GP290 bad connecting rod/crank?

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kenzx

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Hello,

I recently got a new motor GP290 for my Redcat Rampage TT. Started up and idle fine, fresh fuel mixture and all. After break-in, I took it easy around the track but never quite got it to run right. It would just bog down and die and hard to restart. After about 3 tanks, it just would not start any more. I went through all the trouble shooting until finally decided to take the engine apart. Everything else looks fine except I found the connecting rod - section that connects to the crank shaft was done. It was loose up/down and side/side. I double check my fuel mixture and it was 25:1 as recommended. Never seen this happened so soon before. Any idea?

Kenzx
 
they do have side lash on them, maybe a couple mm side to side, but their shouldnt be any up/down motion. does sound like the conrod bearing is bad. where did you purchase the motor and how long ago?

could be a warrenty issue.
 
I bought it from LargescaleRC during a sale last month. I only had it for about 2 weeks - 3 tanks of running that's all. I spoke to Scott at largescaleRC and he said he will take a look. I'm mailing it out today.

thanks guy
 
Scott, Bob and the crew at LSRC are great guys. im sure they ll figure it out, and if its a warrenty concern, you ll be taken care of.
 
Scott said he will look into it for me. I thinking about ordering a 2nd engine just for back up. I'm so itching to get my Rampage going - it's killing me.
 
Sorry to hear that. I am not turning out
to be a big fan of the big cc motors. Always
seems to be something with them. I have
even heard that the 36mm kits when ported
are having an issue .... on one of the bolt
it is already paper thin and once ported
chances are that you can blow a hole
straight threw. That and the worry of a
plating issue is the reason I sold my
35mm 29cc CY motor. Just now waiting on
a OBR 27.2...seems to be a reliable power
house with a good high rpm.
 
most the CY GP290s are good motors. but the cylinder plating issue can still kill the topend, but its much better than the rest of the cy bores.

as far as blowing a hole, i can see that only happening if the porter got too wild with the tools. i have seen a few topends brake around the bolts, but im pretty sure the porting aided in it at all. i would think the ass landing on hard mounted pipes does it alot more.

biggest ISSUE they have is the plating.
the 35mm bores are the WORST ones too.
 
LargescaleRC looked at it and say they are sending me a new one. I think this time I'll mix a bit more oil say 20:1 for the initial break in.
 
25:1 is fine. any more and your getting a bit thick and are likely to foul plugs even on a good tune.


i seat the rings at 25:1 for a couple tanks then go to 32:1
 
Hello everyone,

Thanks for all the input you provided.

Well, since my first engine clunk out so quick and not sure why, I'm taking extra precautions this time. I got the new engine in yesterday. I pre-lube the engine with 3 in 1 oil and let it soak in overnight. Today I got fresh fuel and decided to go with 25:1 Motul 800 100% synthetic 2 cycle oil. After warm up I ran the engine for three 7-8 min cycle for 1/2 tank total (easy run up and down the street). I have not touch the hi/low needle yet and so far so good. Easy start, a lot of smoke (from 3/1 oil) at first but it quickly burned off after few minutes. After final cool down, I took the exhaust and the spark plug off for quick inspection. Piston looks good but as expected, I had to clean up the spark plug a little bit.

I'll run some more tomorrow and pray for me!

Kenzx
 
Hope you get better results then the first time.

Is the head casting not the same on all the CY heads.
they just use a 34mm bit for the 34mm heads and a
35mm bit for the 35mm heads and so one.

If thats true then a 32mm head would have a lot more
room for porting then a 36mm head since it is so much
bigger. Then when a 36mm is ported would'nt it be much
closer then a 32mm to said bolt hole. Then having a better
chance to blow threw that spot.

I am sure that the landings don't help. IMHO I would rather
have a wildly ported 34mm then a wild 35-36 mm. Just my
opinion. I don't want to ruffle anyones feathers and get booted.
 
each topend has its own specs on the cylinder wall thickness. so their isnt much differance between them. the 35mms do seem to suffer a thin wall as if they make it using the 34mm molds. the 36mm topends are different yet due to the involvment of GoPed (the GP in GP290) in the motor specs of the 36mm bores.
 
The 36mm big bores are actually quite good.

They give massive power unported====lots and lots of wheelspin.

If you went all out and race ported it you would only get more wheelspin.

I have just retired my 36mm top end for it now measures 36.6mm......almost at the end of it's life.....mind you it has seen 6 rerings and 120+ litres of fuel.

I have replaced it with a 35mm cy big bore kit as it is $39 cheaper than a 36mm one.

Besides that....28.5cc .V. 27cc really can't be all that different in power....I hope!
 
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kenzx said:
Hello everyone,

Thanks for all the input you provided.

Well, since my first engine clunk out so quick and not sure why, I'm taking extra precautions this time. I got the new engine in yesterday. I pre-lube the engine with 3 in 1 oil and let it soak in overnight. Today I got fresh fuel and decided to go with 25:1 Motul 800 100% synthetic 2 cycle oil. After warm up I ran the engine for three 7-8 min cycle for 1/2 tank total (easy run up and down the street). I have not touch the hi/low needle yet and so far so good. Easy start, a lot of smoke (from 3/1 oil) at first but it quickly burned off after few minutes. After final cool down, I took the exhaust and the spark plug off for quick inspection. Piston looks good but as expected, I had to clean up the spark plug a little bit.

I'll run some more tomorrow and pray for me!

Kenzx
Click to expand...

You shouldn't really use 100% synthetic for break-in. Being that you are, you have to run it hard from slow speed to 3/4 throttle for 1/2 tank otherwise your ring will not seat properly.
 
It is not necessary to break in two-cycle engines with another oil. AMSOIL 2-Cycle Oils may be used immediately in new two-cycle engines.
Click to expand...

There is still debate, but that is not always true anymore. With Amsoil you can break in a 2 stroke.;)

You should check with your dealer for that product.
 
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Ok, 2nd day - engine running good. I started to open it up a bit more at the park but still have not touch the needle setting. Just before finishing the 1st full tank, unfortunately, the plastic tranny gears stripped. Now I see why Redcat include 2nd set of gears with the kit. I installed the 2nd set and planning to take it to the track this weekend, if it don't rain.

I decided to go ahead and order the metal gear set, while I'm at it, also ordered the complete Killer Bee fail safe kit (from DDM). So far about $1000 bucks into the buggy and still got more to buy on my wish list. I'm planning to post my detail experience/review of the car under Redcat Rampage later so anyone thinking about getting this buggy can plan the budget accordingly.
 
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