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83 honda XR500R


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So my supertrapp muffler fell apart while ridein and I had to gather it while dodging traffic. Went home and put the muffler back together. Did not want it coming apart so got it together nice and tight! Well, I started it and it was much quieter. Drove around the block and it was running sweet. Then I got in the throttle. I heard "CRACK CRACK CRACK" coming out of the front of the motor. I let off and it continued to run fine. I tryed it once more. "CRACK CRACK CRACK CRACK". OH NO! I thought. So I drove slowly back home. Just as I got to the driveway it died. So I tryed to restart it- There is absolutely not compression! NONE! What have I done????????

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Crack crack crack out of front of motor... hmmmm

Pretty darn sure your valves just said hello to your piston. Explains the noise perfectly as well as no compression.

check valve clearances, check if compression release is stuck although i doubt that's it, and do a leak test. Get it at TDC and shoot air into the spark plug hole and it should either come out the carb (bad intake valve, bent, burnt), exhaust (bad exhaust valve) or crankcase vent (bad rings).

Crack crack crack out of front of motor... hmmmm

Pretty darn sure your valves just said hello to your piston. Explains the noise perfectly as well as no compression.

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How tight did tighten the end cap?

if you get carried away, the discs can collapse and block off the exhaust

remove the end cap and recheck compression and running

I also thought about this. For sure i'd say you bent your valve(s) pretty good, pretty much all that noise can be. If you tightened the nut on the stem far enough to where it blocked off exhaust and you ran the thing at high rpm's, then your exhaust was not exiting, and getting trapped. I'm thinking the exhaust could of been forcefull enough to not let the valve close, therefore hitting the piston...

Either way, I'd pull the head. Sucks i know!

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:bonk:I'm still waiting on a reply on the valve clearances and comp. release situation. I don't believe too much pressure in the ex. system can cause the ex. valve to not close since the pressure would be close to the same on both sides of the valve. If it is possible to make enough pressure without pushing through the gasket or bending the rod I think the intake valve would be the weak link. I don't know if that is possible unless there were extremely high revs and the muffler suddenly closed off.

I'm going to guess that a valve spring broke close to one of the collars letting it float at higher revs till the valve finally got a good hit with the piston.

I would say gasket, but that's usually a squeak or hi pitch whistle.

Hope we get an update soon.🙂

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:worthy:O.K., I had my 2nd cup of coffee and while playing the workings of the motor over in my head in the thinking:busted: room I can see the possibility of the ex. staying open due to pipe pressure.

With the piston getting close to TDC on the ex stroke and as the inlet valve starts to open excess pressure could possibly rush out the inlet and slow the ex valves closing.

All I know is my bike runs and I think I'll go play in the mud.🙂😏

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Sorry it took so long - Here is the update-- So- as I had posted, the motor was sitting on the workbench. I was in the process of pulling the valve cover off when my neighbor came into the garage and asked me what the heck I was doing! I told him the story. As the cover came off, and I was expecting to see a broken spring or a stuck/bent valve. He was telling me about a guy "Ben" that he knows. Ben has been riding Hondas for several years and would know what was wrong with the bike. Well, the springs were in perfect condition and I did not see anything that was bent and as I worked the kick lever everything was moving- nothing stuck. So, I told him to call Ben. Ben came over and he asked me what the spark plug looked like before I pulled the motor. I told him that I did not check the spark plug before I pulled the motor. Then Ben asked if I had checked to see if it was getting gas before I pulled the motor. I told him I did not check that either. Ben said that he would be happy to help me trouble shoot the motor after it was back in the bike. "No Problem!" I told Ben. The bike will be together by 0800. So we drank a beer or two, Ben left and I got the bike back together. So Ben comes over the next day and we check spark. -No spark. So we take off the round thing on the left hand side of the motor. I forget what he called it. To see if it was broken. It was not. Ben told me that electric problems are a real pain and he knows a guy that has been a Honda mech. for over 20 years. Ben calls him. I take my bike over there and he trouble shoots it. Well, I criss-crossed two wires when I was putting the bike back together and he finds the problem. But- bike will still not run even with spark. So- he told me to leave the bike there and he will check the timing on the bike. He thinks that the timing chain may have "skipped" a tooth and that is why I am not getting any compression. So- here I am- 2 days later.

So- the quick version - Motor has been out of the bike- valve clearance checked, springs checked, and everything moving and not bent- motor back into the bike- has spark and gas the compression release is not stuck- I forced compressed air through the tail pipe before reinstallation and the air flow did not seem to be an issue. I am going to call to see if the bike is in "time" when I leave work tonight. I hope that the bike is just out of adjustment! I will post tomorrow and let you know what he tells me...

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Did you pull the valves? if i had it that far apart i would of pulled the valves and looked at the mating surface, see if some parts are black and some parts are shiny. And I'd put the valves in a lathe and spin them to look for the ever so slightest of a bend.

Being that it had no spark doesn't explain no compression or the noise.

Timing jumping could be it, that would explain the noise... but it brings it back to it being the piston hitting the valve, because the timing was off the valves weren't getting out of the way at the right time.

Did you look at the top of the piston for a slight shiny mark in the dish(s)?

Have you put the engine at TDC of compression and shot air through the spark plug hole to see where it comes out?

Good luck man. And remember i don't know much but i am going through all this right now because my tt500 has no compression but those are the things you need to check.

Let us know how it works out!!

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Dont have a lathe.... Have never pulled valves before..... do I need a special tool to pull the valves? It looked like those springs have a bit of force behind them...... The guy still has my bike. Hope he can get to it today!

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  • 1 month later...

I pulled the head off of the jug and found a small pin (4mm x 0.4 mm) on top of my piston. the sound that I was hearing was the piston smashing the pin into the valves. Luckey to have not trashed anything besides stripping out 2 bolts that hold the head on the jug. So - now the question is do I replace the jug, do I tap it out and replaced the stripped bolts with larger bolts, or do I heli coil the stripped bolts???

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