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23 Posts
Discussion Starter · #1 ·
Hi guys,
I just bought a D16A6 for my hatch and I took it apart to rebuild before putting in the car.

So far everything is decent, the cylinders still have their crosshatch and I'm thinking about not overboring and just putting it back together, however I did decide to measure it with a bore gauge.

The outside cylinders (1 and 4) are all good enough and within spec (taper and out-of-round is less than 0.05 mm and the bore is not larger than 75.07mm in any point)

Problem is with cylinders 2 and 3. At the top measuring location (closest to the head) in the non-thrust direction my bore gauge is reading a diameter of 74.92 mm (the nominal diameter is 75.00-75.02 mm). I've never seen this before and I still can't even wrap my head around how it's possible for a cylinder to shrink. In the thrust side the diameter is 75.05 or so which is fine and then down the bore it's also normal. It's just in the non-thrust axis at the top that the cylinders are smaller than nominal diameter. I am not measuring at the absolute top where there is carbon deposit, I'm measuring below the deposits.

Anyone have any idea what's happening here? I checked this sheet like 5 times and I'm sure it's not my tools because cylinders 1 and 4 are fine as well as 2 and 3 as you get down the bore. Should I take it to a machine shop to get checked? Or just overbore it to be safe and get PG6 pistons while I'm at it (my plan is to slap it together stock for now if possible and save money for PG6 + headwork down the road but if it has to be rebored I might have to fork all the money out now)? Pistons are looking pretty good which is why I don't want to overbore it if I don't have to. Is there any possibility that the block is warped in such a way to affect cylinders 2 and 3 and squish them? Any help I will be grateful 馃槵

23 Posts
Discussion Starter · #3 ·
So the 75mm/2.9527" - 75.02mm/2.9535 nominal specs have a range of .0008", 8 ten thousandths.

Have you measured the piston outer diameters on pistons #2 and #3 with a micrometer or dial caliper yet?

Since you have your bore and bore out of round measurements already, get the piston outer diameter measurements as well. Figure out what your piston diameters are, as well as determine what their out of round is.

Then calc the piston to wall clearance on both the thrust and non thrust sides. P2W gap is just cylinder bore inner diameter at top of cylinder - actual piston outer diameter. See what your P2W is in both thrust and non thrust facing surfaces.

P2W gap being in spec is important, even if both cylinder and piston end up being out of round, if P2W is in spec, then the two have simply warped together as a pair lol.

So the closest nominal reading to your situation is 2.9527 (75mm), and you're measured readings are 2.9496 (74.92mm). In inches thats a diff of 0.0031, so 3 thousandths of an inch, or 31 ten thousandths.

0.0031 away from nominal is not really all that shocking, i have bearing oil clearances close to that number lol. But the piston to wall gap is already tight enough as it is in stock form with stock pistons, so you should see what the P2W is on the affected cylinders. If they are not warped together, and pistons are more true than the cylinders are, then your P2W will likely be too tight on the non thrust surfaces.

In either case, those cylinders are almost guaranteed out of round at .0031 from nominal, and should ideally be machined back to round, and bore top to bottom taper restored, so your piston rings arent hating life as a circle trying to slide in an oval. Depending on your piston out of round measurements to cylinder out of round measurements, and what your determined thrust vs non thrust P2W clearances are, you might need new pistons to go along with a .5mm overbore, so things get trued back up.

You'd be surprised how much thermal cycling can make metal move, I've definitely seen cylinders warp that much before.
Thanks for the help, I ended up leaving the block at my machinist and he said that he has also seen honda blocks "shrink" in one dimension while getting worn in the other. We are going for a 75.5 mm bore and I ordered DNJ PG6 pistons because I might as well get higher compression when I'm rebuilding the block.

My compression will be around 10.7:1 if no machining is required for the head or block (I don't want to go above 11:1 anyways because I'd like to try and tune the car for 95 RON which I think is 91 octane in the US).

It's hard to get aftermarket cams in Europe so now I'm thinking if I should keep the OEM A6 cam and how limiting it will be considering my new increased CR. The most affordable choice I have here is Cat Cams and there is very little info on the forum about people running them except one guy that had 12:1 compression and used the Stage 1 I think. Although, it's still pretty expensive (around 500 USD), it's either Cat Cams or the stock A6 cam. The stock cam is also scored a little so I'm leaning more towards getting the aftermarket one and getting some new rockers to start fresh.

Does anybody here have any idea which Cat Cam would be most suitable for 10.7:1 compression and not sacrificing mid-range? This car will be driven daily for a few years. I heard that Cat Cams have less lift but achieve similar power increases to other cams with more lift so I don't know how they compare and I can't use anyone else's build for reference because there isn't many people that used these cams. Also, is there anything I can do to prevent rocker arm wear in the future, as I heard that aftermarket cams destroy them pretty quick, I have a hard time believing that it's impossible to make a good cam not destroy the valvetrain, there has to be a way to make this reliable for years to come.

