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Old 07-10-2019, 04:55 PM
JesseSands JesseSands is offline
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Default Will it damage my Go Kart Engine (107CM3) if I run it for a while with no Exhaust?

I have a kart I recently picked up and the exhaust hanger broke last weekend, which then caused the exhaust to dangle and then strip out one of the bolts that attaches the exhaust to the engine. I don't want to drive it with it hanging by that other bolt and it will take some time to get the weld fixed and it re-tapped or something to fix it.

So if I take the exhaust all the way off the engine and drive the cart for an hour or two before I get this fixed, is it going to damage my engine or cause any major problems?

Its a small 2 seater kart (possibly an older Tao Tao) with a 107cm3 engine, which is basically a 110cc engine from what I've gathered. Chain driven transmission (not belt).

Thanks guys!
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Old 07-10-2019, 05:39 PM
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I'm not an expert on it, but I am 95% sure I read somewhere that if you run your engine too long without an exhaust, you risk a bent valve.
I'm not sure if it's due to the possibility of physical damage or has something to do with material behavior, but in short:
DON'T DO IT!
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Old 07-10-2019, 05:54 PM
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Not worth the risk. Retap the hole.
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Old 07-10-2019, 07:23 PM
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since when can running an engine w/o exhaust bend a valve?

Sure you must -at all costs- prevent something getting near the valve from the outside; true!
But a simple fine mesh to cover the port should do the trick until the threads are fixed.

Other than that it's not too different from running a short stinger header.

'sid
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Old 07-10-2019, 07:31 PM
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Quote:
Originally Posted by itsid View Post
since when can running an engine w/o exhaust bend a valve?

Sure you must -at all costs- prevent something getting near the valve from the outside; true!
But a simple fine mesh to cover the port should do the trick until the threads are fixed.

Other than that it's not too different from running a short stinger header.

'sid
Thanks for clearing that up, I've been wondering.....
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Old 07-10-2019, 08:00 PM
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Quote:
Originally Posted by itsid View Post
since when can running an engine w/o exhaust bend a valve?

Sure you must -at all costs- prevent something getting near the valve from the outside; true!
But a simple fine mesh to cover the port should do the trick until the threads are fixed.

Other than that it's not too different from running a short stinger header.

'sid
I would disagree. It's not running it that hurts it, it's after you shut it off. The muffler lets everything cool at a reasonable rate since it holds heat in the cylinder. Without it lets everything cool too quickly, which can warp or damage the valves. Not a given, but not worth the risk.
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Old 07-10-2019, 10:00 PM
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Well, first off, it's a possible fire Hazzard depending on where the fuel tank and other flammable items are located in relation to the open exhaust port. Just be aware it will likely have an obnoxious plume of hot exhaust gas with some flames coming out of that port. If you absolutely must run the thing even a short six inch homemade straight pipe held on with that one good fastener is a lot of safety insurance. In the aviation world a short header like that is called a short stack exhaust and is quite common on older reciprocating engines. Just long enough to clear the engine cowling, that's all that was needed. Kept from setting the plane on fire. Often flames would jet out as the engines would run. Never any warped or burned valves.

That brings me to my next item. Warped, bent, and burned valves. I call BS. Your intake valve didn't warp when it pulled in that cold dense charge of fuel soaked supercooled air did it? I didn't think so...use some sense...

You may loose a little bottom end torque as some engines seem to be more efficient with some back pressure at certain points in the exhaust system...and that is a study in fluid Dynamics that Sid is probably better off explaining than me but it's kinda like chamber resonance and pressure waves and all that...

But no... you're way more likely to get foreign debris, be it dirt or moisture or something like that into your engine than warped-bent valves.

But as a mechanic I would also ask why don't you just have some patience and just wait until you get the thing fixed and do it the right way.

Be a good neighbor and everyone will love you for it!
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Old 07-11-2019, 08:19 AM
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Quote:
Originally Posted by BigWes View Post
You may loose a little bottom end torque as some engines seem to be more efficient with some back pressure at certain points in the exhaust system...and that is a study in fluid Dynamics that Sid is probably better off explaining than me but it's kinda like chamber resonance and pressure waves and all that...
Incorrect actually.
It's not the backpressure, it's the velocity of the exhaust gases.
It's the same effect as having an ~1 ft. diameter exhaust pipe.
The same velocity principles apply to the intake ports just as much, so if you port too much out of a cylinder head, it'll lose velocity and you'll have a sad amount of torque.
Just thought I'd explain, hope I don't sound annoying.
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Old 07-11-2019, 08:58 AM
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Yea, I know I should just wait till we get it fixed. I was just hoping to let my brother drive it while he's over since he hasn't seen it yet and it wont be fixed for a couple weeks till I can take it down to the shop and fix both the broken welds and the stripped bolt.

