rods? I always found it odd that Honda went with a larger wrist pin for only a marginal change in piston weight and power output but they must have had some reason to justify it.

I remember seeing @BATMANs press fit his pistons in his build thread so that started me down that path. The main worry here is doing it without overheating the rods. Calico said that with the DLC pins the rods don't even have to be heated up as long as the pin bores are perfectly smooth, which they are thanks to the 1000 grit flex honing, they can just be pressed right in so I might try to make some sort of a fixture to do that without damaging the piston, then just heat the rod to 250 degrees or so in the oven to loosen it up a bit and press it in.

I got my block back from NB Finishing in Illinois with the main saddles built up with electroplating so now I'm shopping around for a shop to do the final line bore, deck surface, and cylinder honing. Mountune in CA seemed like a solid choice at first but they don't bother to answer the phone so I don't think I want to deal with that, so I might take it to a localish place that I've had recommended to me a few times and save the trouble and risk of shipping the block cross country again. So far, I haven't found any correlation between fame and quality of machine work so might as well go small and local to keep an eye on things.

The electroplating process involved some fairly caustic chemicals so this isn't something I'd want to do on a block that's already had final machining done. Lots of nasty corrosion to remove as well as some surface rust spots in the cylinder bores. This was not an engine shop though so I can't really blame them, its a shop that does repairs on specialized printing press components that did this job for me as an experiment. The nice thing about this is I can have the block vapor blasted without worrying too much since it still needs to go for final machining.

Also that's a brand new 6 speed transmission case.

 

[Mac Attack]

The electroplating is very interesting. Cleaning will be a pain but can be done. Besides having it hot tanked again at the local machine shop after they're done with the final machining, I recommend running a bunch of long nylon wire brushes with WD40 through all the oil galleys, and then I used my steam cleaner to blast everything with Dawn, followed by a bunch more WD40 and my air compressor running a long time to force everything out....

The standard Wiseco wrist pin for their NSX pistons is 22mm outer diameter with a 4.1mm thickness. As mentioned earlier, I debated whether or not to upgrade to their 22mm OD pin with a 5.7mm thickness. There is also a material upgrade between them. As I'd already been through multiple iterations with my build at this point due to others mistakes and then my own lack of knowledge/planning, I just decided to stick with what I had and get the standard pins DLC coated. I called Wiseco tech hotline to make sure what I had would work with my desired goals and they said it should (but near the limit). As I was near that limit on other things (like the OEM rods and main caps), I just decided to get 'er done and not mess with new pins and then rebalancing everything.

Honda probably went with 23mm diameter pins for the C32 rods and then reduced the wall thickness to keep the weight less than or equal to the smaller pin but marginally stronger. Their engineers seem to be nutty like that.

 

[MotorMouth93]

Yup I have a set of various sized nylon brushes to use for cleaning. I'm planning on putting the engine block in my guest shower which has one of those hand held sprayer things and using large quantities of soap and hot water for the final cleaning, followed by blowing dry with the air compressor and WD40 on the cylinder bores until assembly time.

The 7 rods are finally ready to go to the machine shop for big end resizing. Swapping the rod bolts for the ARP bolts threw the weights off a little bit and resizing might tweak them a bit too so the plan is to touch the weights up to hit my target 0.2g spread once I get them back, set up my rod bearing clearances, then send them off for WPC along with the rod bearings and a bunch of 6spd transmission internals and maybe the crankshaft. Then the rotating assembly goes to be balanced and the bottom end should hopefully be ready to assemble after that.

After installing the ARP bolts, the rods lost about 4g each compared to the stock bolts, putting them all right around 477g which is over 100g lighter than the Carrillo steel rods I was planning on running before, for a total savings of more than 600g. The factory 90mm 10.2:1cr piston, pin, and ring pack weighs about 533g, the Wiseco 93mm 10.2:1cr setup was 538g, and the Toda 93mm 12.1:1cr piston is 511g, resulting in a total weight savings of 162g compared to the Wiseco pistons and 130g compared to the factory 3.0L pistons.



