Weird clanking noise during rides

There is a weird clanking sound, it sounds like 4-stroking, but instead more of a sharp, metal-to-metal banging. It does sound as if the piston is hitting the head, but it does not always occur. It only manifests itself when I WOT. In this audio clip, you can hear the sound I am referring to. I WOT it for a few seconds so you can hear the sound in question, then back it off slightly so you can compare it with the normal engine sound. I repeat this intermittent pattern throughout the sound clip.

Audio clip of weird "4-stroking-esque" metal clanking sound:
Chirbit - motorized bike noise - userix - share audio easily


Another thing I notice is when I WOT, the engine is considerably louder, as if there was a hole in the muffler, but goes back to normal level as soon as I back off WOT slightly. I will try to find a audio clip of this as well.

frozenveinz said:

Try adding an extra head gasket, also check out the top of the cylinder. Metal likes to stretch when hot and going very fast, which would explain why its only at high speeds.

As for the muffler, take it off and put a new gasket in. Also plug one end and blow into other for leak test.

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I'll check this out next weekend, when I have free time again. The exhaust gasket is brand new. Won't the extra head gasket throw the timing off? With the exception of today's new problems, the engine was running like a champ previously.

rustycase said:

Oops!
just lost a post...

How did you make your recording?
tell me more about chirbit!

tnx
rc

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I just googled "how to share audio" and it was the 1st hit Pretty cool site for sharing short clips of audio. I made the audio clip with my iphone in one hand while I was riding lol

timboellner said:

Sounds like a spoon stuck in the garbage disposal.

I think I'd tear it down and start looking for the origin of that noise before it grenades between your legs.

TiM

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There we go! That's the description I was trying to get at. Was drawing blanks at the time of post. The weird thing is that noise doesn't always appear at WOT. In the audio clip, I intentionally made it occur, but sometimes at WOT, it would sound normal. It had this sound ever since I put this engine on the bike and have ridden it for 50 miles so far. I did go gentle during the break-in period.

maintenancenazi said:

Hmmm, could possibly be an exhaust leak somewhere, check the gasket at the head, and below around the muffler. These tend to loosen up a lot.

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All gaskets/bolts are nice and tight with no signs of leaking. I made sure before each ride to properly torque down the head cylinder bolts to roughly 90 in/lb.

bairdco said:

i just put together a gt5a motor and rode it for the first time today. same thing. sounds like i'm riding a jackhammer. after i investigate it i'll let you know if if i find anything.

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Thanks. Let me know if you find anything.

After some more riding today, I encountered a new problem, which I am not sure if it is related. But when I was riding, I noticed a considerable loss of power on uphill climbs versus yesterday. Leaks came to mind at first and I double-checked all gaskets and bolts. No signs of leak anywhere. Upon further riding and at a stoplight, I smelled plastic burning. I looked around and noticed the spark plug boot was smoking from what seems like extreme heat from the spark plug itself. Upon closer examination once I got home, I noticed the metal portion of the spark plug is discolored from extreme temperatures. The first pic shows a comparison of a spark plug from a previous engine that has had hundreds of miles with the spark plug I have on my fairly new 66cc HT engine. It reminds me of the color found on heat-treated exhaust tips in ricers. Could the plug overheating cause loss in power? What causes the plug to overheat, a bad CDI?

The second pic shows my CDI, which is fairly new as well. I do notice the edges of the shiny (epoxy?) cover is split open slightly from the plastic housing. During my spirited ride, I felt the CDI on a few occassions and it was never hot to the touch. Maybe ever-so-slightly warm, but nothing that seems out of the ordinary. The spark plug boot (and spark plug), on the other hand, got so hot it burned and melted some of the boot off and discolored the spark plug.

bairdco said:

it might be running too lean. i put a different carb on mine and it's a little better.

i'm also running 2 head gaskets for now, because the gt5a's have too much compression. that won't affect timing at all, just makes the combustion chamber larger and reduces compression.

what kind of motor is yours?

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It's one of the no-name china HT engines. The sticker on the box says "Chinalink Motors." The cylinder head has a more square-ish appearance when compared to my previous RAW motors. I'll pull the plug next weekend to see how it is. Is it a problem if the CDI box has a split opening in it? Can that in anyway cause burning at the spark plug boot and/or power loss?

magrider said:

The first question that I'd ask is if you've done any kind of engine mods, and what is your current set up?

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No mods at all. Stock setup straight out of the box to the bike frame.

Here is a pic of the stock chinese plug included with the engine kit. Chocolate brown, cider town.

Here are some updates to my riding. I pulled the NGK B6HS plug after riding for the day and here is a pic of it. Halfway through riding, I experienced a loss in power and the inability to idle right after riding at high RPMs. I took it back home and sprayed carb cleaner over all gaskets and did not find any leaks. The carb idle screw is all the way in, but has been like that when the engine was working perfectly couple days ago.

The engine does spew out white smoke, even though my gas/oil ratio is 32:1 after breakin. Not sure why it is still spitting out white smoke.

I can no longer go up the same hill that I had no problems going up prior. I opened the head cylinder and found that the piston was covered in carbon build up. I attempted to clean it as best as I can. I also notice some rough, what seems like build up around the spark plug area of the head cylinder. I am not sure if this was a result of poor casting or if it is baked on carbon build up. It is pretty hard and cannot be broken off. Seems like it is part of the head cylinder. The piston and cylinder are in good shape; no scoring or gouges and the piston rings are intact and move freely. There are no craters or divots in the head of the piston either. So I am guessing the weird clanking noise is coming from the lower crankshaft area.

