TTR EK4 S2 Project BEAST MODE

[Nitrotrout]

I've been a Thunder Tiger buggy enthusiast for well over 10 years now.
But the model I always wanted but could never locate was the ever elusive and rare EK4 S2.
Finally, after years of searching I found a complete 2004 model EK4 S2 Sport reasonably priced so I jumped on it.

Objective: My plan is to convert a rare and unusual old school truck into a durable, modernized, truggy style basher.

Background: History of the EK4 is blurry because they were short lived and discontinued rather quickly. What I gather so far is, the EK4 was offered from 2004-2006 at a cost of $700.00 retail. I can't confirm if this true though. What I do know is, the EK4 had a fair share of issues.

The Pro .70 helicopter engine was notorious for overheating. The lack of a center diff combined with the torque of the .70 engine often destroyed clutches and diffs. The unusual diameter and deep dish design of the wheels made tire and wheel selection difficult. Possibly the biggest complaint with the EK4 truck was the lack of replacement parts. This is true to a certain degree.

The EK4 is actually an EB4 S2 Buggy with monster truck accessories.Difference being, the EK4 has an extended rear bumper, deep dish monster truck wheels, front shock replacing the sway bar, and two additional rear shocks. The EK4 has slightly different shock towers and body mounts to accommodate a truck body, a center rigid axle replacing the center diff and a monstrous .70 helicopter engine replacing the Pro .21 engine. With the simple addition of a few MT parts, the EK4 could arguably be one of the first ever production truggies.

Although the part numbers differ, the EB4/ EK4 share identical suspension, chassis, and running gear components making parts replacement fairly easy.

A majority of replacement parts for my project are EB4 S2 parts that I found cheap and readily available on ebay.

Parts not so readily available: The original truck body,the rear bumper, Pro .70BX crank case, crank shaft, clutch assembly, carb, front and rear lower shock mounts, wheels and tires.


SO HERE'S MY CANVAS: KINDA CARTOONISH LOOKING NOW BUT I INTEND TO CHANGE ALL THAT

HORIZONTALLY MOUNTED SHOCK (BEHIND FRONT SKID) USED AS A FRONT SWAY CONTROL

DEEP DISH WHEELS WERE USED INSTEAD OF EXTENDED CONTROL ARMS TO WIDEN THE OVERALL TRACK WIDTH

HUGE EXTENDED REAR BUMPER WORKS AS A WHEELIE BAR

NOTICE THE FLAT HEAD DESIGN OF THE COOLING HEAD. THIS IN COMBO WITH NO CUT OUTS IN THE BODY CREATED
THE HEATING PROBLEMS I SUSPECT

MONSTEROUS 12v STARTER, OWNERS MANUAL AND A REALLY COOL COMBO WRENCH
WERE INCLUDED WITH THE TRUCKJ

CURRENTLY WEIGHS 10lbs 12oz. I'M GONNA TRY TO LIGHTEN HER UP A BIT.

 

[Snook Man]

Sweet, I see all kinds of potential. Looks like a fun transformation.

 

[Nitrotrout]

Thanks Snook. I put my other projects on hold to jump into this one.
I'm really looking forward to it.

I'm following your winter build closely too. Great work so far.
I may have to steal some of your ideas.

 

[Nitrotrout]

Project update: Engine teardown.
Engine was in much better shape than I expected.
I suspect the previous owner ran the truck a few times, crashed it, shelved it
and years later,sold it.
All the screws came out without stripping or snapping, that makes me a happy camper.
The only problem I see so far is the clutch.
The carbon clutch shoes are fossilized. I can't save them or replace them.
The "upgrade" steel clutch shoes have no available flywheel. I'll figure something out.

CLUTCH SHOES EXPAND BY SLIDING WITHIN THE FLYWHEEL GROOVES INSTEAD OF
PIVOTING ON PINS

ON THE LEFT IS A TRAXXAS 3.3 PISTON AND CON ROD COMPARED TO A PRO.70 PISTON AND CON ROD
ON THE RIGHT. THE CON ROD HAS TWO OIL HOLES FOR THE CON ROD JOURNAL
ONE ON THE BOTTOM LEFT AND BOTTOM RIGHT

 

[Snook Man]

That's 1 big piston, its also a Hemi head.

