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Top Teardown Advice Needed

  • Thread starter Thread starter paulwd18
  • Start date Start date
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paulwd18

Guest
Hello fellow GS'ers.

I need some advice.. I have re-built my 1983 GS750t with some (brace yourself) modifications. Everything was going swimmingly until I realized that my right side (as I have 2, 2-1's), was running either with a weak spark or with heavy oil getting past the piston rings or valve seals, with puffing smoke etc. I got my fuel to air mixture down but something was still not right with my right side. Back to the drawing board. Pulled the spark plugs and sure enough #3 was soiled in oil. All the rest looked perfect. Looking back I should have completed a compression test.. but I didn't. In any event I got the engine down to the piston tops with all steps being checked TDC etc, chain tensioner removed and timing chain suspended with a hook etc etc. I have found something unreal. On the top of piston three there is what looks to be pebbles. I have smacked a couple with a hammer to see if it could be steel shavings but no, hardened clay or other sediments. The jug walls look fantastic. Zero scoring (I was worried about the piston rings being shot). When Im running my finger along the cylinder walls there is no discernible scoring - AKA - smooth as a babies bottom. Good news but still no smoking gun - no pun intended. Could it be that some of this sediment has got logged in between the piston ring seal and the jug? I think no as there would have been SOME scoring. Perhaps this just points to the valve seals..? What do you guys think? Has anyone seen this before. This bike is new to me. Bought it two years ago to complete my first build. The previous owner, who had it for its entire life, put 30,000 kms on her. If I've missed anything please let me know which will help explain what is going on and what I should do next. There seems to be a lot of sediment around though. Seems somebody left the spark plug hole open too long in a barn.. certainly I am all ears!

Thanks for the help guys!

Cheers from Alberta.

Dustin.

IMG_6840.jpg
 
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Maybe a cridder built a nest in the airbox and some of the crud got sucked in?

Regardless, I'd pull off the cylinder at this point and replace all the gaskets and seals in the top end, including the valve stem seals. Lap the valves at minimum and cut them if pitted. I'd also replace the rings after using a bottle brush hone in the bores. You can skip this part if the engine is low mileage or you have evidence of a excellent sealing.

Good luck
 
Thanks Nessism,

Yeah it seems like there was something funny going on for sure. I should have mentioned I took a small run at taking the jugs off but they are stubborn. I think its because they used the white gunk on the bottom gasket. Any advice on how to get the juggs off without too much damage to the fins etc? This is my first build and for some reason the valve stem seals job intimidates me. Ive been looking for a decent tutorial on this. Do you know of one perhaps?
 
Look for a pry point on the cylinder to get it moving. What ever you do don't try to slip anything between the cylinder and the engine case on the gasket surface and pry. You will mar the surfaces. Maybe try a piece of wood to distribute the load and whack it with a hammer. Don't focus any force on a fin or you will break it off.

Basscliff has a tutorial on how to remove the valves. It's pretty easy using a c-clamp and a modified piece of PVC pipe. Lap the valves before you install them back. There are about a bazillon youtubes on this.
 
Thanks for the point in the right direction cowboyup3371, Nessism.

I managed to get the jugs off last night. There was crap all over the place. The pistons seemed to be fine. The cylinder walls were mirror smooth but all around the base of the jugs there was sediment. It looked like clay or dirt. Im a little stumped, Im still learning about the ins and outs of combustion of engines but there should not be this kind of debris this far down the top end no??

Anyways Ive inspected the pistons and the rings themselves they look fantastic so Im set on lapping my valves and reseating new valve seals. I'd certainly welcome any advice at this point though guys. the back side of the valves are showing their oily state on the exhaust side of the valve set. I suppose confirming what I already know which is oil is getting in there.

At this point my plan is to reseat new valve seals and reseat new piston rings, and lap the valves. What do you guys think?

Thanks!

IMG_6852.jpg
 
Hi guys thought I would follow up with an update on my post. As mentioned I tore down the head replaced all piston rings and replaced all the valve seals. I found a smoking gun with the #3 valve stem and chamber showing signs of oil. It was nice to find a culprit. Ive replaced all gaskets, torqued down all bolts to spec, timed out the chain with TDC and counting the chain pins as per service manual. Im now ready to re-install the engine fill her up with oil and give her a go. Ill update once I get her going but I just wanted to thank you guys for the help. A massive thank you to BikeCliff for this website: http://members.dslextreme.com/users/bikecliff/

Huge help. Thanks again.
 
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