proficient

Hey, im new to R/C and have done all my research ect..
I am planning on purchasing the HPI nitro mt racer truck..
I have been to a couple of shops around my state and have checked all the info ect.
I am interested in a top quality engine but engines are quite expensive here.

So i plan to buy second hand, the workers at the hobby shops says this is fine as long as the engine works, and they show it running for a full tank, so i can see that it is working fine and fluent.

What motors would you recomend look for, i have been looking at the OS .12, but at the moment i am open to all ideas.
thanks

i8tweety

My Feedback: (11)

I agree with your local shop that if you can run a full tank through it (at proper operating temperature) and it idles properly, doesn't bog when moving through it's rpm range, and the price is right. Unless you know the history of the engine, whether it has been run hot, how much fuel has been through it, etc., the price of the used engine plus the cost of a new piston, sleeve, and connecting rod should be no more than the cost of the new engine.

Used price + rebuild parts <= new engine

Lots of luck

proficient

Hi, ive just found a Novarossi CX 12 engine 2nd hand for around $150 Australian.

apparently its in great condition and under a year old.

I will be going to check it out tommoro.

i am a newb. will this work with my hpi nitro mt racer truck?
anysuggestions to look for when i pick it up.

proficient

is their anything i should really look out for... like a way to tell if it has been thrashed and abused? obviosuly if its covered in sand ill give it a miss.. but anything else? is scratches along the top of the heat sink bad??

i8tweety

My Feedback: (11)

Does it have a cut crank? HPI cars require a lot of threads on the crank shaft for the flywheel and clutch assembly (alot more than associated). Bring your flywheel and clutch pieces with you and test fit them.

Does the novarossi .12 have a 2 piece crank shaft (the threads are actually a long setscrew that is threaded into the crankshaft)? My Top 12 (sister motor) is made that way. If it is, you can use the threaded rod from a kyosho 1/8 scale kit (front upper arm) to replace it if necessary.

Good luck

i8tweety

My Feedback: (11)

There are a couple of things you can look for to see what condition the engine is in.

With the glow plug in the engine, slowly turn the crank to top dead center while listening at the exhaust port. If you can hear alot of air leaking between the piston and sleeve, it's not a good sign. When you turn the flywheel over a few times (about 2-3 seconds per revolution), you should hear a nice popping sound from the exhaust. If you hear air leaking during the upstroke, the engine is clapped (d.o.a. - keep your $150 AU).

Bring the piston to the bottom of the cylinder and remove the head. Inspect the sidewalls of the sleeve for scratches and tell tale signs of blow by (compression leak between piston and sleeve will leave a dark line on the side of the cylinder - typically from mixing and matching used pistons and sleeves). If they will not let you do this, keep your money - they are hiding something.

Watch it run at temp for a tank (with load on it) through the entire rpm range. Verify that it can maintain a low idle for at least 5-10 seconds.


Good luck

proficient

thanks i8tweety, i REALLY appreciate your help!!
the first think i will do is turn the flywheel but im not quite sure what to listen for? the sound will come from the exhast correct? and what should it sound like?

i8tweety

My Feedback: (11)

If there is a hissing sound, or the sound of air escaping from the exhaust, it's a bad sign.

proficient

ok so this is just why the engine is off
and by itself away from the car? i just turn the fly wheel and the exhast will make a noise???

i8tweety

My Feedback: (11)

The noise test needs to be done without it running. Ideally, the pipe and header should also be removed.

Yes, it will make a noise.

When you turn the crank, the upward moving piston will compress the air in the combustion chamber. If you hear a faint hissing sound from the engine's exhaust port, some of the air in the combustion chamber is leaking out between the piston and the sleeve. It is not uncommon to hear a small amount of air escape between the piston and sleeve, but not too much.

When you turn the crank over by hand, if there is a good seal between the piston and sleeve, you should hear a popping sound coming from the piston and sleeve. If you do, it's a good sign.

proficient

ok i think i got the hiss is cause by scratches and such in the pistol, or sleeve.. when the pistol pushes the air up if u here a hiss its teh air escaping through the cracks or scratches.
were is the ideal place to listen to this, the exhaust?

dbow

My Feedback: (1)

Im not a fan of buying used engines but here is what I do when I buy one, its real simple.


Take your Temp gauge along with you and simply run the truck as stated in earlier posts. If the engine starts, idles, transitions, and seems to run o.k without overheating then it should be an o.k engine.
The other obvious things are to look at the rest of the car and inspect the parts and such. Does it look like the owner took good care of the care?
In a lot of cases the car may have been cleaned up but there are other things you can look at to get an idea of how the car was treated.
People usually are fairly consistant in how they take care of the things they own.


Dbow

proficient

I just picked it up.
it idled perfect for ages! and ran very well.
the piston and sleeve look perfect and it feels to me that it has HEAPS of compression.
as it gets higher u can reallllly feel its pushing the air.
its clean and the heat sink is not scratched at all..
It looks to me to be in near perfect order.
The guy who sold it was a racer and has been into R/C cars for 3 years and the engione is around a year old, so i guess he knows how to run in an engine pretty good.
thanks for your help all