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Think I screwed up Royally!

  • Thread starter Thread starter lopeha
  • Start date Start date
L

lopeha

Guest
Have been trying to get all the bugs out of my new to me '81 GS750EX. Had a problem with gas getting into the crankcase & found gas in the vacuum line, so put caps on the petcock, the carb & just run it in the prime position. Also replaced the needles & went from 112.5 to 117.5 jets since the bike has a 4-1 & foam pods. was on a short test ride & developed a severe knock in what seems to be the 3 or 4 cyluinder area. Pulled the plugs & they are extremely white. So I'm guessing the I ran the bike way lean & scorched a cylinder wall or two. Still trying to figure out why. The float bowls are full & there seems to be plenty of power.
Now comes the hard part. Do I rebuild the motor with oversized pistions or install the 1100 motor I found at a slavage yard. The gearhead/hotrod
in me says mo power, mo power, mo power; while the 48 year old brain says the 750 is plenty large enough.
Any insight into what went wrong & any pitfalls I might run into doing the swap will be greatly appreciated.
 
When you put the 1100 in you will get more power (lots more) but lose some smoothness. When Tim and I swapped bikes on a Texas Hill Country Ride (he has a '81 GS750E and I have a '81 GS1100E) I was amazed by how smooth his bike was. It wa more comfortable than my bike.

Hap
 
Oh No Mister Bill

Oh No Mister Bill

I would take it apart and check the damage, Having owned a salvage yard all I can say is some times you get a good engine some times you don't, its your wallet, and you can always spend a little money on pumping up that 750!!! Hard time to break down with summer here, I always keep a spare bike.
 
Or a spare enging When my 850 bite the dust I am going to install a
1000G motor that I have
 
Royally

Royally

Well I sprayed some WD-40 thru the carbs to see if I'd scored the cylinder wall & it got no quieter so I'm guessing the problem is in the cam area. Heading out to pull the valve cover now. If you hear a loud scream then it's worse than I thought. Will keep y'all posted on my "adventure".
 
Go for smooth.

I suspect the 1100 motor will change a lot of things. Most not for the better.

It will change the center of gravity, much different handling......

more weigh, ie less responsive handling, more stress on the head bearings and fork tubes

how about a few months worth of fiddling getting your chain alignment right (per some other posts I've seen), ie thrown/broken chains, chewed up sprockets,....getting stranded.

And most importantly...... I'm 49.... so I'm one year wiser....LOL

Go for smooth
 
Royally

Royally

Update; Pulled the valve cover & nothing readily apparent. Started it with the cover off & intake was oiling really well, exhaust not as much. Ran a compression check & 1,2, & 4 went straight to 100 lbs, #3 was 80, but went to 100 on the next try. Now really confused. The knock is still there, so I guess it's time to pull the head & see what the cylinders look like.
Which would be the better route? Bore out & use Suzuki pistons or go big bore with a lower compression? Oh well, I bought it as a project bike. Just wasn't planning this much project this quick, hehe.
 
I think I'd stay with the 750 engine. I think there could be a lot of problems with the 1100 engine. The GS bikes look alot alike, but there are differences. For example, earlier today, I was comparing the exhaust on my two bikes. They both have stock exhaust and, though they look the same, they're not alike at all, and it didn't look like any of the major parts were interchangeable. I checked a few part numbers and none were the same for both bikes.

About the knock... Could it be a rod bearing knock?
 
Update

Update

Well I was in the process of doing a wet compression test today when the motor decided to lock up. So off I went into the great unknown of tearing a motor down. Pulled the valve cover & head, no apparent damage. Pulled the cylinder & found that the #3 rod bearing had seized. Deeper I go into the great unknown & now have the motor upside down on my bench attempting to get the lower case broke free from the upper.
What things should I do while the motor is tore down? Am new to the GS motors so all recommendations will be appreciated. Thanks in advance, Andy.
 
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