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Done by Hand: Mazda's new Renesis engine receives surprisingly low-tech final assembly


By JAMES B. TREECE | Automotive News

HIROSHIMA, Japan - It is a surprisingly low-tech finale for such a high-tech process.

In a sealed, soundproofed and temperature-controlled room at Mazda's engine plant No. 2 here, parts that elsewhere have been engineered and manufactured using computers are painstakingly assembled by hand into the Renesis engines that power the RX-8.

Working with palpable concentration, seven workers hand-assemble rotors, housings, eccentric shafts, stationary gears, seals, bolts and other parts into the final engine. Time per engine: 35 to 40 minutes.

Executives say production could be speeded up but declined to give specifics.

"We could automate it. The question is cost," said Hisakazu Imaki, Mazda's executive vice president and chief engineering and manufacturing officer.

Although it is possible for computer technology to emulate the workers' craftsmanship, doing so would be hugely expensive, he said.

The new Renesis rotary engine features a number of design changes that allowed Mazda to eliminate the turbocharger that had pushed up the price of the former RX-7's rotary engine.

While incorporating those design changes, Mazda introduced several manufacturing changes as well. Here are two:

1. To cast the rotor, which is shaped like a triangle with slightly rounded corners, Mazda in the past poured molten metal into the top of a mold designed to produce two stacks of three rotors each. But the metal cooled at different speeds in different parts of each rotor, leading to different weight distributions.

The weight differences were slight, less than the weight of two pennies, but enough to cause an uneven rotor rotation. Mazda had to drill tiny holes in the rotor to rebalance it, an inelegant solution at best.

Now, Mazda uses a mold that makes only three rotors at a time and pours the molten metal into the center of the rotor. From there, it spreads out evenly toward the three points of each triangular rotor and the cooling occurs evenly in each point.

2. Testing has been computerized. One engine out of every 100 is sent to a coordinate measurement room, where precision equipment measures the dimensions of each part to ensure that all of the drilling and machining is exact. Formerly, tests of the RX-7 engine included a master operator rotating the engine's rotor to feel whether it seemed balanced.

Every engine is tested after assembly. The tests include one that measures compression in each stage of the engine's cycle: intake, fuel compression and exhaust.

To demonstrate to a group of reporters the reduced vibrations of the new engine, testers placed a glass of wine atop an engine, then revved it to 5,000 rpm, which they said would be the typical speed on a Japanese highway.

The wine barely rippled.

zoom44

hrmm only seven people assembling the engines? i hope the sign them or number them somehow, that way we can collect the whole series:D

m477

Hmm, let's see your piston engine do that. :p

Good Duck

So typical highway speed in Japan is around 100mph? I did not know that.

pelucidor

You are assuming they are in 6th gear - more likely 40mph in 2nd or 3rd!

IGOZMZM

It doesn't clarify if each engine is built by only one worker, or by all 7. So if it takes 7 workers 35 - 40 minutes to make 1 engine then your math would be slightly off. at only 41.14 engines per 24 hours. I would hate to be the one that got the engine that was only .14 done. :D

babylou

Yah something is fishy with the 35 minutes per engine. At 35 minutes per engine for one worker and working 48 weeks a year at 8 hours a day this equals 3,291 engines per worker and 23,037 engines for all seven workers. This is half of the projected production level. Plus I saw the assembly video and 35 minutes seems like a long time to assemble one of these pups.

Now that I think about it maybe the numbers are correct. 23,037 engines annual rate is probably correct since they are just now ramping up production. If demand warrants they can always increase the staff.

wakeech

i think that's 35 mins for the ENTIRE engine, including the installation of headers, the induction system, ignition, pumps, yada yada yada... the video only showed us that it takes about <10mins to put the block together

but yes, i sure hope Mazda's got a bunch of "kids" watching these guys through the glass walls, so that there'll be enough people puttin' 'em together to satisfy their global sales target...

visitor

I bet there's a piston engine that could do that.

zoom44

find it and i'll eat my hat! or some other suitable article of clothing that has more caloric value.:D

TJRX8

Visitor has seen it...in his dreams.

pelucidor

About 15 years ago on TV in England they showed an add which featured a V12 (piston) engine in a car - I think a BMW 750iL. They popped the hood and balanced a coin (50 pence piece - 7 sided coin) on the engine and revved it to 5k or thereabouts - the coin didn't move.

