Mugen Seiki restoration

[rambetter]

I found this on eBay. The guy said he found it in an estate sale but had no idea what it was. I started looking at the ad only a few minutes after it was posted. The Buy It Now was kind of high - $250. It looked like a vintage 4wd 2spd tranny car, on-road, from the eighties or nineties, but it definitely wasn't an Associated RC500. I come from a 1/10 electric off-road background and couldn't determine what it was. By that point only minutes later there were dozens of people browsing this ad, as reported by eBay. I knew I could not wait to buy this - either it was now or never. So I bought it without knowing what it was. It came with engine and electronics but no transmitter.

That night I could not sleep and woke up and did some research, trying to identify from eBay photos what car that was. I determined that it was a Mugen Seiki Sting, which was the immediate predecessor to the MRX-2 which won the IFMAR world championship in 1999. I think the Sting was made only for one year - 1998. This car arrived in the mail a week later. In the meantime I located a manual PDF and printed it like a nice original booklet at Staples. The car was dirty as heck! The Duracell batteries that were in the car (4-pack instead of the usual 5-pack NiCd 2/3A rechargeable size) said "best used before 2000" and "best used before 2002". The car had not been driven much, I determined as I started working on it, but it was configured all wrong. The suspension was totally off, it barely even moved due to mis-configuration. One of the shock piston shafts up front was 4mm shorter than the other. One of the king pins in the rear had broken and a metric socket cap screw was used to replace the shiny and round king pin! Wow. Several other things on the car were just totally off, but wear in most places was minimal.

So I spent a lot of days and a lot of money getting to know this genre - the 1/8 scale on-road nitro with foam tires. I'm completely new to this. The mechanical's are done and I'm in the process of cleaning the fuel tank and unfreezing the RB engine. I do plan on driving this soon! Enjoy the photos!

 

[Certified Mike]

Wow! I am VERY much looking forward to the build on this baby! Very cool blast from the past! Good score!!!

 

[WoodiE]

Looks like a real nice Mugen @rambetter!

 

[cbaker65]

That is nice ,I would say that the guy did his research an seen the prices on the used ones ,
they definitely are high an hold their value!...

 

[M3RC1L3SS]

Awesome car!! I'm starting one too mine its a mrx3, I think

 

[DXtreme1]

This is a great find possibly a halo find considering it's very short run. Mugen Seiki has an office in Lake Forest California I believe. I would recommend to go into their website and open an account so you can get parts and tech support if you need it. Also major RC retailers like Nitro House, A Main Hobbies and Tower Hobbies carry Mugen Seiki parts. There are also some parts available for the Sting on EBay. As far as foam tires they come in different front and rear offsets and compounds. You can also buy a car truer which is a lathe to trim the foam tires to the thickness and angle you want. I could not tell from the pictures but did this kit come with the quick release tire hubs? Though this is an older kit (some 1:10 scale kits could only dream to have some of the tech on this car)there is a lot of tech and engineering that went into the design of this kit and is still currently used today on their newer kits except with further design updates. Since this is a 1:8 scale kit the parts are beefier and so much more durable which is the great news here and since it's a Mugen Seiki this kit pretty much has all the upgrades and you just need to buy replacement parts. The only upgrade you may need is the clutch if it does not come with a Centax clutch. I would also recommend to totally rebuild the shocks with new pistons and o-rings to seal it properly. Maybe even get a set of shock shafts to make sure they're not tweaked. I would also rebuild the diffs and tranny as well.

One more thing make sure to get a suspension set up tool and a set up board. 1/8 scale on road is very responsive and sensitive to suspension changes so I recommend not overlooking this part of the car. These kits can carry a lot of speed and people that are new to 1:8 scale on road tend to underestimate their capabilities. Don't ask me how I know LOL.

 

[DXtreme1]

Is the Novarossi motor working. Novarossi and OS are my favorite brands so far. Novarossi for their power and OS for their tuning reliability.

 

[M3RC1L3SS]

My two favorite also!!
And yes the nova has about 12 tanks,
It's a Really strong engine

 

[rambetter]

Well the car is pretty much done but I still have not started the engine. The engine has been rebuilt and lubricated with new o-rings everywhere. The carburetor was rebuilt too. The engine is turning over smoothly and holds good pressure. It seemed that the engine barely had any use, but it's only an RB "CS" (_not_ C5, which is often confused with the CS) so it may not be the top end racing engine from that era.

I had to buy a completely new clutch since the one that came with the car had no chance of working properly - the previous owner had mixed and matched parts from various clutches and it just wasn't right. I decided to go with the original clutch that came with this car, which has four ball bearings that get pushed outwards as the rotational speed increases. I don't necessarily approve of this design as being the best possible but I wanted to preserve the design of the clutch and 2 speed transmission. I know that there have been updates in R/C car design since. I was able to find the original clutch, purple anodized flywheel and all, at a shop in Switzerland, costing one hundred U.S. dollars.

In the meantime I've been challenging myself to some metal machining. Many of the parts on this car are made of steel. The suspension hinge pins are 4mm in diameter, and they're simply shafts. The pulley axles are 6mm in diameter and are nothing more than round rods with a notch or groove here and there. The front king pin suspension balls are 11mm in diameter. This mass adds up quickly, all of it being steel. I plan on making some of these parts out of fancier materials.

Attached are photos of the front suspension king pin balls that I re-made out of lighter materials. I had no luck finding pre-made optimized versions of these because I think the size used in the front of this car were a one-off made only for this car and not used anywhere else. The balls are now 7075-T651 aluminum and the studs going through the balls are grade 5 titanium. The design, besides materials, is more or less the same, with the exception that the end allen socket is now a 3mm instead of the original 2.5mm.

 

[DXtreme1]

Great machine work. If I'm not mistaken this car came with a Centax Clutch which is what I and a lot of racers used back in the days. I haven't done any on road racing and have been out of the scene for a long time now but I'm thinking Centax are still in use by racers still.

 

[rambetter]

Thank you for the compliments. I'm very new to machining but because I tend to strive for perfection, doing things tends to take me a long time but the results do tend to be quite good.

I have to admit that I don't quite know what a Centax clutch is - whether it refers to a design or to a company that makes these things. Attached are three images showing the clutch on my car currently. The first two images are taken from the actual Sting manual and the third image is of the instructions that came with the replacement clutch I ordered.

 

[Certified Mike]

+1 for the ultra impressive machine work! Where their flywheel and clutch were as expensive as there were, I would probably go the 'stock route' at least to start with. Upgrades are plentiful if needed but the centax clutch is definitely a familiar name (and I have no on-road background either). I think you scored BIG on this kit! Congrats!!!

 

[DXtreme1]

The diagram sure looks like like the older version of a typical Centax Clutch. Here's a link to help explain how it works. The article is quite informative and will prove useful in adjusting it to suit your driving style. http://www.rctek.com/technical/clutches/centax/how_they_work.html

 

[HPIguy]

WOW, really nice work so far restoring a former champion. 1/8 on road is incredible, basically the LMP cars of the RC world. Also, I see a Park Tools scale there, you into bikes too?