Here are the Cat Cam specs, I am thinking about the 2501105, 2501106 and 2501108.
Rectangle Font Circle Parallel Number

Here is their website if anyone would like to have a look, they have more extreme cams too: ENGINE SELECTION | CAT CAMS performance camshafts

Also, if I do decide to leave the oem A6 cam what kind of power would I be leaving on the table with this higher compression build? I want to make sure the money that I will spend will make sense given that the cam costs so much.

Thanks in advance.

23 Posts
Discussion Starter · #5 ·
The 1105 or 1106 would be a good match for the 10.7:1 cr for the street, the 1105 would be snappier between 2200 and 3100 rpms but won't pull quite as hard between 6000 and 7200 as the 1106 would, both will still idle ok, and both would see better gains with some diy port matching and gentle port smoothing. That being said, the stock a6 cam will be fine with the raised compression, better than fine with the afore mentioned port matching and smoothing. playing with intake manifold options like a b7 or z6 could help tune power band to where you want it as well.
Thanks for your help.

I have a Z6 manifold that I will be putting on the car. You mention a b7 mani, but isn't that the same as the A6 one and just worse than the Z6? Atleast that's what I got from reading old stuff from like 2009 lol.

Looks like I'm leaning towards the 1105 then because it will be daily driven. Would the 1105 still be a significant upgrade over OEM in the high RPMs? Do you happen to know if those Cat Cams will make power above the stock RPM limit? I'm already putting in ARP rods so it would be helpful to know if I will need some springs to take it to 8k if it's likely that the cams would make power up there.

There is the option of leaving the head stock for now (maybe install aftermarket springs while it's off because it's easier) and just put it together with the A6 cam to get some use out of it before the scoring gets too bad and then just junk it or regrind or whatever and I would run the scored rockers with the A6 cam. And then when it's junk I can upgrade to an 1105 or 1106 with good rockers as I would also have a better idea of what I need more, mid torque or high rpm power. The only thing that will be "wasted" is the A6 tune since I will need to get it retuned but I will do at least half of the tuning on the street by myself so I'm not worried about that.

As you said the A6 cam would be adequate would you advise me to do this (save some money for now and run the OEM until it's junk or time for a timing belt and upgrade later with the engine still in the car)? I know you can't give me an exact number but would the difference between OEM and 1105 or 1106 be as high as 10 whp? What about the 1105 vs 1106? If it's less than that I don't think it's worth the money for me to upgrade the cam right now and will probably run the stocker.

Again, I'm very grateful for all the help I'm getting on this forum, unfortunately I'm only asking questions so far but hopefully I can give back to the community in the future 馃槵

23 Posts
Discussion Starter · #7 ·
I haven't had specific experience with cat cams, just looking at the lift, duration, and ramp rates for a general idea, neither are going to need to be reved past 7200, but upgraded springs and retainers would be recommended.
The b7 manifold is different from the a6 and is aimed at increasing velocity for low-mid range, its fun to pair with a y8 head and slightly raised compression. The z6 is the best option for the broadest power band, where the y8 is aimed pretty specifically at the top end.
In terms of whp maybe 10 above what the a6 cam will make for the 1106, but important to remember it's not JUST peak power its going to increase with a cam change, either of those cams should provide a noticeable increase in the mid through high rpm range, each just coming in a little later.
Thanks for explaining that was really clear. I think I will stick with the Z6 manifold and the stock A6 cam for now and when I get bored/have the money/need to do some work that would make it convenient to change the cam I will buy the 1106 since I'm between 2000 to 3000 rpm only when cruising and if I need the power I can just shift down, so I'm changing my mind about the 1105 but I guess I will enjoy the A6 for a while and decide which one I want in the meanwhile.

Just to be clear, neither cam will result in less torque than the A6 in any part of the powerband right? Like for example there is no possibility that the aftermarket cam makes less power at, say, 2000 RPM than the stocker, right?

I'm not worried about cam and valvetrain wear right now because they are already scored so I will just run them until they are trash, but in the future when I do swap in a Cat Cam how can I prevent premature rocker arm failure, are the horror stories really all true that aftermarket cams will eat rockers in as little as 2000 miles? I want this build to last some hundreds thousand miles, am I way over my head for thinking that it's possible? I think they are currently scored because the oil wasn't changed very often, there was a lot of sludge and carbon and the mains and rod bearings were slightly scored when I took it apart. The rockers get worse as you get further away from the timing side so it could also be an oil pressure thing but I'm getting a new pump or at least porting and checking the old one. On the other hand, I have also seen a couple other D and B series heads that had scoring and wear on the rockers and cams, I really want to know how I could prevent this or worst case scenario I need to stock up on B7 heads 馃槵

23 Posts
Discussion Starter · #9 ·
Some updates, not sure if I should make a new thread but I guess it's still relevant.

I went with the PG6 pistons and the block is back from the machine shop, p2w clearance is 0.03-0.04 mm (1-1.5 thou) across the cylinders (a bit disappointed that they didn't get all of them spot on but it is what it is).