I just used my vice to install the new bolts in the rods. That's a copper crush washer there between the big socket and the rod to prevent the socket from denting the titanium rod, then its a little aluminum bit between the end of the bolt and the vice to prevent damage there as well. I used a little bit of ARP moly lube on the knurled part of the bolts and they slid in pretty easily.



I also cleaned up my VTEC solenoids which were looking pretty crusty. I used hot glue to block off the oil pathways then blasted them with glass bead to remove the rust before painting the steel cap with some high temp gloss black paint.

 

[MotorMouth93]

So fun development, the plating on the block main tunnel is not adhered well at all, some of it flaked off at the slightest provocation, so now I'm trying to chemically strip off the remaining plating so I can explore other options. Concentrated nitric acid seems like it might be viable, it should attack the copper and form a hard oxide with aluminum.

Aaaaand then things got a little out of hand with the rods. I kept coming across rods and buying them.

So now I have 3 full sets of good rods, and one full set of junk rods. I've decided the first set of rods I matched up is basically a test run to make sure my machinist can do a good job on the big ends (its hard to find someone willing to touch titanium rods) and make sure the WPC treatment doesn't strip the plating off the rod caps. They [WPC] claim plated parts are fine but I want to be sure. The first set will just be spares on my parts shelf, the 2nd set will go in this engine, the 3rd set will be up for sale, and the junk rods will end up on @RYU's wall.

The plating on the caps is something I haven't seen mentioned before. I think its to keep the rods from galling against the crankshaft as it turns, I'm not sure what kind of plating it is but its extremely hard and seems to hold up well for the most part as long as the bearings are intact.

Here's something interesting I found. This particular rod had a lot of oil burned onto the big end when I got it, so after pushing the bolts out I tossed it in the ultrasonic cleaner for a few hours to clean it up. On inspection after, I found the cap so warped from heat that its easily visible. I guess the bearing failed and the ID got really hot then shrank down and pulled the sides in.

I also started experimenting with the process of installing press fit wrist pins using junk rods, OEM pistons, and OEM pins since I have a bunch of these things laying around now. The process is simple: create enough of a temperature differential between the rod and pin that the pin just slides in. Thing is, virtually nobody does this on TI rods, so there's almost no info online about doing this since it's all meant for steel rods which expand much more than TI when heated. A lot of shops don't even have rod heaters anymore, and I don't trust anyone not to overheat the hell out the rods on top of that.

I started by looking up the working temperature range for titanium - basically figuring out how hot I can go before damaging the rods. Pure titanium is good up to about 575F, whereas alloys tend to be in the 600-800F range. The NSX rods are supposedly a proprietary alloy, however pretty much all modern titanium connecting rods are 6AL4V titanium so I seriously doubt the C30 rods are too far off from that, and it has a safe service temp range up to 660F. For extreme safety though I would like to stay well under 575 if possible.

Then I looked at thermal expansion coefficients of titanium and took a conservative guess at how much temp change is needed to go from 0.0011" interference to about 0.0010" clearance with the wrist pins. I started by zeroing the bore gauge in the rod at room temp then putting it in the oven at 450F until it came up to temp. I measured a change of about 0.0018" so figured I'd try to get the pin in even though it was only 0.0007" clearance or so.

It worked great for the first 1/4" then seized up. That's how this goes even in the best case, you have maybe 1 second to get the pin in before the hot rod cools and the cool pin heats up and seizes in the bore, so I needed more heat. I pressed the pin out and tried again at 500F and the pin in a glass of ice water and it worked! I measured a clearance of about 0.0010" between the cold pin and the hot rod which was just barely enough to get the pin fully seated before it seized. I'm going to practice this a bit with the the junk rods and old pistons to see if I can do it consistently or if the process needs to be adjusted a bit, because any mistakes at final assembly risk ruining a piston or DLC wrist pin. Dry ice on the pins is something I want to try and I could also increase the heat to 525F or so if needed. I'm also going to build a little jig to help perfectly center the pins in the rod so everything fits together perfectly. I think the final assembly process will be a nerve wracking 5 minutes with the rods all in the oven and the pins in a bucket of dry ice. I could probably call around and find someone to do this for me, but if I can make this work using the oven I'll have a lot more peace of mind knowing that temp was tightly controlled and that I don't need to worry about anything.