 

[WoodiE]

Man I haven't seen an EK4 in a long time. Going to be a neat transformation I'm sure.

 

[Nitrotrout]

That's 1 big piston, its also a Hemi head.

It never crossed my mind but you're right. It is a hemi head.

Man I haven't seen an EK4 in a long time. Going to be a neat transformation I'm sure.

Taking it back to old school for sure. I hope it all works out. onder2:

 

[Nitrotrout]

Project update: Engine rebuild is complete.

First thing to go was the notorious , flat head heat sink.
I replaced it with the TTR cooling head upgrade and it's frickin huge.
It may cause me problems with the body I'm using but I'll deal with it later.


List of things replaced:
Piston ring and piston sleeve
All O rings in the carb and backplate
Complete exhaust header assembly
Internal engine bearings
Complete clutch and flywheel assembly

SMALL HEADER FLANGE PORT WITH A LARGE DIAMETER HEADER
PIPE MADE NO SENSE, SO I ENLARGED THE PORT WITH A DREMEL

I THINK I CURED MY CLUTCH DILEMA WITH A BUKU ADJUSTABLE
CLUTCH. TIME WILL TELL IF SHE'S HOLDS UP TO THE ABUSE

SIDE BY SIDE COMPARISON WITH A LRP ZR .30

 

[Snook Man]

That thing is massive, nice job on the clean up. Looks like new.

 

[Ckeithnitro]

+1 that great job on refurbishing the engine..
I'm will def follow this build...
Do you have any chassis plans??

 

[Nitrotrout]

Thanks for the kind words guys.:thumbup:

I'm not gonna do much with the chassis plate really, just scrub it down a bit.
It has quite a few scratches on the under side, but I'm goin to leave 'em.
I am going to do some suspension and shock upgrades though.

 

[Nitrotrout]

Project update: Center diff issues.
I ran into an obstacle with my center diff, or lack thereof.
I have a 60t spur gear attached to a center torque shaft. Clutch bell is 14t.
I think this center torque shaft is gonna wreak havoc with the rest of my running gear
so I'm looking to replace it with a center diff.

The problem is all the diffs I've seen so far are either 46t or 48t.
I don't know squat about gear ratios but I suspect my power band would be thrown way out of whack if I went this route.
The engine has a top end range of 18,000 rpm. I know I can change clutch bells, ranging from 11t- 18t.

Maybe you guys can offer some advice?

 

[Snook Man]

Aah it’s got a spool for the center diff.
I would look at the Ofna LX 2 center diff, they use a 51T spur and hold up well. You can get them on the bay for $20.00 shipped with the brakes included.
14T bell and 60T spur = 4.28:1 ratio
12T bell and 51T spur = 4.25:1 ratio, that would put you right in the ballpark.
What size ball ends (diameter) are on the center bones & what’s the length of the CD (distance between the pins of the bones when installed in the cups) and what’s the spread pattern for the CD mounting to the chassis? I can measure 1 of my LX diffs to compare.

 

[sv250]

I ruined a few clutches on mine with that lock diff. I used a losi 8t center diff with the thunder tiger bearings and the alu center diff mount from thunder tiger eb4. You wont use your old top plate.

Works great. You need the thunder tiger bearings because the flanges fit in the mount. Ill try and post pics in a bit

 

[sv250]

This mount

http://www.ebay.com/itm/NEW-Thunder...Control_Parts_Accessories&hash=item5adf2d5c42

this diff

http://www.ebay.com/itm/NEW-LOSI-8I...Control_Parts_Accessories&hash=item20dd24955f

Now I only use 1 steel brake disk because the losi cups are a tad shorter. Still stops on a dime.

 

[Snook Man]

SV250, what diff oil are you using with just a front brake? I would assume its pretty thick to have decent braking.

 

[sv250]

My EK4 exp.

