I seem to be constantly around EVOs so I decided to write a series of tech tips for the EVO X and the 4B11T engine. There’s no guarantee of when the next tech tip will come since I am busy as hell and MotoIQ is free.99, but I can tell you I have every intention of writing a series of them. I’ve been driving EVO Xs off and on since they were new in the US and almost non-stop for the last year or so. Since 2007 we (as in Cosworth in Torrance) have learned quite a bit about the EVO X and the 4B11T engine. While we haven’t been doing much modifying to the cars themselves, we’ve been disecting EVO Xs for product development, testing OE and aftermarket components, working with the engine on the engine dyno extensively, designing and refining engine components, evolving our engine build process, and I’ve been working on the soon to be released (hopefully) Cosworth ECPro stand alone ECU off and on. This series will share some of that knowledge.
The origin of this particular tip comes when Tyler was driving my 2008 EVO X MR that Peter usually drives when he’s not driving his 370Z. Sound confusing? We were confused too when we first saw the probelm. Tyler called me from the Chevron on Crenshaw and he said the serpentine belt broke. He also mentioned that there was power steering fluid all over the ground and that the power steering no longer worked probably due to the broken belt. Being that Chevron is only about half a mile away, Jeremy and I decided to hop in the van and bring some big thick nylon straps with us that are usually used to lift Champ Car race engine crates to serve as towing straps. We got to the car, hooked a strap up to the strut tower bar, put a big thick moving blanket over the hood latch so the towing strap wouldn’t destroy the latch, and Jeremy got in the EVO. Tyler wussed out and hopped in the EVO IX with Clayton. I drove the van and pussy footed it back to Cosworth at about 15 mph while Jeremy pretty much rode the brakes lightly. We git r dun one way or another.
Unfortunately, the belt happened to break on Tyler’s shift when we were borrowing the car to double check the intercooler tube fitment on an MR. (BTW, look out soon for the Cosworth intercooler tube upgrade. They are pimp if you want the best.) So this meant Tyler had to fix it. The serpentine belt from Mitsubishi was like $108. Since Tyler is smart, he quickly called NAPA and got the identical length belt for $30. If you are ultra cheap, you can even get the basic MICkey Mouse (made in China) Pep Boys house brand belt for less than $15. The power steering hose had to be ordered from Mitsubishi, but luckily it was a low pressure return hose that only cost $35 from the dealership. After the hose came, Tyler installed the power steering hose and the new belt. Upon startup, the serpentine belt immediately jumped off several pulleys and the center of the belt was riding on the outer guides of those pulleys. Tyler came and grabbed me from the dyno and we just kind of stared at it for several seconds wondering WTF.
The problem was that the original belt was broken in half…the long way. So there were 3 out of the 6 ribs still left on the belt. And while what remained of the belt still spun all of the accessories, it sure as hell wasn’t right. We had assumed the belt tore from general wear or some other external cause because the car is so damn low (Peter slammed it with HKS coilovers, not me). The front and rear edges of a pulley are taller because they are meant to keep the belt in place. Something must have been seriously jacked because the center of the belt was riding on top of the front edge of all of the pulleys. This must have meant that good old Peter must have actually been driving around like this for a while and the belt ripped apart from the stress. Since I keep the car at Peter’s place, he gets to drive it whenever he wants. He’s taken that liberty to the max recently and has recently even taken it to the track. While he takes good care of the car generally, he must have missed this one or it happened before he had a chance to catch it.
So Tyler and I put the belt back in its correct position, unplugged the injectors, and Tyler cranked the engine while I examined the belt at low engine speed during cranking. As the engine turned at 250 rpm or so, the belt sure as shit slowly made its way off the ribs of the pulleys after the upper idler. We stared at the belt again for a second wondering WTF again. Tyler then decided to remove the upper idler. He discovered it was worn badly. I pulled the lower idler off and also discovered it too was worn badly. It would be a hassle to order some idlers from Mitsubishi and wait for them to deliver the parts, but just then I remember that we had the Hyundai Genesis 2.0L turbo disassembled on a cart in the build shop that we used for some analysis in the past.
The idler on the left was the upper idler and the one on the right was the lower idler. Both are significantly worn. I can only assume that this is due to their plastic construction.
Here’s another look at the wear. You can see why the belt was forced off of the other pulleys.
I ran inside and grabbed the Hyundai idler pulleys. That engine has four idlers, but three of them were identical. By some miracle, the Hyundai pulleys were identical in diameter and offset to the Mitsubishi parts. Even the bolt thread was the same albeit the Korean non-JIC standard bolt head was a 15mm. As an added bonus, the idler pulley was made of STEEL which guarantees an exponentially longer lifespan. Tyler installed the upper Hyundai idler and I installed the lower. We put the belt back on, plugged the injectors back in, and fired it up. The belt stayed exactly where it should have of course.
The idler pulley on the right is the one you want. There are three of these idlers on the Hyundai 4B, oh sorry, Theta II. It looks like the one on the left might even work, but I didn’t bother trying. The Hyundai part number is 25287-2C000 and you can pick them up for $49.48 each at Dealer Direct Parts.
Its been about 800 miles since the Hyundai idler pulleys were installed and there have been no issues with the Hyundai idler pulleys so far. I think they’re a winner.
While this MR was raced across China in the Gumball back in 2008 and had a pretty damn hard life for the first 20,000 miles, the car only had 49,800 miles on the clock when this belt fiasco occured. While this car’s average RPM is probably a bit higher than yours, this issue will very likely occur on your EVO X eventually. And now you know what to replace those shitastic plastic idlers with. If you’re smart, you’ll even get some of these idlers now and change them out to the steel Hyundai parts as preventative maintenance. It would suck if you lost a belt on the way to Vegas, overheated the engine, ruined your trip, pissed off your girl and had a $1000 towing bill now wouldn’t it?
