MP 7.5 Sport Hop Ups

[supertux1]

Hi All!

I got an MP 7.5 Sport kit for my birthday last year.

It ran great for awhile but I think I cooked my engine.
Yes I did follow new engine break in procedures.

I never took apart a glow fuel engine before, but it didn't
look too complicated so I gave it a shot. The engine
with this buggy was the GS21R.

After blowing my engine, upon inspection I came upon
some startling results. The first was that the recoil
was only affixed with one screw to the crank case body!
(The engine came preassembled in the kit mind you.)

The screw that it was affixed with wasn't even a metric
hex head screw as referenced in the instructions.

It appeared to me that the recoil assembly was not fitting right, so when I opened up the engine I found the reason:
The crankshaft was too long, by about 1/16th of an inch!
The flywheel on MY crankshaft was more triangle shaped
with no holes, while the flywheel in the manual for the GS21R is circular with multiple holes. If I tried to put a second screw into
the recoil starter, it would be so tight against the crankshaft that
it was impossible to pull.

So now I figured out why I blew the engine. Someone gave
me the wrong crankshaft. It looks more like a GX21 crankshaft.

I examined the connecting rod, piston, and cylinder and all seem to be damaged. (Rough metal as opposed to burns) In addition, this engine had no head gasket! I have come to surmise that the RC shop where it was bought from either screwed me over or
someone at Kyosho was asleep when assembling this engine.

I'm hoping to repair this engine, because most of it is intact.
Also seems like a fun little project -- reviving a dead engine.
If it doesn't repair, I'm going to buy a new one anyway and
keep the old one around for parts.

Now I've bought the corresponding repair parts as well as a few hop ups: Head Gasket, Cylinder/Piston, Connecting Rod, Screw Set, Crankshaft.

So at first glance I was not all impressed with my MP 7.5 Sport.
Technically, It's a miracle the engine would even run at all.
I am hoping that with the repair parts the engine will run
a whole lot better. It had virtually no accelleration from stop
and my friends with electric cars were laughing at it It
would eventually get up to an impressive speed but it often
would stall.

So this winter it is my mission to outfit this beast to the max, but only with parts that actually do something

I've ordered the following hop ups:

3-Piece Flywheel/Clutch/Spring Set -- for acceleration from stop.
Foam air filter replacements -- old one was dirty.
Adjustable Upper Rear/Front and Tie rods -- I can tell by the wear on the wheels that the non adjustable stock ones suck.
Front and Rear Stabilizer Rods -- for driving on rougher terrain.
New tires and foam inserts for them -- driving off curbs at high speed.

Now I ask you my friends -- is there anything worthwhile
that I would need that would noticably improve performance?

What about shocks? A non-Kyosho engine?

[robriguez]

-Unless you bought your 7.5 Sports in another country it comes with a GX21... not the GS21. The GS21 only comes in the standard 7.5 kit or 80% prebuilt.
-These are the first hopups I made to my sports and it made all the difference in the world
--Steel Spur gear 46t
--13t Clutch bell
--change diff fluid
--Kanai II 3.5 shocks all around with 35wt in front and 40st in rear
--long White hard springs
--Proline Knuckles with foam
--Alum Front and rear stabilizer bars (not sway bars)
--new servos
--Front universals
--TI adjustable tie rods all around
--TI suspension shafts (rods that connect the arms to the chassis)
--Alumimun radio posts

[supertux1]

The RTR version comes with the GX21 and the kit comes with the GS21R. I built the kit. I have the Inferno Sports etc...

http://www.kyosho.com/cars/kyoc0590.html
http://www.kyosho.com/cars/kyod66.html

For the clutch bell -- would that be this one:
http://www2.towerhobbies.com/cgi-bin...p&I=LXU470&P=7

Spur Gear - Theres another one 48t but it requires sanding of the chassis:
http://www2.towerhobbies.com/cgi-bin...p&I=LXVD38&P=7

[Kuma]

Yes, the blue & white Sports comes with a blue head GX21, pretty easy motor to tune and run. I'd say an OS 21RG, steel spur gear, Kyosho or Kanai diffs later on, and some parts from teambluestar off ebay such as:

shock towers, chassis braces, steering slider & block, and perhaps better shocks

Also get a good high-torque servo like a Hitec HS-645MG and put the stock steering servo on the throttle for better braking power.

[robriguez]

lol...sorry.... guess I missed the KIT part. For some dumb reason i though you had the RTR.

Your links for Tower dont work for me.
My 13t CB is part IFW046
My 46t Spur is part IF105

The 48t is slightly larger than the 46t but only by a fraction. Depending on the clearance you may have to slightly elongate the opening in the chassis but I seriously doubt it.

For the most low end go with the 13t CB and 48t Spur but its only a minimal difference over the stock 15t CB and 46t Spur.