Another A15 build thread, piston selection and such.

[pdp8]

The goal here is a warmer than factory motor with factory reliability, good efficiency, and good low-end manners,  on the cheap(ish).

I already do have a nice header, .25" over exhaust, and Webber on a flowed intake manifold for the car.

I'd rather have a nice idle and have things get winded at 6K than something with a lumpy idle that pulls to 8K, mostly I've driven low-revving trucks so a screaming motor just isn't natural for me.

 

I finally tore down the A15 bottom end I had sitting around.  It had blown a head gasket a dozen years or more ago but had been running fine before the head gasket (and regrettably overheating to the point it quit running).  Tearing it down the pistons did have some light scuffing, but not bad, three of the bores were in spec for a STD motor, but number 4 had about .004" of wear and lip on one side of the bore, so it's time for an oversize.

I know it's unlikely I'll ever need to oversize it again, but since I'm already replacing a 1400 (which replaced the 1200 the car was built with) with this bottom end, I'd rather go with a smaller overbore and have stiffer cylinder walls than a couple extra cc of displacement.

So, I'm looking for a .5mm or .75mm oversize I suppose.

I'm also planning on replacing the H95 head with a H72.

I've rebuilt some of the British A-series 1275 motors BITD, including some offset overbores to .080" or .120", but that's been decades so I'm pretty out of touch with what's happening these days.

I have a CNC mill and boring head, so I could do the overbore myself or hire it out.  If I do it, I'd be inclined to torque on a head and main caps and bore from the bottom to get the straightest bore job I could, but I don't own a honing machine, so would have to use a ball-hone after boring.  Hiring a shop would be the other way to go, but they would likely bore and hone from the top and unless anybody knows a shop with a dummy-head to bore-through, then I'm sacrificing some straightness of the bore for a better hone job, so I'd be interested in what folks think. 

Local rents and labor costs are crazy and the A15 block is small, so I wouldn't even doubt there might be a specialty shop someplace I should mail this to that could be cost-competitive.

 

As to pistons, cast are preferred and I have a very precise scale, so I'm content to do my own balancing work to match them and the rings.  The ones used with the closed H95 head were offset dish, but I'm seeing some offset dish and some centered-dish pistons for sale, not sure it really matters for the more open H72 head?

There's a huge price range on the pistons, from $120/set to over $1250/set.  I'm only wanting just a bit over factory, so don't need anything crazy.

The options I'm seeing on the cheaper end:

Endurotek, offset dish, .040" over.

ART Centered dish, .5MM over, comes with NPR rings

Sterling .75mm over

or this set from a forklift parts house, 1mm over https://forkliftengineparts.com/product/a15-nissan-piston-set-4-1-00mm/

Of course, I'm happy to have suggestions as well if someone knows of a good deal on, for instance a NOS factory set of .5mm pistons.

 

As to rods, I have no reason to suspect the factory rods aren't fine, so my natural inclination is to polish and re-balance the factory set and reuse them.  Still, if there were rods that didn't cost a fortune that had less weight or windage, I might be persuaded.

I did see fancy rods, but they look heavier than stock for no reason unless you are trying to make a lot more power than I need.

https://www.ebay.com/itm/275829147456

 

The crank looks fine in terms of continuing to use STD bearings, but I did plan on replacing the bearings since they saw some heat.  Anybody see quality bearings around on the cheap lately?

 

My lifters look pretty OK, but if I do have the cam ground, I assume I'll wind up with new ones.

As to cam, something efficient and useful from idle would be the thing.  Is there a more efficient cam than the factory grind?

 

Pushrods.  Anything to do other than factory?  When I was building the British A-series, they were making carbon-fiber pushrods, but I gather those turned out to have real reliability problems.

 

Roller rockers.  Seems like the A-series isn't suffering from a lot of power loss to the rockers, so it might be hard to cost-justify roller rockers for a low-revving motor, but if I were able to (for instance) just use a slightly higher ration rocker with a factory cam to get more torque without sacrificing idle, then it might be a consideration?

 

I'm also torn on balancing.  I'll match the pistons and rods (big end and small end), but hadn't decided if I should clean the casting on the crank and send it out for re-balancing or leave it as-is.  If I were to have it balanced, I suppose I should send it out with the flywheel, pulley, and perhaps pressure-plate as well?

