Oops... gx390 bit the dust

[areams]

Just got the chain and new drive sprocket on today to give myself a little lower gearing and then this happened about 5 minutes in... (see pictures). only mods were air filter, exhaust, just above stock cam, and governor removal. Thought valves were supposed to float before these engines give way? Oh well, anyway..

Anybody have any information on the DuroMax 16 horse motors? Appears to be a Honda look alike? Reviews all look good but want to know if anyone has any experience with them. Also, like the charging system.

DuroMax XP16HPE 16 hp Electric/Recoil Start Engine https://www.amazon.com/dp/B0040ZWU18/ref=cm_sw_r_cp_api_TeGwBb54681C4

 

[Tpdingo]

Ouch. That's a brand name Honda. That has got to hurt. Well, this is the reason we all mod Predators instead of Hondas.

 

[areams]

Ouch. That's a brand name Honda. That has got to hurt. Well, this is the reason we all mod Predators instead of Hondas.

Engine itself was a freebie anyway. Needed rings so I put a cam in while doing that. I wasn’t really expecting much other than for it to get me through the summer... lol guess not. Not really out that much.

 

[mckutzy]

Just above stock is where it let go....

So what actually blew up... The con rod???

 

[areams]

Just above stock is where it let go....

So what actually blew up... The con rod???

Yes. Connecting rod let go and went through the block.

 

[areams]

Out with the old and in with the new.. any suggestions on how to hook up throttle and keep my governer in tact?

 

[Tpdingo]

Out with the old and in with the new.. any suggestions on how to hook up throttle and keep my governer in tact?

Don't modify your motor. That's all.


It comes stock connected, so leave it connected, and your connected rod will remain connected to the connected crankshaft.

 

[Kansaskart]

When you put rings in did you use a torque wrench? Engine probably just had a hard life, no oil changes etc. Unless you like to drive wide open for long stretches they hold up well.

 

[areams]

Don't modify your motor. That's all.


It comes stock connected, so leave it connected, and your connected rod will remain connected to the connected crankshaft.

Had to replace rings lol hard to leave it connected!! Lesson learned though, like I said it was a freebie except for the filter and exhaust.

---------- Post added at 07:25 PM ---------- Previous post was at 07:23 PM ----------

When you put rings in did you use a torque wrench? Engine probably just had a hard life, no oil changes etc. Unless you like to drive wide open for long stretches they hold up well.

Yes, I rebuilt to specs. Torqued everything. I think like you just was rode hard and put away wet.

 

[anickode]

Valve float holds true on predator 212s. It is not an ideal form of governing an engine, and was not an engineered safeguard. It just happens to be how it works out. It doesn't necessarily apply to other engines.

For instance, if you float the valves in a Tecumseh powersport, it tends to destroy the cam, and thus the entire valvetrain.

If you float the valves on a car engine, you're liable to destroy all sorts of stuff.

 

[Tpdingo]

Not sure why all you guys are having so many problems with valve float. They just float naturally.

 

[areams]

Valve float holds true on predator 212s. It is not an ideal form of governing an engine, and was not an engineered safeguard. It just happens to be how it works out. It doesn't necessarily apply to other engines.

For instance, if you float the valves in a Tecumseh powersport, it tends to destroy the cam, and thus the entire valvetrain.

If you float the valves on a car engine, you're liable to destroy all sorts of stuff.

Agreed! I just never heard the engine sound like it ever stopped revving to where I noticed it having any sort of valve float. Then kaboom.

 

[bob58o]

A good read...
Aftermarket camshafts are apparently no good with otherwise stock internals in a big block.

http://www.buggiesgonewild.com/clon...ttle-clones-dyno-run-write-up-surprising.html


-A Built Clone with a Billet Rod, Hard-Face-Welded Camshaft, Stainless Valves, Chrome Silicon Springs, Aluminum or Titanium Retainers. Chromoly Pushrods, and Shaft Rockers, is going to be MUCH stronger and more reliable than stock. The stock rod flexes and deforms under high power, it also is a **** poor design for high speed lubrication and will gall the crank. I ran a stock rod and valves for ALONG time and ALOT of abuse. I didnt have 1 problem until the day I put a cam in it. Even the small cam was such a drastic power increase, the stock rod and valves ate the sheets within 4 hours. Stock valves are junk and cannot withstand the higher valvespring pressures of dual springs, so bottom line is, they dont call it a "Built" engine for their health. Its "Built" so it can RELIABLY take the abuse associated with a high horsepower application. Both ARC and Parsons rods have taken tons of abuse on the go kart tracks which are significantly harder on any engine than a Golf Cart is. 6500+ rpm for 30 mins at a time.