After riding for 30 some minutes today, the engine straight out died completely. It does not want to start at all, as if the spark plug wasn't connected. All connections to the CDI and stator are still there and no errant wires are prematurely grounding to the bike frame. Fuel is flowing to the carb, which I cleaned prior to today's ride. I tried a brand new CDI and the engine still refuses to start. Next weekend when I have time, I will try replacing the magneto. But I find it strange for a magneto to go out so fast just after breaking in the engine. Could there be any other causes? Would the problem of the engine not wanting to idle after high RPMs cruising be related to a faulty magneto? I invested in a TT tach hour and noted that the engine normally idles around 2000rpm and WOT/Max speed around 8000rpm. Not sure if I configured the tach hour correctly, but it is set on default, which is 1 cycle per RPM. When I am experiencing the weak idling with subsequent stall, the RPMs drop to ~1500rpm.

I also have a pic of the engine itself. Can someone tell me what brand/type of 66cc engine I have? Like I said before, the cylinder head has a more squarish form than my old RAW 66cc.

vachon644 said:

tldr: You might had oil at the bottom of the tank which entered the carb thus:
Too much oil caused smokey exhaust fumes and overheating
Overheating ate up the rings and dirtied the chamber
Rings that lost compression caused poor performance for a while until it became impossible to start
Rings didn't give enough compression to the engine to start up

Fixing it shouldn't be very hard (if that is your problem):
Remove piston, throw away circlips, rings and piston, replace, clean the carburetor and fuel lines, tank. Start with fresh gas. Unless the head is warped, cylinder wall scorched, bearing rough they should be ok. Change head gasket because it's cheap, given the opportunity, buy 2.

Good luck

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That is interesting theory. I have never had this issue with the previous two HT engines and I never bothered shaking the tank prior to riding to ensure mixture of gas/oil. And I never had white smoke issues with either of the previous two RAW engines. Does gas/oil mixture seperate over time? I have looked into the tank after leaving the bike alone for a week and did not notice any separation of gas/oil. The mixture still seemed homogenous.

As for compression, The piston rings look fine. They still have springiness (sp?) to them, move freely, are not fused at any point to the piston, and are not cracked/broken anywhere, does that mean they can still be bad beyond what I can visibly see? With everything put together and with clutch engaged, the bike is extremely hard to move (engine is hard to turn), ergo the rings are making good seal and there is compression. I remember when I blew rings in one of the previous HT engines, I could move the bike forward with clutch engaged and the turn the engine fairly easily.

bairdco said:

i had a magneto go out on a Grubee GT5a after 2 weeks. could be the problem.

the blow by on the piston is at the ring keeper pins, and is pretty much normal for these motors. as long as it's not excessive, shouldn't be a problem.

it sounds like you blew a head gasket, but you'd notice that right away. usually you get a loss of power and a puffing feeling against your leg, and from the pics, there's no blown out oil on the head.

you can clean the inside of the head with carb cleaner and a scotchbrite pad, or sandpaper, a wire wheel, etc.

is long as you don't actually gouge the metal away, it won't hurt it.

that's some weird build-up at the base of the plug threads. i'd clean that off. most of the slant heads have really poorly done threads for the plug, and i take a dremel and grind the edges smooth. it looks like those sharp edges could break off.

as far as the engine maker goes, were there any stickers on the side that says which factory it was made in? or on the side of the box? otherwise, you'll probably never know. all those chinese look the same to me... (sorry, bad joke. )

looking at pic4, do you have the bigger intake? the grubee GT5A's have the larger intake port. if it's the same size as the exhaust port, looks like you might have a Grubee. if it's smaller, i couldn't tell ya what it is. also, the GT5A's have the 6mm head studs, while every other slants i've seen have the larger 8mm studs with acorn nuts.

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I thought it was head gasket as well, but upon inspection, there was no oil residue on the outside of the gasket. I wore long jean pants, so I can't feel any puffing, if there was any. But I did spray carb cleaner around all gaskets and did not notice any changes in the revs.

I believe the intake port is smaller than the exhaust, but I have to double check next time, as I didn't pay attention to it (sorry didn't take a side profile pic). What I do notice is the piston on this engine is different from my previous two RAW engines. My head studs are also 6mm, unlike the 8mm studs on my two RAW engines. The wrist pin holes are in a different position and the piston itself seems longer than the RAW motor. Are Grubee and Flying Horse engines identical? There were no tags or label present anywhere on the engine. The box has some codes on it. I'll go check it out in a bit and report back.

magrider said:

To check if the engine is getting a spark, take the plug out of the cylinder head and put it in the spark plug boot, ground the electrode to something steel, like the head nut and turn the engine over. This will be easy because there will be no compression in the engine. If the electrical system is working correctly you will see a spark jump at the electrode.

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haha. Totally forgot about this simple test. Thanks. I will try it out next weekend.

I swear, I have the worse luck with these engines. I've ridden this engine for less than a month (couple weeks at most) and it's already developed serious problems. The one before this lasted roughly 2 months.

Speaking of which, I rebuilt the top end of the previous engine but for some reason, it ran a lot weaker than when it was new. I made sure all the gaskets (which are all new) were tight and not leaking. Piston rings, piston head, cylinder body, and cylinder head were all brand new, correct parts. I tried a new CDI and magneto with no success. During test rides, there were no signs of oil leaking anywhere, yet it was still weak as ever. I still can't figure out why it's weak.