[datzenmike]

Bore to the max 1mm and oversize pistons and rings. Costs the same to do for 0.5mm might as well maximize your results. Wall thickness is not an issue or Nissan wouldn't have 1mm oversize pistons for the A series. The critical thing here is ring end gap if you plan on pushing this slightly. Bore for 1mm over A15 is 77mm so the ring gap for a regular hypereutectic piston is 0.005" of end gap for every inch of bore. 77mm= 3.0338" X 0.005" = 0.015194" end gap. Street and strip gap is 0.055"/inch this would likely be more than you need.

 

These rods are used with a floating piston and pin and need special pistons to take full advantage of their lower friction. Again this is a bit esoteric for a slightly warmed over engine.

 

Any increase in duration and overlap benefits high RPM at the expense of the idle so keep this increase to the minimum. Instead, increase the lift or opening of the valve.

 

While carbon fiber are lighter and reduce valve train inertia the stock ones are more than capable of the RPM range you plan.

 

Again roller rockers, carbon fiber push rods, floating pistons etc. only make sense on a flat out race engine where even a 1/2 hp gain is desirable and only when all are added together becomes a significant gain that can make the difference between winning and loosing a race.   

 

To make the bottom end more bullet proof install ARP rod bolts.

 

Good choice on the Webber. 32/36? Slightly larger pipe is also good.

 

 

 

Get a manifold gasket and place on the head using the studs to align it. Scratch the outline of the ports with a nail and open up the ports to this line. Now do the same with the intake and the exhaust manifolds. Exhaust will be harder because they are cast iron but this will eliminate any miss match from core shifts during the casting process. Remove and smooth into the ports over an inch and blend. These do not need to be mirror smooth.

[pdp8]

Well, leaving some metal means if something goes wrong I can rebore the block rather than scrapping it, but some of it is habit.  On the British A-series motors, you can bore .120" over, but anything over .060" over uses more oil when you step on it because the block and bores twist a bit.  Not sure if the Datsun block is different enough it's not an issue.

Are folks using piston coatings these days?

 

Oh, I'll do the usual stuff, volume-match the combustion chambers, port-match the head to the intake and the header, polish the runners and bowls, etc.

 

Increasing the lift without changing duration is why I was considering the roller rockers since they are offered in a wide variety of lift ratios, but I'm open to other ways.

[datzenmike]

A 1mm is more than safe enough.

 

Ceramic coatings on pistons? combustion chamber and valves would need this too. It reduces heat absorption into the cooling system and this will increase efficiency. The heat saved increases the expansion of combustion gasses pushing down on the piston. It's a small amount but it's free. There are some products you can apply and bake on in your oven.

[pdp8]

14 minutes ago, datzenmike said:

A 1mm is more than safe enough.

 

Ceramic coatings on pistons? combustion chamber and valves would need this too. It reduces heat absorption into the cooling system and this will increase efficiency. The heat saved increases the expansion of combustion gasses pushing down on the piston. It's a small amount but it's free. There are some products you can apply and bake on in your oven.

They use heat-resistant on the piston top to improve efficiency, cooling, and reduce detonation.  Anodize the ring grooves to reduce ring-welding, and coat the skirts to reduce friction losses and scuffing.  Now I'm not worried about the ring issues, but lower friction and more heat doing work is interesting.

I did see there are DIY kits, but I'm not convinced that one can really get the coating thickness even.  I guess it seems to work though.

 

Looks like they are milling golfball divots in pistons now as well to improve combustion.  If I didn't have so many projects, I'd be tempted to DIY something on the CNC, but not for this motor.

[datzenmike]

Floating rather than press in piston pins reduce friction between piston skirts and cylinder. hat's a whole other story. Rings today are narrower and this lowers piston/cylinder friction but again would need the design built into the piston.

[Stoffregen Motorsports]

16 hours ago, pdp8 said:

Well, leaving some metal means if something goes wrong I can rebore the block rather than scrapping it, but some of it is habit.  On the British A-series motors, you can bore .120" over, but anything over .060" over uses more oil when you step on it because the block and bores twist a bit.  Not sure if the Datsun block is different enough it's not an issue.

Are folks using piston coatings these days?

 

Oh, I'll do the usual stuff, volume-match the combustion chambers, port-match the head to the intake and the header, polish the runners and bowls, etc.

 

Increasing the lift without changing duration is why I was considering the roller rockers since they are offered in a wide variety of lift ratios, but I'm open to other ways.

If something goes wrong? You need to be confident in your work. Datsun A motors are a bit more stout than the A series BMC motors.

 

Piston coatings are superfluous in a street engine. 