 

[areams]

Ended up going with a Northern Tool PowerHorse 420cc 12.5 horse engine. On sale for $329 with the charging system. Threw it on the kart yesterday with the governor removed so I could quickly hook my throttle cable up and test it out. Kept my foot out of it for engine brake in.

I would like to keep the governor on here for future use and was wondering two things:

1) Would 4000 RPM be a safe bump for this engine? I've read that these stock internals are good with 4000-4500 RPM, is that true?

2) Going to leave the governor hooked up, just think I'm going to turn out the throttle stop and adjust the gov. spring to gain a few hundred RPM. Any problems in doing this?

Not looking for anything crazy, just was wondering if I could turn say 4000-4200 or so RPM over the stock setting of 3600.

If not, then I will just leave it and live with the governed 3600 RPM.

 

[KartFab]

The problem is that you did other modifications that require a billet connecting rod, then you skipped that step.

I’ve got a gx340 with stage 1 mods (intake/exhaust/rejet). No governor bypass or removal. Runs great. Extra hp/torque and the rod isn’t stressed and it can still oil itself.

If you don’t buy s billet connecting rod and you keep doing other mods (springs, governor bypass, governor removal, governor modification, etc) you will eventually end up with another hole in your block because the rod will break because it cannot oil the crank journal at high rpms.

 

[areams]

The problem is that you did other modifications that require a billet connecting rod, then you skipped that step.

I’ve got a gx340 with stage 1 mods (intake/exhaust/rejet). No governor bypass or removal. Runs great. Extra hp/torque and the rod isn’t stressed and it can still oil itself.

If you don’t buy s billet connecting rod and you keep doing other mods (springs, governor bypass, governor removal, governor modification, etc) you will eventually end up with another hole in your block because the rod will break because it cannot oil the crank journal at high rpms.

No I am putting the gov back on no matter what. I was just wondering if I could squeeze out a few hundred more RPM and still be good with a bone stock motor. I’m talking going from 3600 stock RPM to anywhere from 4000-4200ish and still be good withstock internals.

 

[anickode]

I'm confused... You're going to the trouble of opening ng up the crankcase, removing the governor components, and reassembling the motor so you can use your current throttle linkage because you don't want to wait for a different cable? and then when you do change your throttle setup you're going to take the motor back apart and reinstall the governor.

Why not just buy the right parts, wait a couple days for them to show up, and put them in?

 

[areams]

Sorry, I’m not explaining this very well. Start over! I apologize, let me clarify.

I did not open the case up. I just removed the gov arm to the carb and used my previous throttle linkage. A gov bypass? Still new to some of the terms. I set my accelerator pedal stop so I could only open the throttle about half way (or less) just to start the motor and putt down the gravel road for break in. I guarantee I was not hitting the 3600 rpm and if I was I am going to be severely disappointed with this new engine. Lol

I decided I would keep the gov assembly in place after doing this to protect the motor. Also, if I keep the factory throttle set up and add in my new cable, I can use the gas tank that came with the engine as well. So I ordered a longer throttle cable to make this all work but it won’t be in for a few more days.

The main Reason I went ahead and got it going was it is pretty hard to say no to your almost 4 year old nephew begging to go for a ride on his birthday tomorrow lol.

In the mean time, I was just curious if these “big blocks” can take 4000 rpm all day with stock internals. I’ve read somewhere that it was maybe even up higher than 4500.

 

[mckutzy]

Well there you have it... the gov bypass with more powered cam caused the explosion... Gov removal/stock cam probably let it go till the float stopped it...

 

[Randy H]

The answer is you can probably increase the RPM some amount (within the confines of an operational governor) without immediate catastrophic failure.

A Plastigauge check might give you some piece of mind. Rod clearance is a big deal.