1st if you stay with that engine you need to relocate your pressure fitting on the pipe. TT has an addition to their manual showing where to put it (closer to the header) At its current location the engine starves for fuel and will lean out erratically. Go to the last page and notice where their pressure fitting is. This is the newer manual. I can't find a link to the old one.www.midmad.com is gone. That was the only source of info for this truck.

http://ebookbrowsee.net/thunder-tiger-ek4-s2-rtr-manual-pdf-d162446426


I really liked the heli engine and wheels just like you. I spent some coin on a rebuild to have it last 4 tanks. New ring, rod, bearings and cooling head. Then it started pouring fuel from the front of the case at the bearing. I did heat the block to remove and install. Just a piss poor design. The .70 is known for that.

Another thing, if you hate 3 needle carbs as much as I do esp the finiky TT carb, the OS carbs fit. I ran one off a OS.28 Much easier to tune.

After all that I gave up on the .70 and installed an LRP.32 with Ofna 086 pipe and Savage mount. Way faster and as much grunt.

Also the stock tires are really poopy and the centers of the rims break easily. I upgraded to Ofna Monster Pirate wheels. Same size, much stronger and tires are way better. The dont look as nice though.

---------- Post added at 9:42 AM ---------- Previous post was at 9:39 AM ----------

SV250, what diff oil are you using with just a front brake? I would assume its pretty thick to have decent braking.

What ever came in the diff. I figureds I'd start there and I liked it so I stuck with it.

Braking isnt an issue with this heavy truck and obscenely wide tires. Its too heavy to endo.


My build thread

https://www.rcnitrotalk.com/forum/showthread.php?t=103762&page=2

 

[Nitrotrout]

Snookman and sv250, I can't thank you guys enough for your help. Thanks a million!

Snook, these are the measurements I came up with:
Distance between bearings (inside measurement) is 24mm.
Ball ends on the dogbones are 8mm diameter
With the dogbone bottomed out in the drive cup, there's
a 3mm gap between the pin and the bottom of the pin recess.

With the dogbone centered in the cup there roughly a
5mm gap +/- between the pin and the bottom of the pin recess.

Do you think I go up or down a tooth on the clutch bell with a 51t Diff?
The final ratio seems pretty darn close as is.

@sv250, I read every EK4 related thread on just about every forum
I could find before starting this project, your thread was by far
the most informative. Huge thanks.

I have one of those anodized red center diff mounts you suggested.
I'm going to use it with the diff that Snookman suggested if it fits.
Should I be using the red top plate or the EK4 top plate?

Here's the stock pipe, never occurred to me how odd the design was.

I'm considering replacing it with a ERCM pipe, I also have a JP2 pipe
I could try out.
Thankfully I have options if the Pro .70 doesn't work out
I want to run this engine if I can, if it doesn't work out I have a
modified LRP.30 I can just throw in and go.
I'm not a big fan of three needle carbs either and I hope I don't
regret removing that 3rd needle to replace the O ring.
As far as I can tell it's seated flush with the carb body.
If it doesn't work out, I have a TTR Pro .21 carb which is nearly identical
except for the 3rd needle, or I'll look into the OS carb you suggested.

What kind of fuel did you run with your .70?
I just bought some VP helicopter/airplane fuel. Its 18% oil, 15% nitro.
That's the closest I could find at my LHS to the recommended fuel.

 

[sv250]

Use the ek4 plate the red one is different.

I ran 30% werks

---------- Post added at 11:50 AM ---------- Previous post was at 11:49 AM ----------

Maybe thats why it wore out. 18% oil and 12 nitro that sucks.

 

[Nitrotrout]

Weird blends. I guess what I have will work for break in. Its against my nature
to run anything less than 20% nitro, so I'm gonna step up the nitro percentage later on.
Here's the recommendations: onder2:
BREAK-IN or a new engine, a fuel with low nitro rating and high oil content is highly recommended for the first 10 F tanks (125cc per tank). Although one can use a fuel with nitro and oil rating combination stated within the recommended guidelines, 5% nitro and 25% oil is best during break-in period

A good quality, commercially available model engine fuel containing 5% to 30% nitro with 15% to 25% oil is recommended for initial break-in and regular run-in of this engine. Thunder Tiger also recommends that the oil composition to be made of caster oil or a caster/synthetic blend. Fuel containing only synthetic lubricant is much less tolerant of high temperature and lean carburetor settings; thus, may cause the engine to become difficult to operate under normal conditions.