[pdp8]

1 hour ago, Stoffregen Motorsports said:

If something goes wrong? You need to be confident in your work. Datsun A motors are a bit more stout than the A series BMC motors.

 

Piston coatings are superfluous in a street engine. 

There's a difference between confidence in my work and things happening.  This engine was built by the factory and yet needs an overbore.  Was it rough service, neglect, or just an unfortunate incident. oil pan gets holed and the debris also takes out the oil pressure light... remote possibility, sure, but I'm old enough to have seen all sorts of one-in-a-million situations and there are only just so-many Datsun blocks in the world.  Honest wear also happens, seems like most A-series motors go 100-200K and I've driven more miles than that in my life, and who knows, the next owner might put a ton of miles on.  I won't pass on a 1mm set of pistons that are cheaper or better than a .5mm, but if they are otherwise identical, it's nice to know the block can be rebored should something happen.

 

Good to know the Datsun A-series is better.  I mean, of course they are since they aren't British and have a real rear-mainseal and whatnot, but I wasn't sure if they were sufficiently rigid to not have excess oil consumption with overbored motors.

 

Considering the majority of new cars ship with coated pistons, there is clearly something there.

[datzenmike]

Newer car have several ways to save gas and most are to reduce friction. Synthetic oils in o viscosity, narrower rings, coated pistons. Here's one...

 

Which is the 100 hp L20B main bearing and which is the '89 150 hp KA24E main bearing???

 

 

 

[Stoffregen Motorsports]

20 hours ago, pdp8 said:

There's a difference between confidence in my work and things happening.  This engine was built by the factory and yet needs an overbore.  Was it rough service, neglect, or just an unfortunate incident. oil pan gets holed and the debris also takes out the oil pressure light... remote possibility, sure, but I'm old enough to have seen all sorts of one-in-a-million situations and there are only just so-many Datsun blocks in the world.  Honest wear also happens, seems like most A-series motors go 100-200K and I've driven more miles than that in my life, and who knows, the next owner might put a ton of miles on.  I won't pass on a 1mm set of pistons that are cheaper or better than a .5mm, but if they are otherwise identical, it's nice to know the block can be rebored should something happen.

 

Good to know the Datsun A-series is better.  I mean, of course they are since they aren't British and have a real rear-mainseal and whatnot, but I wasn't sure if they were sufficiently rigid to not have excess oil consumption with overbored motors.

 

Considering the majority of new cars ship with coated pistons, there is clearly something there.

BMC A series has three main bearings, vs the Datsun 5 main bearings.

 

I get the longevity thing, but you also have to consider the vehicle. It's no longer just a new car used for daily transport by someone who doesn't care what they are driving. It is now an enthusiast car owned and driven by someone who knows what it is, likes it a lot and will take better care of it. So the only danger here is the bathtub curve. Daner at first fire, danger for the first 100 miles, but after that, no danger until years and tens of thousands of miles from now. And besides that, if the car is still around by the time it hits another 100k, it will be an antique. Anything goes for an antique. Sleeve the block if need be at that time.

[Stoffregen Motorsports]

You're not wrong. You're just seeing through a different lens.

[datzenmike]

1 hour ago, Stoffregen Motorsports said:

BMC A series has three main bearings, vs the Datsun 5 main bearings.

 

 

 

This!!!

 

Five main bearings make it a formidably stout block. The cylinders are not going to move around.

[pdp8]

Any preferred piston brands for a simple street motor guys, or thoughts about if it's worth boring from the bottom or is the 5-mains block so rigid I shouldn't care?

[Stoffregen Motorsports]

Cast pistons? Or forged?

 

Cast - any engine shop brand. ITM, Silvolite, etc. They are all basically the same, no matter the name brand.

 

Forged - I like JE and Wiseco. Both of those companies use modern designs. Cosworth and Arias are also good, but last I saw, their designs were still a bit antiquated.

[Tom1200]

I've been racing a 1200 for the last 34 years and I will chime in:

 

In my so-called A15 race engine I now have 77mm cast pistons I bought from Rockauto, ITM brand.

 

On my A12 engines I've used cast pistons; I've revved them as high as 8600 rpms on a regular basis. I also use bone stock rods.

 

I too am familiar with BMC A-series. The Datsun A12-15s are superior in everyway..........and I like BMC A series.

 

Your concern about the bores is unfounded. The blocks can be bored to 79mm. The only issue is you'd need custom pistons or have to modify some Mazda pistons.

