Replace or rebuild?

[pistolpete]

I'm trying to decide what i should do? Yesterday on my way home from work my bike developed what sounds like a rod knock. It is a 1983 gs750es with 28,589 miles on it. i've gone over the shop manual and looks like i'll pretty much be taking the whole drive train apart just to get to the rods. I've search ebay and craigs list for an engine but i'm very weary about buying online. any suggestins would be apreciated.

[Turtleface]

I'm trying to decide what i should do? Yesterday on my way home from work my bike developed what sounds like a rod knock. It is a 1983 gs750es with 28,589 miles on it. i've gone over the shop manual and looks like i'll pretty much be taking the whole drive train apart just to get to the rods. I've search ebay and craigs list for an engine but i'm very weary about buying online. any suggestins would be apreciated.

I had the same thing happen to me on my 1100 EZ. I was positive it was a rod knock at first listen, sounded exactly like rods I've heard go bad in small block chevys. Check your clutch hub. It might just be a loose nut, or it may be the springs on the back of the hub have loosened up, necessitating a rebuild. Turns out these roller bearing motors are unable to develop a rod knock like a plain bearing engine. The clutch hub is a dead simple thing to check, and you have to pull it to tear apart the cases, so might as well start there.

[teddux]

Turns out these roller bearing motors are unable to develop a rod knock like a plain bearing engine.

Maybe that's because it SITS in oil, unlike a chevy engine, FTW!

[Nessism]

Maybe that's because it SITS in oil, unlike a chevy engine, FTW!

I'm not following?? The crank bearings don't sit in oil.

[Don-lo]

83 750 motors don't have roller bearing cranks, according to bike bandit

[teddux]

I'm not following?? The crank bearings don't sit in oil.

Damn, lemme go split me engine, have a see wtf, FTW!

[Turtleface]

83 750 motors don't have roller bearing cranks, according to bike bandit

Indeed, they are plain bearings. Wouldn't change my plan of attack though. You'd still have to remove the clutch first before taking it down to the cases. Unless there's something we don't know about (full throttle missed shift, extreme overheating/under-lubrication), I'd still bet on the clutch hub. If the clutch hub turns out to be good, I'd look at the starter clutch next.

[tkent02]

Got a lot of bikes to ride?
If not, being early spring and all, I might be tempted to look for a parts bike with a decent engine and ride this one until you find the replacement.
Tearing an only bike down now is just wrong, unless you can just take it down and get it back together in a day or two.

But check the clutch and the starter clutch, those are easy fixes.

[TheCafeKid]

Easiest way to tell if you have spun a bearing is to get a dowel rod small enough to fit into the plug hole. Turn the motor by hand till whichever cylinder its JUST past TDC and I mean barely, not to the point where the piston starts to move back down in the bore. If you can push the piston down with the dowel its likely spun the bearing. Its not 100% accurate, but it should give you a good idea. Compare that to the rest of the cylinders if you're not sure. Also, a blown bearing on one of these plain crank motors generally sounds like a jackhammer, and will increase with RPM... A loose tappet adjuster nut could also kinda sound like that, as well as the clutch hub nut coming loose as previously mentioned.

Im not saying its not possible, as you have no idea what POs do to their bikes, but Ive not heard of many of the 83 and up 750s having bearing issues. the 80-82s, yeah, but that was a different animal.

If the dowel doesnt tell you much, and you finally relegate yourself to at least breaking down the top end, you can grab ahold of that piston, and if it waggles, its toast.. Hope this isnt the case dude, but good luck either way

[Dave8338]

I've used a similar approach to Josh, with a little different "twist".

If indeed it is a rod bearing, with the plugs pulled and the clutch cover off (needed to rock the crank back and forth with a sense of feel) put the dowel into the plug hole(s) and IF the bearing has failed, you will be able to slightly rotate the crank (a degree or two) back and forth and feel wether the dowel moves in direct relation to the crank.

There should be NO play, wrist pins or otherwise in an engine with that few miles on it.

[pistolpete]

I will start looking at the clutch first. The clutch has been acting a little wierd but not too sure what is normal since this is my first and only bike and i've only rode it for 536 miles so far. Another thing that sucks is my road test is april 6th, one week away so I really can't tear it down too far.

[pistolpete]

Well i have figured out what it was. It is the spark plug wires. They are arcing and when that happens it creates piston slap. When i rode the bike to work the morning i heard the noise it was drizzling out and the same thing on the way home. the next day when i got out of work to diag it, the noise had disapeared. Then i washed the bike and when i started it up it started knocking again. only this time i wasn't wearing my helmet and i could also hear the wires arcing, as soon as i dried the wires it was fine. I feel a little dumb thinking it was a base engine issue but i'm glad it is something simple.

[teddux]

Unlike other hateful members in here that liberally stated that they wish me dead, in so much words, I on the other hand am GLAD that you didn't blow off your limbs from a gas tank explosion.

Good job!

[Rick65Cat]

Unlike other hateful members in here that liberally stated that they wish me dead, in so much words, I on the other hand am GLAD that you didn't blow off your limbs from a gas tank explosion.

Good job!

???
What does a base engine issue or even arcing wires have to do with what you just said?

[teddux]

???
What does a base engine issue or even arcing wires have to do with what you just said?

your only friend?

• Spyderman