Will you be wanting ketchup with that hat?

TJRX8

Wakeech, Reminder where that video is please! :D

Quick_lude

Correct.. I've also seen this done with a Mercedes and BMW engine.. Lexus stacked a champagne glasses in a pyramid configuration on their V8's.. Sometimes the ignorant contempt for piston engines and "rotary elitism/snobism" on a rotary related site makes me laugh and shake my head in wonderment.. Are you guys really that insecure? The rotary is a great engine design, no doubt about it.. But bashing other designs, especially using unjustified claims makes you look weak and ignorant. Shrug.

It's interesting that the Renesis is hand assembled.. Would you say this will make it a better quality product or less?

Hercules

You have to watch the video of them putting it together... I don't see how the engine would BENEFIT from a computer/robot controlled assembly.. It's a disgustingly simple process that would as Mazda said themselves, just be a waste of setting up the machinery and computers in order to assemble the motors.

Besides, I think as demand increases for the RX-8 and also the RX-7 later, they will move to a robot assembly to save time on delivery. But I rather like the fact that my engine was lovingly put together by hand

Quick_lude

I just hope those guys don't stay out late and party.... then assemble my Renesis hung over.. haha..

Hercules

Every 100th engine is tested, so I think the QC is quite good. Considering they have a 30k production goal, 10% of those engines will pass, which for any industry is a good QC number.

Puppy1

If 1 in 100 is tested, then that would be 1%. And if only 10% of them pass, that would be 1 in 1000. What am I missing?

Hercules

You're not.. I misread the article :p

P00Man

1 in 1000 is 1/10 of a percent.....
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TJRX8

Both of these examples are results of great engines. Just to stick up for Zoom44 so he can maintain his diet, do a test. Put a coin on it's edge, stack some champagne glasses on a table, and put one glass with some wine. Now start pounding on the table. The glass with the wine will ripple long before the coin will fall over or the glasses will tumble if stacked properly. Besides the European coins are thick as bricks. I bet you piston supporters think David Copperfield really cuts women in half and puts them back together!.
Just kidding guys. We're not ignorant though, no need to resort to that. We just dig that new engine that's all. Peace.

zoom44

thanks TJ as i had missed Quickludes remark.

Quick i was not dissing piston engines. i am not a rotary elitist snob and in fact have never owned a rotary before. i dont believe 1 i bashed any design. but i don't think i could balance a coin or stack of coins or whatever on piston engines i have had in the past. i'm sure there are there some really good well balanced engines out there that can perform a similar feat. but in general i would say that most of them could not. actually i dont think you were directly flaming or intending to flame me but i hope this clarifies my position.

sheesh the first time i metion eating an article of clothing i lose a while ago everyone was saying things like that and noone called them on it. you could have at least offered me something to wash it down with or some hot sauce or something:p :D

TJRX8

No prob Zoom, you're welcome.
Have that glass of wine, just keep it away from a piston clanker...wouldn't want it to spill

Quick_lude

Haha.. How about some Dave's Insanity Sauce with that clothing article? That stuff will blow your mouth and intestines to hell..
I wasn't really directing this at you guys, just the general attitude of rotary boards. Maybe I'm just not that passionate about engine design, to me both rotary and piston engines have their plusses and minuses.. I just never understood why people get so hot and bothered to the point of posting innacurate info to bring something down and thus improving the image of the product you like.. shrug..

In Canada we have a show on TSN called Motoroing. For the longest time during Test Drives, Graham Fletcher would do the loonie test.. he would stand up a loonie coin on the engine while at idle. Now I'm sure if he revved the engine to 5K rpm, most would not pass that.. not too many piston engines would. The rotary definitely wins in the smoothness department, this is one of the reasons I'm dying to test drive one asap.