 

[Mac Attack]

Sorry about the plating. Why can't you have it aluminum welded and then machine and line bore?

Also, with all of those rods, and especially considering the deformed big end cap, you should measure each rod for bend and twist. You want to be sure. My rods were machined with the latest Rottler system that bored both big and small ends at the same time.

FYI - Long story, but I'm 99% sure our rods are SP-700 alloy (basically added iron and molybdenum).

I think we've talked about peening, but the rod big end and cap thrust faces are nitrided. That's another reason why I didn't want to do any conventional peening after my rod machining. I wouldn't bother with WPC on your Ti rods. WPC won't hurt your hard coatings because it doesn't do much other than impart a small compressive stress just on the first few microns of material. For reducing friction, sure I've used WPC. But you don't need that for rods. The problem is that Motoiq/Kojima really hype it to the fast and furious crowd and then its effects get exaggerated. Is Kojima/Moto sponsored by WPC? Hmmm.

Honestly, my $0.02 after going through all this during my own rebuild ten years ago, is that I probably should have gone aftermarket rods. After spending all the time and money reconditioning my OEM Ti rods, the fact is they will most likely fail by fatigue at some point. My rods now have about 135k miles on them. 75k miles have been under my ownership for the past 20 years and of those, 65k miles were as a daily driver and the last 10k miles have been very heavily stressed.

 

[MotorMouth93]

I always appreciate your thoughtful responses @Mac Attack.

Welding the mains is kind of a last resort, it would impart a lot of residual stress into the block and potentially require the entire block to be machined again so is something I'd like to avoid. Boring the main tunnel oversize by a few thou and using precision shim stock under the bearing shells is seeming like the least invasive option with this block, there should be no real downsides with that approach as long as adequate bearing crush is maintained. It's definitely not a conventional method but used to be common a few decades before I was born.

To clarify, I'm not trying to use those warped rods, any rods with signs of damage or indications of a questionable past went into the junk pile, it just so happened that I ended up with exactly 6 junk rods. The only thing I’m using those for is practicing installing the interference fit wrist pins. I’ve done a few more and so far it’s seeming like putting the pins in the freezer and heating the rods to 500F in the oven is the magic number to get the pins in smoothly.

In my testing, I found that shot peening strips away the surface treatment on the cap thrust faces so is a no go. As far as I can tell, the surface treatment is only on the thrust faces of the caps, as the caps are wider than the big ends so they handle all of the thrust forces. I'm still on the fence about WPC, I don't expect it to work miracles but it seems to have some solid benefits as far as resisting cracking and it's not very expensive for rods. The MotoIQ articles/videos about it definitely seem like paid promotions lol.

If I had known what sort of rabbit hole these rods would turn into I probably would have just stuck with my Carrillo steel rods, but I'm enjoying the process so might as well see it through now that I have them. To take it a step further, I'm thinking I might switch from the standard 2.24" wrist pins to a longer 2.5" pin since I no longer have the circlips to keep the pin centered in the piston.

Very interesting info about SP700, it seems to have better fatigue strength than 6AL4V and not really any downsides so I wonder why it's not more popular.

 

[Mac Attack]

I always appreciate your thoughtful responses @Mac Attack.

Welding the mains is kind of a last resort, it would impart a lot of residual stress into the block and potentially require the entire block to be machined again so is something I'd like to avoid. Boring the main tunnel oversize by a few thou and using precision shim stock under the bearing shells is seeming like the least invasive option with this block, there should be no real downsides with that approach as long as adequate bearing crush is maintained. It's definitely not a conventional method but used to be common a few decades before I was born.