 

My motors typically see 7-10 seasons of racing before I need to rering them. The motor I kept to 8000rpm went 12 seasons. It'll be 20 years before you'd need to rebuild one.

 

My recommendation: get the 77mm pistons, clean up the ports in the head and run a moderate camshaft. The Delta 278 cam I run in my motors is very streetable.

 

The only thing these motors will not tolerate is repeated  overheating.......the head gasket will fail in a pretty catastrophic manner. It will melt holes in the head and trash all of the bearings......ask me how I know. LOL

 

 

[pdp8]

Having a hard time with valve guide stuff. 

In an effort to not buy junk I'm trying to at least source stuff made in USA or Japan and in an effort to not go broke I'm working from online sites like a popular online auction site. 😕

I see on the wiki that there are different Nissan part #s for intake and exhaust, but they sure do seem *very* similar.

I found some sealed power VG-914 which claim to be the same as TRW G1178 and I have reason to believe these are intake guides.

The Perfect Circle 217-3996 I suspect are exhaust.

Can anyone confirm those part #s or suggest alternatives?

 

Edited July 23, 2023 by pdp8

[datzenmike]

On 7/10/2023 at 6:34 PM, Tom1200 said:

 

 

On my A12 engines I've used cast pistons; I've revved them as high as 8600 rpms on a regular basis. I also use bone stock rods.

 

 

 

With a 70mm stroke in theory just under 8,900 RPMs is the red line. This is the point under which stock rods and bolts and pistons will not stretch past their yield point during sustained revving. (it assumes all else a good; oil supply and cooling)

 

This is impressive

[Stoffregen Motorsports]

My A12 would go to 11.

 

Jk, but really, 8000 RPMs was achievable with a DGV.

[Tom1200]

On 7/23/2023 at 9:45 AM, datzenmike said:

 

With a 70mm stroke in theory just under 8,900 RPMs is the red line. This is the point under which stock rods and bolts and pistons will not stretch past their yield point during sustained revving. (it assumes all else a good; oil supply and cooling)

 

This is impressive

 

Not on purpose but I've revved the motors to 9100 a few times....on stock rods and rod bolts.

[pdp8]

Red line on my diesels and even one of my gas motors happens under 3800, so that's the band I'm most interested in.  It's very hard for me to wrap my head around anything good happening north of 7K!

 

I did reach out to Rebello Racing.  After some searching, (no, that's too big like for an L... what's that tiny one in the corner under that stuff?) they do still have a torque-plate for an A-series.

They are willing to do it as a side-job with bore+hone being $350-375.  A little rough since a local shop said $200, but the local shop doesn't have a torque-plate, so I guess getting straighter bores while supporting Datto racers is worth a premium.

[datzenmike]

17 hours ago, Tom1200 said:

 

Not on purpose but I've revved the motors to 9100 a few times....on stock rods and rod bolts.

 

Most likely but not held there continuous. A quick buzz never hurt anyone.

[Stoffregen Motorsports]

On 7/28/2023 at 11:44 AM, datzenmike said:

 

Most likely but not held there continuous. A quick buzz never hurt anyone.

It hurts valve springs. Since those keep the valve away from the piston, it's a real concern. 😁

 

There are a few pistons in my collection with damage from valve contact.

 

[Tom1200]

Those pictures remind me of why I run mildish cams..........mmm I've floated the valves once or twice.

[Stoffregen Motorsports]

@Tom1200 that little piston in the back left is an A12A piston. I built a handful of GT5 motors for, oh man, I can't remember his name, way back when. They were national winning motors, even against Huffaker's rear wheel drive Mini.

 

I do really love the A motors. They are thoughtfully designed and built tough and sound great when rung out.

[pdp8]

On 7/30/2023 at 2:50 PM, Tom1200 said:

Those pictures remind me of why I run mildish cams..........mmm I've floated the valves once or twice.

I think I floated a valve on my Daimler Ferret at under 4K enough to drop a pushrod, but to be fair it had been sitting for years/decades and the valves might have been a bit sticky still.

 

Luckily the rod itself was unbent, just the cup area, so while I look for a replacement I just chucked that one in a collet and pounded it straight.  Now trying to keep under 3300 for the next hundred miles or so to let things get settled.

 

Back in Datsun news, I pulled another 1500 out of another Datsun I have sitting and so far the bottom end looks like it might be good.  If not, hoping that I might get a break on doing both at the same time. 🙂

Edited August 1, 2023 by pdp8