1983 Gs450 makes a jack hammer sound?

[Muddin_Mavric]

My brother got a gs450 a while ago and he put about 700 miles on it and it ran fine.  then all of a sudden he was driving down the highway at 60 mph and it started to sound like a jack hammer and it lost power.  He had to keep it wide open and he could barly go 20 mph.

it wont make the sound when its cold.  it dont sound like its coming from the bottom end.  the sound seems to start around 3,500 rpm but only when your on the gas. if you hold it at 4,000 (not it gear) you can just bearly hear it and it sounds kinda random.  it has the same power as it use to when its not making the sound.

what do you guys think it could be?  piston slap?  

the bikes not in that great of shape is it worth spending the money to fix it even if we did the work our selves?

thanks for any help you can give me

justin

[Blueknyt]

sounds like abit of piston slap (maybe)

[Kerry]

Is the 450 a twin cylinder?  If so, it sounds like an electrical problem that that randomly prevents one of the spark plugs from sparking.

Running on one cylinder does make a very odd sound.  Drastic loss of power is a fairly good diagnostic symptom, and the fact that it seems to happen mostly when it's warm kinda indicates an electrical problem, too.

Hopefully you can locate repair manual with a good wiring diagram and resistance values for the various components.  Grab an ohmmeter and check it out!

[Muddin_Mavric]

thanks i will look into that, my brother got a repair manuel with it but to me i dont think its electrical.  if i drive down the road at 7,000 rpm in second gear it wont do it unless i give it a little more thorotle than it needs to maintain 7,000.  the more thorotle i give it the louder and less random it gets.

but around 3,000 to about 5,000 it does it even just maintaining speed.  but more random and not as loud.

i dont think its doin it as bad as the first time it happend to my brother.


thanks for all your help.  i hope i can get it fixed since i bought a bike to ride with him and now his blew up and he is still in tech school and doesnt have a lot of cash to fix it.


justin

[Blueknyt]

yeah kerry, the gs450 is the 500's little brother, shares same bottom end cept output shaft (nut holds sprocket on) and shift drum. its a reverse cut from 500 as the shifter points forward to the front of the bike, the 450 gears are identical to 500 and will fit on shaft, shift drum will change out too. drop the 500 top end (pistons ,cyl, head) and you have the 500. with silver cases

[scratch]

Sounds more like you threw a bearing or a rod. Pull the spark plugs and look into the cylinders. Also, rotate the crank by hand while looking into the cyls to see if the pistons rise and fall. Actually, before you do any of that, you can see if you're gettin' good exhaust from both exhaust pipes. You do have the seperate exhaust pipes, right? Left cyl, left exhaust pipe...