To clarify, I'm not trying to use those warped rods, any rods with signs of damage or indications of a questionable past went into the junk pile, it just so happened that I ended up with exactly 6 junk rods. The only thing I’m using those for is practicing installing the interference fit wrist pins. I’ve done a few more and so far it’s seeming like putting the pins in the freezer and heating the rods to 500F in the oven is the magic number to get the pins in smoothly.

In my testing, I found that shot peening strips away the surface treatment on the cap thrust faces so is a no go. As far as I can tell, the surface treatment is only on the thrust faces of the caps, as the caps are wider than the big ends so they handle all of the thrust forces. I'm still on the fence about WPC, I don't expect it to work miracles but it seems to have some solid benefits as far as resisting cracking and it's not very expensive for rods. The MotoIQ articles/videos about it definitely seem like paid promotions lol.

If I had known what sort of rabbit hole these rods would turn into I probably would have just stuck with my Carrillo steel rods, but I'm enjoying the process so might as well see it through now that I have them. To take it a step further, I'm thinking I might switch from the standard 2.24" wrist pins to a longer 2.5" pin since I no longer have the circlips to keep the pin centered in the piston.

Very interesting info about SP700, it seems to have better fatigue strength than 6AL4V and not really any downsides so I wonder why it's not more popular.

I hear you on avoiding any more machining of the block. When I was working with King on custom bearings for my application, I was also concerned about the right crush. Dr. D typically specifies slightly higher crush for his applications than OEM in order to get a tighter press-fit AND to aid heat transfer. The OEM aluminum-silicon bearings are more sensitive to high oil temps than aftermarket (I researched this a long time ago and would have to look for specific numbers), and my concern with shimming them would be reduced heat transfer. Probably not a real issue unless you're endurance racing and limited with oil cooler capacity, but something to be aware of. When assembling the shims and bearings, definitely don't put any oil or lube on the non-bearing facing surfaces so you can maintain that conductive heat transfer. Of course, too much bearing crush will result in side-pinched bearing distortion so its a balancing act (as with everything).

I had assumed you weren't going to use the defective rods, but just wanted to point out for others that if re-using rods or buying them used, its a good thing to measure bend and twist. I skipped measuring bend because I didn't have a good way to check, but you can easily check twist.

As far as peening, that is exactly what I was getting at. Your own peening process had intensity (you were even measuring with Almen strips, right) such that the nitride coating was being stripped away. In the FAQ on the WPC site, they say its OK to apply over DLC and other nitride coatings applied via PVD or CVD (consistent with what they personally told you). Therefore, how is it going to impart sufficient surface compressive stress to enhance strength and fatigue life? The WPC process has its place for some applications, but I see zero benefit for our rods. Again, my $0.02!

Since I never considered a pressed wrist pin and therefore didn't think about the length, I'm curious what your reasoning is for a longer wrist pin please?

 

[MotorMouth93]

I've been researching potentially using copper shim stock to help with heat transfer, but I would need to be sure of what the alloy was to ensure it doesn't squish out over time - ideally I'd use something harder than the aluminum of the block. Brass is another option as well, that should transfer heat significantly better than steel but still not as good as aluminum or copper.

My own peening process was far higher in intensity than is considered ideal so I wouldn't be surprised if the surface treatment held up once it was reduced to a reasonable level. That said, after reading more research papers on shot peening 6AL4V and similar alloys, its seeming to be less useful than I had first expected so I'll probably just polish the rods in the areas where I've removed material and call it good.

My thinking on the longer wrist pins is that the lightweight forged Toda pistons have smaller pin bosses and are designed with the intent that the wrist pin will be held in place within the piston by the circlips. I'm not using the circlips since the wrist pin will be held by the rod, but as the rod moves around a bit while the engine is running (in theory it shouldn't move much) the load bearing surface would be reduced on one side of the piston as the rod moves away from it. That said, this is probably overthinking it, as running pistons designed for full floating pins on fixed pin rods is pretty common and I've never heard of anyone using a longer pin to do it. But on the other hand, longer pins aren't that expensive and would add maybe 10-12 grams to each piston assembly so may be worth it for peace of mind.