One thing I didn't mention is that we already had to re-tap this bolt and we used a "Thread Repair Insert" to be able to use the same size bolt still in the engine. I am not sure how we are going to fix it this time. I'll have to get under there and truly see the damage. I lost the bolt also when the hanger broke and pulled it out, so I'll have to get new ones once we figure out how to fix it this time.
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Old 07-11-2019, 10:29 AM
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I always thought the exhaust pipe draws heat away from the cylinder head, that way the head and valves don't get damaged from excessive heat.
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Old 07-11-2019, 10:50 AM
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Quote:
Originally Posted by JTSpeedDemon View Post
Incorrect actually.
It's not the backpressure, it's the velocity of the exhaust gases.
It's the same effect as having an ~1 ft. diameter exhaust pipe.
The same velocity principles apply to the intake ports just as much, so if you port too much out of a cylinder head, it'll lose velocity and you'll have a sad amount of torque.
Just thought I'd explain, hope I don't sound annoying.
No, you don't sound annoying you are annoying.

Did you not read the part where I mentioned fluid Dynamics and what not? Like I said Sid can explain it better than me. He has a knack and talent for such...I don't. That back pressure, in a proper designed system, will cause a scavenging effect and actually increase the flow of exhaust gas out of the cylinder. It's just one part of that volumetric efficiency thing. Just know that if it's done right it works.

Sometimes I wonder if I need to get out some crayons and draw you a picture.
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Old 07-11-2019, 10:57 AM
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Quote:
Originally Posted by BigWes View Post
No, you don't sound annoying you are annoying.

Did you not read the part where I mentioned fluid Dynamics and what not? Like I said Sid can explain it better than me. He has a knack and talent for such...I don't. That back pressure, in a proper designed system, will cause a scavenging effect and actually increase the flow of exhaust gas out of the cylinder. It's just one part of that volumetric efficiency thing. Just know that if it's done right it works.

Sometimes I wonder if I need to get out some crayons and draw you a picture.
Sheesh.
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Old 07-11-2019, 12:21 PM
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Woah,everyone needs to have a beer or two!
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Old 07-11-2019, 12:37 PM
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If it was me I would just jb weld it on.
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Old 07-11-2019, 12:43 PM
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Quote:
Originally Posted by txluke View Post
If it was me I would just jb weld it on.
You are the second person that has mentioned that to me. With all the vibration of this engine do you guys think JB weld would hold? That literally might be my only option if there's not enough space left to retap it even larger...
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Old 07-11-2019, 12:52 PM
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Saw a guy fix a 4 inch hole in a motorcycle crankcase once. It looked terrible, but worked.
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Old 07-11-2019, 02:01 PM
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Saw a guy fix a 4 inch hole in a motorcycle crankcase once. It looked terrible, but worked.

Yea, it's actually good stuff. Not my first choice. Admittedly, I patched a hole in the pan of a TH350 transmission with that stuff one time. Used it for several things. There is actually JB weld made for industrial purposes.
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Old 07-11-2019, 05:24 PM
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Everybody just as well better shut up. JTSpunk is a friggin' expert at this. He read it on the interwebz for Pete's sake!
Next time do a better copy/paste. Sheesh.



I wanna see this engine and the dangling exhaust. And can we please stop calling it a something, something centimeters cubic cm³ engine? That's like for lab use, not automotive.

Let's call it what it is, a Jing Dong 110cc (107cc, 108cc or whatever).

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Old 07-11-2019, 05:28 PM
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Quote:
Originally Posted by Crash87 View Post
Woah,everyone needs to have a beer or two!

This


Once emtpy poke a hole in the bottom of the left over can and screw that too your one good exhaust bolt hole.


Now i know i got at least one of you thinkin....hmmm
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Old 07-11-2019, 05:33 PM
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Quote:
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This
I wanna see JT with a few beers in him. Might mellow him out some. That'd be some funny stuff right thar.
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