They also had to deck the block 0.111 mm (4.4 thou) and the head was milled 0.1 mm (4 thou), so the pistons will stick 0.111 mm out of the hole, I've read on here that the MLS gasket thickness is actually around 26 thou and the info on the calculator is wrong. So using that the calculator gives me 11.35 compression which doesn't worry me, however my piston to head clearance would be 21.5 thou which does worry me a little as I've read on here that the tightest it should be is 20 thou and I don't really want to be that close to the limit. I think piston to valve will be fine considering that I will be sticking with the stock A6 cam for now but the piston to head clearance I'm not sure about.

I am thinking about buying 2 OEM MLS gaskets because cometic gaskets are hard to source here and taking the middle layer from the 2nd gasket and adding it to the 1st. I will then use a 4 layer gasket that will have a thickness of about 36 thou and a p2h clearance of 32 thou which is perfect and 11:1 compression. I will be using ARP headstuds so I will also be tightening the head more. I will also have a spare 2-layer gasket for a future build or something 馃槵

Would stacking gaskets like this give good sealing or is it a risk? Should I instead run a single MLS gasket and hope that 0.0215 in clearance will be good enough (I won't be revving above 8k ever, most likely 7500 at most)? I would rather stack the gaskets and have peace of mind that the clearances are good but if it's a coin flip regarding sealing I can run with tighter clearance as long as it's sure to not be a problem.

23 Posts
Discussion Starter · #11 ·
This would largely depend on the design of the gasket you pick, which way the bossing is facing, weather the inner layers have bossing, ect. If you pick one with a flat inner layer you can use copper seal spray gasket adhesive between the center layers for some added insurance. Or just use a composite oem gasket and call it a day.
I don't want to use a composite because I will be building a separate head with an aftermarket cam later on and I will at some point remove the head so I don't want to go through cleaning that gunk off again.

I will look into what the gasket is, it will be from Elring and they make very high quality products. I'm not sure what you mean by bossing but I will read into that now. The copper spray and the fact that I will be using ARP studs make me feel a bit better about stacking gaskets since the higher clamping force will be able to squish the gasket more.

What if I run a regular MLS, am I correct to think that 0.0215 clearance is too little or am I overthinking it?

23 Posts
Discussion Starter · #13 ·
The bossing is the stamp around the bore circles that creates a spring seal at the sealing point, some gaskets even use an insert there that crushes, it can be 銆妡銆媜r 銆媩銆 or, on a few 4 layer gaskets ive seen run 銆娿嬨娿媠pecifically designed for boosted applications.
The piston to head clearance is mildly concerning, and worth looking into a way to broaden a bit.
I guess it will make more sense once I actually look at the gasket. Since the Elring gasket is 3 layer I am assuming that it doesn't matter if the bossing is facing "in" or "away" as long as the middle layer has no bossing, is that correct?

23 Posts
Discussion Starter · #15 ·
Correct, some do have bossing on the center layer, that kinda locks up with the bossing of the outer 2.
So I just got an Elring head gasket and there is bossing in the middle layer, but unfortunately I can't source an original gasket and even if I could it would be extremely expensive.

On the outer layers there is basically no embossing around the combustion chamber, the embossing is done on the water jacket area. On the middle layer there is only embossing around the combustion chamber. The pattern around the combustion chamber looks like this 銆嬨 銆. I'm attaching some pictures for reference.

How would you advise me to stack the middle layer? I am thinking like this 銆嬨 copper spray on both sides銆 銆媋s the copper spray will help the middle layers create a bond and the rest of the interfaces are sealing like they were designed to. Or would it be better to perhaps stack two full gaskets on top of each other (with the copper dowels removed so that they can lie flat against each other) with copper spray in between the two gaskets?

Sorry for the pics, I tried but it's really hard to capture this.
Automotive tire Automotive lighting Automotive design Motor vehicle Bumper
In this image the embossing peak is facing down
Eyewear Goggles Audio equipment Coffee Headgear
This is the middle layer, the peak is facing up
Automotive lighting Audio equipment Gadget Tints and shades Eyewear
Peak facing down again

23 Posts
Discussion Starter · #17 · (Edited)
I would probably do an extra center and bottom layer under a full set, from what I can tell of the pictures thats going to be the best chance of everything locking in as intended.
I get it now, so the embossings would be , which would actually give me even more p2h clearance which is nice. Last question, would you advise to use copper spray and if so, where? I am thinking maybe on both middle layers (orange) since they are not coated unlike the sealing layers (green) but perhaps copper spraying the middle coated layer would help? Or is copper spray not even needed since the layers are designed to interlock like that without it? And should I even bother separating the first gasket, is the copper insert going to affect sealing if I leave it intact?
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